Keywords: Near-field scanning, magnetic field probe, dosimetry, exposure, RFID, RF-welding machine, prediction algorithm

The work presented in this manuscript have been carried out at IMEP-LaHC laboratory in collaboration with Pheline, a test lab that is specialized in the study of the electromagnetic fields phenomenon and its interactions with the environment, at CSTB -Grenoble. I would like to express my sincere gratitude to my supervisors, Prof. Fabien Ndagijimana and Prof. Jalal Jomaah. They have been true mentors during my doctoral study. This thesis was not to be possible without their invaluable support, guidelines and help, as well as their great advices, and unfailing commitment in my research project and beyond.

I would like to take this opportunity to thank Prof. Joe Wiart for chairing the defense jury. I would also like to sincerely thank Prof. Philippe Descamps for examining this thesis, as well as Prof. Philippe Leveque and Prof. Jean-Lou Dubard for their much appreciated involvements in my thesis review and defense.

Moreover, I would like also to express my thanks to the engineers and technicians, at IMEP-LaHC and CSTB, who offered me a strong support during this journey, as well as the administrative staff for their help in all administrative procedures. I am also thankful for all my colleagues and friends at IMEP-LaHC as well as CSTB, for their support and their good humor. We had a lot of great discussions and we shared beautiful moments.

Finally, I would like to express a deep sense of gratitude to my parents, my sister, and my brother. You helped and supported me a lot all along my studies. I would like also to take the opportunity to express my love to my spouse, Fatima, who supported me the most, during the good and the bad days. x

Grenoble, December 2018

Kassem

List of Figures

List of Tables

General Introduction

Over the past few decades, the increasing usage of electromagnetic waves has spawned a proliferation of new applications creating a real revolution, particularly in areas related to wireless communications. Some of these applications have spread rapidly and massively, resulting in increasing exposure of people to electromagnetic waves. Among this rapid evolution several questions raises about their possible health effects, especially in the industrial environment where the workers are exposed daily and for a long period of time to electromagnetic waves. The proximity of the human body to the radiating source makes the tissues of the body a potential target for the electromagnetic energy emitted.

Different studies are done on the effects of radio frequencies on the brain or the head focusing on cell phones and mobile applications. Epidemiological studies have mainly focused on the incidence of brain tumors since the increase in the use of mobile telephony. On the other hand, few studies have examined the exposure to industrial systems that contribute to the electromagnetic phenomenon. In view of the general anxiety generated by the industrial sector, it is necessary to verify their safety in real conditions of use. At each site, safety zones should be defined in relation to the level of exposure and the access perimeters should be determined. Staffs working in the most exposed areas are thus strictly regulated. At the same time, the European directive 2013/35/EU, released in June 2013, defines the reference and action levels in terms of electric and magnetic fields applicable in the industrial sector, making the employers responsible of their applications.

It is in this perspective that this thesis work was done, as it focuses on the exposure assessments and characterization of the emitted electromagnetic fields, in particular in the industrial environment and provides the employers the necessary tools to understand worker's exposure. The analysis was performed mainly on two applications; the first was the characterization of electromagnetic fields near RFID systems especially those used in libraries, while the other application was the industrial RF welding machines. This analysis made it possible to evaluate the levels of the electromagnetic field in the near-field region and to check if it meets the reference levels given in the international guidelines and directives. A special effort has been made to establish experimental conditions that are consistent with reality.

This work was under two projects, expo@Lyon and EXTI, supported and funded by ANSES (French Agency for Food, Environmental and Occupational Health & Safety).

This manuscript is composed of five chapters. The first one is a reminder of electromagnetic fields in general where their main characteristics are recalled. It also addresses the possible interactions between electromagnetic fields and the matter, where the general parameters that make it possible to quantify this energy are presented. In addition of introducing the main international guidelines and European directives that specifies the exposure limit values and action levels. This chapter was followed by the description of several techniques for measuring electromagnetic fields in the near field region, as well as the electromagnetic field probes in general.

Then the development of a new 3D scanning system for near-field measurements is presented. After that, and for high precision measurement purposes, a new tri-axial magnetic field probes has been designed. These probes measure the three components of the magnetic field simultaneously, that reduces the time of scanning by a factor of 3. Two different probes was designed, the first consists of 3 conventional loops that are combined in a plastic cube with a total dimension of 10×12×13 mm 3 , whereas the second probe is a PCB probe printed on an FR4 substrate with a reduced dimension of 9×9×3.2 mm 3 . These probes were calibrated and the whole measurement system was validated.

The third chapter presents a reconstruction algorithm that requires just the tangential components of the magnetic field in an initial plane to reconstruct the 3D magnetic field distribution above the radiating device. In addition of the tri-axial probe presented in chapter 2 that reduce the scanning time, sometimes multiple scans is needed to build the 3D map of the radiated electromagnetic fields and this is time consuming especially if high resolution is needed. Hence the proposed algorithm solves this problem and reduces the scanning time to the minimum.

The fourth chapter is devoted for the near field characterization of RFID systems used in Libraries. In site measurements was carried out at different libraries in Lyon, using a commercial electromagnetic field probe. And for more detailed study, the analysis was done in the Lab using the fabricated probes near different antenna types including a commercial RFID loop antenna.

Finally, the exposure analysis near RF welding machines is presented in chapter five.ThiskindofmachinesgeneratesastrongRFenergywhileit'sinoperation,as consequence workers are exposed to this energy. This work aims to characterize the field levels in the vicinity of these machines. The effect of a human body immersed in an RF electromagnetic field was studied by simulating a virtual phantom having different material layers. Moreover a numerical model of the machine was developed to compare the experimental data with simulations. Three measurement campaigns were done near a real machine that exists at the site of INRS, where the magnetic and electric fields were characterized.

At the end, the conclusion of the work done within this thesis is presented as well as some perspectives. hence they may be exposed to higher levels than the general public. Moreover, each equipment has its own characteristics, such as the type of the signal generated (continuous, modulated, pulsed…), that can affect the exposure analysis.

Imperceptible in most work situations, electromagnetic fields can, beyond certain thresholds, have effects on the health. Overexposure effects varies from one source to another, for example radiations from high frequency applications may leads to severe burns while the induced currents from low frequency applications may affects the nervous system and the exposed person may experience vertigo and nausea. It is therefore important to recall a few notions in order to assess the risks associated with exposure to electromagnetic fields at the workplace and in the work environment.

This assessment serves as a basis for the implementation of preventive measures to reduce occupational exposures.

In the first part of this chapter, the main characteristics of the electromagnetic fields are recalled, with the possible interaction of EMFs with matter. In order to highlight the different elements of this interaction, the second part of this chapter will be devoted to RF dosimetry reminders and to the general parameters that make it possible to quantify the power absorbed and the rise of temperature in the corresponding biological objects.

ELECTROMAGNETIC FIELDS

1.2.1. Electromagnetic Waves An electromagnetic wave is the combination of an electric field and a magnetic field propagating in the free space at the speed of light. These waves are characterized mainly by their:

 Frequency: which is the number of oscillations at a given point during one second; it is denoted by f and expressed in hertz [Hz]. (IRs) are the waves having their wavelength below 10 nm. Examples of these radiations are X-rays and γ-rays which can break the molecular bonds, normally these waves are used for medical imaging applications [1] [2]. On the other hand, the non-ionized radiations (NIRs) include static electric and magnetic fields, low frequency electromagnetic fields, radio frequencies, infrared radiation, visible light and ultraviolet light. These electromagnetic fields can be from a natural or a manmade origin and they are used for many applications (Figure 12).

Electromagnetic waves in this range can cause biological effects due to the heating produced when interacting with biological objects. The domain of interest concerns the range of radio frequencies (RF) which extends from 30 kHz to 300 GHz.

PW D PRI  ( 1-2)
The PRF corresponds to the inverse of the PRI:

1 PRF PRI  ( 1-3)
In a pulsed electromagnetic wave, the peak or the maximum power P max of a pulse is large compared to the average power P avg . The latter corresponds to the integration of the instantaneous power over the signal period, and we can say that it is the peak power multiplied by the duty cycle; the lower the duty cycle is the lower the average power.

EM Wave Propagation Zones

The electromagnetic wave does not have the same propagation properties in the entire space around a radiating source. Starting from the different components of the electromagnetic field of an elementary dipole or loop, we find that these zones are characterized by the wave impedance. The behavior of transmitted fields is dependent on the nature and the frequency of sources that generates these waves.

Moving away from the radiating source, we distinguish mainly two propagation zones, the near-field and the far-field zones, Figure 1234.

……

Power

Time

PW PRI P avg P max

Near field zone

The near field region is mainly defined when the distance from the radiating source r is:

2 r   ( 1-5 )
In the near field zone, the radiated electric and magnetic fields are independent of each other. The origin of the radiated field depends on the nature of the source. Indeed, the magnetic loop (magnetic dipole) essentially provides a magnetic field and in the same way an electric dipole mainly provides an electric field. The wave impedance is obtained with equations ( 1-6 ) and ( 1-7 ) for the electric and magnetic dipoles respectively, with approximation according to (1)(2)(3)(4)(5) In this zone, the characteristic impedance is proportional to 1/ kr for the electric dipole and to kr for the elementary magnetic loop. For the value of /2 r   , the impedances tend towards the intrinsic impedance . This distance is commonly used in electromagnetic compatibility to define the boundary between the near field area and the far field regions.

The characteristic impedance modules of the elementary electric dipole Z E , the elementary magnetic loop Z H and the vacuum  are presented in Figure 12345. The near field zone is divided into two regions, reactive near field and radiating near field. The reactive near field region is very thin and is at a distance R 1 from the antenna: In this zone, the waves are evanescent and the phenomenon of propagation is negligible. The radiative near field region, also called Fresnell zone, is an intermediate zone located between R 1 and R 2 .

3 1 0.62 d R   ( 1-8 )

Far field zone

The far-field region, also known by Fraunhofer zone, lies beyond the distance R 2 , or when the distance r is:

2 r   ( 1-10 )
The far-field zone is introduced to simplify the formulation of wave equations.

The radiated energy is confined in a conical beam and the waves are locally almost planar. In this zone, the notion of separation between purely electrical behavior and purely magnetic behavior is no longer valid. Indeed, the wave impedance is equal to the characteristic impedance of the vacuum , that is equal to 120π or 377 Ω,and the wave formed by the electric and the magnetic fields is a transverse plane wave. In addition, the E and H fields are orthogonal and their amplitudes decrease in a ratio of 1/ r .

In this work, we are interested in the near field region where the transverse wave hypothesis is no longer valid. The calculation of the electromagnetic fields then requires the implementation of direct numerical calculation of the Maxwell's differential equations.

ELECTROMAGNETIC COMPATIBILITY

Electromagnetic Compatibility (EMC) is the ability of a system to function satisfactorily and without producing intolerable electromagnetic disturbances for any other system in its environment. Human beings are considered as systems as well, so human safety is also a subject of EMC analysis.

A general model of all EMC configurations mainly consists of:

 Source: the transmitter of the disturbing or parasitic signal  Coupling: the interaction between the source and the victim  Victim: the receiver of the transmitted signal  Radiated emissions: when the source produces an electromagnetic field that propagates in the space. The effect on the victim depends on the nature, frequency and distance from the radiating source.

 Conducted emissions: here the electromagnetic disturbances are transmitted via the electrical connections between different devices.

Source Victim

Coupling Path

-Conductive -Radiative

Obviously currents and parasitic voltages circulating in the cables interconnecting equipments will radiate themselves. Similarly, the radiated disturbances will be able to induce stray currents and voltages in the various interconnections. The conducted and radiated perturbations are therefore intimately coupled. EMC refers, in general, to the effects on equipments, devices, electronic systems. However, several electromagnetic phenomena are to be considered: thermal and non-thermal effects on biological tissues. In this case another definition is used, bio-electromagnetic compatibility.

Near-field characterization

Near-field characterization is a necessary step in EMC measurements as well as exposure analysis of electromagnetic radiation in the space surrounding a device under test (DUT). Near-field measurements are carried out using a bench that consists of probes, sensitive to different components of the radiated electric and/or magnetic fields, and a scanning system that maps the amplitude and/or phase of the radiated field. These measurements make it possible to locate the sources of radiation in electronic cards and to extract the electromagnetic behavior near different devices.

A near field test bench is adapted to perform automatic measurements in the space surrounding the DUT. There are several techniques for measuring electromagnetic fields in the near field region. We are interested in those using electromagnetic field probes because it

Analyzer Positioning System

DUT

Probe

PC

is the easiest to implement. Here we can differentiate between two configurations of the used probe; the first one is the direct probe method that uses a small antenna or probe. This probe is placed in the environment close to the device to be characterized and the mapping of the electromagnetic field is obtained by scanning the probe above the surface of the device (Figure 1234567) or by moving the device under the probe. The second one is to use an array of probes (Figure 12345678) to capture the radiated electromagnetic field. In the latter, the field is captured by a one-shot or multi-shots depending on the dimensions of the probe array as well as those for the DUT. The near-field scan (NFS) measurement technique relies on the use of measurement probes based on miniature magnetic loops, for magnetic field measurements, or electric dipoles, for electric field measurements. The detection of the electromagnetic field is carried out using, for example, a diode detector, spectrum analyzer or network analyzer. The probes are connected using transmission lines such as coaxial cables and an amplifier can be used to improve the sensitivity of the test bench.

DUT

Array of Probes

INTERACTION BETWEEN EM FIELDS AND MATTER

The propagating electromagnetic wave can meet different obstacles. Depending on its wavelength and the electromagnetic characteristics of the material encountered, such as permittivity, different types of interactions can occurs as reflection, refraction, diffraction, diffusion, and absorption. This section aims to provide a better understanding of the specific properties of NIRs in the radiofrequency range. In contact with matter, the electromagnetic wave is splitted into a reflected wave and a transmitted wave (Figure 123456789). The transmitted wave is the most significant parameter for quantifying the dissipation of energy within the material. Depending on the frequency range, wave penetration and interactions with biological tissues are not identical and the wave-matter interactions of NIRs do not rely on the same physical properties of the wave. As a result, the physical quantities are not the same and the biological effects vary according to the type of radiation.

Sensitive tissues and organs vary depending on the type of interaction. For the low frequencies, the main effects concern the stimulation of excitable tissues such as the muscles, the cardiovascular system, and the central nervous system. The higher frequencies cause a warming (temperature increase) of the tissues with a penetration that is lower as the frequency is high.

To know precisely the effects produced by an electromagnetic field in a biological medium, it is important to know the electrical characteristics (relative permittivity ε r and the conductivity ζ) of this medium. Biological media have both free charges and bound charges which, under the effect of an applied electric field, are responsible for conduction and polarization currents. The human body is globally considered non-magnetic with regard to the study of induced electromagnetic fields;

the magnetic permeability of biological media is thus assimilated to that of vacuum μ 0 . In biological tissues, the free charges that can create conduction current are ionic in nature. These ions are more or less free to move under the effect of an applied electric field and are subject to friction forces and stresses due to the structure of the medium. Their mobility is a function of the frequency of the applied electric field.

The presence of polar molecules of different size, also subjected to friction forces, gives biological media lossy dielectric behavior.

A thermal effect is caused by a heating of biological tissues. Indeed, because of their polarized nature, water molecules subjected to an oscillating electric field tend to follow the orientation of this field. Due to the intermolecular friction generated by sufficient power, a rise in temperature occurs. This heating varies according to the power of the electromagnetic field. The threshold of appearance of a thermal effect corresponds to a rise of 1°C in body temperature in humans [8]. Below this value, the body's thermoregulatory system is able to maintain body temperature.

A non-thermal or athermic effect is not induced by a significant rise in temperature. It appears at exposure levels for which the thermoregulatory system of the exposed organism is able to regulate the temperature and to dissipate a possible heating. In recent years, many results on wave-living interactions have been published. The study of physical and biological phenomena is very complex and therefore imposes extreme rigor in the development of experimental, measurement and observation procedures.

In this work we are not going to check the effect of the electromagnetic fields on the tissues and biological organisms, rather the aim is to quantify the exposure parameters refereeing to the international guidelines and standards that defines the corresponding limits that may leads to thermal effects.

RADIOFREQUENCY DOSIMETRY

RF dosimetry is the quantification of the electromagnetic fields being absorbed by biological objects that are exposed to electromagnetic waves. RF dosimetry is the study that addresses the effects of electromagnetic radiations on the living organisms.

Different dosimetric quantities are used to characterize the radiation levels.

Depending on the considered frequency band, the interactions of an EM wave of NIRs with matter are not based on the same physical quantity. The relevant measurement units to characterize the interactions are thus not the same and biological effects vary depending on the type of radiation.

The purpose of the dosimetric study is to evaluate the impact of electromagnetic radiation on living beings by quantifying the levels of EM fields as well as the absorbed powers.

It can be conducted both experimentally, requiring the implementation of specific exposure systems and the use of dedicated sensors, and by numerical simulation.

Dosimetric studies are also essential for defining and updating national and international standards and recommendations related to the use of radiofrequency technologies.

Quantification Parameters

Electric field (E)

The electric field is defined by the force F that appears due to an electric charge q. An electric field appears as soon as electric charges are in motion. This field propagates at the speed of light in the free space. The magnitude of the electric field at a distance r from a charge q canbederivedfromcoulomb'slawasfollows:

2 0 4 r q E r    ( 1-11 )
It is expressed in volt per meter [V/m]

Magnetic field (H)

Magnetic fields appear when an electric current passes through a conductor; its intensity is expressed in ampere per meter [A/m]. Certain materials such as those intended to manufacture magnets emit in their environment a magnetic induction without the presence of a current. As an example, suppose that we have a wire with a radius r, the passing electrical current I through this wire generate a magnetic field in the region surrounding the wire with an intensity H given by: 2

I H r   ( 1-12 )

Specific Absorption Rate (SAR)

At the interface between the biological medium and the external environment, part of the radiated electromagnetic wave is transmitted within the tissues. Faced with the difficulty of formally correlating the external electric and magnetic fields with the biological effects generated, the quantification of the energy absorbed by the tissues proves to be the most coherent approach for the study of the interactions between waves and the biological medium. SAR is the appropriate parameter for quantifying the tissue absorption of electromagnetic fields. It is rigorously defined as the time derivative of the quantity of energy absorbed dW by a tissue of mass dm contained in an volume dV of a known density density ρ:

d dW d dW SAR dt dm dt dV         ( 1-13 )
To evaluate SAR expression, it is necessary to know the physical quantities involved in the interaction phenomena between the electromagnetic wave and the biological medium. The electric field within the tissues has the effect of causing a heating of the medium. Thus the power absorbed by the tissues is evaluated in two ways: either by the determination of the electric field in situ or by the characterization of the temperature rise induced by the RF exposure:

 by the electric field in situ:

2 E SAR    ( 1-14 )
where ρ and ζ are respectively the density and the electrical conductivity of the medium and E is the effective value of the electric field  by the temperature rise in the tissue:

T SAR C t    ( 1-15)
where ∂T is the temperature rise (in degrees Kelvin, K) during the exposure time ∂t (in second, s) and C the heat capacity mass of the tissue (in J/(kg.K)).

SAR has two forms:

 average SAR: it is averaged over the whole body and corresponds to exposures whole body (case of the base stations for example)

 local SAR: it is averaged over 1 g or 10 g and corresponds to localized exposures (case of mobile phones for example).

Numerical Dosimetry

Numerical dosimetry is the numerical modeling of the exposure system with the biological medium exposed to an electromagnetic field. Numerical methods have been developed to solve Maxwell's equations in the biological medium taking into account the electrical properties (electrical conductivity and dielectric permittivity) of this medium. The interest is then on the evaluation of the intensity of the electric and magnetic fields within the structure. In numerical calculations a segmentation process is applied on the studied medium, so it is decomposed into elementary volumes called voxels.

Since the late 1970s, numerical computational methods have developed rapidly, with major interest in modeling human and animal anatomy. One of them is the method of moments (MoM) in which the human body is divided into blocks each containing its own electrical properties [9][10]. This method was widely used in the 1980s for the numerical evaluation of the average SAR. Since the 1990s, it has been superseded by the finite difference time-domain method (FDTD), first introduced by Kane Yee in 1966 [11]. It allows, at any point of the discretized space, to calculate the components of the electromagnetic field at a time t from those calculated at the previous step at the neighboring points. The advantages of this method are the relatively simple formulation, the robustness of the algorithm, and the resolution capability over wide frequency bands. This method allows modeling both the sources of exposure and the propagation of electromagnetic waves in vacuum or in complex materials (such as the biological human tissues) in the temporal and spatial domain.

The spatial approach therefore implies the possibility of determining the SAR at any point in the structure from the components of the electric field calculated in each cell and the dielectric parameters of the studied tissues or numerical models. There are also other SAR evaluation methods based on the hybridization of the FDTD method as we can found in [12][13].

Numerous software programs are available for electromagnetic computation where the interaction between electromagnetic fields and different objects can be analyzed, based on different methods, including the numerical mapping of the, Efield, H-field, and SAR within a biological structure. For example, High Frequency Structure Simulator (HFSS) is a software from ANSYS that is based on the finite element method (FEM), also CST Microwave Studio is based on different methods mainly finite integration technique (FIT) for transient solver, FEM for frequency domain solver, and MoM for integral equation solver as well as the transmission line matrix method (TLM).

Experimental Dosimetry

Experimental dosimetry is complementary to the numerical one. The experimental approach encounters difficulties related to in vivo measurements, since there are some problems related to the implantation of the measuring instrument in a living organism and also due to the strong heterogeneity of the tissues. On the other hand, in vitro experiments, does not encounter these difficulties. The instrumentation required for the measurement of the electromagnetic field will be presented in the next chapter. In order to ensure a good repeatability of the measurements and duo to the difficulty of in vivo measurements, phantoms have been developed. These phantoms are filled with liquids or gel substances simulating the electrical properties of the human body tissues. Numerous experimental evaluations have been conducted

on phantoms [14]- [16]. The made phantoms are mostly homogeneous because it is difficult to manufacture heterogeneous structures based on liquid or gelled substances. However, some heterogeneous achievements have emerged, notably using solid materials for bones and liquids for tissues containing a lot of water [10], [11].

The tissue simulated liquid (TSL) depends on the type of each tissue and on the frequency of study. Numerous studies have established suitable compositional formulas for the fabrication of the materials used in these phantoms. These materials are referenced in international standards for RF dosimetry [19], [20]. The solutions contained in these phantoms are generally composed of high permittivity liquids, such as water, in which liquids having lower permittivity are added. The value of the conductivity ζ is then adjusted by adding salt.

STATE OF THE ART IN MEASUREMENTS OF EM FIELDS

The evaluation of exposure to electromagnetic fields consists of measuring the intensity of electric and magnetic fields at a given point away from the radiating source. In the far-field region it is enough to measure only one of them, either the electric field or the magnetic field, and then the other can be calculated based on the relation between them in the fee space that is E =120π×H. However, in the near-field region it is not the case, where both the electric and the magnetic fields should be measured separately. Different equipments have been used to measure electric or/and magnetic fields levels near radiating devices. For electric field measurements in the frequency range of 440 MHz to 3 GHz, ETS-Lindgren's 3125 balanced dipole series [21] can be used, these antennas are designed to match the operating frequencies of mobile phones and wireless applications, also bi-conical antennas like AP2000 can be used for environment exposure measurement in the frequency range from 60 MHz to 2.5 GHz [22]. On the other hand, for magnetic field measurements different loop antennas are used, for example the active HMDA 1545 ETSI 3125 series loop antenna HMDA 1545 is a magnetic field strength meter that measures the field in the frequency range of 9 kHz to 80 MHz [23]. This kind of probes needs to be connected to a measuring instrument, like spectrum analyser, to record the field levels. However, there exists different kind of meters that integrates their own analyser like NIM-511, NBM 520, SRM3006, and others from Narda test solutions (Figure 1 -11), where both electric and magnetic field probes can be found for different frequency ranges for these meters [START_REF]NedapLibrarySolutions,-PG45Stylishand discreet protection of your librarycollection[END_REF].

These measuring instruments are used in wide variety of applications, from EMC testing to exposure measurements. Nevertheless, their spatial resolution is a limitation in some applications as their sizes is not so compact, in addition to their high price. This leads us for fabricating other compact probes for EMC and exposure measurement applications that will be presented in chapter 2.

NIM-511 NBM 520 SRM 3006 1.7. STANDARDS AND GUIDELINES

Different guidelines and standards have been established to manage people's exposure to electromagnetic radiations. In 1998, ICNIRP (International Commission on Non-Ionizing Radiation Protection) established in its guidelines the exposure limit values for a spectrum extending up to 300 GHz [8]. ICNIRP defines the reference levels for the general public and workers (Table 1-1). Exposure limit values (ELVs) are defined and reassessed regularly in articles published in peer-reviewed scientific journals on the thermal and non-thermal effects of radiation. The standards are based on the assessment of the biological effects whose health consequences have been established. Reference levels were used as the basis for the definition of the European Recommendation 1999/519/CE [25], setting the limit of public exposure to electromagnetic fields, and the Directive 2004/40/CE concerning the minimum safety and health requirements relating to worker exposure [START_REF]29 avril 2004 concernant les prescriptions minimalesdesécuritéetdesantérelativesàl'expositiondestravailleursauxrisques dusauxagentsphysiques(champsélectromagnétiques).‖Journalofficieldel'Union européenne[END_REF]. CENELEC (Comité Européen de Normalisation ELECtronique) has also taken these values into standardization [START_REF]CENELEC,-Humanexposuretoelectromagneticfields,ENV50166-1(low frequencies) and ENV 50166-2(highfrequencies)[END_REF]. In the United States, IEEE (the Institute of Electrical and Electronics Engineers) itself has published several standards [19], [START_REF]IEEEC95.1-1999 Standard for Safety Levels with Respect to Human ExposuretoElectric,MagneticandElectromagneticFields,0Hzto300GHz[END_REF], [START_REF]IEEEC95.3-2002 Recommended practice for measurements and computations of radiofrequency electromagnetic fields with respect to human exposure to such fields, 100 kHz-300GHz.‖IEEEStandardsAssociation[END_REF]. The reference levels or the electric and magnetic fields limit values for the protection of users against the harmful effects of non-ionizing radiation, ensure compliance with the basic restriction. These limit values are established on the basis of the proven thermal effect of microwaves and are accompanied by a margin of safety between workers and the general public. For example, for whole body SAR, the critical biological effects are notable, in animals, from 4 W/kg, ICNIRP considers that the first effects appear from this threshold of SAR which corresponds to a rise of 1° C in temperature. In humans, and based on a safety factor of 10, the exposure limit was set at 0.4 W/kg (whole body SAR). For general public, an additional safety factor of 5 in relation to the occupational exposure limit has been introduced. The safety factor with respect to the occurrence of proven effects is therefore 50. The SAR limit of whole body exposure for the public was therefore set at 0.08 W/kg. These reduction factors are introduced to account for scientific uncertainties related to experimental errors as well as taking into account people who are not informed about their environment and the varying sensitivities of people according to their physiological or pathological state (sick, elderly, children, etc.). ICNIRP also recommends limits on local SAR in the case of inhomogeneous exposure (Table 1-2). particular on the basis of scientifically well-established short-term and acute direct effects, i.e., thermal effects and electrical stimulation of tissues. However, it does not address long-term effects since there is currently not enough scientific evidence for this. The Directive also allows for exceptions in medical applications using magnetic resonance imaging (MRI), for some special sectors subject to the Member State's decision, but only if the circumstances duly justify exceeding the ELVs, and this on a temporary basis [START_REF]Electromagnetic fields in working life A guide to risk assessment[END_REF].

In order to facilitate assessment, the Directive gives ELVs for health effects as well as sensory effects and action levels (ALs) for the EMFs. Since the exposure limits values are given in quantities that are not possible to measure in a workplace, the action levels will become in most cases the de facto limits. The ALs are given for electric and magnetic fields, induced and contact currents which are measurable quantities [START_REF]Electromagnetic fields in working life A guide to risk assessment[END_REF].

CONCLUSION

In this chapter we have presented a general review about the electromagnetic field phenomenon including the possible interaction between these waves and the biological mediums. Then we introduced the RF dosimetry in its two branches the numerical and experimental. As well as the used probes and field measurements devices that exists nowadays for exposure analysis. The end of the chapter was about the existing standards and international guidelines that give the exposure limit values and the reference levels to be respected from the general public as well as the professionals.

The next chapters will be mainly divided into 2 parts. The first is about the development of a near-field measurement system with a new tri-axial magnetic field probe, and also an algorithm for predicting the 3D magnetic field distribution above a radiating device starting from the tangential components at an initial plane. The second part is dedicated for the exposure assessment of two applications, RFID systems used in libraries, and RF welding machines used in the industrial sector. Different types of probes are used to measure the components of the electric and magnetic fields (coaxial probes, electro-optical probes, PCB probes…). These sensors convert the local electromagnetic energy radiated by the device into a voltage to be measured by the receiver. These probes have the main characteristic of being of small dimensions with respect to the wavelength in order to limit the induced disturbances and to allow a local detection of the electromagnetic field with a good resolution. NFS method has the advantage of being transposable in an industrial environment. However, the many metal parts present at the probe and the connection cables disturb the local electromagnetic field causing a bias in the measurement. In addition, the presence of flexible transmission lines can lead to precision problems with amplitudes and phases measured at high frequencies.

This chapter has been devoted to the description of the developed near-field measurement test bench. To do this, we will begin with an introduction on the electromagnetic field probes in general. Next, we describe the developed near field test bench that includes the measuring instrument and two scanning systems. After that we present the designed tri-axial magnetic field probe as a new three axis probe that measures the three components of the magnetic field simultaneously, as well as the calibration method of the measurement chain. In the last part, the validation of the whole system is shown.

ELECTROMAGNETIC FIELD PROBES

An electromagnetic field probe is a sensor that captures the field radiated by an electrical device or system in operation. The electric or magnetic character of this field depends respectively on the variation of voltage and the fluctuations of current inside this device. Once produced, the radiation of the field is propagated in a given direction in the space.

It is therefore essential to choose a specific probe for the detection of this field.

There are two types of electromagnetic field probes: electric field probes and magnetic field probes.

Electric-field Probes

Generally the electric field probes are in the form of a dipole, or monopole, and they are sensitive to voltage variations. When subjected to an electric field, a potential difference appears at its terminals. Indeed, the voltage across the probe is related to the electric field by the following

relation [1],[2]:   /2 /2 sin 2 h x h h V k x E x dx          ( 2-1 )
This relationship shows that the sensitivity of this sensor depends on the length of the dipole. The longer the strand, the more sensitive the probe is. On the other hand, the shorter the strand is the better the spatial resolution. The orientation of the probe specifies the corresponding E-field component measured. The orientation of the Electric field probes can be made with a coaxial cable or printed circuit board (Figure 2-3).

Magnetic-field Probes

In general, magnetic field probes are in the form of a loop, they are sensitive to current variations. When a magnetic field crosses the loop, an induced electromotive force (emf) appears at its terminals. This emf can be measured using an oscilloscope or spectrum analyzer in the form of an electrical voltage. The amplitude of this voltage depends on the surface of the loop and the amplitude of the magnetic field crossing the surface of the loop.

Magnetic field passing through a loop generates a voltage across its terminals accordingtoFaraday'slaw,whichstatesthattheinducedvoltageisproportionalto the rate of change of magnetic flux through a circuit loop [2]:

. For a given probe, there is a relation between the voltage obtained at its terminals and the field value which passes through it. These two quantities are linked by the antenna factor which is presented in the next section. Several architectures can be used to design near-field probes (Figure 234). Coaxial probes can be made with or without shielding. Without shielding, the loop may be small, but it has a higher capacitive coupling coefficient than shielded probes. However, shielded probes do not provide good spatial resolution due to the large size of their loop. A printed circuit can also be used to make a magnetic field probe. The orientation of the probe specifies the corresponding H-field component measured, the axis that it is orthogonal to the loop surface is the measured component.

emf S dd V B dS dt dt       ( 2-2 )

Coaxial probe PCB probe

EM-FIELD PROBES PARAMETERS

Different parameters define the performance of the electric and magnetic field probes. We recall these parameters below:

Antenna Factor

The antenna factor (AF) represents the ratio between the amplitude of the magnetic or electric field and the amplitude of the voltage induced across the probe terminals.

      . / 1/ ind E V m AF m VV  ( 2-3 ) Coaxial probe PCB probes       . / / ind H A m AF S m VV  ( 2-4 )
The probe should be placed in an area that we can know the H or E fields inside it either theoretically or by calculation. Then the AF can be calculated by evaluating the ratio between the theoretical or simulated value of the fields of the radiating circuit and the voltage measured by the corresponding probe (V ind. ) in its frequency band. The analytical expressions of the various EM field components are a function of the geometrical parameters and the power injected to the used circuit. The process of extracting the AF of probe also called calibration; we will talk about different techniques in section 2.7.2 .

Selectivity

The selectivity corresponds to the separation of the probe between the components of the electric and / or magnetic field. In other words, it represents the ability of a probe to measure predominantly a component of the EM field for which it is intended.

Sensitivity

The sensitivity corresponds to the minimum detectable level of the measured quantity. This quantity is directly related to the antenna factor of the probe and the noise level of the measuring instrument. It is necessary that the probe has a good sensitivity to allow the measurement of even lower values of the electric or magnetic field. The magnitude is proportionally related to the geometric dimensions of the probe. On the other hand, the spatial resolution is inversely proportional to the size of the probe. Therefor a compromise between the sensitivity and spatial resolution must be taken into consideration during the design of the probe.

Spatial resolution

The spatial resolution represents the minimum distance between two adjacent sources that a measurement probe can dissociate. This parameter is related to the size of the sensor and the distance to the device under test. It is necessary that the sensor has the smallest possible dimensions to have a good spatial resolution. The lower this parameter for a probe, the more accurately it will be able to accurately distinguish the fields emitted at measurement points, but this is affects the probe sensitivity.

Frequency band

The frequency band reflects the frequency range in which the probe must be functional [f min -f max ]. The value of the minimum frequency f min is determined by the sensitivity of the measurement probe while the value of the maximum frequency f max is strongly related to the selectivity. These different criteria are somewhat contradictory, which sometimes makes it difficult to make a compromise in order to obtain an acceptable solution allowing the realization of measurement probes appropriate to the desired application.

DEVELOPMENT OF THE 3D NEAR-FIELD SCANNING SYSTEM

The near-field test bench is intended to be an EMC diagnostic tool for printed circuits, integrated circuits, and also for small antennas near field characterization. It must be able to selectively measure the different components of the electric or magnetic fields with a good sensitivity and a good spatial resolution. The displacement of the probe above the device under test is provided by scanning system that should be able to make a 3D scan in the region of interest. In this work we developed 2 scanning systems for different applications depending on the physical size of the DUT, one dedicated to small devices and the other for large ones.

The first, is a delta robot from ALIRA [3] having three translation axes x, y and z. This Robot features a single arduino-based electronic board megatronics version 2.0, which has a powerful ATmega2560 processor with 256kB of memory, clocked at 16 MHz. It is programmable from the standard arduino integrated development environment (IDE). The system is designed by the company for 3D printing applications,but we'd modified it to fit our application in near field scanning. The useful area is 18 cm for the x-and y-axes and 20 cm for the z-axis. The mechanical resolutionofthesystemis100μmforallaxes.Oneachaxisthereisasensorallows returning to the initial position of the robot as well as limiting the moving block, indicating if one of the axes exceeds the allowed margin. The robot arm then offers the possibility of mapping a surface of 18×18 cm 2 . Its mechanical resolution of 100 μm offers the possibility of good field mapping resolution depending on the used probe.

Design & Characterization of Tri-Axial Magnetic Field Probes A software interface based on a Labview program was developed in order to automatically control both the mechanical movement of the robot and data collection from the measuring instrument. The measuring instrument, that is the WaveRunner oscilloscope in our case, is connected internally to a PC via GPIB while the scanning robot is connected to the PC via USB type B serial com port. The developed program is integrated with Labview run-time engine; hence it can be run on any PC without having the Labview software.

The program was done such that at each point in the scanned grid, it sends a run command to the Visual Basic Script (VBScript) on the WaveRunner oscilloscope to perform the corresponding data acquisition. The used measurement instrument has various functions that could be assigned on the measured signal, in both time and frequency domains. Up to 8 functions could be applied at a time. These functions are x min.

x max.

y min.

y max.

y-axis x-axis Scanning Path Scanned Area

programmed in a VBScript with the specific commands defined by the LeCroy automation manual [4].

The software interface has 2 main windows, positioning and scanning configuration. In the positioning window; one can assign manually the point of interest and click on the corresponding bottom that leads to the movement of the robot arm to the desired position and the needed measurement is done. The measured data is then saved in a .txt file in the selected directory.

The scan window, shown in Figure 2

MEASUREMENT CHAIN

The near-field test bench will then be as shown in Figure 1234567. A probe is connected to a measuring instrument (network analyzer, spectrum analyzer or oscilloscope) and placed in the environment close to the device to be characterized.

Mapping of the electromagnetic field is achieved by scanning the probe over the device on a predefined surface by the user. A computer controls the movement of the probe and ensures the acquisition of data from the measuring instrument.

The vector network analyzer (VNA) is a measuring instrument that is used to recover both the amplitude and the phase of the electromagnetic field, which gives the possibility to develop models of radiated emissions and in the post-processing of the near-field data [5]- [8].

x-axis y-axis Robot arm

For passive circuits, the use of VNA allows simultaneous measurement of the amplitude and phase of the electromagnetic field. The excitation of the DUT is injected from one port of the VNA and the other port is connected to the used probe, hence the transmission coefficient S 21 will then be used to extract the desired electromagnetic field. In this work we propose a new measuring instrument to be used instead of the VNA and the SA. We will use Teledyne LeCroy WaveRunner 640Zi oscilloscope. It is an oscilloscope that has the option to measure in frequency domain as if it is a spectrum analyzer, and it has 4 input channels [9]. The probes are attached to the robot arm which moves them over the device under test to perform the needed scan. The PC acquires data measured by the oscilloscope. These data (voltages) are converted into electric or magnetic fields using the specific antenna factor of each probe.

EM-FIELD PROBES CALIBRATION TECHNIQUES

Electromagnetic field probes are indirect sensors, the measured quantity at the probe terminals is an intermediate quantity that represents the field measured. In order to extract the correct value of the corresponding field a probe factor should be used. Calibration is the process done to find the probe performance factor which is also called the antenna factor (AF) or calibration factor. It is a transfer function between the measured voltage across the loop / dipole and the magnetic / electric field in the scanned geometry. For calibrating electromagnetic field probes we need to generate a reference field whose intensity and spatial configuration are known with good accuracy inside a certain volume where the calibrated probe is placed.

Several probe calibration techniques are available in literature. For example, for low and medium frequency bands (9 kHz -10 MHz), Helmholtz coil can be used, but it is not a preferred method. However for large size probes or high field levels this method is used [11]. For a frequency band of 200 MHz -450 MHz, an openended wave guide is used, and for higher frequencies (450 MHz up to 40 GHz) the pyramidal horn antennas, and conical transmission lines are used [12]. Transverse Electromagnetic (TEM) and Gigahertz TEM (GTEM) cells are also used for probes calibration with a moderate frequency band (9 kHz -1 GHz) that is common in different EMC applications [13].

The fact that TEM cells are fully shielded makes it good for probes calibration as there is no interference between the calibrated probes and the nearby devices. As well as it features a long term stability of the calibrating system. The TEM cell is a section of a strip line that has a middle conductor (called septum) between two plates that are tapered from the ends. Normally the septum is located in the midway between the top and the bottom conductor plates, and the wave propagates in a TEM mode in the area in between. The dimensions of the section are chosen to have characteristic impedance of 50 Ω along the cell. Wave Impedance 377Ω

The field strength can be theoretically calculated from the geometrical parameters of the cell, its impedance at the measurement plane, and the input power as shown in the equations below [14]:

. [watt] [ / m] [] c in ZP EV hm  ( 2-5 ) Port 2 Septum Outer Shield Port 1 h ( 2-6 )
Where c Z is the input impedance of the measuring instrument in ohms is the input power in watts is the distance in meters between the septum and the outer conductor of the TEM cell is the intrinsic impedance of the free space in ohm 0 0 120 377

      ( 2-7 )
The antenna factor then can be calculated by placing the probe inside the TEM cell and measuring the induced voltage across the loop terminals, according to the following equation:

(

where V ind. is the induced voltage in the loop (in volts)

Depending on the measuring instrument V ind can be calculated. When using a VNA, we measure the transmission coefficient (S 21 ), while if we use a spectrum analyzer the power is then measured. These two quantities can be easily converted into voltages by using the following expressions respectively: In the center of the TEM cell between the septum and the upper (or lower) conductor, the electric field is vertically polarized while the magnetic field is horizontally polarized and orthogonal to the electric one and both are quit uniform in this region. If the dimension of the calibrated probe is less than on third of the height h, the effect of the probe insertion on the perturbation of the field is less than 10% [15], [16]. A numerical simulation of the used TEM cell was performed on HFSS in order to check the field uniformity. The first port of the cell was excited with a 10 dBm signal, while the other one was terminated with a 50 Ω impedance. The simulated model is shown in Figure 2

( 2-9 ) . [ ] . ind c SA watt V Z P  ( 2-10 ) [ / ] [ / ] [] E V m H A m    in P h  . / [A/ m] [dB ] 20log [] ind A m H AF V V V    

SINGLE MAGNETIC FIELD PROBES

As stated in section 2.2, the magnetic field probe is formed from a loop that it could be made from a simple wire or fabricated on a PCB. In this section we will address two configurations of magnetic field probes, the first one is a circular loop of a simple wire and the second one is a square loop designed on an FR4 PCB. These proposed probes was designed and simulated on HFSS, then validated using a standard circuit.

Probes Description

The first probe, named P1 xy consists of a circular loop with 3-turns of 0.5 mm wire with a spacing of 0.5 mm between each turn and having a total diameter of 6 The connection of these probes to the measuring instrument will be via a coaxial cable that it is connected to the top the probe (loop terminals as shown in The equivalent circuit for a simple circular loop, with a radius r 1 , can be as shown in Figure 2-21. Where L is the self-inductance of the loop, C is the selfcapacitance of the loop, and R is the radiation resistance given by:

1 0 1 2 8 ln 2 r L r r          ( 2-11 ) 0 1 2 1 r C   ( 2-12 ) 0 1 2 2 r R r    ( 2-13 )
where the loop wire has a radius r 2 andconductivityσ.

Assuming that a plane wave hits the loop having the electric field along the loop surface while magnetic field is perpendicular to it; this configuration corresponds to the maximum interaction between the loop and the EM wave. In this case only firstorder electric response V E and ideally pure magnetic response V H are considered, with:

1 E V r E   ( 2-14 ) 2 0 1 H V j r H    ( 2-15 ) Figure 2-21: Simplified equivalent circuit model of a loop C L Z V H V E V m Z V m ~ R r 2 r 1
AF can be calculated theoretically for the studied probes, depending on the geometrical parameters of each one. The corresponding formula for a loop probes is given by:

1 theoretical AF j NS   ( 2-17 )
Where ω is the angular frequency given by ω=2πf µ is the permeability of the medium S is the area of the loop surface N is the number of turns The results are in good agreement compared to the theoretical calculations, however at high frequencies the AF for P1 xy is little bit different and this is expected due to the fact that the wavelength at these frequencies starts to be comparable to the probe size, and the effect of the 3 turns of the loop in the probe.

Selectivity

As we stated before, the selectivity of a probe is the ability of this probe to distinguish between the main component measured by the probe and the other field components. In other words, in the case of a magnetic field probe, the selectivity is how can it differentiate between the normal component of the magnetic field, that is perpendicular to the loop surface, from the tangential components. The measured S 21 for the first probe P1 xy shows that the probe selectivity is acceptable below 300 MHz, in which it is more than 10 dB, but at higher frequencies it starts to decrease to reach about 3 dB at 1 GHz. This is expected as the probe has 3 turns which leads to such problems at high frequencies. The electromagnetic field above the reference circuit was computed theoretically using the expressions of the transverse electric and magnetic field components that are obtained by electrostatic calculation with the use of image theory [21][22], and they are given by:

2 2 2 2 8 ( ( ) )( ( ) )
y yzn E K y z n y z n            ( 2-18 ) 2 2 2 2 2 2 2 ( ) 4 ( ( ) )( ( ) ) z n y z n E K y z n y z n              ( 2-19 ) 1 y z H E   ( 2-20 ) 1 z y H E   ( 2-21 )

Cylindrical Conductor

the theoretical plot are not detected by the probe, and this is due to the small wave length at these frequencies. Also at low frequencies the sensitivity of the probe is not good but the peak of the field is still detectable. Adding a LNA between the probe and the measuring instrument can solve the problem of sensitivity. The z-component of the magnetic field H z measured with P1 z seems to be good until hundreds of MHz, but at higher frequencies the sharp valley is not detected. This is due to the small wavelength at these frequencies if compared to the probe size and on the other hand the measurement is affected by the bend made in this probe for detecting the z-component as presented in 2.7.1.

On the other hand, measurements with the PCB probe P2 xy are better than those measured using P1 xy , this can be clearly seem in Figure 2-32. At 1 MHz the probe is more sensitive and at high frequencies the measured field is in good agreement with the theoretical one.

For z-component measurements using P2 z , at low frequencies the results are quite good but it seems that the probe is little bit sensitive, while until hundreds of MHz the measured values are very good if compared to the theoretical values as shown in Figure 2-33. However at high frequencies the probe is affected by the DUT itself, as it is clear that one peak is detected while the other is not and this is due to the coupling between the cylindrical line and the probe.

DEVELOPMENT OF TRI-AXIAL MAGNETIC FIELD PROBES

In near-field characterization it is necessary to have all the three components of magnetic or electric field. This requires a large number of scans if using single probes, which measures one component of the field at a time, and therefore large scanning time in order to complete one surface near the DUT. In order to minimize the scanning time we propose a three axis probes which measures the three components of the magnetic field at the same time. In this section we present the design and the calibration of these probes. They are based on the single probes presented in the previous section. with an SMA connector at the other end to be connected to the measuring instrument. Also a 10 cm plastic road holds the probe and it is used to be attached to the scanning robot arm, in addition the probe and the road was covered with a plastic shield that makes it possible to perform measurement inside liquids.

Design

For better spatial resolution as well as suffering from fabricating the probe manually (that is the case in P1), we propose another tri-axial probe P2 that is made in PCB technology. The printed circuit probe P2 consists of 2 P2 xy probes and one P2 z probe, the 3 loops oriented in 3 different directions x, y, and z. As stated before, each square loop have a dimension of 3.2 mm×3.2 mm and it is fabricated on both sides of an FR4 substrate with a thickness of 3.2 mm. The probe has an overall dimension of 9×9×3.2 mm 3 . The connecting pads for all individual loops are provided at the top surface in order to be able to connect it to the coaxial cable. The volume of this probe is only 16 % of the previous tri-axial probe P1. Compared to the conventional circular loop probes printed circuit probes are easy to miniaturize and less susceptible to damage. Also, these probes have the advantage of being low cost, compact and easy to handle. The electrical connection of the loop terminals in the probes is critical especially in near-field measurements. The field profile can be distorted due to a lack in this connection. Also another loop can be formed due to this connection. For this reason we optimize the connection to reduce the coupling effect in the measured medium as

Coupling Analysis

Coupling analysis between the loop elements of each tri-axial probe was done with the help of the VNA. Each two loop elements of the tri-axial probes was connected to the two ports of the VNA whereas the third element is terminated by 50 ohm impedance, then the transmission coefficient is measured. Figure 2-36 shows the coupling between the loops of the probe P1, the coupling is less than -30 dB until 700 MHz and it increases at higher frequencies. For P2 the coupling is less than -40 dB till 350 MHz and less than -30 dB until 600 MHz as shown in Figure 2-37. This is expectable as in P1 the loop elements have 3 turns while in P2 there is just one turn.

Calibration

The calibration setup for these tri-axial probes is the same used in section 2.7.2.

Both probes were placed inside the FCC-TEM-JM1 TEM cell in the usable area, which is 6×6×1 cm 3 , whereas the cables of the probe are outside the cell. P1 have a height of 1 cm so it can fit in the specified usable volume of the cell. The field inside the cell is calculated as stated in 2.6. It is obvious that the antenna factor for probe P1 is smaller than probe P2 because of its larger dimension compared to the printed circuit probe P2. The AF for probe P1 is 46 dB[A/(m.V)] at 10 MHz and reduces by 20 dB for every 10 times increase in frequency. In the case of probe P2 the AF is 58 dB[A/(m.V)] at 10 MHz (for x and y elements) and decreases by 20 dB for every 10 times increase in frequency. In Figure 2-38 the AF of each loop in the probe P1 is plotted along with the theoretical AF of a single loop. Compared to the theoretical AF, the antenna factor of each loop in the tri-axial probe has small fluctuations above 300 MHz in probe P1; these are due to the coupling between the loops probe. Similarly, in the case of printed probe P2, these coupling effects are increased above 300 MHz.

Validation

To validate these probes we use the same validation test bench used in 2.

CONCLUSION

In this chapter we have presented the development of a new near-field scanning system. It consists of two types of scanners, a 3D one for small size applications and a 2D scanner for larger applications. In addition, the measuring instrument in the proposed system is an oscilloscope that can perform both time and frequency domain measurements. This system is dedicated for both EMC measurements and dosimetric applications.

In the second part of the chapter, a new tri-axial magnetic field probes has been proposed. They can be used to measure the three components of the magnetic field separately and at the same time. The calibration of these probes was performed using a TEM cell where the antenna factors are extracted. After that the coupling analysis between the probe elements was studied and they were validated showing a good performance.

The developed scanning system including the new probes was used for the nearfield characterization and exposure analysis near radiating sources as demonstrated in the next chapters. ( , )

INTRODUCTION

Near field characterization is a challenging process in electromagnetic compatibility studies. Several approaches have been proposed to achieve the required scanning of the radiating source throughout the space. Radiated emission and immunity tests of electronic circuits are important tasks of system electromagnetic compatibility analysis and they have become growing concerns in prediction of system reliability [1]- [3]. In addition, dosimetric analysis shows the necessity of having three dimensional (3D) field mapping in the vicinity of the radiating source.

For this kind of applications, several scans of the near fields should be done within different planes in order to build the 3D field mapping. Being a challenging process in electromagnetic compatibility studies, near field characterization is being treated by several algorithms that propose different approaches to achieve the required scanning on the radiating source, where great efforts have been made in recent years in the scientific community to develop numerical methods to solve temporally and spatiallyMaxwell'sequations.

In this context, several near-field scanning systems were introduced [4], [5]. In the previous chapter, we introduced a 3D scanning system with a tri-axial magnetic field probes. Having such probes allow the simultaneous measure of the three components of the magnetic field based on a single planner scan (scan in one plane only) above the DUT. However, to perform multi-planes scan is time consuming and it would be better to find an analytical solution that reduces the number of scans needed and hence the time requirements. For this reason it is better to find an analytical solution that reduces the number of scans needed. Here comes the Plane Wave Spectrum (PWS) method which has been found useful for determining the far field from near field measurements [6], [7]. The reconstruction algorithm implemented by PWS requires just the 2D scan of the tangential components, in an initial plane, to reconstruct the 3D magnetic field distribution.

In this chapter we present the near field characterization near two different antennas. The first one is a square loop antenna operating in HF band, while the second one is a PIFA (planar inverted-F antenna) antenna that operates at UHF band.

The PWS method is applied to extract the three components of the magnetic field in the near field region, at different planes above the antenna, from the tangential components at an initial plane near the radiating source.

ELECTROMAGNETIC WAVE PROPAGATION

The propagation of an electromagnetic wave in a given medium of permittivity ε In order to completely model the electromagnetic phenomena, it is necessary to add the following equations, for isotropic and homogenous materials, the relation between the field quantities and flux densities is given by the following relations:

[F/m],
B E t       .. LS B E dl dS t      -Faraday'slawof induction‖
BH   ( 3-5 ) DE   ( 3-6 ) JE   -Ohm'slaw‖ ( 3-7 )
Relative permittivity ε r and permeability µ r are normally used for simplicity, they are normalized to their values in vacuum (ε 0 and µ 0 ), i.e. whereωistheangularfrequency.

PRINCIPLE OF THE PLANE WAVE SPECTRUM ALGORITHM

Electromagnetic fields can be represented as plane waves propagating in the space in all directions and with different amplitudes. PWS transformation allows the decomposition of the electromagnetic field components mapped in a plan as being the sum of 2D harmonic spectrums of the propagating plane waves. Hence the knowledge of the transverse field components over a plane near a radiating antenna can be used to extract the plane wave spectrum of the radiated electromagnetic fields.

In harmonic regime, plane waves satisfy Helmholtz equation given by:

2 2 0 A k A    ( 3-9 )
where A is the field quantity vector, which can be either electric or magnetic field, and k is the wavenumber.

A general solution of ( 3-9 ) can be:

( ) ( )

A jk r A r F k e   ( 3-10 )
where ⃗ is the wave vector, given by:

x x y y z z k k u k u k u    222 x y z k k k k       ( 3-11 )
r is the position vector, expressed by:

x y z r xu yu zu    ( 3-12 )
and A F is the plane wave spectrum vector of the field A .

From the wave vector relation one can notice that knowing the frequency and two of the components it is possible to calculate the third one. Assuming that the direction of propagation is along u z direction, the transverse field components will be in the xy plane, so we can obtain the following:

2 2 2 2 2 2 2 2 2 x y x y z x y k k k if k k k k i k k k other              ( 3-13 )
In the case of the non-evanescent wave (k z is real) we could have chosen the opposite sign for k z . This arbitrary choice is dictated by the fact that we implicitly assume that the source of the field is "down", that is to say in the half-plane z < z 0 , and thus the waves propagate "upwards". With regard to the evanescent wave (k z is imaginary), it is desired that the wave amplitude vanishes for z → + ∞, which explains the minus sign.

In this work, we will focus on the magnetic field quantity. At a given frequency, any solution of the Helmholtz equation ( 3-9 ) could be represented by a superposition of plane waves and can be determined by Fourier transform that leads to a solution expressed in terms of the plane wave spectrum [8] we can find a relation between the three spectral components of the magnetic field:

.0

h kF  ( 3-17 ) 0 x hx y hy z hz k F k F k F    ( 3-18 ) x hx y hy hz z k F k F F k   ( 3-19 )
The magnetic field component H z can then be reconstructed from ( 3-19 ) by using the inverse of the plane wave spectrum (IPWS) method: Moreover, the spectral components of the magnetic field at a high z 0 above the plane P 0 can be obtained from the spectral components at z 0 by the following relationship:

0 0 (z z ) ( , ) ( , ) z jk h x y h x y z z F k k F k k e    ( 3-21 )
The magnetic field components at height d can then be calculated by IPWS method as in (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). In the near field region the plane P 0 at a height z 0 above the DUT should satisfy the following relation:

0 2 z    ( 3-22 )
where λ is the wavelength of the signal at the operating frequency f.

ALGORITHM IMPLEMENTATION

The corresponding formulations of the presented algorithm were developed via MATLAB and they are presented below. The goal is then to find a way to approach equation ( 3-26 ) with a twodimensional IFFT. For this purpose, we impose the following equality:

( , )

x  y  y x z 0 z L x L y   2 y y x x x m y m x x x y x y L i n L i m j k x k y j k m k n j N N N N                       ( 3-24 )  2 xx x ki L   ; 2 yy y ki L   ( 3-25 )
then:

L L H e NN L L H e x y L L IFFT H NN

                                                ( 3-26 )
where 2 2 ,

xy ii h x y x y F F i i L L            ; , y x mn x y L L H H m n N N         

( , ) h x y F k k Calculation at z=d

In order to obtain the value of ( , )

h x y zd F k k 
, we must apply the transformation in (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). We could apply this formula as it is, but the result wouldn't be good. Indeed, if 0; 1 xx iN  , 0; 1 yy iN  according to the values of k x and k y would necessarily be positive. To solve this problem, let us observe that in the result is not modified if we replace i x by i x ±N x , because: This amounts to replacing with the following equation:

  2 2 2 2 x x x x x x x i N m i m i m j j j N N N
  2 /2 2 x x x x x xx x i if i N L k i N other L             ;   2 /2 2 y y y y y yy y i if i N L k i N other L             ( 3-

( , , ) H x y d Calculation

We could repeat the same calculations that led us to , but it is much simpler to observe that for d = z 0 we must obtain the starting field. So, we get:

0 1 1 . . . ( )
xy mn mn i i xy x y x y H FFT L L IFFT H FFT F z L L L L               ( 3-29 )
so for any value of d we will have:

( ) . ( )

xy mn i i xy H d FFT F d LL      ( 3-30 )
Indeed, the direct calculation gives the same result:

L L N N j i m i n k d L N L N ii ii xy jk d ii xy L L H d H m n d F k k e dk dk NN F d e LL Fe LL                                       2 2 1 1 00 1 .
( )

y x y x xy xy xy i i N N j m n NN ii ii xy e FFT F d LL                    ( 3-31 )

VALIDATION OF THE ALGORITHM

To validate the presented algorithm, we carried out 2 tests on different antenna types operating at different frequencies. The first one is a rectangular loop antenna operating at 13.56 MHz, and the second is a PIFA antenna operating at 840 MHz.

The calculations of the magnetic field profile at different planes above the antenna were performed and compared to the simulated ones.

Loop Antenna

These antennas are made of a loop with a conductor that may have various shapes: circular, rectangular, triangular, elliptical, etc. They are widely used in communication links up to the microwave bands and also as electromagnetic field probes. In this work, a rectangular small loop antenna operating at 13.56 MHz was modeled on MATLAB and simulated on HFSS in order to test the PWS algorithm.

Feeding port L W t

This antenna is a typical RFID reader antenna used in library RFID systems [10].

The antenna was modeled on MATLAB based on the theoretical formulations loop antennas given in [9]. The loop has a length L=140mm, width W=140mm and a copper trace thickness t=5mm. The feeding point is at the center of one of the sides.

The antenna is excited by a time-harmonic voltage signal with the amplitude of 1 V and a frequency of 13.56 MHz at the feeding port. The HFSS designed structure is shown in Figure 3 The discretized tangential wave vector components used in the numerical computation are calculated using the following formulas:

2 x x k L   ; 2 y y k L  
The spatial and discretization parameters should be chosen according to the following condition:

  2 , xy Max k k     
The first step in the proposed algorithm is to obtain the normal magnetic field H z from the tangential components. As introduced in section 3.3, this occurs by calculating the plane wave spectrum of the tangential components using (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), and then by applying (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) we obtain the normal spectral component of the magnetic field F hz , after that H z is reconstructed with the inverse of PWS as stated in (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20).

The results are shown in Figure 345; it shows the theoretical, simulated, and the calculated magnitudes of H z . It is clear that the reconstructed filed is in good agreement with the theoretical one.

PIFA Antenna

CONCLUSION

From a dosimetric point of view, the knowledge of the electromagnetic field distribution in the area near the radiating element/device is essential. In this context, we have presented in this chapter the PWS method applied on the near-filed data above a radiating device. Two antenna types were chosen, each operating at a different frequency addressing by that two frequency bands, HF and UHF. The algorithm was computed to extract the 3D magnetic field components from the tangential ones at an initial plane above the antenna under test (AUT), as well as the extraction of the magnetic field components at different heights above the AUT. The calculations of the magnetic field were performed via MATLAB and the results are compared to the simulation, showing a good agreement.

INTRODUCTION

The everyday use of devices and systems emitting radio frequency electromagnetic fields is continuously increasing, especially in internet of things (IoT) technologies [1], [2]. Some of these devices are operating in the vicinity of RFID systems used in libraries are mainly addressed under the project Expo@Lyon funded by ANSES (Agence Nationale de Sécurité Sanitaire de l'alimentation). This project proposes to carry out a study of the professional exposure to electromagnetic fields in libraries. As a result, we have performed some measurements in some libraries in Lyon. The ANFR / DR 15-3 measurement protocol adopted by the ANFR (National Frequency Agency), which follows the standard EN 50492, is the basic standard for measuring the electromagnetic field on site. Measurements in site was done using commercial EM-field probes while for in lab experiments the designed probes, presented in chapter 2, was used for more detailed analysis.

RFID SYSTEMS

The term RFID is the acronym of the expression RadioFrequency IDentification that corresponds for a broad set of applications for identifying objects remotely by means of radio waves. The term RF covers all types of wireless or contactless links made using electromagnetic waves, ranging from very low frequencies to infra-red and visible light.

The most common identification technique is the storage of a serial number in a chip to which is attached a transmitting / receiving antenna. The chip-antenna assembly is generally called RFID tag. An interrogator sends an identification request to the labels, which in turn communicate the information contained in the chip. The information can then be processed by a computer system to meet a wide variety of application needs [4].

Data Base

An RFID system consists of:

 Interrogator: or sometimes called RFID reader which can be fixed or movable (handheld).

 Reader antenna: that is responsible for converting the electrical signal into a wireless radio wave signal.

 Tag: deported elements that can be named differently depending on the markets and applications. We can talk about contactless smart cards, electronic tags or electronic access badges, for example. The general term tag is frequently used.

 Transmission medium: it is the surrounding environment around the system (e.g. air, water, or a combination of air and water, glass, metal, etc).

 Digital link: that links the RFID reader to the database through a computer system. We can also differentiate between two types of RFID systems: passive and active systems, depending on the way in which the communication between the label and the interrogator is assured.

RFID uses different radio frequencies depending on the

In passive RFID systems the tag consists of an electronic chip that stores the digital identification data and an antenna that transmits this recorded information. The RFID interrogator emits an electromagnetic wave that induces a current in the antenna of the tag. The RFID tag then transmits back a fixed alphanumeric sequence serving as an identifier to the tagged object. While in active RFID systems the tag returns information to the interrogator by producing itself an electromagnetic wave (it therefore integrates a transmitter).

RFID Readers

An RFID reader is a device that is used to interrogate the RFID tag. The reader acts as transmitter and receiver. The reader has an antenna that emits radio waves so the tag responds by returning its data. The reader uses its antenna to collect the data received back from the tag. It then transmits this data to a computer for processing.

The RFID system communication is based on the Master-Slave relationship, where the RFID reader acts as the master and the tag as the slave [4].

RFID readers can take many shapes and sizes, and can offer a wide range of applications. Currently, many applications rely on fixed devices. The readers may be stationary in a shops or factories, or integrated in electronic devices and in vehicles.

RFID readers can also be integrated into handheld mobile devices. reader is shown, it has 4 channels and RF output power up to 30 dBi, it is a fixed RFID system that can be used in different types of applications [5]. Figure 4-3 shows a handheld RFID system that can be linked to a smart phone and can display the locations of tagged items in 3D from a range of about 10 meters, and it has an RF power of 30 dBm that can be lowered manually [6]. In Figure 4-3 we can see ZK-RFID101 system, it is an UHF RFID system with an built-in 8dBi circular polarization antenna. It has an output power up to 30 dBm with a reading range of 5 m [7].

The choice of the RFID reader is mainly done according to the desired reading range. RFID readers with reading distances of a few centimeters are referred to nearfield RFID readers. While those whose ranges to several hundred meters are referred to as long-range readers. To increase the range of the reader (up to 20 m), the power needed to reach the tag must be greater. A number of factors can affect the reading range: the frequency used, antenna gain, orientation and polarization of the reader and tag antennas, as well as tag placement on the object to be identified

The exchange of data between the RFID reader and the tag can use different types of modulation and coding. The reader uses carrier modulation to send information to one or more tags. The most commonly used modulations are: Amplitude Shift Keying (ASK) which is the most widely used [8], Phase Shift Keying (PSK) and Frequency Shift Keying (FSK).

RFID Tags

The RFID tag consists of an integrated circuit, also called RFID chip, connected to an antenna in a compact and robust housing. The package is structured to allow the RFID tag to be attached to the object to be tracked [9].

Mainly there are two types of RFID tags:

Chip-less RFID tags

These are low-cost RFID tags without the use of any chip inside, commonly known by chip-less tags [10]. These tags are usually used in electronic article surveillance (EAS) applications. EAS tags, shown in Figure 4-4, are usually found in stores as an anti-theft system. They are often referred to as "1-bit" RFID tags. The reason for this is simply that they are only designed to communicate a bit of information. If the RFID tag is present and active, then it means that the item was not at checkout. These tags are rarely nowadays due to several disadvantages in this technology.

RFID tags with chip

These tags are divided into three categories: active, semi passive, passive.

Activetagscontainaninternalbatteryanddon'tdependonanexternalsignalto generate a response. The power source is used to activate the chip and to broadcast a signal to the reader. As a result, active tags can have higher reading ranges, with distances up to 100 meters. Active Tags can be read-only or read/write, allowing the reader to modify the tag data.

The semi-passive tags use a battery to communicate with a reader using back scatter power. The battery used to power the chip that allows more energy from the reader antenna to be reflected back, thereby giving a longer reading range than ordinary passive tags. Active and semi-passive tags are useful for tracking valuable goods that need to be digitized over long distances, such as the railroad, but they cost more than passive tags.

Passive RFID tags are very similar to semi-passive tags but without having any

RFID READER ANTENNAS

For near-field RFID systems, the inductive coupling is preferable for most applications, since most of the reactive energy is stored in the magnetic field. The inductively coupling RFID systems are able to operate in close proximity to metals and liquids but are affected by objects of high magnetic permeability. For many years, the conventional loop antennas, sensitive in reception to the magnetic field, have been used as antennas for RFID pads in LF and HF bands because these so-called magnetic framework antennas are capable of producing an intense and uniform magnetic field in the area around the antenna. Loop antennas feature simplicity, low cost and versatility. They are made of a loop of a conductor that may have various shapes: circular, triangular, square, elliptical, etc. They are widely used in communication links up to the microwave bands (up to 3 GHz). They are also used as electromagnetic field probes.

Loop antennas are usually classified as electrically small and electrically large antennas as described in 3.5.1. Small loop antennas of a single turn have very small radiation resistance. Their radiation resistance can be substantially improved by adding more turns. Multi-turn loops have better radiation resistance although their efficiency is still poor. Because of that they are poor radiators and usually used as receiving antennas or for short range applications. Also small loop antennas have a far-field radiation pattern similar to an electric dipole as shown in Figure 456supposing the plane of the loop is xy-plane and it is centered at the origin [11]. However, when the operating frequency of the system rises to the UHF band, the perimeter of the loop antenna becomes comparable to the wavelength. So the antenna cannot produce a uniform magnetic field anymore, because the current flowing along the loop has phase inversion and the current vanishes along the circumference. As a result, the antenna produces a relatively weak magnetic field in certain regions of the loop antenna which degrades the RFID tag detection reliability. The antenna design challenge for the near-field UHF reader is to ensure that the current is in phase and almost of the same magnitude along the loop antenna, and to produce a strong magnetic field distribution and uniform in the near field region.

By segmenting the loop antenna, the perimeter of the antenna becomes large and greater than the wavelength. Segmented antennas have been constructed to operate at the desired frequency while ensuring good magnetic coupling [12], the authors in [13] present electrically wide frame antenna design, with an overall size of 160mm×180mm at the UHF band with a uniform magnetic field distribution. The segmented coupling line sections provide a very low phase delay between adjacent sections so that the current flowing along the segmented lines is kept in a single direction. In addition, knowing that the magnetic field strength of the antenna decreases as the size of the antenna increases, the antenna presented in [14], with an overall size of 175mm×180mm, has demonstrated the ability to produce a strong magnetic field in the near field region, even though the perimeter of the antenna is greater than twice the wavelength of the antenna. Another types were also developed, for example in [15] a fractal antenna that operates at 897 MHz was developed. This antenna gives a reading distance of 9.5 cm for an input power of 13 dBm.

x z y

C=0.1λ

Some RFID applications require near-field and far-field communication. Although several works has been done on near-field RFID antennas, we hardly find publications on the design of the reader's antenna for near and far-field operations at the same frequency and at the same time. As the antenna requirements for the near-field RFID systems are different from those for the far-field systems. In [16] authors propose a patch antenna included inside a segmented loop operating simultaneously in near and far field. The segmented loop technique is implemented for near-field operation, while the patch antenna is included within the loop for far-field operation. The reading capabilities of the antenna are up to 9 cm in the near field and 6 m in the far field. In [17], the authors made a metal plate-supported segmented loop antenna that showed a uniform magnetic field distribution in the near-field region, and acceptable far-field radiation characteristics. Also in [18], authors proposed a compact dipole antenna folded with a Split Ring Resonator (SRR) for mobile RFID applications. This antenna has a compact size of 31mm31mm and it works in near-field and in far-field regions. It has a strong surface current distribution with a gain of -2.0 dBi in the far field. The near-field reading range can be up to 48 mm with a transmission power level of 20 dBm.

IN SITU MEASUREMENTS

As mentioned in the introduction of this chapter, our work is focused on the analysis of RFID systems used in libraries. For this reason we performed several measurements at different libraries located in Lyon-France where different RFID systems are addressed. In this section we will present the results obtained, and in the following section we will present a more accurate analysis that was done in lab. In particular, this section presents the results of the real measurements made in -Vaise

Library‖ that is equipped with 3M RFID systems, while you can find other measurements done in different libraries in the Appendix.

Instrumentation Used

The measurements was done using the probe EHP-200A from Narda [19]. It is a magnetic and electric field probe that measures accurately the magnetic field ranging between 6 mA/m and 300 A/m, as well as the electric field from 0.02 up to 1000 V/m in a frequency band of 9 kHz to 30 MHz. The corresponding sensors and the electronic circuits are all assembled in a plastic cube having the dimensions of 92×92×109 mm (Figure 4567). The magnetic field sensor system is composed of three orthogonal loops whereas the electric field sensor system is composed of three orthogonal parallel capacitors installed on opposite side of the magnetic loops. The probe is connected to the PC via an optical fiber where an FO to USB adapter is used to convert the optical signal into a digital one to be processed. The PC software is used to visualize the results, where the frequency spectrum analysis is displayed with frequency ranges that can be adjusted within the band of operation of this probe. Each component of the electric or magnetic fields can be measured separately as well as the total field (peak and average values). The RMS value, over a duration of 6 minutes, of the field was measured based on the European directive on the exposure of workers [20] that is based on ICNIRP guidelines [21]. The field

.2. Measurements at "Vaise Library"

There are four different types of RFID pads used in this library:

 3M™MiniRFIDPadModel210(BluePad)  3M™PadStaffWorkstationModel800(BlackPad)  3M™Self-Check System Model 8420  Automated Material Handling (AMH) System
The magnetic field strength measurements of each type were done and the results are tabulated as shown below, comparing the measured values with the guidelines action levels (AL). The EHP-200A probe was placed at the center of each pad, and the RMS value of both E and H fields was recorded over 6 minutes.

3M™ Mini RFID Pad Model 210 (Blue Pad)

In this section we present the measurements that was done near two similar 3M mini RFID (model 210) pads. They are normally used by the workers at the library, where they can be found on almost all the library staff tables. The pad has the dimensions of 18.4cm × 16.5cm with a read range up to 15.2cm. The reader and the electronic system is dedicated in the pad itself and it is connected directly to the PC via a USB cable with 5V power supply. The following figure shows one of these pads in the presence of the used probe. In this section we present the measurements done near three similar 3M pad staff workstations (model 895) dedicated for library staff to program the tags before attaching them into the corresponding library materials (reports, books, CDs…).

This system consists of a reader (model 810), an RFID Pad (model P12), and the conversion and workstation software [22]. The RFID pad is a loop antenna that has the dimensions of 28.9cm×28.9cm. It is excited by a coaxial cable connected to the RFID reader and the system has a reading range starting from 20 cm. Figure 4-10

shows one of the pads under test in the presence of the measuring probe.

3M™ Self-Check System Model 8420

In this section measurements were done near two similar 3M Self-Check systems (model 8420, kiosk) used by public users [23].

Automated Material Handling (AMH) System

This RFID system shows different structure than the previous ones, the RFID pad is hidden inside a metallic cover that is not near the user. It consists of conveyor and sorting systems that can check-in the library materials and sort them by category into separate bins. The measurement near this system was done in two places, the first in the area dedicated for users and the second one in the workers place. Figure 4-12

shows the probe position in these two places. Notes:

 Outside: Measurements in the area dedicated for users (Figure 4-12, left)

 Inside: Measurements in the area dedicated for workers (Figure 4-12, right)

Conclusion

The measurements near the different RFID systems show a great variability in terms of the electric field and a relatively small variability in terms of the magnetic field. Near the different RFID pads and kiosks, no overshoot is observed in terms of the E-field, while the values of the H-field have exceeded the ALs sometimes for several orders of magnitude. Concerning the anti-theft gates, at certain positions the values of E and/or H field exceeds the ALs sometimes. However, given the pulse character of the signal, no overshot was observed in all RFID systems if the measured values are compared to 32 times the standard AL value. Finally, for the AHM RFID system, both the electric and magnetic fields are very weak and blew the reference levels. For better understanding of the field distribution near the RFID systems we performed more detailed analysis in the Lab that will be presented in the next section.

IN-LAB EXPERIMENTAL ANALYSIS

In the previous section we presented the measurements that were done at different libraries in Lyon using the EHP-200 electromagnetic field probe. These measurements were performed in the free space by placing the probe, that have the dimensions of 92×92×109 mm, in the center of the corresponding RFID pad and by measuring the RMS value of the field strength over a duration of 6 minutes. In order to have more precise analysis and higher resolution field mapping we performed a detailed study on a typical RFID system (i.e. 3M Pad Staff Workstation -Model 895)

that is used normally by library staff. The near-field characterization of this system was done using the near-field test bench presented in chapter 2 with the designed probes P1 and P2. First, we validated the test bench by designing an RFID loop antenna where the simulated magnetic field was compared to the measured ones.

RFID 1-turn loop antenna

As stated in 4.3 most RFID antennas at HF frequency band are loop antennas. In this section we present the design of a rectangular loop antenna operating at 13 MHz, it has the dimensions of 140 mm×140 mm with a copper trace width of 5 mm. In order to match the antenna to the 50Ω feed line at the operating frequency, an impedance matching circuit was added at the input of the antenna. Loop antennas have inductive input impedance; hence a parallel RC circuit should be used as a matching circuit. The latter was designed using SMD (surface mounted device) lumped elements and it consists of two capacitors connected to the loop in series with a resistor and all in parallel to another capacitor, where the values of these elements was optimized to meet the design requirements. The circuit is shown in The 3D scanning system, presented in chapter 2, 2.4, was used to map and characterize the magnetic near-field radiated by the designed RFID reader antenna. The scanning measurement system consists of the 3D scanning robot, Teledyne In this analysis, the RFID loop antenna was excited with two signal types, CW signal and a modulated signal, and the radiated H-field was studied in both cases.

The CW signal was generated at 13.56 MHz with a source power of 20 dBm.

The modulated signal, shown in Figure 4-20, is a pulsed RF signal with pulse width PW=32ms, pulse repetition period PRT=250ms, and a duty cycle D = PW / PRT = 0.128. This modulated signal is usually used in RFID library systems. According to ICNIRP Guidelines, and for the operating frequency of 13.56 MHz, the reference levels for a human exposure scenario, for both general public and occupational, are as listed in Table 4-5 [21]. The maximum recommended magnetic field value for RF pulses is 32 times higher than the reference magnetic field values [20]. At our operating frequency the reference level in the Guidelines is equal to 0.073A/m for general public and 0.16A/m for occupational exposure. We notice that the previous measured H-field values exceed these limits. Normally this limit value refers to full body exposure for 6 minutes period. Considering the RFID reader used in library systems, there is a potential arm and hand exposure which lasts just for few seconds. Moreover, in some configurations, the RFID reader antenna in Library systems is placed under a table so there is about 2cm between the antenna and the table surface.

RF input Signal

For the modulated signal, the magnetic field strengths of the three components In this case, by comparing these measured results with the maximum recommended magnetic field for RF pulses (2.336A/m for general public & 5.12A/m for occupational exposure), the limits are not exceeded if we consider the special limits for RF pulse signal.

Exposure Analysis near the 3M RFID Pad -Model P12

RFID pad P12 is the corresponding reader antenna of the 3M staff workstationmodel 895. It is a 2-turns loop antenna with total dimensions of 28.9cm×28.9cm. This work station is intended to be used by library staff for programming the corresponding RFID tags attached to library materials. We have studied the exposure to this pad in terms of the magnetic field strength as it is the dominant field due to the loop antenna type of the pad. Figure 4-23 shows the measurement setup including the 3D scanner and the tri-axial probe that was used to measure the radiated field above the RFID pad P12. The latter was excited via a coaxial cable by a signal generated from the RFID reader (model 810); it is a pulsed signal as shown in The exposure limit values in terms of H-field at 13.56 MHz, presented in Table 4-5, indicates that the maximum permissible level is 2.336 A/m for general public and 5.12 A/m as the occupational ALs. By comparing the results obtained in the several scans that were done in different scenarios, we noticed that the occupational action levels were respected. However the field strength at the height h 1 exceeds the ALs of the general public. In the previous analysis we were measuring the radiated magnetic field in the free space above the RFID pad. In order to check field levels in the presence of a human body, another scan in a cylindrical phantom containing TSL (tissue simulating liquid) was performed. The TSL was prepared in the lab by adding 2.5 g/L of sodium chloride (NaCl) to pure water. The electrical properties of this liquid was extracted using a coaxial fixture and by applying the marital properties extraction technique presented in [25]. By comparing the measured field levels in the two cases, we can notice that the field inside the TSL is slightly less than that is the free space. Figure 4-31 shows the comparison between the three H-field components separately while Figure 4-32

shows the comparison of the total H-field mapping.

CONCLUSION

In this chapter we have presented the analysis of the radiated electromagnetic field near RFID loop antennas that are used in Libraries. The exposure assessment in terms of the H-field was studied near different RFID systems. In-situ measurements were done at different libraries in Lyon where a commercial EMF probe (EHP 200A)

from Narda STS was used. More detailed study was performed in lab using the developed near field scanning system with the designed tri-axial probes presented in the previous chapter. Two loop antennas was fabricated, the first one that is a simple 1-turn loop antenna was used to validate the test bench by comparing the measurements to a simulated HFSS model. The near field characterization was then performed near the second 2-turns loop antenna and near a commercial RFID pad P12 from 3M Company. The field levels were compared to the action levels stated in the international and European guidelines. Even though they exceed the ALs given in the directives, but from the performed measurements we see the strong decrease in the level of the field (between 1 and 5 cm above the antenna). This clarifies that the general public and users of such systems are not exposed to the high field levels; however workers should be aware not to be too close to the RFID antennas during their job.

INTRODUCTION

The implement a new method of exposure characterization by numerical dosimetry. For mobile radio waves that have been studied a lot, the sources are well identified and their radiation can be characterized. On the other hand, in the case of industrial machines generally using RF microwave category (heating for dielectric welding, induction heating ...), it is sometimes difficult to calculate the exposure levels of workers in the work environment, due to the fact that:

 The machines are being large (radiation sources are often distributed)

 The posture of the operator is variable

The focus of this chapter will be on a particular type of industrial systems that is the RF welding machines, which radiates a strong electromagnetic field at 27.12 MHz. The exposure to these machines takes place in the near field region, where the spatial distribution of the electromagnetic field is very complicated. We have an industrial RF welding machine on the site of INRS (in Nancy-France), in which we carried out three measurement campaigns, which allowed us to establish the cartography of the electric and magnetic fields around the machine.

In the present work we also carried out a numerical modeling of the machine from a realistic CAD. This model allows us to make a comparison with the experimental measurements, and on the other hand to perform simulated measurements, which would be too long and complicated to perform experimentally.

Moreover, the effect of a human body immersed in an RF electromagnetic field was studied by simulating a virtual phantom having different material layers. The measurements obtained will be also used to feed the numerical FEM formulation that is under development on ONELab software that aims to extract the EM field inside a phantom from the measurements in the free space near a radiating source.

INDUSTRIAL RF WELDING MACHINES

Machines using high-frequency (HF) dielectric heating can weld, mark, bend or glue different insulating materials (wood, plastics, etc.). In this process, the energy expended by the HF alternating electric field polarizes the molecules within the materials. The intermolecular friction develops a heat allowing the needed process (welding, marking, bending or gluing, etc.) of these materials according to the application. For example, the microwave oven is a device used mainly for the rapid heating of products by stirring the water molecules they contain under the effect of a microwave radiation (f = 2.45 GHz). However, the dielectric loss welding process is used for instant sealing of thermoplastics [2]. The molecules in the product are subjected to a high frequency electric field with a certain pressure. This leads to vibration that generates, by the friction of the molecules, an internal heating sufficient to cause the welding between the molecules of a material [3], [4]. This method has the advantage of requiring no added material like glues or other fillers.

However, an electromagnetic radiation is emitted by these machines in particular by the RF applicator, commonly called the electrode. Figure 5-1 shows a basic schematic for an RF welding machine where the equivalent electrical circuit is shown in Figure 5-2. The material to be welded is placed between the electrode and the bed plate, under the pressure of the hydraulic press, before the RF energy being applied.

Signals emitted by industrial equipments can extend over a wide frequency band, from few MHz up to several GHz. These bands are known internationally as ISM (industrial, scientific and medical) radio bands and they are dedicated for applications that use RF energy in industrial, scientific and medical applications other than telecommunications. In the case of the RF welding machines, the signals are generally at one of these frequencies: 6.78, 13.56, 27.12, or 40.68 MHz [4]. RF welding machines generates a strong electromagnetic field in which the workers using such appliances are daily exposed to this field, thus it is important to quantify their exposure.

Industrial RF Welding Machines EMF Characterization proportional to the square of the intensity of the electric field. The RF current circulating in the metal parts of the machine is considered as another source of the EMF radiation. The field emitted by welding machines dealing with small-sized products can be considerably reduced by shielding. This can be done by enclosing the radiating parts of the machine by a metallic shield, precisely enclosing the volume containing both the electrode and the product to be welded as shown in Figure 5-3 [5]. However, this solution is not feasible for machines dealing with large products. For this reason another solution was suggested that is based on adding a ground plate to the welding system, which leads the current back to the machine and therefor decreasing the radiated energy. Recent welding machines design, have this ground plate as an alternative field reduction solution. It consists of a metal plate made of aluminum or copper that is arranged parallel to the electrode of the welder and having the same length of the electrode with a width of about 15 to 20 cm. These dimensions are determined so the plate-table electrical capacitance large enough to prevent heating of the material under it. The thickness of the plate is not important electromagnetically. The plate can be entirely rigid or be constituted by a flexible foil itself fixed on a rigid support. However, field strength of several hundreds of V/m are still commonly found near old welding machines that have no ground plates, who are still exists in different industrial sectors, even though there is some work on adding the ground plates to these machines. For this reason the aim of this work is to characterize the emitted RF energy near these machines and to perform the corresponding numerical and experimental analysis in order to have more details about the workers exposure.

The gooseneck welding machine used by S.E.F. Company in France, which exists at the site of INRS, was selected. It works at 27.12 MHz (26.957 MHz -27.283 MHz) and has a power of 7.5 kW.

Ground Plate Electrode

Asthismachineisanoldone,itdoesn'thaveagroundplate.However, a detailed work was done by INRS [6] for adding a ground plate in order to decrease the radiating field. But still there is a fear of having high radiated EMF.

A 3-dimensional mapping of the field radiated by this machine was performed in the space in front of it. The measurement system and calculations that was used are generic and can be applied in the industrial environment having such RF energy radiators. In the framework of this work we focused on a particular machine, in which it represents fairly a wide range of industrial machines.

Given the frequency of operation of these machines that have a wavelength of about 11 m in vacuum, and due to the fact that the worker is in the vicinity of the machine, the exposure takes place in the reactive near-field region. This is the most delicate situation because the electric and magnetic fields are coupled and have a complex spatial distribution [7].

Effects of human tissues dielectric parameters

The presence of the worker's body in front a radiating source may have a significant influence on the radiation. To check that an RF model implemented for finite element simulations in ANSYS HFSS was developed. The model, shown in Figure 5-5, was built from a simple electrode above a ground plane and having a PVC material (ε r =2.7) in between, in the addition of a realistic multilayer anthropomorphic computational phantom. The latter is an anatomical voxel body model Duke from the virtual family, it is 70kg male that has a high of 1.74m with a voxel size of 5mm [8]. For living tissues, the dielectric properties from IT'IS Foundation were used [9]. The source is simulated as a lumped port between the electrode and the ground plane with a power of 3 kW and at 27.12 MHz. The

RF welding machine numerical model

As stated in 5.2, the exposure analysis will be performed near the industrial welding machine that exists at the site of INRS. A numerical model of this machine was designed on HFSS, based on a realistic CAD from INRS, as it is shown in Figure 5-12. Themodelwasbuiltwiththeadditionofthegroundplate,thatdoesn't existintheinitialCAD.ThisgroundplatewasbuiltonthebasisofKlein'sdesignas stated in [10]. A 2.7 mm PVC layer, simulating the plastic material to be welded in the real case, was added between the electrode and the machine table (bed plate in Figure 5-1). The source is simulated as a lumped port between the electrode and the bed plate with a power of 4 kW at 27.12 MHz. The simulation is sensitive to many parameters including the different layers of ground system, copper connections, and the dielectric layer on the welding table (PVC layer). The radiated electromagnetic field in the space in front of this model was extracted at different planes in which it will be compared to the real measurements.

EXPERIMENTAL ANALYSIS

The RF energy emitted by an industrial welding machine was characterized in terms of the magnetic and electric fields. We carried out three different measurement campaigns near the Gooseneck machine located at INRS site in Nancy (presented in 5.2). This allowed us to make the mapping of the radiated magnetic and electric fields in the place where the operator is normally located in front of the machine.

Measurements were done without the presence of the operator in order to know the cartography of the radiated field as it is strongly distorted by the presence of a worker. The distance between the machine and the nearest wall was greater than 2m.

The evaluation of the exposure to electric and/or magnetic fields is carried out at different planes in front of the machine taking into account that the average height of an operator is about 1.75 m. In the first campaign the commercial EHP200A probe from Narda was used, the purpose was to have an idea about the spectrum of the radiated field and to have an initial plot of the distribution of the EMF around the machine. After that we used the tri-axial magnetic field probe P2, presented in Chapter 2, to measure the H-field in front of the machine. And in the final campaign we measured the E-field using electro-optical probes (eoProbe) from Kapteos.

Preliminary measurements using EHP200A

The commercial electromagnetic field probe EHP200A (presented in 4.4.1) was used to determine the frequency spectrum of the radiated field, and to have an initial idea about its distribution around the welding machine. The probe can measure both the electrical and magnetic field components in a frequency range from 9 kHz to 30

MHz.

The spectrum of the radiated electromagnetic field was measured with the probe, having a span of 10 MHz and RBW of 100 kHz in the probe's software configuration. We notice that the signal is around 27 MHz, and it depends on the configuration of the machine. The latter has a ground plate that can be used or not.

When it is not used, we observe that the spectrum has two peaks at 26.9 and 28.8

MHz, as we can see in Figure 5-13. On the other hand, when the ground plate used, we observe the presence of just one peak at 27.3 MHz (Figure 5-13) with much lower E-field level than the previous case and this is really the role of the ground plate, i.e. to reduce the radiated RF energy. Where E fi is the measured electric field at the frequency f i and E AL,fi is the corresponding action level given in the directive. Unsurprisingly, the intensity of the electromagnetic field decreases as we move away from the machine as we can see in the plots. the exposure index for the other configuration in which the ground plate in the machine is used. The observed asymmetry in the distribution of the field is probably due to the asymmetry in the machine itself as the RF generator cabinet is not centered, which leads to more reflections. The results shows that the ALs are exceeded in the vicinity of the machine in both cases (with and without the ground plate), while the place of the control panel seems to be in a safe region just in the case if using the ground plate.

Magnetic field measurements

For more precision and higher resolution field mapping, we performed the measurements in vertical planes in front of the machine using the tri-axial magnetic field probe P2, presented in details in 0 in chapter 2, where the three components of H-field was recorded. The measurement setup (Figure 5-16) consists of the WaveRunner 640Zi oscilloscope that was used to measure the RF signals, in addition to a 3D robotic system which will allow more measurement points to be taken in less time and with greater precision. The signal that is generated by the RF welding machine is a modulated signal and has the shape of an AM signal. The maximum amplitude level extracted from the measured signals (V MS,max ) should be corrected before converting it to the corresponding magnetic field. The correction factor given in equation ( 5-2) was used. Where V CW,rms is the RMS value to be used for magnetic field extraction and V MS,max is the maximum amplitude of the modulated signal measured by the oscilloscope.

The CF was calculated with a signal generated at 27.12 MHz at different power levels, with and without modulation, and it was found to be 0.027. The measurements were done at 4 different vertical planes in the free space in front of the machine. The dimension of each plane is 50cm × 50cm with a step size of 10cm; therefore we have 36 points at each plane. The first plane, P 0 , was at 15cm away from the machine table, whereas the other planes P 1 , P 2 , and P 3 were respectively at 25cm, 35cm, and 45cm from the table. The corresponding configuration is shown in Figure 5-18. Each component of the magnetic field was measured separately, and then the total value was calculated by the root sum square of all the field components. The magnetic field distribution in the same planes was extracted from the HFSS model (shown in Figure 5-12). The measured and simulated magnetic field values in plane P 0 have the same distribution while the values are quite different. The H-field in the upper section of the scanned plane shows a level of about 0.7 A/m which is much higher than the ALs (0.16 A/m at 27.12 MHz) given in the guidelines, hence workers must avoid being in this area while the machine is in operation. In the other planes, the measurement shows some hot spots in the cartographies (dotted circles in Figure 5-19)thatweren'tfound in the simulation. This is probably due to the robotic metallic arm, even though the tri-axial probe P2 was attached to a plastic bar having a length of 40cm away from the robot arm, but this didn't prevent enough the reflected RF waves. Especially at certain positions, when the end of the robot metallicarmcoincideswiththemachine'stableedge,andonthesidewheretheRF generator exists, i.e. to the right side of the machine.

Other measurements were made in the presence of a phantom represented by a cylindrical glass, filled with 2.5L of TSL, which has a diameter of 15cm and a height of 21cm. The prepared liquid was water plus NaCl salt (2.5 g/L of Sodium Chloride).

Electric field measurements

The measurements of the electric field radiated from the RF welding machine were performed using an electro-optical probe (eoProbe) from Kapteos (shown in . It is an ultra-wide band sensor that measures one component of E-field with high precision [11], [12]. The probe must be used with the eoSense instrument.

The latter converts the optical signal transmitted by the eoProbe into an electrical signal that can be analyzed with another data acquisition instrument like an oscilloscope or a spectrum analyzer [13]. The scan was performed in three vertical planes with dimensions of 80cm × 120cm along z-and y-axis respectively, with a step size of 10cm. The three planes P 0 , P 1 , and P 2 wererespectivelyat37cm,46cm,and56cmawayfromthemachine's electrode. Each plane was scanned 3 times, each time having different orientation of the eoProbe, so that the 3 components of the electric field E x , E y , and E z are measured. The antenna factor of the eoProbe is given by the eoSense and it was noted at the beginning of each mapping, and adjusted at the end, according to the variations observed. A spectrum analyzer (Anritsu MS2724B) was used to measure the electrical signal at the output of the eoSense. The signal was at 27.3 MHz and the measured power is converted to electric field using the following formula: Where E i is the corresponding E-field component (i = x, y, or z), AF i istheprobe's antenna factor, and P SA is the power measured by the spectrum analyzer. Then the total electric field was calculated.

Conclusion and Perspectives

This thesis presents the development of a new near-field scanning system for electromagnetic near-field characterization, in particular for occupational exposure and dosimetric analysis. As well as the dosimetric assessments near two applications used by professionals.

In the first chapter, a general review on the propagation of electromagnetic fields and the corresponding interactions with matter has been presented. An overview of RF dosimetry is presented stating the different parameters used to quantify the electromagnetic phenomenon, in addition of introducing numerical and experimental dosimetry. At the end of this chapter, the main standards and guidelines that have been established to manage the exposure of people to electromagnetic fields are presented.

The existing electromagnetic field probes for exposure analysis are either designed to measure one component of the field or their size is somehow large. These limitations lead to designing new compact low coast tri-axial probes, in particular for magnetic field measurements. Two versions were presented; the first is based on conventional loop elements while the other is based on printed circuit board technology. The design of these probes was presented in chapter two, as well as the corresponding calibration. The probes was validated and then used in characterizing different radiating sources. In addition, a near-field scanning system was developed including two scanners foe different types of applications. The developed system can perform near-field measurements in both time and frequency domains.

Using the designed probes the scanning time near a radiating source is reduced by a factor of three. However, for some applications the 3D field mapping is needed.

In this context, a computational algorithm has been reported. It is based on the decomposition of the electromagnetic field components and computing Maxwell's equations. Passing from spatial to spectral domain, the tangential magnetic field components are used to extract the third component and then from the near-field scan in a single plan above the DUT, the 3D magnetic field distribution is constructed.

Résume

L'étude des émissions rayonnées d'une source dans tout l'espace, est essentielle pour l'analyse dosimétriques et l'analyse des interférences électromagnétiques. L'importance du dernier augmente en raison de la nécessité d'avoir une prédiction de la fiabilité des circuits électroniques. De plus, l'utilisation quotidienne des dispositifs et des systèmes émettant des champs électromagnétiques radiofréquences ne cesse d'augmenter. Certains de ces dispositifs fonctionnent à proximité du corps humain, et les opérateurs se trouvent dans la région des champs proches de la source rayonnante, et ils sont exposés à des niveaux de champs électromagnétiques pouvant être élevés. Pour cette raison, l'analyse dosimétrique, qui passe par une cartographie tridimensionnelle (3D) au voisinage de la source rayonnante, doit être effectuée. Pour ce type d'applications, plusieurs scans des champs proches doivent être effectués dans différents plans afin de construire la cartographie de champs 3D. Étant un processus difficile dans les études de compatibilité électromagnétique, la caractérisation en champ proche est traitée par plusieurs algorithmes qui proposent différentes approches pour réaliser le scanning requis au voisinage de la source rayonnante.

Dans ce travail, nous introduisons un système de scanning 3D avec des sondes de champ magnétique à trois axes à faible coût. Le fait de disposer de telles sondes permet la mesure simultanée des trois composantes du champ magnétique sur la base d'un seul scan au voisinage du dispositif testé. Les sondes conçues se composent de trois boucles orthogonales combinées ensemble; la première sonde contient trois boucles conventionnelles réunies dans un cube en plastique d'une dimension totale de 10×12×13 mm 3 , tandis que la deuxième sonde est une sonde PCB imprimée sur un substrat FR4 de 3,2 mm avec une dimension réduite de 9×9×3,2 mm 3 . Les sondes conçues ont été étalonnées avec une cellule TEM et les facteurs d'antenne correspondants ont été extraits. Le système de scanning présenté utilise comme un instrument de mesure un oscilloscope RF-4 canaux, qui donne la possibilité de mesurer à la fois dans le domaine temporel et dans le domaine fréquentiel. La deuxième partie de cette thèse présente un algorithme de reconstruction basé sur la méthode du spectre d'ondes planes. Afin de réduire le nombre des scans et donc les exigences de temps, l'algorithme présenté nécessite juste un scan en champ proche 2D des composantes de champ, pour reconstruire la distribution du champ magnétique 3D au-dessus du dispositif rayonnant.

La troisième partie de la thèse est consacrée à l'analyse dosimétrique des champs électromagnétiques rayonnés à proximité des systèmes RFID et des machines de soudage RF. L'évaluation de l'exposition en champ proche des champs rayonnés des antennes de lecture RFID, fonctionnant à 13,56 MHz et utilisées dans les bibliothèques, a été réalisée. Les mesures du champ magnétique près de l'antenne ont été établies à l'aide des sondes conçues. Les résultats sont ensuite analysés et comparés aux réglementations des normes européennes et des lignes directrices de l'ICNIRP. En outre, l'exposition aux champs électromagnétiques RF des travailleurs à proximité de machines de soudage RF dans un environnement industriel est étudiée. Ces machines, fonctionnant à 27.12 MHz, émettent de forts rayonnements et l'exposition a eu lieu dans la région de champ proche. La distribution spatiale des champs électromagnétiques dans cette région est étudiée à la fois dans des simulations numériques et des mesures réelles.

Mots clés: Scan champ proche, sonde de champ magnétique, dosimétrie, exposition, RFID, machine de soudage RF, algorithme de prédiction.

Figure 1 - 1 :

 11 Figure 1-1: Representation of an electromagnetic wave. The electric field, in blue, and the magnetic field, in red, propagating rectilinearly and perpendicularly to each other .........................................................................

Figure 1 - 2 :

 12 Figure 1-2: The Electromagnetic Spectrum ................................................................

Figure 1 - 3 :

 13 Figure 1-3: Pulsed wave signal ....................................................................................

Figure 1 - 4 :

 14 Figure 1-4: Electromagnetic field regions around a radiating source ........................

Figure 1 - 5 :

 15 Figure 1-5: Wave impedance of magnetic (Z H ) and electric (Z E ) dipoles as a function of k×r .............................................................................................

Figure 1 - 6 :

 16 Figure 1-6: General EMC model ...............................................................................

Figure 1 - 7 :

 17 Figure 1-7: Near-field test bench with scanning system ............................................

Figure 1 - 8 :

 18 Figure 1-8: Near field system with array of probes ...................................................

Figure 1 - 9 :

 19 Figure 1-9: Electromagnetic incident wave decomposition .......................................

Figure 1 - 10 :

 110 Figure 1-10: Examples of electric and magnetic field probes for exposure measurements ...............................................................................................

Figure 1 - 11 :

 111 Figure 1-11: Narda electromagnetic field meters samples .........................................

Figure 2 - 1 :

 21 Figure 2-1: Electromagnetic wave and the corresponding sensitive sensors .............

Figure 2 - 2 :

 22 Figure 2-2: Small dipole as an example of E-field probe ..........................................

Figure 2 - 3 :

 23 Figure 2-3: Electric field probes ................................................................................

Figure 2 - 4 :

 24 Figure 2-4: Magnetic field probes ..............................................................................

Figure 2 - 5 :

 25 Figure 2-5: Mechanism of the robot scanning in the plane above the DUT ..............

Figure 2 - 6 :

 26 Figure 2-6: Scanning configuration window .............................................................

Figure 2 - 7 :

 27 Figure 2-7: 2D Scanner for large devices ..................................................................

Figure 2 - 8 :

 28 Figure 2-8: Measuring Near-field of passive devices via VNA .................................

Figure 2 - 9 :

 29 Figure 2-9: Measuring Near-field of active devices via SA ......................................

Figure 2 - 10 :

 210 Figure 2-10: Measurement system setup ...................................................................

Figure 2 - 11 :

 211 Figure 2-11: Typical TEM cell ..................................................................................

Figure 2 - 12 :

 212 Figure 2-12: Typical probe calibration setup using TEM cell ...................................

Figure 2 - 13 :

 213 Figure 2-13: Simulation model of the used TEM cell................................................

Figure 2 -

 2 Figure 2-14: (a) Transversal and (b) Lonigtuidinal cross-sections of the TEM cell ................................................................................................................

Figure 2 -

 2 Figure 2-15: (a) Transversal and (b) Lonigtuidinal cross-sections of the TEM cell ................................................................................................................

Figure 2 - 16 :Figure 2 - 17 :

 216217 Figure 2-16: Commercial magnetic close-field probes from Agilent ........................

Figure 2 - 18 :

 218 Figure 2-18: HP1140A magnetic field probe antenna factor .....................................

Figure 2 - 19 :

 219 Figure 2-19: Geometrical parameters of the magnetic field probes; P1 xy (left) P2 xy (right) ....................................................................................................

Figure 2 -

 2 Figure 2-20: magnetic field probes; P1 z (left) P2 z (right) ..........................................

Figure 2 - 21 :

 221 Figure 2-21: Simplified equivalent circuit model of a loop .......................................

Figure 2 - 22 :

 222 Figure 2-22: Calibration Setup ...................................................................................

Figure 2 - 23 :

 223 Figure 2-23: Antenna factor of P1xy probe ...............................................................

Figure 2 - 24 :

 224 Figure 2-24: Antenna factor of P2xy probe ...............................................................

Figure 2 - 25 :

 225 Figure 2-25: Probe selectivity measurement configuration .......................................

Figure 2 - 26 :

 226 Figure 2-26: P1 xy Probe selectivity ............................................................................

Figure 2 - 27 :

 227 Figure 2-27: P2 xy probe selectivity .............................................................................

Figure 2 -

 2 Figure 2-28: (a) Reference Circuit; (b) Cross section, showing the geometrical parameters ....................................................................................................

Figure 2 - 29 :

 229 Figure 2-29: Validation setup using P1 xy probe .........................................................

Figure 2 -

 2 Figure 2-30: Theoretical values compared to measurement results of H y using P1 xy at different frequencies .........................................................................

Figure 2 - 31 :

 231 Figure 2-31: Theoretical values compared to measurement results of H z using P1 z at different frequencies ..........................................................................

Figure 2 -

 2 Figure 2-32: Theoretical values compared to measurement results of H y using P2 xy at different frequencies .........................................................................

Figure 2 -

 2 Figure 2-33: Theoretical values compared to measurement results of H z using P2 z at different frequencies ..........................................................................

Figure 2 -

 2 Figure 2-34: Fabricated 3D H-field probe P1 ............................................................

Figure 2 -

 2 Figure 2-35: Fabricated 3D H-field probe P2 ............................................................

Figure 2 -

 2 Figure 2-36: Coupling between P1 loop elements .....................................................

Figure 2 -

 2 Figure 2-37: Coupling between P2 loop elements .....................................................

Figure 2 -

 2 Figure 2-38: Measured antenna factor versus frequency for the probe P1 ................

Figure 2 -

 2 Figure 2-39: Measured antenna factor versus frequency for the probe P2 ................

Figure 2 -

 2 Figure 2-40: Standard validation circuit with the tri-axial probe P1 ..........................

Figure 2 -

 2 Figure 2-41: Tangential H-field component H y for (a) Probe P1 (b) Probe P2 .........

Figure 2 -

 2 Figure 2-42: Normal H-field component H z at for (a) Probe P1 (b) Probe P2 .........

Figure 3 - 1 :

 31 Figure 3-1: PWS method for magnetic field extraction .............................................

Figure 3 - 2 :

 32 Figure 3-2: Spatial domain parameters representing the plane P 0 at z=z 0 .................

Figure 3 - 3 :

 33 Figure 3-3: Single turn rectangular loop antenna with the corresponding radiation pattern diagram .............................................................................

Figure 3 - 4 :Figure 3 - 5 :

 3435 Figure 3-4: RFID Loop Antenna structure .................................................................

Figure 3 - 6 :

 36 Figure 3-6: Comparison between theoretical, simulated, and calculated magnetic field profiles at z=5cm above the DUT (units: colorbar in A/m, x & y axis in m) ..................................................................................

Figure 3 - 7 :

 37 Figure 3-7: Comparison between theoretical, simulated, and calculated magnetic field profiles at z=10cm above the DUT (units: colorbar in A/m, x & y axis in m) ..................................................................................

Figure 3 - 8 :

 38 Figure 3-8: PIFA antenna design structure ................................................................

Figure 3 - 9 :

 39 Figure 3-9: Simulation and calculated values of the Hz magnetic field component at P1 above the PIFA antenna (colorbar unit: A/m) ..................

Figure 3 - 10 :

 310 Figure 3-10: Simulation and calculated values of the magnetic field components at P 2 above the PIFA antenna (colorbar unit: A/m) .................

Figure 4 - 1 :

 41 Figure 4-1: RFID self-check system used in libraries ................................................

Figure 4 - 2 :

 42 Figure 4-2: Main blocks of an RFID system ..............................................................

Figure 4 - 3 :

 43 Figure 4-3: ZK-RFID406 RFID reader (a), ASR-R250G handheld RFID reader (b), ................................................................................................................

Figure 4 - 4 :

 44 Figure 4-4: EAS RFID tags ........................................................................................

Figure 4 - 5 :

 45 Figure 4-5: RFID tags, for HF bands (a) and UHF bands (b) ....................................

Figure 4 - 6 :

 46 Figure 4-6: 3D radiation pattern of a small loop antenna (plane of the loop is xy plane) [11] ....................................................................................................

Figure 4 - 7 :

 47 Figure 4-7: EHP-200A electric and magnetic field probe .......................................

Figure 4 - 8 :

 48 Figure 4-8: Measurement setup using EHP-200A probe .........................................

Figure 4 - 9 :

 49 Figure 4-9: Mini RFID pad (model 210) with the presence of the EHP-200A probe ..........................................................................................................

Figure 4 -

 4 Figure 4-10: 3M RFID pad (model P12) with the presence of the EHP-200A probe ..........................................................................................................

Figure 4 - 11 :

 411 Figure 4-11: 3M self-check system (model 8420) ...................................................

Figure 4 - 12 :

 412 Figure 4-12: AMH Library RFID system. Area dedicated for users (left), Area dedicated for workers (right) .....................................................................

Figure 4 - 13 :

 413 Figure 4-13: Impedance matching circuit with the loop antenna equivalent circuit .........................................................................................................

Figure 4 - 14 :

 414 Figure 4-14: Simulated and measured reflection coefficient of the antenna ...........

Figure 4 - 15 :

 415 Figure 4-15: Fabricated 1-turn RFID loop antenna (top) with the HFSS model (bottom)......................................................................................................

Figure 4 - 16 :

 416 Figure 4-16: Near-field mapping system with the designed RFID reader antenna .......................................................................................................

Figure 4 - 17 :Figure 4 - 18 :

 417418 Figure 4-17: Magnetic field components above the RFID reader antenna measured with probe P1.............................................................................

Figure 4 - 19 :

 419 Figure 4-19: Fabricated 2-turns RFID loop antenna ................................................

Figure 4 - 20 :

 420 Figure 4-20: Pulsed modulated RFID reader signal .................................................

Figure 4 - 21 :

 421 Figure 4-21: Magnetic field strength above the RFID reader antenna with CW signal, .........................................................................................................

Figure 4 - 22 :

 422 Figure 4-22: Magnetic field strength above the RFID reader antenna with modulated signal, .......................................................................................

Figure 4 - 23 :

 423 Figure 4-23: Measurement setup for H-field characterization above 3M RFID pad P12 .......................................................................................................

Figure 4 -

 4 Figure 4-24: 3M RFID reader (model 810) signals: without any tag near the antenna (blue signal) ..................................................................................

Figure 4 - 25 :

 425 Figure 4-25: Magnetic field components measured with P1 above the RFID pad P12 along y-axis ..................................................................................

Figure 4 - 26 :

 426 Figure 4-26: Magnetic field components measured with P2 above the RFID pad P12 along y-axis ..................................................................................

Figure 4 -

 4 Figure 4-27: 2D cartography of the H-field components above RFID pad P12 ......

Figure 4 - 28 :

 428 Figure 4-28: Total H-field mapping above the RFID pad P12 at h 1 & h 2 ................

Figure 4 - 29 :

 429 Figure 4-29: Measurement setup in the presence of the cylindrical phantom with TSL ....................................................................................................

Figure 4 -

 4 Figure 4-30: Electrical properties of the TSL used to fill the cylindrical phantom ......................................................................................................

Figure 4 -

 4 Figure 4-31: H-field components measured in a vertical plane above the RFID pad ..............................................................................................................

Figure 4 -

 4 Figure 4-32: Total H-field measured above the RFID pad ......................................

Figure 5 - 1 :

 51 Figure 5-1: Schematic of an RF welding machine ...................................................

Figure 5 - 2 :

 52 Figure 5-2: RF welding machine equivalent electrical circuit .................................

Figure 5 - 3 :

 53 Figure 5-3: Small RF welding machine: with no shielding (a), with shielding (b) ...............................................................................................................

Figure 5 - 4 :

 54 Figure 5-4: RF welding machine with the ground plate [] .......................................

Figure 5 - 5 :

 55 Figure 5-5: Duke Phantom in front of the electrode model of the welding .............

Figure 5 - 6 :

 56 Figure 5-6: E-field distribution for different models (defined in Table 5-3) at 27.12 MHz .................................................................................................

Figure 5 - 7 :

 57 Figure 5-7: E-field vectors on the surface of the body .............................................

Figure 5 - 8 :

 58 Figure 5-8: Cumulative distribution function of the electric field for the 5 different models .........................................................................................

Figure 5 - 9 :

 59 Figure 5-9: H-field distribution for different models (defined inTable 5-3) at 27.12 MH ...................................................................................................

Figure 5 - 10 :Figure 5 - 11 :

 510511 Figure 5-10: Continuity of the magnetic field at 27.12 MHz ...................................

Figure 5 - 12 :

 512 Figure 5-12: RF welding machine HFSS model ......................................................

Figure 5 - 13 :

 513 Figure 5-13: Spectrum of the radiated signal in front of the RF welding machine, measured using EHP200A probe. The machine with the ground plate (left) and without the ground plate (right) ............................

Figure 5 - 14 :

 514 Figure 5-14: Exposure index calculated from the measurements made without ground plate (RFWM = RF welding machine position, CP = control panel position) ............................................................................................

Figure 5 - 15 :

 515 Figure 5-15: Exposure index calculated from the measurements made with ground plate (RFWM = RF welding machine position, CP = control panel position) ............................................................................................

Figure 5 - 16 :

 516 Figure 5-16: Measurement setup for H-field measurements in front of the RF welding machine using P2 probe ...............................................................

Figure 5 - 17 :

 517 Figure 5-17: Example of the recorded waveforms for each measured point ...........

Figure 5 - 18 :

 518 Figure 5-18: Measurement planes configurations in front of the RF welding machine ......................................................................................................

Figure 5 - 19 :

 519 Figure 5-19: Magnetic field plots in the planes in front of the welding machine. Measurements (top row) and simulations (bottom row) ............................

Figure 5 - 20 :

 520 Figure 5-20: Measurement planes configurations in front of the RF welding machine in the presence of the cylindrical phantom ..................................

Figure 5 - 21 :

 521 Figure 5-21: Magnetic field plots in the planes in front of the welding machine in the presence of the cylindrical phantom. Measurements (top row) and simulations (bottom row) ....................................................................

Figure 5 - 22 :

 522 Figure 5-22: Electro-optical probe used for the E-field measurements [11] ...........

Figure 5 -

 5 Figure 5-23: E-field eoProbe measurement configuration .......................................

Figure 5 - 24 :

 524 Figure 5-24: Electric field plots in the planes in front of the RF welding machine ......................................................................................................

Figure 1 - 1 :

 11 Figure 1-1: Representation of an electromagnetic wave. The electric field, in blue, and the magnetic field, in red, propagating rectilinearly and perpendicularly to each other

Figure 1 - 2 : 1 . 2 . 2 .

 12122 Figure1-2: The Electromagnetic Spectrum[6]

Figure 1 - 3 :

 13 Figure 1-3: Pulsed wave signal

Figure 1 - 4 :

 14 Figure 1-4: Electromagnetic field regions around a radiating source

Figure 1 - 5 :

 15 Figure 1-5: Wave impedance of magnetic (Z H ) and electric (Z E ) dipoles as a function of k×r

  the largest dimension of the antenna.

Figure 1 - 6 :

 16 Figure 1-6: General EMC model

Figure 1 - 7 :

 17 Figure 1-7: Near-field test bench with scanning system

Figure 1 - 8 :

 18 Figure 1-8: Near field system with array of probes

Figure 1 - 9 :

 19 Figure 1-9: Electromagnetic incident wave decomposition

Figure 1 - 10 :

 110 Figure 1-10: Examples of electric and magnetic field probes for exposure measurements

Figure 1 - 11 :

 111 Figure 1-11: Narda electromagnetic field meters samples

(

  WHO) has been asking the different countries for a global harmonization of regulatory exposures that would establish a framework of reference. The professional protection regulations are mainly based on the European Directive 2013/35/EU of the European Parliament and of the Council of 26 June 2013 [30]. This Directive is part of the package of four directives on the exposure of workers to the risks arising from physical agents: noise, vibration, EMFs and optical radiation. It is an individual directive under Framework Directive 89/391/EEC on the introduction of measures to encourage improvements in the safety and health of workers at work. It is based on ICNIRP 2009 and 2010 guidelines. It introduces a system of ELVs on the basis of biophysical and biological considerations, in

Figure 2 - 1 :

 21 Figure 2-1: Electromagnetic wave and the corresponding sensitive sensors

Figure 2 - 2 : 2 .

 222 Figure 2-2: Small dipole as an example of E-field probe

Figure 2 - 3 :

 23 Figure 2-3: Electric field probes

Figure 2 - 4 :

 24 Figure 2-4: Magnetic field probes

Figure 2 - 5 :

 25 Figure 2-5: Mechanism of the robot scanning in the plane above the DUT

  -6, contains the geometrical parameters for the 3D scanning configuration. The coordinates of the boundary points on each axis can be assigned; on x-axis from X min to X Max , y-axis from Y min to Y Max , and on z-axis (the height) from height min to height Max . Also the step size is assigned in the corresponding box (Pas), and it is the same for the three axes. After filling these parameters, one can start the measurement by clicking start the measurement bottom, then the scanning starts from the point (X min , Y min , height min ) and it continues in the row-wise manner as described in the previous section.

Figure 2 - 6 :

 26 Figure 2-6: Scanning configuration window

Figure 2 - 7 :

 27 Figure 2-7: 2D Scanner for large devices

Figure 2 - 8 :

 28 Figure 2-8: Measuring Near-field of passive devices via VNA

Figure 2 - 9 :

 29 Figure 2-9: Measuring Near-field of active devices via SA

Figure 2 - 10 :

 210 Figure 2-10: Measurement system setup

Figure 2 -

 2 Figure 2-11: Typical TEM cell

  of Tri-Axial Magnetic Field Probes

Figure 2 - 12 :

 212 Figure 2-12: Typical probe calibration setup using TEM cell

  -13.

Figure 2 - 13 :

 213 Figure 2-13: Simulation model of the used TEM cell

Figure 2 -Figure 2 -

 22 Figure 2-14: (a) Transversal and (b) Lonigtuidinal cross-sections of the TEM cell showing the E-field distribution inside the cell

Figure 2 - 16 :Figure 2 -

 2162 Figure 2-16: Commercial magnetic close-field probes from Agilent

Figure 2 -Figure 2 - 18 :

 2218 Figure 2-17: HP1141A magnetic field probe antenna factor

Figure 2 -

 2 Figure 2-19 and the main parameters are summarized in Table 2-3. The calibration and the performance of these 2 probes were studied in details.

Figure 2 - 19 :

 219 Figure 2-19: Geometrical parameters of the magnetic field probes; P1 xy (left) P2 xy (right)

Figure 2 -

 2 Figure 2-19). To measure the z-component of the magnetic field the loop surface should be orthogonal to the z-axis, for this purpose we propose the probes P1 z and P2 z which are a modified version of the probes P1 xy and P2 xy . P1 z have the same geometrical parameters as P1 xy just bended 90 o . P2 z is a square small loop with the dimensions of 3.2×3.2 mm in a planar structure on the bottom layer of the substrate and connected to the pads at the top layer by 2 via with a diameter of 500 µm.

Figure 2 -

 2 Figure 2-20: magnetic field probes; P1 z (left) P2 z (right)

Figure 2 - 23 :Figure 2 - 24 :

 223224 Figure 2-23: Antenna factor of P1xy probe

Figure 2 - 25 :z

 225 Figure 2-25: Probe selectivity measurement configuration

Figure 2 - 26 :Figure 2 - 27 :

 226227 Figure 2-26: P1 xy Probe selectivity

Figure 2 -

 2 Figure 2-28: (a) Reference Circuit; (b) Cross section, showing the geometrical parameters



  The propagating waves along the cylindrical conductor in the circuit are characterized by a quasi-TEM mode. So we will only measure the transverse components of the magnetic field (H y and H z ).

  of Tri-Axial Magnetic Field ProbesThe near-field scanning system presented in section 2.4 was used to perform the validation setup. The reference circuit was placed such that the cylindrical conductor is along x-axis, then the scan is done along y-axis from -40 mm to 40 mm, with a step size of 1 mm. Different signals was generated from SMIQ 06B, each having a specific frequency. The corresponding probe was attached to the robot arm and connected to channel 1 of the oscilloscope, and it was placed at a height d according to Table2-4. The height is measured from the top of the conductor to the center of the probe loop as shown in Figure 2-29.

Figure 2 - 29 :

 229 Figure 2-29: Validation setup using P1 xy probe

Figure 2 -Figure 2 - 31 :

 2231 Figure 2-30: Theoretical values compared to measurement results of H y using P1 xy at different frequencies

Figure 2 -Figure 2 -

 22 Figure 2-32: Theoretical values compared to measurement results of H y using P2 xy at different frequencies

Figure 2 -

 2 Figure 2-34: Fabricated 3D H-field probe P1

Figure 2 -

 2 Figure 2-35: Fabricated 3D H-field probe P2

  as possible. The terminals of each loop are connected to a 2.5 mm (diameter) coaxial cable.

Figure 2 -

 2 Figure 2-36: Coupling between P1 loop elements

Figure 2 -

 2 Figure 2-39 respectively.

Figure 2 -Figure 2 -

 22 Figure 2-38: Measured antenna factor versus frequency for the probe P1

  7.4. The magnetic near-field components of the reference circuit are measured and compared to theoretical ones. The measuring instrument which is the WaveRunner Z640i Oscilloscope contains 4 channels; three of them were used in this setup. The plastic arm of the robot holds the probe above the DUT as shown in Figure 2-40. The triaxial probe terminals are connected to the oscilloscope, via coaxial cable, such that each channel corresponds for one component of the magnetic field as shown in the can be connected to the fourth channel of the oscilloscope if measuring in time domain; hence the phase can be also measured. As the 3 loops in the tri-axial probe don't have the same center, the difference between the loop centers was taken into account in post processing. Knowing that in P1 the centers are in the same plane. And in P2, the centers of the loops corresponding to H x and H y are in the same plane and the difference of H z component was taken into account in calculating the theoretical H z value.

Figure 2 -Figure 2 -

 22 Figure 2-40: Standard validation circuit with the tri-axial probe P1

Figure 2 -Figure 2 -Figure 2 -

 222 Figure 2-42: Normal H-field component H z at for (a) Probe P1 (b) Probe P2

  Calculation at z=0 ..........................................................................Calculation at z=d ............................................................................81 3.4.3. ( , , ) H x y d Calculation ......................................................................................82 3.5. Validation of the Algorithm ..........................................................................................83 3.5.1. Loop Antenna .....................................................................................................83 3.5.2. PIFA Antenna .....................................................................................................87 3.6. Conclusion ....................................................................................................................89 3.7. References ....................................................................................................................90

  H is the magnetic field in [A/m] E is the electric field in [V/m] B is the magnetic induction in [T] D is the electric flux density in [C/m 2 ] J is the electric current density in [A/m 2 ]and  is the electric charge density [C/m 3 ]

  their relative permeability µ r close to 1. For loss-less materials ε and µ are real numbers however most of materials exhibit dielectric losses called loss-tangent tan and that can be defined in terms of the complex permittivity j

Figure 3 -

 3 Figure 3-1summarizes the whole PWS algorithm and its inverse showing the spatial and spectral components.

Figure 3

 3 Figure 3-1: PWS method for magnetic field extraction

Figure 3 - 2 :

 32 Figure 3-2: Spatial domain parameters representing the plane P 0 at z=z 0

28 )

 28 By calculating k x and k y with this last equation, then k z with ( 3-13 ) we can calculate the plane wave spectrum () xy ii F d on any plane z = d, with d ≥ z 0 . This last condition d ≥ z 0 can be somewhat relaxed, as long as the plane z = d remains in the vacuum, otherwise the Helmholtz equation must be modified to take into account the discontinuities of ε and μ.

Figure 3 - 3 :

 33 Figure 3-3: Single turn rectangular loop antenna with the corresponding radiation pattern diagram

  -4 including three different planes above the antenna at heights of 1, 5, and 10 centimeters and with 2D dimensions of L x = 40cm and L y = 40cm. The three magnetic field components H x , H y , and H z are exported at these planes with a grid size of 10mm. In order to obtain high accuracy in the exported data, the planes are meshed by a length based operation with a maximum length of 10mm.

Figure 3 - 4 :

 34 Figure 3-4: RFID Loop Antenna structure

Figure 3 - 5 :Figure 3 - 7 :

 3537 Figure 3-5: Comparison between theoretical, simulated, and calculated values of the Hz magnetic field component at P 0 (units of x & y axis is m)

Figure 3 - 8 :

 38 Figure 3-8: PIFA antenna design structure

Figure 3 - 9 :

 39 Figure 3-9: Simulation and calculated values of the Hz magnetic field component at P1 above the PIFA antenna (colorbar unit: A/m)

Figure 3 - 10 :

 310 Figure 3-10: Simulation and calculated values of the magnetic field components at P 2 above the PIFA antenna (colorbar unit: A/m)

  human body, in which people are in the near-field region of the radiating source, and they are exposed to electromagnetic fields. Radio Frequency Identification (RFID) systems are used today in wide variety aspects of everyday life. RFID refers to technologies that are intended to recognize or identify remotely labels placed on an object, animal or person using radio waves. The corresponding applications are numerous and widespread such as: cashless payments, transportation ticketing systems, residential door keys, antitheft protection systems, library systems (Figure 4-1) [3] etc.

Figure 4 - 1 :

 41 Figure 4-1: RFID self-check system used in libraries

Figure 4 - 2 :

 42 Figure 4-2: Main blocks of an RFID system



  technology used. There are mainly two major classes of RFID technologies: Systems that operate by magnetic coupling (also called inductive coupling): the operation is in the near-field region at 125-148 kHz and 13.56 MHz frequency bands. These systems are for short-range applications (few cm to 50 cm), such as standard labels or contactless smart cards which are mostly passive tags. The bidirectional transfer of the digital data is performed by the energy emitted by the interrogator and modulated by the tag. Systems that operate by electrical coupling: The operation is in the far-field at 434 MHz, 860 MHz, 2.45 GHz and 5.8 GHz bands. The operating distances can reach several meters. The transfer of the data from the label takes place this time through the back propagation of the signal transmitted by the reader, and if necessary using a transmitter in the label. Tags in these systems are often active labels.

Figure 4 - 3 :Figure 4 - 3

 4343 Figure 4-3: ZK-RFID406 RFID reader (a), ASR-R250G handheld RFID reader (b), and ZK-RFID101 UHF RFID reader (c)

Figure 4 - 4 :

 44 Figure 4-4: EAS RFID tags

  power source. Instead, they are powered by the reader antenna, which sends electromagnetic waves that induce a current in the tag antenna. Passive tags are the most used today, an example of the HF tags (13.56 MHz) is shown in Figure 4-5 and another one for the UHF tags (860-960 MHz) is shown in Figure 4-5. 98 RFID Near-field Characterization

Figure 4 - 5 :

 45 Figure 4-5: RFID tags, for HF bands (a) and UHF bands (b)

Figure 4 - 6 :

 46 Figure 4-6: 3D radiation pattern of a small loop antenna (plane of the loop is xy plane)[11]

Figure 4 - 7 :

 47 Figure 4-7: EHP-200A electric and magnetic field probe

  measurements are carried out according to the recommendation of the ICNIRP guidelines and the directive on the exposure of workers (2013/35/Eu): RMS values, over a duration of 6 minutes.

Figure 4 - 8 :

 48 Figure 4-8: Measurement setup using EHP-200A probe

Figure 4 - 9 :

 49 Figure 4-9: Mini RFID pad (model 210) with the presence of the EHP-200A probe

Figure 4 -

 4 Figure 4-10: 3M RFID pad (model P12) with the presence of the EHP-200A probe

Figure 4 -

 4 11 shows the kiosk in the presence of the measuring probe. It consists of a touch screen, a bar code scanner, and an RFID pad that is at height of 90 cm.

Figure 4 -Table 4 - 3 :

 443 Figure 4-11: 3M self-check system (model 8420)

Figure 4 -

 4 Figure 4-12: AMH Library RFID system. Area dedicated for users (left), Area dedicated for workers (right)

Figure 4 -

 4 Figure 4-13 with the equivalent circuit of the loop antenna. The reflection coefficient measurement shows that the antenna resonant frequency is exactly at 13 MHz and it is in good agreement with the simulation as shown in Figure 4-14.

Figure 4 - 13 :Figure 4 - 14 :

 413414 Figure 4-13: Impedance matching circuit with the loop antenna equivalent circuit

Figure 4 - 15 :

 415 Figure 4-15: Fabricated 1-turn RFID loop antenna (top) with the HFSS model (bottom)

  oscilloscope, signal generator, and the tri-axial H-field probes P1 and P2. The plastic arm of the robot holds the corresponding probe where the desired scan above the antenna is performed within the pre-defined margins.

Figure 4 - 16 :

 416 Figure 4-16: Near-field mapping system with the designed RFID reader antenna

Figure 4 -

 4  shows the plots of the 3 components of magnetic field (H x , H y , and H z ) using probe P1 whereas Figure4-18 shows the plot of the measured field components using probe P2. The measured components are very close to the simulation, however the small difference in the H x component is due to the coupling between the probe elements and its effect is somehow negligible as the level of the field is too small compared to the other components.

Figure 4 - 19 :

 419 Figure 4-19: Fabricated 2-turns RFID loop antenna

Figure 4 - 20 :

 420 Figure 4-20: Pulsed modulated RFID reader signal

Figure 4 - 21 :

 421 Figure 4-21: Magnetic field strength above the RFID reader antenna with CW signal, at heights 1cm (a) and 5cm (b)

(

  H x , H y , and Hz ) above the RFID reader antenna are shown in Figure 4-22. The Hfield here is extracted from the RMS measured value, since the signal is an RF pulses. In this case, at h=1cm the H z component has a maximum level of 2.3 A/m while H y is below 2 A/m where H x has a maximum level of 0.6 A/m. At h=5 cm the H z component has a maximum level of 0.8 A/m while H y has a maximum level of 0.4 A/m where H x has a level below 0.25A/m.

Figure 4 - 22 :

 422 Figure 4-22: Magnetic field strength above the RFID reader antenna with modulated signal, at heights 1cm (a) and 5cm (b)

Figure 4

 4 Figure 4-24.

Figure 4 - 23 :Figure 4 -

 4234 Figure 4-23: Measurement setup for H-field characterization above 3M RFID pad P12

Figure 4 - 25 :

 425 Figure 4-25: Magnetic field components measured with P1 above the RFID pad P12 along y-axis at h 1 =1cm (a) and at h 2 =5cm (b)

Figure 4 - 26 : 1 & h 2 .

 42612 Figure 4-26: Magnetic field components measured with P2 above the RFID pad P12 along y-axis at h 2 =1cm (a) and at h 2 =5cm (b)

Figure 4 - 27 :Figure 4 - 28 : 2 HFigure 4 - 29 :

 4274282429 Figure 4-27: 2D cartography of the H-field components above RFID pad P12

Figure 4 -

 4 Figure 4-30: Electrical properties of the TSL used to fill the cylindrical phantom

Figure 4 -

 4 Figure 4-31: H-field components measured in a vertical plane above the RFID pad in free space (left column) and inside the cylindrical phantom (right column)

Figure 5 - 1 :Figure 5 - 2 :Figure 5 - 4 .

 515254 Figure 5-1: Schematic of an RF welding machine

Figure 5 -

 5 4 shows a new welding machine equipped with the ground plate.

Figure 5 - 3 :Figure 5 - 4 :

 5354 Figure 5-3: Small RF welding machine: with no shielding (a), with shielding (b) (a) (b)

Figure 5 - 10 :

 510 Figure 5-10: Continuity of the magnetic field at 27.12 MHz

Figure 5 - 11 :

 511 Figure 5-11: Cumulative distribution function of the magnetic field for the 5 different models

Figure 5 -

 5 Figure 5-12: RF welding machine HFSS model

Figure 5 - 13 :Figure 5 - 14 :Figure 5 - 15 :

 513514515 Figure 5-13: Spectrum of the radiated signal in front of the RF welding machine, measured using EHP200A probe. The machine with the ground plate (left) and without the ground plate (right)

Figure 5 -

 5 14 corresponds for the exposure index distribution for the field radiated in the case without using the ground plate, the place of the welding machine is shown as well as that of the control panel. On the other hand Figure5-15 showsDistance along x-axis [cm]

Figure 5 - 16 :

 516 Figure 5-16: Measurement setup for H-field measurements in front of the RF welding machine using P2 probe

Figure 5 -

 5 17 shows an example of the recorded signals; the measured voltage levels were converted to Hfield values using the AF of the probe P2 at 27.12MHz (Figure 2-39).

Figure 5 - 17 :

 517 Figure 5-17: Example of the recorded waveforms for each measured point

Figure 5 - 18 :

 518 Figure 5-18: Measurement planes configurations in front of the RF welding machine

Figure 5 - 19 :

 519 Figure 5-19: Magnetic field plots in the planes in front of the welding machine. Measurements (top row) and simulations (bottom row)

  The electrical properties of this TSL were extracted in the frequency range of[10- 100] MHz and it is shown in Figure4-30.Scanning was done in 3 vertical planes (P c , P t1 , and P t2 ) along x-and z-axis as shown in Figure5-20. P c is in the center of the phantom with the dimensions of 12cm ×12cm, and the other two are tangential planes that are tangent to the surface of the phantom with the dimensions of 18cm ×18cm with a step size of 3 cm. The measurements and simulations results, shown in Figure5-21, have almost the same distribution however the levels are not the same, where the measured values are much higher. This analysis shows that the magnetic field is strongly influenced by the presence of the phantom, and the ALs are exceeded.

Figure 5 - 20 :

 520 Figure 5-20: Measurement planes configurations in front of the RF welding machine in the presence of the cylindrical phantom

Figure 5 - 21 :

 521 Figure 5-21: Magnetic field plots in the planes in front of the welding machine in the presence of the cylindrical phantom. Measurements (top row) and simulations (bottom row)

Figure 5 -

 5 Figure5-22: Electro-optical probe used for the E-field measurements[11]

Figure 5 -

 5 Figure 5-23: E-field eoProbe measurement configuration

Table 1 -

 1 1: Occupational and general public exposure reference levels[8] ...............

Table 1 -

 1 2: ICNIRP Recommended ELVs [8] ............................................................

Table 2 -

 2 1: Oscilloscope technical specifications [10] ................................................

Table 2 -

 2 2: FCC-TEM-JM1 TEM cell specifications .................................................

Table 2 -

 2 3: Conventional magnetic probe and PCB probe main parameters ..............

Table 2 -

 2 4: Distance between the probes and the reference circuit .............................

Table 4 -

 4 1: Measured RMS field values near the mini RFID Pads, compared to Action Levels .............................................................................................

Table 4 -

 4

2: Measured RMS field values near the 3M RFID pad (model P12), compared to Action Levels ........................................................................

Table 4 -

 4

3: Measured RMS field values near the 3M self-check system (model 8420), compared to Action Levels ............................................................. Table 4-4: RMS measured values near the AMH RFID system, compared to Action Levels ............................................................................................. Table 4-5: Recommended Exposure Limit Values at 13.56 MHz [20] ................... Table 4-6: Antenna factor of P1 and P2 at 13.56 MHz ...........................................

Table 5 -

 5

	RF: radiofrequency
	EMF: electromagnetic field
	RFID: radiofrequency identification
	PCB: printed circuit board
	NFS: near field scan
	PWS: plane wave spectrum
	PIFA: planar inverted-F antenna
	PW: pulse width
	PRT: pulse repetition period
	AF: antenna factor
	HF: high frequency
	UHF: ultra-high frequency
	LF: low frequency
	EMC: electromagnetic compatibility
	SAR: specific absorption rate
	CW: continuous wave
	IRs: ionized radiations
	NRIs: non-ionized radiations
	AL: action levels
	EVL: exposure limit values
	TSL: tissue simulating liquid
	DUT: device under test
	AUT: antenna under test
	RMS: root mean square
	EAS: electronic article surveillance
	SMD: surface mounted device
	SA: spectrum analyzer
	VNA: vector network analyzer
	RBW: resolution bandwidth
	LNA: low noise amplifier
	USB: universal serial bus

1: Gooseneck welding machine specifications ........................................... Table 5-2: Action levels at 27.12 MHz ....................................................................

Table 5-3: Different human models material configurations (units: length in mm, permittivity (ɛ) in F/m, and conductivity (ζ) sigma in S/m) .............. xi List of Abbreviations

Chapter 1: Literature Review Contents Chapter 1: Literature

  .1. Introduction ....................................................................................................................6 1.2. Electromagnetic Fields ...................................................................................................7 1.2.1. Electromagnetic Waves ........................................................................................7 1.2.2. Continuous and Pulsed Waves .............................................................................8 1.2.3. EM Wave Propagation Zones ...............................................................................9Electromagnetic fields nowadays are found everywhere in our environment. They are used in different types of applications, starting from the electrical power lines and not ending with telecommunications and medical applications. The extremely rapid evolution of different technologies that radiate electromagnetic fields has led to an increase in the number of users exposed to these waves, and raises several questions about the possible effects from this exposure. Public concerns about the effects of electromagnetic waves emitted by the cell phone on human health are growing especially their long-term effects. In this context, numerous studies have already been carried out and others are in progress[1]-[3]. Various studies have been done

Review ............................................................................. 5 11.3. Electromagnetic Compatibility .....................................................................................12 1.3.

1. Near-field characterization .................................................................................14 1.4. Interaction between EM fields and matter ....................................................................16 1.5. Radiofrequency Dosimetry ...........................................................................................18 1.5.1. Quantification Parameters ..................................................................................18 1.5.2. Numerical Dosimetry .........................................................................................20 1.5.3. Experimental Dosimetry .....................................................................................21 1.6. State of the art in measurements of EM fields ..............................................................22 1.7. Standards and Guidelines .............................................................................................24 1.8. Conclusion ....................................................................................................................26 1.9. References ....................................................................................................................27 1.1. INTRODUCTION on different biological tissues that are affected by the radiation, focusing more specifically on the human head tissues. The thermal effect depends on the amount of radiation absorbed by the human body. The respect of safety standards makes it possible to protect oneself from it. On the other hand, the non-thermal effects are not clearly established. In industrial environment, workers are exposed to electromagnetic fields generated from different kinds of applications such as: induction heating, welding, glue drying, sealing, electrolysis, etc. Workers are usually more close to the sources;

Table 1 -

 1 1: Occupational and general public exposure reference levels[8]

	Frequency	Electric field intensity [V/m]	Magnetic field intensity [A/m]	Power density [W/m 2 ]
	Band	Occupational	General Public	Occupational	General Public	Occupational	General Public
	10 MHz -400 MHz	61	28	0.16	0.073	10	2
	400 MHz -2 GHz	3f	1.375f	0.008f	0.0037f	f/40	f/200
	2 GHz -300 GHz	137	61	0.36	0.16	50	10

Table 1 -

 1

		Whole body SAR	Local SAR (10g)
	Occupational	0.1 W/kg	4 W/kg
	General Public	0.08 W/kg	2 W/kg

2: ICNIRP Recommended ELVs

[8]

However, we must be careful if we want to compare the limit values of different countries because of the large number of different parameters (calculation methods, sources taken into account, and places of application of more restrictive values...). It is therefore difficult to finally determine which countries apply more drastic exposure rules than others. Disparities in electromagnetic field standards between some countries contribute to public fears. Since 2008, the World Health Organization

Table 2 -

 2 1: Oscilloscope technical specifications[10]

	WaveRunner 640Zi oscilloscope Specs
	Bandwidth	4 GHz
	Number of Channels	4 simultaneously
	Channel-Channel Isolation	DC -2.5 GHz: 40 dB
	Sampling Rate	20 GS/s on 4 Ch
		40 GS/s on 2 Ch
	Memory Length	16M on 4 Ch
		32M on 2/1 Ch
	Maximum Input Voltage	50Ω:5VRMS±10Vpeak
		1MΩ:400Vmax.
	Time/Division Range	20 ps/div -1.6 ks/div with standard

memory The developed scanning system consists of a 3D scanning robot, Teledyne LeCroy WaveRunner 640Zi oscilloscope, PC and the corresponding electromagnetic field probe (Figure 2-10).

Table 2 -

 2

	2: FCC-TEM-JM1 TEM cell specifications
	Specifications	FCC-TEM-JM1
	Frequency Range	DC-1GHz
	Height	44 mm
	Max. Input Power	500 W
	Dimensions (L×W×H)	33.8×15.2×9.9 cm
	RF-connector	Type-N50Ω
	Cell Impedance	50Ω

Table 2 -

 2 3: Conventional magnetic probe and PCB probe main parameters

		Classical Probe P1 xy	PCB Probe P2 xy
	Loop type	Circular	Rectangular
	Number of turns	3 turns	1 turn
	Loop surface area	Pi×(3mm) 3	3.2×3.2mm 2
	Isolation	Air (ε r =1)	FR4 (ε r =4.4)

Table 2 -

 2 4: Distance between the probes and the reference circuit

	Probe	Height (d)
	P1 xy	4 mm
	P1 z	4 mm
	P2 xy	3 mm
	P2 z	2 mm

Chapter 3: Radiated EMF Prediction Method Based on PWS Algorithm Contents Chapter 3: Radiated EMF Prediction Method Based on PWS Algorithm ... 73 3

  .1. Introduction ..................................................................................................................74

3.2. Electromagnetic wave propagation ...............................................................................75 3.3. Principle of the Plane Wave Spectrum Algorithm ........................................................76 3.4. Algorithm Implementation ...........................................................................................80 3.4.1.

Table 4 -

 4 1: Measured RMS field values near the mini RFID Pads, compared to Action Levels

		Measured RMS Value (over 6 minutes) Electric field in [V/m] Magnetic field in [A/m]	Limitation Action Level (AL)	Percentage with respect to the reference level	Limitation Action Level for RF pulses (32×AL)	Percentage with respect to the reference level for RF pulses
		10.68 V/m	61 V/m	17.51 %	1952 V/m	0.55 %
	Pad #1	0.66 A/m	0.16 A/m	412.5 %	5.12 A/m	12.89 %
		11 V/m	61 V/m	18.03 %	1952 V/m	0.56 %
	Pad #2	0.64 A/m	0.16 A/m	400 %	5.12 A/m	12.5 %
		Note: For RF pulses, the reference level is 32 times the Action level given in the
		guidelines
		4.4.2.2.	3M™ Pad Staff

Workstation Model 895 (Black Pad)

Table 4 -

 4 2: Measured RMS field values near the 3M RFID pad (model P12), compared to Action

			Levels
		Measured RMS Value (over 6 minutes) Electric field in [V/m] Magnetic field in [A/m]	Limitation Action Level (AL)	Percentage with respect to the reference level	Limitation Action Level for RF pulses (32×AL)	Percentage with respect to the reference level for RF pulses
		45.9 V/m	61 V/m	75.25 %	1952 V/m	2.35 %
	Pad #1	2.75 A/m	0.16 A/m	1718.75 %	5.12 A/m	53.71 %
		32.4 V/m	61 V/m	53.11 %	1952 V/m	1.66 %
	Pad #2	2.99 A/m	0.16 A/m	1868.75 %	5.12 A/m	58.4 %
		9.32 V/m	61 V/m	15.28 %	1952 V/m	0.48 %
	Pad #3	0.83 A/m	0.16 A/m	518.75 %	5.12 A/m	16.21 %

Table #

 #

		7.89 V/m	61 V/m	12.93 %	1952 V/m	0.4 %
	1	2.26 A/m	0.16 A/m	1412.5 %	5.12 A/m	44.14 %
		10.05 V/m	61 V/m	16.48 %	1952 V/m	0.51 %
	Table #2	2.46 A/m	0.16 A/m	1537.5 %	5.12 A/m	48.05 %

Table 4 -

 4 4: RMS measured values near the AMH RFID system, compared to Action Levels

		Measured RMS Value (over 6 minutes) Electric field in [V/m] Magnetic field in [A/m]	Limitation Action Level (AL)	Percentage with respect to the reference level	Limitation Action Level for RF pulses (32×AL)	Percentage with respect to the reference level for RF pulses
		0.29 V/m	61 V/m	0.47 %	1952 V/m	0.015 %
	Outside	0.0045 A/m	0.16 A/m	2.81 %	5.12 A/m	0.088 %
		3.22 V/m	61 V/m	5.28 %	1952 V/m	0.16 %
	Inside	0.016 A/m	0.16 A/m	10 %	5.12 A/m	0.31

Table 4 -

 4 5: Recommended Exposure Limit Values at 13.56 MHz[20]

		General Public	Occupational
	Reference Magnetic field [A/m]	0.073	0.16
	Maximum Recommended
	Magnetic Field for RF pulses	2.336	5.12
	[A/m]

Table 4 -

 4 and h 2 respectively. We then performed the scan by adding 1-tag to the region of the RFID pad; we noticed that the H-field strength has increased. The field level increases as the number of tags near the pad increases, in the presence of 8-tags the H z component reaches 4.7 A/m at h 1 and 1.5 A/m at h 2 whereas H y component has the values of 3.2 A/m and 0.7 A/m at h 1 and h 2 respectively, with a slight difference in the H x component.

	6: Antenna factor of P1 and P2 at 13.56 MHz
	H-field Probe	AF in dB[A/(m.V)]
	P1	42
	P2 (x & y components)	54
	P2 (z component)	52
	The RMS value of the signal measured by the oscilloscope was recorded then it
	is converted to the corresponding magnetic field component. First, the near field scan
	was performed above the RFID pad without having any tag. The dominant H-field
	component is H z as the pad is a loop antenna and it has a maximum value of 2.8 A/m
	at h 1 and 1 A/m at h 2 . H y component has a maximum value of 2 A/m at h 1 and 0.48
	A/m at h 2 , whereas the third component H x has strength less than 0.5 A/m and 0.2
	A/m at h 1

  French national research and safety institute for the prevention of occupational accidents and diseases INRS (INstitut national de Recherche et de

	Sécurité), estimates around 100000 RF industrial machines in France, which generate
	a high electromagnetic field [1]. Due to this reason and in order to develop an
	effective tool for easily obtaining relevant information on workers exposure to RF
	electromagnetic fields and, if necessary, to propose appropriate measures to reduce
	exposure, EXTI project was lunched.
	EXTI (EXposition des Travailleurs aux champs électromagnétiques Industriels)
	is a scientific project (PNREST 2015/2 RF/002 -ANSES) that aims to study the
	exposure to RF electromagnetic fields of workers in industrial environments and to

Table 5 -

 5 1: Gooseneck welding machine specifications

	Generator Type	GS7500	Number	3079-1
	Sector Voltage	3×220 V	Frequency	27.12 MHz
	Sector Current	45 A	Power	7500 W

Table 5 -

 5

				2: Action levels at 27.12 MHz
	Frequency [MHz]	E-field [V/m]	Magnetic flux density, B [µT]	H-field [A/m]
	27.12		61	0.2	0.16
	5.3.	NUMERICAL ANALYSIS

Design & Characterization of Tri-Axial Magnetic Field Probes

Design & Characterization of Tri-Axial Magnetic Field Probes (b)

Acknowledgements

First, foremost, and forever, thanks God Almighty. Thanks for blessing me much more than I deserve, thanks for everything.

1.9.

Design & Characterization of Tri-Axial Magnetic Field Probes

The voltages across the receiver are correspondingly V mE and V mH and the ratio of the H-field response to the E-field response is approximated by equation (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) [18] [19].

where c is the speed of light.

Equation (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) indicates that the E-field response increases rapidly as the radius of the loop and the frequency increases, and thus the H-field measurements are affected.

Probes Calibration

These two probes were calibrated using the TEM cell as presented in the previous section. ZVL vector network analyzer (VNA), from Rohde & Schwarz, was used to measure the S-parameters [20]. The induced voltage V ind. is then extracted from the transmission coefficient S 21 using the equation (2)(3)(4)(5)(6)(7)(8)(9). After that the AF of each probe is calculated using the formula ( 2-8 ). The other part of the PWS method is to extract the field components at different planes in the space above the DUT just from the field quantities in a single plane near the radiation source. By applying (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) we can obtain the spectral components of the magnetic field at the needed height z. Then by performing IPWS we can have the magnetic field at this height. In RFID near-field characterization, we aim to study the field levels in the near-field region in order to see the dosimetric levels of the radiated magnetic field. For this reason we would chose 2 planes that relay in the normal region of operation of the RFID systems. We chose the plane P 1 and P 2 that are respectively at 5 and 10 centimeters above the reader antenna. Then the reconstruction algorithm is applied based on the magnetic field quantities at P 0 . The results are shown in Figure 3-6 and Figure 34567, good agreement can also be found by comparing the theoretical, simulated, and extracted magnetic field profiles at the chosen planes P 1 and P 2 . We can observe a little noisy profile in the normal extracted magnetic field H z at the edges of the computed area; this could be solved by adding zero padding to the initial data at P 0 . the electric field, with respect of the case where the phantom is absent (model number 1). However, the internal structure of the phantom seems to play a quite minor role.

Figure 5-6: E-field distribution for different models (defined in Table 5-3) at 27.12 MHz Moreover, in the presence of any phantom it is observed that the electric field approximately satisfies quasi-static hypotheses outside the worker's body (in particular, the field is almost orthogonal to the body surface), but not at all inside it (Figure 567). This can be easily explained by the high permittivity and conductivity of the phantom with respect of air (Table 5-3).

E-field [V/m]

#2 E-vector field on the surface of the body. nxE is quite null.

E-field [V/m]

Industrial RF Welding Machines EMF Characterization

H-field [A/m]

weldingmachine'stable,andthereddotsrepresentsthemeasuredpoints.Thelevel of the E-field ranges between 60 V/m and up to 300 V/m as it is clear in plane P 0 , these levels exceeds the ALs given in the directives. The observed asymmetry in the field plots is explained by the fact that the machine's RF generator, located at the back, is being shifted to the right.

CONCLUSION

In this chapter we presented the analysis and characterization of the electromagnetic fields emitted by industrial machines, in particular RF welding machines. These machines radiate a strong electromagnetic field that may causes hazardous problems to the exposed workers. Numerical simulations show that the presence of human body significantly alters the electric and magnetic fields, as they are strongly modified by the presence of the body. However the internal structure of the human body has a lite effect on the field. Measurements were performed on a real machine that exists at INRS; this welding machine operates at 27.12 MHz with a power of 7.5 kW. Magnetic field was measured using the tri-axial probe P2

(presented in Chapter 2) while for the electric field an electro-optic probe was used.

Good precision cartographies were obtained (to be used for the numerical formulations) showing that the intensities of the measured quantities are extremely dependent on the environment near the machine. Even though the ground plate in the machine is used, the field levels still high, and ALs are exceeded in some places, hence workers should avoid being in these places while the machine is in operation. The performance of this algorithm has been realized in the third chapter, where it was validated near two applications; a loop and PIFA antennas.

y-axis [cm] y-axis [cm] y-axis [cm]

In chapter four, the exposure assessment near RFID reader antennas was performed. A detailed study was presented on the radiated electromagnetic field from RFID systems used in libraries which operates at 13.56 MHz. Electromagnetic field measurements, both in situ and in the laboratory, made it possible to evaluate the field levels to which users of these systems can be subjected. The strength of the field degrades rapidly as we go far from the antenna, whereas in the vicinity area the levels were found high, but it still within the reference levels when it is averaged.

In the fifth chapter, the exposure of workers to the strong energy emitted by RF welding machines is studies. A numerical simulation was performed at the beginning to check the effect of the presence of an operator on the field distribution near the machine. Then, both electric and magnetic fields were measured near a real machine in the place of the presence of workers while it's in operation. It has been demonstrated that the presence of any metallic element near the machine strongly affects the field distribution. The recorded field levels have shown high values near themachine'selectrodethatexceedsthereferencelevels.

Concerning the presented measurement system, the further enhancement that can be done in terms of the scanning time is the development of an array of probes. Some applications have large sizes and there is a need of having the filed map in different planes near these devices. The presented tri-axial probes in this thesis reduce the scanning time by a factor of 3. For more optimization in the measurement time we can go forward and developed an array of these probes. This helps in making the measurement at different locations in the space at the same time. We have already started in fabricating a linear array of 8 elements form the P2 tri-axial probe, in Finally, we are developing another prediction algorithm which aims for extracting the electromagnetic field distribution in a phantom present near a radiating device starting from the magnetic field values measured in the same area without having the presence of the phantom. The necessary FEM formulations of this method are developed using ONELab and preliminary simulation results show the validity of his method. The performed measurements in this thesis will be used to feed the developed algorithm and to validate it on real radiating applications. In this library there is just one type of RFID systems that is used, in addition to an anti-theaft detection system based on RFID technology. Both systems are from Nedap Library Solutions. The radiated near field is measured using EHP-200A and the results are tabulated, comparing the measured values with the guidelines levels.

A.1.1. Nedap Flex-desk Station

This section shows the measurement that was done near two similar self-check RFID systems from Nedap (type: C-O Station Flex B). The probe was placed in the center of the table where the RFID pad is found. The figure below shows one of these systems in the presence of the probe, followed by the results table.

A.1.2. Nedap PG45 detection system

In this section the measurement was done at different positions near the anti-theft detection system (PG45-4W-PCC12-3) from Nedap. It has the dimensions of 480mm×1665mm, with a gate opening of one meter. The measurement positions are sown below.

A.2. Bachut Library

In this library the measurements were done near two types of RFID Systems and an anti-theft detection system, and all of them are from 3M Company. The near fields are measured and the results are tabulated as in the previous sections. The used probe was placed at the center of the RFID pads and at different positions in the detection system, and the RMS over 6 minutes was measured.

A.2.1. 3M™ Pad Staff Workstation Model 800

Measurements was done near this Black pad, used by the workers at the library, at two situations with and without a presence of a tag. The following figure shows this pad in the presence of the used probe.

A.2.2. 3M Self-check System (Classic)

In this section measurements were done near two similar 3M self-check systems (R-series classic) used by public users. The following figure shows one of these systems in the presence of the measuring probe placed in the center of the RFID pad.

159

A.2.3. 3M Detection System (Model 9100 BC)

In this section the measurements was done at different positions near the 3M antitheft detection system (model 9100 BC). It has gate width of 91.4 cm. The corresponding results are tabulated below.

Abstract

The analysis of radiated emissions from a source throughout the space, is very essential for both dosimetric and electromagnetic interference analysis. The concerns about the latter are growing because of the need to have prediction of the system reliability of the electronic circuits. Moreover the everyday use of devices and systems emitting radio frequency electromagnetic fields is continuously increasing. Some of these devices are operating in the vicinity of human body, and operators are in the near-field region of the radiating source, and they are exposed to electromagnetic fields. For this reason, dosimetric analysis, that shows the necessity of having three dimensional (3D) field mapping in the vicinity of the radiating source, should be performed. For this kind of applications, several scans of the near fields should be done within different planes in order to build the 3D field mapping. Being a challenging process in electromagnetic compatibility studies, near field characterization is being treated by several algorithms that propose different approaches to achieve the required scanning on the radiating source.

In this work, we introduce a 3D scanning system with a low cost three axis magnetic field probes. Having such probes allow the simultaneous measure of the three components of the magnetic field based on a single planner scan above the device under test. The designed probes consist of three orthogonal loops combined together; the first probe contains three conventional loops joined in a plastic cube with a total dimension of 10×12×13 mm 3 , whereas the second probe is a PCB probe printed on an FR4 substrate of 3.2 mm with a reduced dimension of 9×9×3.2 mm 3 . The designed probes were calibrated with a TEM cell and the corresponding antenna factors were extracted. The presented scanning system uses an oscilloscope as a measuring instrument that gives the possibility of both time and frequency domain measurements. The second part of this thesis presents a reconstruction algorithm based on plane wave spectrum method. In order to reduce the number of scans and hence the time requirements, the presented algorithm requires just a 2D near field scan of the field components, to reconstruct the 3D magnetic field distribution above the radiating device.

The third part of the thesis is devoted for the dosimetric analysis of the radiated electromagnetic fields near RFID systems and RF-welding machines. The near-field exposure assessment of the radiated fields from RFID reader antennas operating at 13.56 MHz and used in Libraries was performed. The measurements of the magnetic field near the antenna were established using the designed probes. The results are then analyzed and compared to the regulations in European Directives and ICNIRP Guidelines. Moreover, the exposure to RF electromagnetic fields of workers near RF-welding machines in industrial environment is studied. These machines, operating at 27.12 MHz, emit strong radiation and the exposure takes place in the near-field region. The spatial distribution of the electromagnetic fields in this region is studied in both numerical simulations and measurements.