Laure Arbenz

Abdelkader Benabou

Stéphane Clénet

Jean-Claude Mipo

Pierre Faverolle

Characterization of the local incremental permeability of a ferromagnetic plate based on a four needles technique

The performances of electrical machines depend highly on the behavior of ferromagnetic materials. In some applications, these materials operate under DC polarization, i.e. when the magnetic field oscillates around a DC bias. In that condition, it is required to know the incremental permeability which characterizes the magnetic behavior of the material around the operating point. In this paper, a non-destructive approach, involving a combination of experiment and Finite Element (FE) technique, is presented in order to determine the incremental permeability. The proposed sensor is based on the four-needles method. With this sensor, Bowler et al. have proposed a method to determine the initial permeability of homogeneous metal plates based on an analytical model. Here we propose to use the same kind of sensor to determine the incremental permeability. The measurement process is analyzed using a FE model. It is shown that the analytical approach reaches its limits if the permeability of the plate and its thickness become too high. A combination between the measurements and a FE model is introduced to overcome this difficulty to determine the incremental permeability. The study of two magnetic steel samples illustrates the interest of this method.

Index Terms-Finite Element modeling, Four needles probe, Incremental permeability, Material characterization

I. INTRODUCTION

HE performance of an energy conversion device made up of ferromagnetic materials is highly dependent on their magnetic and electrical properties. The material behavior has to be characterized and modeled in order to study and predict the performance of the energy conversion device. To that end, the normal magnetization curve is usually used to represent the material behavior. Nevertheless, for some devices, such as the rotor of synchronous machine, the material is polarized and, in some regions of the rotor, the magnetic field can oscillate around a mean value. Therefore, the relevant magnetic characteristic is the incremental permeability that also depends on the magnetization level.

In the standard experimental approaches for magnetic measurement (Epstein frame, Single Sheet Tester), the characterization techniques require samples with a specific and simple geometry (steel sheet with standardized dimensions). This characterization is often carried out on the raw material before any manufacturing process. But an important aspect for the performance of the ferromagnetic pieces is related to the manufacturing process of the magnetic core that can modify the properties of the material. In fact, these can be worsened compared to the raw material [START_REF] Ramarotafika | Experimental Characterization of the Iron Losses Variability in Stators of Electrical Machines[END_REF]. Moreover, during the manufacturing process, this impact is not necessarily repetitive and can also lead to a dispersion of these properties. Characterization at the end of the process is sometimes preferable in order to identify the real behavior of the material. Therefore, a method of characterization, that must be non-destructive and local, is required.

The simple and obvious nondestructive approach consists in using a ferromagnetic yoke surrounded by an excitation coil. The magnetic field can be measured by a Hall sensor and the induction by a pick-up coil [START_REF] Stupakov | Applicability of local magnetic measurements[END_REF]. This method is largely used for nondestructive measurement and control in industry [START_REF] Gabi | FEM Simulations of Incremental Permeability Signals of a Multi-Layer Steel With Consideration of the Hysteretic Behavior of Each Layer[END_REF]. But this approach has some drawbacks. The main one is caused by the inevitably existing air gap between the yoke and the sample. Because this air gap cannot generally be controlled and is not necessarily the same from one sample to another, it is difficult to consider this method as quantitative.

Another interesting approach based on a four-point measuring sensor, known as ACPD (Alternating Current Potential Drop), is proposed in [START_REF] Bowler | Four-point potential drop measurements for materials characterization[END_REF]. The ACPD method was historically developed as nondestructive testing since many years [START_REF] Michael | The Measurement of Surface Cracks in Metals by Using a.c. Electric Fields[END_REF] [START_REF] Michael | Detection and Measurement of Cracks in Threaded Bolts with an a.c. Potential Difference Method[END_REF]. Bowler et al. have proposed to use this approach to measure the initial permeability quantitatively.

In this paper, and starting from the ACPD method, a quantitative method is developed in order to measure locally the incremental permeability of a ferromagnetic material up to saturation. A non-destructive approach, combining the experiment and the Finite Element (FE) technique, is proposed to extend the range of validity of the method. For the FE simulations, the 3D electromagnetic field calculation software code_Carmel is used [START_REF]code_Carmel (Code Avancé de Recherche en Modélisation Electromagnétique)[END_REF].

First, the experimental method is detailed with the model used to identify the incremental permeability. Then, the proposed method is validated and used to characterize two kinds of magnetic steel plates.

II. EXPERIMENTAL PROCEDURE

A. Definition

The major (or main) hysteresis loop is the loop for which the material is magnetized up to saturation. Conversely, a minor loop is a loop for which the material is not magnetized to saturation. In Fig. 1., the major hysteresis loop and two minor loops are shown. The normal B(H) curve is obtained by connecting the tips (H max , B max ) of minor loops with increasing values of H max . Experimentally, this curve is similar to the T initial magnetization curve (or commutation curve). This latter is obtained when, from the demagnetized state, a strictly increasing field is applied [START_REF] Bozorth | Ferromagnetism[END_REF]. If the material is initially demagnetized, a special case of minor loops is defined when the magnetization field is extremely small. Indeed, under these conditions, the magnetic behavior is in the Rayleigh region and the permeability is the initial permeability:

µ i = lim (H→0) ∆B/∆H (1)
Note that, to perform a rigorous demagnetization of a material, this one has to be heated to a temperature above its Curie temperature. Then, the material is cooled in the absence of any external magnetic field. It is well known that, starting from this magnetic state, if an increasing magnetic field is applied, the obtained magnetization curve is known as the "virgin curve". In our case, a commonly used procedure is applied to obtain a magnetic state close to the demagnetization one. It consists in applying an alternating field with a magnitude high enough to cause the saturation of the material followed by a slowly decreasing magnitude to zero.

The initial permeability µ i is therefore graphically represented by the slope of the initial minor loop (Fig. 2). The normal permeability µ N is the slope of the normal curve. The incremental permeability µ ∆ is the slope of minor loops superimposed at various levels of biasing magnetic field (Fig. 2). For a given magnetic field, the normal and incremental permeability are different. For the experimental part, the developed sensor is based on the principle of the four-point method proposed by Valdes in 1954 [START_REF] Valdes | Resistivity measurements on germanium for transistors[END_REF]. In a previous work this approach was used to measure the electrical conductivity of electrical parts with a non-trivial geometry [START_REF] Arbenz | Characterization if the local electrical properties of electrical machine parts with non -trivial geometry[END_REF]. To measure the electrical conductivity, a DC current is imposed between the outer pair of points and a voltage is measured between the inner points (Fig. 3). But, to measure the magnetic permeability, it is necessary to impose an AC current through the outer pair of points.

This measurement method, named four-point alternatingcurrent potential drop (ACPD) method, has been studied in the case of ferromagnetic plates by Bowler et al. [START_REF] Bowler | Four-point potential drop measurements for materials characterization[END_REF], [START_REF] Bowler | Model-Based Characterization of Homogeneous Metal Plates by Four-Point Alternating Current Potential Drop Measurements[END_REF]. The authors were interested in the case of homogeneous metal plates of which they proposed an analytical model to determine, from the experiment, the conductivity and the initial permeability of the plate. The voltage U is linked to the current I by the following expression:

, f<f v (2)
With ω the angular frequency, σ the conductivity, µ i =µ ir µ 0 the initial permeability, parameters T, l, q, s defined in Fig. 3 and Fig. 4 and f v = π/(2µ i σT 2 ). Indeed, from this expression, the conductivity σ (or the thickness T) and the initial permeability µ i can be determined from the measurements of the real and imaginary parts of the voltage U. Nevertheless, this approach allows measuring only the initial permeability µ i . To obtain the incremental permeability µ ∆ versus the polarization field H pol , it is necessary to add to the four-point sensor a polarization device and a field sensor.

C. Experimental device

A ferromagnetic yoke (30x40mm 2 of section for a height of 130 mm and a length of 150 mm), carrying a bias coil (200 turns, 0.6 mm wire diameter), is added to the experimental device to create the polarization magnetic field H pol in the sample. The magnetic field at the surface of the sample can be estimated from a measurement with a Hall sensor. But, the magnetic field gradient in the air gap between the Hall sensor and the surface of the sample can lead to significant measurement errors. So, a more accurate technique consists in using a probe made with two Hall sensors (Allegro MicroSystems Inc A1389LLHLX-9-T), superposed one on the other below the sample. The magnetic field H 1 (respectively H 2 ) is measured by the Hall sensor at the distance z 1 (respectively z 2 ) from the sample surface. Then, the surface magnetic field H pol is obtained directly by a linear extrapolation. Indeed, H pol is the intercept point of the linear function as z(H pol )=0, so:

H pol =(z 2 H 1 -z 1 H 2 ) / (z 2 -z 1 ) (3)
The probe is placed next to the four-point sensor to measure the field and the voltage at the same location (Fig. 4). The fourpoint sensor is made with four spring loaded needles of 1mm diameter (Ingun HSS118) with round tip style to ensure a good point contact and gold plating.

D. Raw measurement interpretation

In practice, considering the alternating excitation current i in the outer points as the phase reference, the measured voltage U between the inner points (see Fig. 3) is postprocessed in order to extract its real and imaginary parts (U r and U i ). To do so, the RMS values (i eff and U eff ) and the average power P are calculated:

, , (4)
with t 0 a time instant arbitrary chosen and T p the period of the excitation signal. The integration is performed numerically by applying the trapezoidal rule. From the result of equation ( 4), the phase lag between the current and the voltage is deduced by: cosφ =P/(i eff U eff ) and U amp = U eff √2

(5)

Then one can easily determine the real and imaginary parts of the signal by: U r = U amp cosφ and U i = U amp sinφ [START_REF] Michael | Detection and Measurement of Cracks in Threaded Bolts with an a.c. Potential Difference Method[END_REF] To summarize, the polarization field H pol is directly measured with the field sensor (see Fig. 4). The incremental permeability µ ∆ must be deduced from the real and/or imaginary parts of the voltage (U r and U i ) using an analytical or numerical model. Indeed, equation ( 2) can be used replacing µ ir by µ ∆r . We assume that the hysteresis loop of interest is just shifted on the first magnetization curve. As mentioned previously (see equation ( 2)), the analytical model proposed by Bowler et al. having a limited range of application, we propose to perform the extrapolation of the incremental permeability from a numerical model.

III. NUMERICAL MODELING

A. Presentation of the approach

For the analytical development proposed by Bowler et al., some hypotheses are necessary, such as constant permeability and far-field regime [START_REF] Bozorth | Ferromagnetism[END_REF], [START_REF] Valdes | Resistivity measurements on germanium for transistors[END_REF]. Moreover, the obtained analytical model is valid if the frequency is less than f v =π/(2µσT 2 ), with µ=µ i or µ ∆, corresponding to the skin effect limit. However, in practice this frequency limit can be quickly reached. For example, in the case of a 2 mm thick plate with electrical conductivity 5.5MS/m and relative permeability 800, the limit frequency is only 70 Hz. This limit frequency f v reduces the experimental data available, which is limiting to identify with accuracy the permeability.

Therefore, we propose to use a FE model instead. The numerical model was built upon several hypotheses. The first one is the delimitation of the studied domain that includes the plate with the needles and an air box surrounding the device. This air box is chosen with its boundaries sufficiently far from the plate in order to allow the leakage magnetic flux to flow through the air. On the needles side, the air box boundary coincides with the top of the needles in order to impose the current, in the excitation needles, at the boundary of the studied domain. Regarding the needles, these have been idealized with a cylindrical shape so that the contact with the plate is a surface delimited by a circle. Also, the needles were considered with a conductivity equal to 60 MS/m. Another modelling hypothesis is the neglecting of the magnetic shield on the opposite side of the plate as it was verified experimentally that it does not influence the AC field produced by the excitation needles. As previously mentioned, its usefulness is relevant for the experimental estimation of the magnetic field at the surface of the plate. Finally, the simulated geometry consists in the sample (2mm x 50mm x 200mm), the four-point sensor and the air around the device (88mm x 250mm x 400mm) (Fig. 5). The solution is obtained by solving a quasistatic problem using the electric potential (A-φ) formulation with the Finite Element Method. The quantities of interest are the voltages and the currents at the terminals of the needles under sinusoidal excitation and in steady state. Since the problem is linear, it has been solved in the frequency domain. To get accurate results, the global quantities have been either imposed or calculated in post-processing using a method presented in [START_REF] Henneron | Calculation of Extra Copper Losses with Imposed Current Magnetodynamic Formulations[END_REF] which imposes a power balance (the mean of the eddy current losses is equal to the active power and the mean of the magnetic energy is equal to the reactive power provided by the external circuit). For a fixed thickness T and a fixed conductivity σ and different values of the relative permeability µ r , the AC current flowing through the external needles of the sensor is imposed and the resulting voltage between the internal needles is calculated in a post-processing step for different frequencies. The discretization of the domain leads to a mesh of 250 000 nodes and 1 500 000 tetrahedral elements.

As illustration, some results are presented in Fig. 6 and Fig. 7 where the real and imaginary parts of the simulated signals are reported obtained with the FE model and the analytical expression [START_REF] Stupakov | Applicability of local magnetic measurements[END_REF]. Since the FE model can be considered as the reference one, from these results, the limit of validity of the analytical approach appears clearly. Above a given frequency (close to f v ) the analytical and the numerical models are not in agreement anymore.

B. Current density and magnetic flux distribution

To further analyze the behavior of electromagnetic quantities in the plate, an example of current density distribution is given in Fig. 8. It is observed that the current is widely distributed in the plate. Fig. 9 shows the magnetic flux density component along the y axis, in the plane containing the four-point sensor. It is very interesting to notice that the magnetic flux flowing between the measurement points (i.e. inner points) is unidirectional (here, in the opposite direction of the y axis orientation). Indeed, the magnetic flux path closes outside of the sensor measurement region. Consequently, at the measurement points, the magnetic induction profile is quite simple. The Fig. 10 (f=5Hz) shows the magnetic induction component along the y axis for different cross-sections along the y axis. It is noted that, for the sample having an incremental permeability µ r =5, the magnetic flux density is not distributed in all the plate. In fact, the magnetic flux closes rapidly in the region outside the sensor. But, for the sample with a higher incremental permeability µr=800 (Fig. 11, f=5Hz), the magnetic flux is distributed in all the plate and reaches greater distances before changing its direction. The end effect should be taken into account which is naturally done using the FE model but not with the analytical approach where the plate is assumed to be infinite.

C. Application to the measurement of the permeability

The FE simulations allow the extraction of the voltage response for several values of the incremental permeability µ ∆ . These results are used as an abacus for identifying the practical incremental permeability by a comparison with the measured voltage. To perform this operation, it is necessary to know the thickness and conductivity of the studied sample. Then, for fixed thickness (T=2 mm), fixed conductivity which can be measured with a DC method [START_REF] Arbenz | Characterization if the local electrical properties of electrical machine parts with non -trivial geometry[END_REF] (σ=5,5MS/m) and different values of the relative permeability µ r , the numerical results are used to calculate the real and imaginary voltages (U r and U i ) versus the frequency of the AC current flowing through the external needles of the sensor (Fig. 12). The experimental results (real and/or imaginary parts) can be then plotted together with the numerical results in order to identify the closest incremental permeability. To ensure a robust identification, a frequency sweep is performed to find the best curve fit. In the example of Fig. 12, the deducted permeability in both cases (real and imaginary parts) is 200.

IV. VALIDATION OF THE MEASUREMENT METHOD

A. Sample description

The following study proposes to compare the incremental permeability of two samples of magnetic steel (SAE 1006). The aim is to validate the ability of the proposed method to quantitatively estimate the incremental permeability. Both studied samples have a thickness T=2 mm and a conductivity σ=5.5 MS/m. The conductivity of the material has been determined by the method presented in [START_REF] Arbenz | Characterization if the local electrical properties of electrical machine parts with non -trivial geometry[END_REF] which is based on four needle technic supplied by a DC voltage coupled with the FE model. From the same experimental device and FE model the conductivity and the incremental permeability can be determined. They have the same chemical composition but a different microstructure due to a different heat treatment. Indeed, the sample noted B0 is raw and the sample note B1 has been annealed.

Both of these samples were magnetically characterized by a single sheet tester (SST, Brockhaus measurements) at 1Hz. Normal curves of samples are deduced from a set of centered minor loops (Fig. 13). The obtained normal curves show that the magnetic properties of both samples are indeed different: the annealed has improved the magnetic characteristics of sample B1.

B. Reference incremental permeability

Regarding the reference incremental permeability that will be used to validate the four needles technique, a graphical approach, using the minors loops measure using the SST device is adopted. In Fig. 14, we present the principle to determine the incremental permeability for a given value of the magnetic field H pol . More precisely, for a given width ∆H, at the extremity of the minor loop, an interval of the magnetic induction ∆B is identified. Then, the ratio of these two values allows deducing the incremental permeability µ ∆ . In addition, the polarization field H pol is assumed to be the center of the interval ∆H. This operation is reproduced for all minor loops and the curve µ ∆ =f(H pol ) is obtained. We can see that the value of the incremental permeability is dependent of the width ∆H. Consequently, the width of the incremental loop ∆H should be chosen to be of the same order of the one met with the fourpoint technic. In the four needles method this width ∆H is linked to the amplitude of the AC current imposed through the needles. So it is important to measure the corresponding ∆H in order to extract the correct reference incremental permeability from the minor loops. The approach of incremental permeability identification is then applied to the samples B0 and B1. The experimental results are given in Fig. 16 where the real and imaginary values represent the results of the identification procedure performed with the simulated curves of, respectively, the real and imaginary parts of the voltage. We can notice that experimental results obtained from both real and imaginary parts are close. Moreover the measured data are also close to the reference values. We can see that this method enable to it is possible to distinguish the samples from each other with the proposed method.

V. CONCLUSION

The proposed approach enables to deduce the magnetic characteristics of steel plates without extracting specific samples. The procedure was applied to steel plates with the same thickness and composition but with different magnetic characteristics. The results show that the studied samples exhibit different incremental permeability which evolution versus the polarization field, being clearly different, allows to distinguish the magnetic steels.

This study shows also that the behavior of the incremental permeability is complex as it depends on the width of the minor loop and considered material. This method is attractive as it is easy and fast to carry out experimentally. Moreover, using the combined experimental-numerical approach, the method can be easily applied to more complex geometries in a non-destructive context.

Fig. 1 .

 1 Fig. 1. Major hysteresis loop, minor loops and normal curve

Fig. 2 .

 2 Fig. 2. Initial, Incremental and Normal permeability

Fig. 3 .

 3 Fig. 3. Four-point device

Fig. 4 .

 4 Fig. 4. Proposed experimental device Moreover, a magnetic shield is added to reduce the magnetic field gradient in the vicinity of the Hall sensors. This allows a better estimation, from equation (3), of the magnetic field at the surface of the sample. The shielding is made of two magnetically soft steel sheets.

Fig. 5 .

 5 Fig. 5. Geometry of the studied model

Fig. 6 .Fig. 7 .

 67 Fig. 6. Imaginary voltage divided by imposed current versus frequency of the imposed current

Fig. 8 .

 8 Fig. 8. Current density distribution (f= 5Hz, µr=5)

Fig. 9 .

 9 Fig. 9. Magnetic induction along the y axis (f= 5Hz, µr=5)

Fig. 10 .Fig. 11 .

 1011 Fig. 10. Magnetic induction along the y axis on all the sample (µr=5)

Fig. 12 .

 12 Fig. 12. Numerical results (T= 2 mm, σ=5,5 MS/m) with experimental measurements represented with +

Fig. 13 .

 13 Fig. 13. Normal curves of the studied samples

Fig. 14 .

 14 Fig. 14. Method to obtain the reference incremental permeability In Fig. 15, we have represented the incremental permeability in function of H pol for three values of ∆H determined from SST measurement and the method described

Fig. 15 .

 15 Fig. 15. Reference incremental permeability -effect of ∆H

Fig. 16 .

 16 Fig. 16. Experimental results -comparison with reference values


Rhode Ghislaine

Nguewo Ngassam
email: ngassam@etu.umontpellier.fr

Roxana Ologeanu Taddei
email: roxana.ologeanu-taddei@umontpellier.fr

Isabelle Bourdon
email: isabelle.bourdon@umontpellier.frjoricklartigau2

Digital service innovation enabled by the blockchain use in healthcare: the case of the allergic patients ledger

Keywords: Allergology, pikciochain, blockchain, digital innovation, co-construction, social innovation

By combining the institutional approach and the rational model of digital innovation, there is increasingly a great interest in the implementation of blockchain solutions in healthcare but, until then concrete evidence for this type of project is missing. At the same time the healthcare sector, allergology in particular seems to face security (confidentiality, availability and integrity) issues and information audit trail weaknesses. For these reasons, our study focuses on the co-construction of a distributed ledger for patients allergies with healthcare professionals. The aim is to design and implement a reliable tool to deal with the availability , integrity and confidentiality of information about new allergies and distinguish between validated allergies and declarative allergies for the purpose of mitigating negative effects of unavailability of reliable information about patients allergies. This article defers the first step of our methodological cycle by explaining how collaboration is organized between Pikcio (blockchain technology provider) and allergists. As a result, we have first versions of some deliverables such as formal specifications, risk matrix document and a UML design (class diagram, use case diagram and sequence diagram) as the research project is iterative.

Introduction

In recent years, digital innovation has attracted great interest from the information system community with the rapid expansion of digital technologies in business and society in general. As a definition, digital innovation is the use or production of digital technologies in the innovation process [START_REF] Nambisan | Digital innovation management: Reinventing innovation management research in a digital world[END_REF]. The digital innovation has two main approaches: institutional and rational model [START_REF] Hinings | Digital innovation and transformation: An institutional perspective[END_REF]. The institutional approach of digital innovation emphasizes the belonging of organizations to a society that imposes on them behaviours that must be adopted in order to comply with the law or socially acceptable rules [START_REF] Hinings | Digital innovation and transformation: An institutional perspective[END_REF]. From this point of view, the fashion phenomenon has a lot to do with the adoption of new tools in companies and organizations. The most striking example is that of blockchain technology, which is originally use in the field of cryptocurrency and is found to attract great interest in other sectors, one of which is healthcare [START_REF] Hölbl | A systematic review of the use of blockchain in healthcare[END_REF]. However, in spite of the multiplication of studies on the application of this technology in healthcare, it is far from visible and concrete applications of blockchain potentialities in this sector [START_REF] Hölbl | A systematic review of the use of blockchain in healthcare[END_REF]. Far from contradicting the potential of the blockchain technology, this last remark aims to put things in context by finally recalling the rational purpose of the digital innovation that is to bring solutions to specific problems encountered by users [START_REF] Tolbert | The institutionalization of institutional theory[END_REF].

Nevertheless, beyond the hype, the blockchain has strong promises in the healthcare sector, where existing systems have failed [START_REF] Rabah | Challenges & Opportunities for Blockchain Powered Healthcare Systems: A Review[END_REF]; especially in terms of security [START_REF] Manaouil | Le dossier médical personnel (DMP) : « autopsie » d'un projet ambitieux ?[END_REF] and compliance with health data regulations [START_REF] Lucas | Le partage des données personnelles de santé dans les usages du numérique en santé à l'épreuve du consentement exprès de la personne[END_REF]). Since security is made up of the availability, integrity and confidentiality of data (2013), it also involves looking at the audit trail in the system for the purposes of control and audit [START_REF] Cruz-Correia | Analysis of the quality of hospital information systems audit trails[END_REF], mainly related to the question of forensic responsibility or accountability of healthcare professionals.

The security issue is particularly visible in healthcare with a great negative effect on patient safety especially in the field of allergology where reliable information concerning the patients allergies are often not available nor accessible, which causes a lot of medical incidents [START_REF] Demoly | Identifier et comprendre les allergies médicamenteuses[END_REF]. On the other hand, the few information available are of dubious quality especially for penicillin allergy with approximately 10% of patients who report a penicillin allergy while up to 90% of these patients do not have a true allergy what causes anaphylactic reactions or antibiotic resistance after administration of inappropriate treatments [START_REF] Sullivan | Skin testing to detect penicillin allergy[END_REF]. The low quality of these data is often related to the fact that the validations are not made or are made by non-expert professionals who do not finally establish the correct diagnosis [START_REF] Demoly | Identifier et comprendre les allergies médicamenteuses[END_REF]) which leads to questioning the source of the data by keeping in mind that the data will be more reliable if the validator is legitimate. This lack of reliable and traceable information causes the increasement of morbidity and mortality rate as well as a significant socio-economic cost [START_REF] Bousquet | Une synthèse sur l'épidémiologie des hypersensibilités médicamenteuses[END_REF], hence the importance to deal with the construction of solutions that enable the permanent availability of such healthcare information in a secure way. In this sense, our research question is about how to use blockchain technology to design and implement a reliable and secure healthcare information system in the allergology field in order to improve the safety of patients during the treatment?

Before answer the question "how?" we must return our attention to the primordial question of "what?" since it is demonstrated that the success of a solution is based on the value it has in relation to the problems that arise [START_REF] Pozzi | Affordance theory in the IS discipline: A review and synthesis of the literature[END_REF]. Hence the importance of clarifying the state of needs to bring out relevant solutions, especially since the literature describes needs as being generally unknown and technologies as unintelligible [START_REF] Cohen | A garbage can model of organizational choice[END_REF]. Meanwhile, the literature of social innovation advocates, for studies focused on the social interest of users to integrate them in the construction of the solution because they ultimately better know what they need [START_REF] Mulgan | The process of social innovation[END_REF]. This last remark brings us back to the problems of misunderstanding that can occur during the collaboration between technology experts and users, given the heterogeneous knowledge they hold and which must be combined for the success of the project [START_REF] Ratcheva | Integrating diverse knowledge through boundary spanning processes-The case of multidisciplinary project teams[END_REF]. For these reasons, we believe that the co-construction approach [START_REF] Oudshoorn | How users matter: The co-construction of users and technologies[END_REF] is relevant to complement the concept of boundary objects [START_REF] Mark | Boundary objects in design: An ecological view of design artifacts[END_REF]) in order to design the best suited solution for users' needs.

This research project focuses on the involvement of healthcare professionals and patients in the co-construction of a digital and social innovation of a distributed ledger for allergies that allows the reliable identification of each patient and healthcare professionals, the distinction between validated allergies and declarative ones, as well as patient consent access management for the purpose of improved patient safety during the treatment.

The remainder of this paper concerns successively a background on the blockchain concept follow up by the theoretical framework, methodology, preliminary results and expectations as well as implications of this research project.

Background : blockchain technology

Blockchain technology has a lot of definition either holistic or specific [START_REF] Fosso Wamba | Bitcoin, Blockchain, and FinTech: A Systematic Review and Case Studies in the Supply Chain[END_REF]) but can easily be described by four main technical characteristics [START_REF] Dinh | Untangling blockchain: A data processing view of blockchain systems[END_REF]: distributed ledger as all participants in the chain has the same version of data records, block and cryptography as data are organized in block and each block is cryptographically linked to his predecessor and many cryptographic techniques are used to avoid data alteration or redundant records, consensus protocol as the achievement of a transaction depends on the validation of participants, finally Smart contracts as the system verifies conditions and apply automatically changes [START_REF] Watanabe | Blockchain contract: A complete consensus using blockchain[END_REF]. Overall, we can say that the blockchain ensures the secure transfer of data in a secured environment without the intervention of any third party that would validate operations [START_REF] Yli-Huumo | Where is current research on blockchain technology?-a systematic review[END_REF]. This technology was first used for financial transactions with bitcoin cryptocurrency before being gradually adapted for other purposes with several other technologies such as Hyperledger and Ethereum among others [START_REF] Dinh | Untangling blockchain: A data processing view of blockchain systems[END_REF].

However, whatever the field of application or the implemented tool, the blockchain technology faces several challenges that can be summarized in three main terms [START_REF] Swan | Blockchain: Blueprint for a new economy[END_REF] namely: correctness that describes the capability for a blockchain system to distinguish fraudulent transactions, agreement that describes the mechanism set up to ensure that all or almost all participants in the network accept a transaction and finally the utility that describes the necessity for a blockchain system to be useful. These challenges are more and more taken into account in the different developments of blockchain and according to the domains, we can have public or private blockchain [START_REF] Dinh | Untangling blockchain: A data processing view of blockchain systems[END_REF]

Parity, Hyperledger

The first adaptation of blockchain in healthcare was reported in 2014 [START_REF] Ashoor | Blockchain Infrastructure Acceptance in the Gulf Cooperation Council Countries: An Overview[END_REF] after what many other papers and white papers had been written to describe the potentialities or a particular tool made for an application in healthcare [START_REF] Hölbl | A systematic review of the use of blockchain in healthcare[END_REF]. Rabah Kefa (2017) presents a list of possible usage of blockchain in healthcare sector and we can summarize them in few terms: audit trail, access grant, data integrity or electronic health record. In the literature, the identified challenges for blockchain in healthcare and the proposed solutions can be summarised in the following table. [START_REF] Kuo | Blockchain distributed ledger technologies for biomedical and health care applications[END_REF] indexes saved on the chain -Data stored locally by users and exchanged peer-to-peer when it is necessary

The new legal requirements General data protection regulation (GDPR) and good practices regarding health data in Europe are related to the security, integrity, the right for patients to give their consent for the visibility of their data and to change their mind as whenever they want [START_REF] De Hert | The right to data portability in the GDPR: Towards user-centric interoperability of digital services[END_REF]. In addition to this requirements, healthcare information system needs to be improved in the way of audit trail (Cruz-Correia, Boldt et al. 2013) for the purpose of data integrity and accountability of healthcare professionals of all transaction for the purpose of audit and forensic responsibility. All these requirements seem to match with the potentialities of blockchain technology which answer all these requirements with the following's characteristics: transparency, data immutability and traceability, hence the great interest of healthcare in this technology.

Epistemological and theoretical framework

Tolbert and Zucker (1999) distinguish two models of innovation adoption process by explaining the fact that while the institutional approach of digital innovation focuses on the over socialised nature of organisations in the process of adopting a solution, the rational actor model remain very important in that it is the best way to have a successful innovation because it involves taking into account the value of a solution for a given need. In this perspective, the issue involved in a research project must address a real problem in practice, in our case the information traceability issues and security of data encountered by health facilities for the purpose of improving patients safety. This idea is supported by Wainwright, Oates et al. [START_REF] Wainwright | Evidence-Based Information Systems: A New Perspective and a Road Map for Research-Informed Practice[END_REF]) who developed the evidence based practice in information system from the model found in medicine called evidence-based medicine which is the basis of the decision support system [START_REF] Stavrou | Archibald Cochrane (1909-1988): the father of evidence-based medicine[END_REF]. In addition to deal with the idea of involving real information system problematic, the evidence-based practise emphasizes on the importance of evidences during the conclusion phases and research results diffusion.

In the same way, Greeno [START_REF] Greeno | Gibson's affordances[END_REF]) points out the notion of affordances in its original sense that defines the explicit or implicit existence of needs, leaving thus to show the importance for a researcher to be able to synchronize with practitioners without being influenced by fashion effects [START_REF] Baskerville | Fashion waves in information systems research and practice[END_REF] but more by the possible value of an artefact for users and their needs. In the same vein, [START_REF] Gregor | The anatomy of a design theory[END_REF] propose the design theory to show its definite impact both in research and in practice with the influences it has had, among other things, in the analysis of structured systems. Nunamaker Jr, Chen et al. (1990) and [START_REF] Gregor | Introduction to the special issue on design science[END_REF] argue in this sense the usefulness of "design science research" for research and practice in information systems. This concept highlights three aspects: proof of concept, proof of value and proof of usefulness which are important and make it possible to describe the need for information system researchers to find solutions to practical problems but also to ensure that these solutions are used to promote the benefits they imply. Moreover, these notions can be crossed with those found in "evidence-based" where a particular emphasis is placed on the definition of the problems to be solved, the sources of information necessary for the resolution of those problems, the resolution of those problems and the dissemination of the solution [START_REF] Goeken | Evidence-based structuring and evaluation of empirical research in requirements engineering[END_REF][START_REF] Wainwright | Evidence-Based Information Systems: A New Perspective and a Road Map for Research-Informed Practice[END_REF] since in both cases, it is a question of broadcasting an innovation that is useful and used by the target audience. However, to deal with the need of the organizational relevance of a solution, the design science research has been improved to the action design research by emphasizing on the importance of continuous evaluation along the process rather than conduct evaluations ex-post [START_REF] Sein | Action design research[END_REF]. This last approach deal with the challenge of clarifying the needs with users in order to design the best suited solution.

The importance of the clarity of needs and the usefulness of solutions lead therefore to be more interested in the theory of affordances which is defined as the value of a solution for a user [START_REF] Pozzi | Affordance theory in the IS discipline: A review and synthesis of the literature[END_REF]). Transposed into an information system, the notion of affordances describes the fact that the possibilities of a tool may not be systematically perceived by the user. This view leads to the conclusion that users would not always be aware of their need or that the values of a solution would not always be easily perceptible as argued by [START_REF] Cohen | A garbage can model of organizational choice[END_REF] and [START_REF] Lomi | The garbage can model of organizational choice: Looking forward at forty. The Garbage Can Model of Organizational Choice: Looking Forward at Forty[END_REF] through the notion of organized anarchy (garbage can theory) which highlights the fact that in the organizational reality the solution can pre-exist the problem, and that it can be in adequacy or no with a pre-existing solution. This idea runs counter to the basic premise of design science which is that we design and develop a solution to answer a problem or a need. It should also be noted that problems in organizations are almost poorly defined, especially in professional organizations such as schools / universities [START_REF] Glaser | Pervasive decentralisation of digital infrastructures: a framework for blockchain enabled system and use case analysis[END_REF] which have the same organizational structure as hospitals [START_REF] Romelaer | Structure & dynamique des organisations[END_REF].

We propose to complete the approach of action design research by considering organized anarchy in a process of co-construction of digital innovation. Our research approach is inspired by the new theory of digital innovation [START_REF] Nambisan | Digital innovation management: Reinventing innovation management research in a digital world[END_REF]) that puts forward a strong link between the innovation process and outcomes by describing a collaborative work environment that needs to be orchestrated in order to match solutions to existing problems. This collaborative environment is made up of future users who are likely to know their needs better and therefore help the designers of the solution to build a better tool with a real social contribution [START_REF] Mulgan | The process of social innovation[END_REF]. In doing so, we wish to base ourselves on the recommendations of [START_REF] Haki | A Value Co-creation Perspective on Information Systems Analysis and Design[END_REF] to move from an approach emphasizing the technological originality brought to an approach that takes into account the multitude of actors at stake in a collaborative approach of co-construction [START_REF] Oudshoorn | How users matter: The co-construction of users and technologies[END_REF] with the concept of boundary objects to facilitate the communication between project team members.

Methodology

Based on the principles of action design research [START_REF] Sein | Action design research[END_REF], we propose to carry out action research for the co-construction of a distributed and secure allergy ledger. It consists of several iterative loops for refining needs and solutions involving the designer and the users, as well as the design of the innovation, materialized through an application allowing the registration and the management of allergies with patients and healthcare professionals. The design process of this application can be drawn as follow: The three main steps involved in the circle (specification of needs, conception, and evaluation) can be summarized in two stages since we deal with the action design research: intervention and evaluation.

The intervention stage is made up of two steps:

-The iterative refinement of problem through a co-construction process between allergists and pikcio. In this step, data gathering will take place during meetings, speed trainings and online discussions with the use of boundary objects such as Business Process Model Notation (BPMN), Unified Modelling Language diagram to facilitate the communication between interdisciplinary team project members.

A particular case of co-construction at this stage of the project is shown in Erreur ! Source du renvoi introuvable. below. It is related to the definition of the global purpose of the project -The iterative refinement of the prototype is conducted with the use of interactive mockups as a boundary object to facilitate the understanding and the visualization. For this purpose, we use the software Balsamiq mockup 3.

Concerning the evaluation stage, we distinguish in this research level of evaluation:

-Functional evaluation to assess user benefits (e.g. before / after comparisons to evaluate the decrease in the input time). it will include both data from the monitoring of tests (e.g. time for the identification, numbers of bugs) and directive interviews with the users to evaluate their perceived ease of use and usefulness about the solution. For the last purpose, we will use some constructs of adoption theories such as Theory of Acceptance Model (TAM) or Unified Theory for Adoption and Usage of Technology (UTAUT) in order to analyse the acceptability of the solution in view of patients. -Technical tests will be processed with digital libraries such as JavaScript library or any other units test library available depending on the technology involved during the development.

-Usability evaluation consisting in ergonomics evaluations with real life scenarios -Clinical trials organized by allergists in order to ensure that the safety of patients is met with the solution.

During all the process, data collection will be done in several levels using a qualitative methodology with interviews and observations. This will occur during the following activities -Analysis of the state of art, mainly related to the actual process of the management of allergies and dispositions to make information on allergies available.

-Observation of meetings allowing the co-construction of innovation. The so called coconstruction will be enabled by the discussion on each other ideas and the enrichment of the solution with each other knowledge -Prototype design and technical tests involving UML modelling, development and unit tests -The construction of scenarios and functional tests with users

Preliminary results and expectations

Our methodological cycle was initiated by the need's specification stage, which was done through meetings, modelling and discussions in which allergists and the solution provider Pikcio were better able to identify needs and the possibilities of the pikciochain technology to match with these needs.

As a result we were able through to better understand the actual processes with the description made by allergists either textual and schematic. This exercise allows to highlight the followings specifications:

-There are three user groups: patients, healthcare professionals and allergists -The patient, his doctor or his allergist can declare an allergy concerning him, but only the allergist after conclusive tests can validate an allergy.

Through meetings and online discussion on the implications of blockchain for traceability and data regulations both about healthcare data and consent management, those specifications had been added:

-Each user must be reliably identified -The patient has total control of his data and has the right to authorize or not access to other users -The patient chooses his trusted third parties to manage his access rights in case of his unavailability -The healthcare professional can urgently access a patient's file if he / she cannot grant him the rights and he / she has not been able to reach any trusted third party Then, a document referencing the different risks -risk matrix, was assembled from the clinical point of view by allergists and from the technological point of view by Pikcio. The purpose of this matrix is to identify all or almost all the elements that can undermine the effectiveness of the solution in order to improve specifications in a way of mitigating some risks.

Clinical risks

False information

Tests ill processed or processed by a nonspecialist

The validation of allergies functionalities in the application will be right granted and available only for allergists.

A criteria of trust capital index will be involved for the evaluation and filtration of bad validators These specifications have been formalized and signed by both parties. All the previous elements were used by pikcio to build the UML (Unified Modeling Language) analysis document which describes the technical specifications of the solution This document was explained, discussed and improved during a meeting with allergists.

Here is the general class diagram of the application in its first version drawn in UML. This sequence diagram describes the identification process that begins with the form that the user completes, then he loads his vouchers and from the hash done by the system of all these elements, the duplicate check is performed. If the hash already exists in the chain, the user will have to reconsider his existing account by resetting his code. If the duplicate does not exist, a more detailed risk analysis is performed on the vouchers to verify compliance with the information given by the user. In the best case, the user's account is created. Graphically we have materialized this process by interactive mockups some of whose screenshots are below.

Theoretical and practical Implications

The framework of this research project being posited by the evidence-based practice, we enrich it with the action design research as a working methodology. In doing so, we will create evidence of concrete implementation of blockchain in healthcare by highlighting details on aspects such as needs and solution refinement in the intervention stage, as well as a full evaluation even technical, functional, ergonomic and clinical. Moreover, by highlighting the collaboration between interdisciplinary actors, we enrich the literature on digital innovation, the co-construction and the orchestration of various skills in a project. In the literature, a special emphasis is placed on the role of boundary objects to facilitate understanding between actors of different skills in a project, we complement this approach with a co-construction process by seeing this beyond the improvement of communication, as a way to better understand the needs by enriching each stage of the project specifications with the skills of each other. In addition, this co-construction approach will also enrich the theory of organized anarchy, which highlights the gradual construction of solutions to meet needs that become clearer over time.

We also enrich the literature on social innovation in that beyond the technological and functional aspect generally evoked in information system, our solution will answer a social problem related to the high mortality and morbidity rate around the lack of information on patients allergies. Moreover, the social aspect comes from the fact that we have integrated users throughout the process in the idea that they know better their need and could help to build a better adapted tool in an iterative step.

Beyond the enrichment of theories, this project through the evaluation phase, will enrich the literature on the acceptability and usability of blockchain solutions by patients and healthcare professionals.

In practical terms, we propose the modelling and evaluation of the blockchain solution (pikciochain) for the case of allergology, thus producing proofs of concepts and interesting axes of deployment of a solution that seems still lacking in France. But more importantly, the solution we are building will be a social innovation in addition to being a digital innovation in that it will concretely reduce the negative effects related to the unavailability or inaccessibility of reliable information on patient allergies. In doing so, we are opening up possibilities of adaptations of this solution for other cases of interesting use in healthcare.

Figure 1 .

 1 Figure 1. Methodological circle

Figure 2 .

 2 Figure 2. A co-construction case: definition of the general purpose for the project

Figure 3 .

 3 Figure 3. Class diagram

Figure 4 .

 4 Figure 4. Sequence diagram for the identification process

Figure 5 .

 5 Figure 5. Screenshot of identification process mock-up

Table 1

 1 whose comparison can be summarized in the following table: Public VS private blockchain

		Key	Data	Consensus	Frequent	Examples
		proprieties	model			applications
	Public	Free access Coins or	All nodes are	Crypto	Bitcoin,
	Blockchain		account	involved,	the	currencies,	ethereum,
				consensus		general	openchain
				process is time	applications
				and	energy
				consuming
	Private	Access	Accounts,	It could have	Finance,
	blockchain	control	assets	master nodes for	healthcare (Linn
				the consensus	and Koo 2016)
				process		and	closed
						organizations
						networks	in
						general

Table 2 .

 2 Challenges of blockchain in healthcare

	Challenges	Solution				References
	Anonymity	Patients grant access to	(Hölbl, Kompara et al.
		identified	persons	or	2018)
		institution
	Security / confidentiality	Access control, right granted	(Hölbl, Kompara et al.
		by patients				2018)
	Data management	-Data	lake		(Data	(Yue, Wang et al. 2016)
		repository	enabling
		the storage of diverse
		data type) with only

Table 3 .

 3 List of some risks and the proposed solutions

	Identified risk		Description		Proposed solution
			Technological risks
	Data loss	Since data are saved by	-Users may choose some
		users and exchanges are	trusted third parties to help
		made	application	to	them save their data in case
		application the risk of data	of loss
		is too high			-A healthcare data host
						(HDS) may be requested to
						serve as a warehouse for all
						data
	Misalignment of system	The tool could impose a	A user-centric approach will be
	with local practices and	particular new behavior to	processed	with	a	circle
	processes	users				methodology involving needs and
						solutions refinement
	Choice of support	The mobile version is a	Both mobile application and
	hardware suitable for any	suitable choice but, in	desktop version may be developed
	type of users	some situation, users may	to encompass all scenarios
		want to access their data
		with	their	personal
		computer