Gabriel Hermosillo

Julien Ellart

Lionel Seinturier

Laurence Duchien

A Traceability Service to Facilitate RFID Adoption in the Retail Supply Chain

Nowadays, companies are suffering changes in the way they deal with their inventories and their whole supply chain management. New technologies are emerging to help them adapt to the changes and keep a competitive status, but the adoption of such technologies is not always easy. Even though a lot of research has been done for RFID, there are still some areas that are being left aside, like the traceability aspect, which is one of the most important concerns in the retail supply chain. We propose a service named TRASER (TRAceability SErvice for the Retail supply chain) that will help the companies adopt the new technologies into their existing environments, dealing with persistence and traceability, and allowing the users to manage their operation according to their business rules, workflows and historical data.

Introduction

Radio Frequency Identification (RFID) is a technology used to identify a tagged object using radio frequency. It is mainly composed of an electronic tag attached to an object, a reader that gathers the tag's information and a computer system connected that receives and processes the information provided by the readers [START_REF]EPCglobal's website[END_REF]. RFID has come as a relay to the bar code systems, bringing several advantages such as not to require a line-of-sight between the tag and the reader, multiple tags read at once, possibility to hide the tag or make it part of the design. The tags can be read from a short distance up to considerably long distances (tens of meters with an active tag). Because of these advantages, RFID applications are growing widely in different domains, including health care and medicine [START_REF] Tu | Identifying RFID-embedded objects in pervasive healthcare applications[END_REF][START_REF] Lai | Enhancing medication safety and reduce adverse drug events on inpatient medication administration using RFID[END_REF], warehouse management [START_REF] Tan | The Application of RFID Technology in the Warehouse Management Information System[END_REF][START_REF] Yan | RFID Technology Applied in Warehouse Management System[END_REF], aerospace and automobile industry [START_REF] Ahmad | Closing information loops with extended PLM[END_REF][START_REF] Strassner | The Promise of Auto-ID in the Automotive Industry[END_REF], construction and maintenance of oil facilities [START_REF] Domdouzis | Radio-Frequency Identification (RFID) applications: A brief introduction[END_REF], retail and supply chain management [START_REF] Albrecht | Supermarket Cards: The Tip of the Retail Surveillance Iceberg[END_REF][START_REF] Sabbaghi | Effectiveness and efficiency of RFID technology in supply chain management: strategic values and challenges[END_REF][START_REF] Tu | Reducing false reads in RFID-embedded supply chains[END_REF] and anti-counterfeit [START_REF] Chen | Anti-counterfeit ownership transfer protocol for low cost RFID system[END_REF].

RFID has evolved during the last few years, from being an obscure technology, almost unknown, used only by a small group of companies, to a fundamental technology that is now adopted and used worldwide by many important companies, consumer applications and governments. In commerce, RFID technology is mainly used for monitoring inventory and identifying different assets (i.e. pallets, containers, etc.), while in the industry, it is mainly used for monitoring production processes. In either environment, RFID can provide immediate and tangible benefits throughout the supply chain. Rather than displacing bar codes, RFID will complement them, helping to facilitate all the supply chain logistics in the companies that adopt it. According to some authors, there are three main research streams in RFID applied to the supply chain: conceptual analysis of opportunities (benefits and risks), case studies, and business values [START_REF] Madlberger | A Model of Antecedents of RFID Adoption Intention in the Supply Chain[END_REF]. Others say that research publications are mainly focused on technology, applications, and security [START_REF] Ngai | RFID research: An academic literature review (1995-2005) and future research directions[END_REF]. The truth is that RFID is beginning to become a key part of the industry, and its adoption is eminent for those who want to keep a competitive status.

To correctly use and exploit the RFID technology, we need specific services that will allow us to take advantage of the gathered information and to use it in a business model. Some of these services are already defined by the EPCglobal's standards, like the use of ONS, EPCIS and ALE, as shown in Figure 1, but others are not so deeply considered, such as traceability and event storing. The lack of research and implementation of these services has made it harder for the industry to adopt RFID and integrate them to their existing applications, specially for the retail supply chain, where these approaches are some of the most important.

Our project intends to cover those needs. In the following sections we propose an RFID service named TRASER that will deal with persistence and traceability, allowing the users to manage their operations according to business rules, workflows and historical data. This service will be part of a whole platform, which has for objective to create a shared technical infrastructure, generic and parametrized, capable of managing the communication of heterogeneous systems (RFID, bar codes, NFC, etc.) among them and with existing IT services, to help the companies exploit and benefit from the current technologies. This research takes place within the ICOM project, funded by "Pôle de compétitivité" PICOM and the Région Nord-Pas-de-Calais in France.

This paper is organized as follows: Section 2 explains the motivation of the project. Section 3 describes our proposal. Section 4 presents some of the related work. Finally, section 5 concludes and discusses some future work.

Motivation for a traceability service

In the retail supply chain, it is important to know the amount of inventory held, where the products are located, in what condition they are and sometimes even to what environment they have been exposed. This information is usually gathered manually, and occasionally registered and then fed into a business application to be considered. The use of bar codes has been used to keep track of products and to relate them with the rest of the information, but unfortunately it is not very accurate. Bar codes are generic, so a reading of a bar code does not provide information about an individual product, but rather of a particular kind of products. That means that if we have 10 identical products, we can scan each one or just scan the same one 10 times and get the same result. This often leads to human errors during the stock receiving and inventory processes, where the employees just scan one product and multiply it by the number of identical products that they think they have, instead of scanning each product individually. Another problem is that if during the process one of the products is lost, we would not know for sure in which step of the process we lost it, because there is no individual tracking and normally the employee will not scan all the products again on each step of the process.

A solution for these problems is to use an RFID infrastructure, which will allow each tag to be considered individually, and then add a traceability service to get the information about the product's location and environment and complement the package with persistence, so that not only the present status of the product is considered, but also the historical data that has been gathered about it can be used. The process has to be relatively easy for the industry to adopt the RFID services, and it needs to have useful results and be quite simple to manage. In this context, the data contained in a tag is not interesting when it is isolated, but when it is used within a business application it becomes very important. Every information sent by the RFID or bar code readers creates an event, which can be used to go from one state of the process to another, but not all the events cause a state change, sometimes it is a group of events, or even the order in which they happen, what is needed to create such a transition.

An example of such transitions can be seen in Figure 2. If we have a product X in a warehouse, when the tag of X is read by reader A in the exit of the warehouse, and a few minutes later it is read by reader B in the sales floor, it will create a transition of product X to be on sale , but if instead it is read by reader C on the shipping area, the transition of product X will go to shipping . So depending on the business process, the status of the product will change according to its location. Gathering all the possible information from the created event, like cause, time and place, will help the final user to create a workflow that will fit better to their business process by adding Complex Event Processing (CEP) to the system [START_REF] Wang | Research and Design of RFID Data Processing Model Based on Complex Event Processing[END_REF]. This can even be used to create on-the-fly reports that are updated with each event and create alerts when an anomaly is found, which help the user to keep a live monitoring of the process. It is in this context that we propose TRASER, a traceability service for the retail supply chain, that will allow the companies to know the status of their products and incorporate that information into their business management.

3 TRASER: a TRAceability SErvice for the Retail supply chain

An overview of TRASER

The objective of TRASER is not to create a completely new approach to solve the problems, but to bring together the existing standards and research projects to create a complete and useful service that can be easily adopted in the retail supply chain. In order to understand how our system works, Figure 3 shows a basic architecture, based on the EPCglobal's standards [START_REF]EPCglobal's website[END_REF]. The system receives the events created from the readers (after being filtered), containing the reader ID, the time of read and the Electronic Product Code (EPC) (step 1), among other fields that can be added according to the user's needs. These events will be translated to a business event (step 2), to have a more significant meaning. To increase the usefulness of the events, there is a need to store them so they can be available at any time and be considered for the decision making process or be consulted by any system interested in them, and to cover this need, we use the EPC Information System (EPCIS) repository (step 3), following the EPCglobal's standards [START_REF]EPCglobal's Standards[END_REF]. For the external entities, it is not so easy to know where the information about a tag is being stored, so there must be a service which can provide the relation between a tag and the EPCIS repository containing it's information. Here is where the EPCglobal's architecture requires the Object Name Service (ONS) (step 3'), a service based on the Domain Name System (DNS) [START_REF]EPCglobal's Standards[END_REF]. Finally, an application interface will allow the existing applications to exploit the generated information (step 4) or even send new business events through it (step 4'). This last step allows the generation of events that are not related to the readers (i.e. a manual intervention in a certain step of the process).

Traceability service

To simplify and improve the traceability service, we divided the whole process in two main parts: Event Translation, which will transform the ALE events into business events, using Complex Event processing (CEP) and a rule engine, and the Process Manager, which will receive the business event and create the transitions accordingly in the Business Process Manager (BPM), as shown in Figure 4. Both parts are explained in more detail in the following sections.

In the Event Translation part, the service has an Application Level Event (ALE) interface that receives the events from the readers after being filtered, or any other source that can generate an ALE event (like intelligent readers). The input of this interface shall be an XML file containing the fields and information specified in the EPCglobal's ALE standard 1.1 [START_REF]EPCglobal's Standards[END_REF]. After that, the events are transformed into EPCIS events (or business events), using the business rules defined by the user. The EPCIS events are defined in the EPCglobal's EPCIS standard 1.0.1 [START_REF]EPCglobal's Standards[END_REF], and are introduced into the system using the Core Business Vocabulary created by EPCglobal for a better, and yet standard, use and understanding of the events. Once the translation is done, the EPCIS events are then sent to the process manager, where they will be analyzed and will allow the process to move from one state to another, according to the provided workflow of the business. This will be done using a state-transition diagram, that will show the different states in which a tag (or the object containing the tag) will be followed. At the end, the process engine will trigger a new event for the business applications or an alert, in case some conditions are not met.

Complex Event Processing

In Complex Event Processing (CEP), the main goal is to figure out a meaningful and complex event by analyzing multiple streams of simple events. These complex events can be either the occurrence of a group of simple events in any order or the sequence of them [START_REF] Wang | Research and Design of RFID Data Processing Model Based on Complex Event Processing[END_REF]. An example of this could be when a delivery is received and a sample of the items is taken for quality purposes, if the sample is not sent back to the warehouse within 2 hours, then an alert of missing stock will be generated. These kind of event analysis can also be used to prevent merchandise theft from stores [START_REF] Huber | Minimizing Product Shrinkage across the Supply Chain using Radio Frequency Identification: a Case Study on a Major Australian Retailer[END_REF], which is also one of the goals of this project. For example, if a product's tag is read in the exit reader, without being read before at the register machine, the system can assume that a possible theft is in progress and alert the security guards.

CEP is an essential tool for the retail supply chain, since it allows the relation of tags to a specific business scenario. It can be used for simple things, like relating the reads of a product tag and a container tag at the same time by the same reader and assume that the product is being shipped inside the container, to the most complicated business rules that a user can introduce, by relating time, cause and place, and trigger an action accordingly [START_REF] Ku | A Novel Complex Event Mining Network for Monitoring RFID-Enable Application[END_REF].

We will be using the ASPIRE project as the base of our work [START_REF] Kefalakis | Supply chain management and NFC picking demonstrations using the AspireRfid middleware platform[END_REF][START_REF]ASPIRE's website[END_REF], since it's design is very close to our needs and especially because it is an Open Source Fig. 5. BEG interaction solution, which will allow us to adapt it exactly as we need to, and finally it also has an active community, eager to contribute with the adoption and correct use of RFID technologies. The ASPIRE project's specifications include a middleware component that deals with CEP, called Business Event Generator (BEG), a configurable component which captures the raw events sent by the readers and generates new business events [START_REF]ASPIRE Middleware and Programmability Specifications[END_REF]. As shown in Figure 5, the BEG receives the filtered events captured by the readers and then queries the EPCIS to get the context information needed for interpreting the incoming data. With all the gathered information, it finds the rules that can be applied to it and then creates the corresponding business event, which in our case will allow the process to move from one state to the other in the process manager.

Process manager

The process manager is the service in charge of relating the business events, created by the BEG, to the business processes. The products follow steps during their life cycle: they are moved, packaged, shipped, received, etc. Those steps are part of a business process. The RFID events are part of the transition between steps in the process. The process manager aims to process the RFID events in order to follow the provided business processes. To implement this part we will use Bonita, a workflow and BPM open source solution [START_REF]Bonita's website[END_REF].

The formal definition of a process allows to specify the expected steps that it will follow and the expected triggers (i.e. RFID events) to go from one step to the other. If an unexpected business event is received at a step where there is no corresponding transition, that means there is an error in the process, either in the design or in the execution of it. All the information obtained from the process (transitions, errors, etc.) can be used by existing software applications, once the information is translated to the format expected by them, which allows an easy adoption of RFID by the companies. Figure 6 shows an example of a simple process representing the states of a product inside a store. The store is equipped with RFID readers between the areas. A normal process for a product that is In stock , will be to go from the warehouse to the sales floor, after receiving the Leaves stock event. Then it can enter and leave the fitting area, with its corresponding events. Finally, it can go to the cash machine to get sold, which would generate an event to update the stock and then leave the store. When the steps are followed as expected the process continues normally, but when an unexpected event arrives, it means we have a problem. For example, if we receive a Leaves store event, without being in the Sold step, it gets an error and generates an alert. This kind of alerts are an excellent feedback, since they can make the users realize some mistakes in their process design or show them that the process is not being followed as expected, either by the employees or by the clients.

Related work

A lot of research is being done in different areas, in order to facilitate the adoption of RFID mainly for governments, hospitals and retail suppliers. Most of the recent works propose the use of CEP for obtaining meaningful information from the gathered data and there are different approximations for this topic.

An attempt to apply the principle of separation of concerns in CEP has lead a research to create a layered middleware for it, which consists on a logic structure layer, a temporal constraint layer and an event detection layer [START_REF] Hu | Complex Event Processing in RFID Middleware: A Three Layer Perspective[END_REF]. They support their approach by standing that a layered design provides a better understanding for RFID events.

A tool called Cascadia, capable of extracting and managing meaningful highlevel events from raw RFID data is another work on this area [START_REF] Welbourne | Cascadia: A System for Specifying, Detecting, and Managing RFID Events[END_REF]. Cascadia offers a complete system for managing RFID events, but it doesn't use any standards for this, so the interaction with other systems depends on specific development for the tool.

A research similar to our project presents a middleware for RFID and Wireless Sensor Networks (WSN), using CEP in a partial EPC architecture, including an EPCIS [START_REF] Wang | Complex Event Processing in EPC Sensor Network Middleware for Both RFID and WSN[END_REF]. They present a good work for monitoring products, considering the environment, but they lack of interaction with an ONS and don't consider traceability in their application.

Conclusions and future work

Being able to get the present and historic information about a product is very important in the supply chain management, since it helps to make the right deci-sions in the right moment. That is why traceability is one of the most important aspects for it, and the lack of research and solutions that successfully implement traceability and persistence has caused the retail supply chain to take longer to adopt RFID. In this paper we presented a service that covers those needs with an easy-to-use tool that will allow the users to exploit the benefits of RFID by integrating it into their business processes, helping them also to get feedback about certain processes that are not being followed as expected.

We propose a service that integrates several existing solutions (like Bonita [START_REF]Bonita's website[END_REF] and ASPIRE [START_REF]ASPIRE's website[END_REF]) to offer the final users a complete, interesting and easy-touse application. We are still in the process of implementing the service, working with the ASPIRE team and talking with different companies in the retail supply chain to gather their needs and offer solutions.

Fig. 1 .

 1 Fig. 1.EPCglobal's standards[START_REF]EPCglobal's website[END_REF]

Fig. 2 .

 2 Fig. 2. Transition example

Fig. 3 .

 3 Fig. 3. System architecture

Fig. 4 .

 4 Fig. 4. Traceability service

Fig. 6 .

 6 Fig. 6. Store process

Acknowledgments -This project is partially funded by the "Pôle de compétitivité" PICOM and the Région Nord-Pas-de-Calais in France.


domain: spi phys

text:
Jeuland Hervé
email: herve.jeuland@onera.fr

Martel Cédric

Bolioli Sylvain

Dorlé Aurélie

Barka André

Development of Antenna Array Technologies at ONERA

Keywords: antenna array, PCB technology, wideband application, radar

This paper presents the recent activities carried out at ONERA in the field of antenna arrays using PCB technologies. These activities cover principally wideband applications with strong integration constraints, which require very low profile antennas. Two examples of antenna array developed at ONERA are presented in the paper.

I. INTRODUCTION

The DEMR (ElectroMagnetism and Radar Department) combines all ONERA's skills in electromagnetism and its applications for future radar and communication systems: ground or on-board radar, communications (space, aeronautical, terrestrial), radio navigation, electronic warfare (listening-in ELINT (electronic intelligence) or jamming). In this context, one mission of the DEMR is to conduct research studies and developments of antennas in the frame of internal projects and through national and European projects in collaboration with industry and research institutes. Its fields of activity cover the development of antennas for radar, communications, Satcom and EW applications [START_REF] Jouade | Massively Parallel Implementation of FETI-2LM Methods for the Simulation of the Sparse Receiving Array Evolution of the GRAVES Radar System for Space Surveillance and Tracking[END_REF][START_REF] Barka | Circularly polarized Kaband radiating element unit-cell for SatCom wide-angle electronically steered phased arrays[END_REF][3]. These activities are based on the use of proprietary and commercial modeling tools, antenna measurement facilities (VHF to Q frequency bands) and a set of material characterization benches (2-60 GHz frequency band).

In this paper, we present two antenna arrays developed at ONERA. The first deals with an ultrawideband antenna array solution dedicated to multifunctional RF systems. The second is an antenna array for SAR (Synthetic Aperture Radar) application in Ku-Band. Those designs are based on the use of PCB technologies in order to be compliant with integration requirements onboard operational platforms. Moreover, operating frequencies up to the Ku band, possibly with a scanning capability, implies antenna designs compliant with a small sized unit cell. The two examples given in this paper meet these requirements. Others examples of recent antenna array developments will be also given during the presentation.

II. ULTRAWIDEBAND ANTENNA ARRAY FOR

MULTIFONCTIONAL RF SYSTEMS UWB (Ultra Wide Band) antenna arrays are needed for multifunctional RF systems, which have to support electronic warfare, communications, and radar applications. In addition to their large bandwidths, these arrays must also exhibit wide scanning capability, polarization diversity, and they have to be compliant with strong size constraints onboard the platform.

Starting from the Current Sheet Array (CSA) concept with high coupling between elements introduced by Munk [START_REF] Munk | Finite Antenna Arrays and FSS[END_REF], ONERA has developed new concepts and optimization procedures for the design of single and dual-polarized UWB multilayered arrays with high scan capabilities and very low-profiles. Such designs are based on an iterative optimization process of the dielectric layers and the radiating element of a unit cell in an infinite array. The radiating element shape is optimized using a genetic algorithm while the dielectric arrangement (permittivity and thickness of each superstrate and substrate in the unit cell) is optimized using an equivalent circuit model of the resulting element shape.

Moreover, a specific transition is required to perform the impedance matching between the radiating element and the feed source (typically a 50 ohms coaxial cable) and the balanced to unbalanced transition between the feed and the radiating element. The resulting transition has also to be compliant with the integration within the unit cell. This constraint may be severe specifically for high frequency RF systems as the unit cell size depends on the maximum operating frequency and the highest desired scanning angle. For example, a 10 mm by 10 mm unit cell allows a maximal operating frequency at 16 GHz with no grating lobes for scanning angles up to 60° in all planes. Moreover, the array thickness has to be limited since very low-profile devices are expected.

ONERA has first developed and manufactured a singlepolarized array based on the CSA concept (tightly coupled dipoles) [START_REF] Jeuland | Ultrawideband Multilayer Printed Antenna Arrays With Wide Scanning Capability[END_REF]. Next researches were carried out to increase the array performances by modifying the radiating element shape. It is well known that the bandwidth of a dipole antenna may be improved by inserting slots and notches. Starting from this statement, we have optimized simultaneously the radiating element shape and the dielectric arrangement.

Figure 1 shows the resulting unit cell of a single-polarized UWB multilayered array and the simulated active VSWR (voltage standing wave ratio) for E-plane scanning (infinite array configuration). The unit cell thickness, including the wideband impedance matching transition, is 7.6 mm (~λhigh/2) and the active VSWR is below 2 over a 5-18 GHz frequency band with scanning angles up to 60°. Figure 2 shows the manufactured 16x16 element array using the optimized cell and the comparison between measured and simulated active VSWR. Figure 3 shows the unit cell resulting from the optimization process for a dual-polarized printed array considering an infinite array condition. One challenge in designing such a dual-polarized printed array is to integrate a dual-polarized radiating element (H-Pol and V-Pol) with two impedance matching transitions into a very small unit cell (whose size depends on maximum operating frequency and scanning angle). Unit cell dimensions including the impedance matching transition are 7 mm by 7 mm with a 10mm-thickness (~λhigh/2). The active VSWR less than 2 over a 3.25-18 GHz band with scanning angles up to 50° in all planes (active VSWR < 2.5, up to 60°). The optimization procedure has been applied later for the design of a wideband printed antenna array for a SAR application in the Ku-band (see next section).

In the frame of the European CROWN project [START_REF] Gil Heras | CROWN Project, towards a European Multifunction AESA system[END_REF], ONERA is involved with THALES and ELETTRONICA in the design of array radiating panels with a wide frequency band, i.e. a ratio of 5 between the maximum and minimum frequencies of operation, a large scan sector with scan angles as high as 60°, a dual linear polarization capability. More specifically, ONERA is designing a radiating panel considering a sub-band of operation from Y to 18 GHz where the lower frequency Y should be as low as possible.

III. WIDEBAND ANTENNA ARRAY FOR KU BAND SAR

The design of airborne antennas can be a challenging task, especially due to the limited space available on-board most aircrafts. Recently, ONERA was involved in the development of two reception array antennas for SAR (Surface Aperture Radar) and GMTI (Ground Moving Target Identification) applications in Ku band [13.5 -17.5 GHz].

The required radiation pattern of the antenna is a fixed main beam at broadside. No scanning capabilities are required. The integration of the antenna into the pod imposes some physical constraints. With the current pod, the antenna aperture size must be limited to 400 mm × 200 mm. This specification is valid for an antenna integration providing either a lateral or a frontal field of view with respect to the aircraft. Moreover, to provide sufficient moving amplitude inside the pod to the beam pointing mechanism, the antenna thickness must be as small as possible with a maximum acceptable value of 50 mm.

The size of the array unit cell has been set to 9.4 mm, which is well below the minimal size, for which grating lobes appears in the visible region at the maximum frequency of 17.5 GHz with a beam at broadside. A first antenna solution, referred in this paper as the antenna with one sub array, has been developed in a multilayered PCB technology. The multilayer PCB is comprised of an array of 64 closely coupled radiating dipoles in the shape of a bowtie and a 1 to 64 beamforming network (Fig. 4). The overall thickness of the multilayer PCB is 5.45 mm. Similarly to [START_REF] Munk | Finite Antenna Arrays and FSS[END_REF] and [START_REF] Jeuland | Ultrawideband Multilayer Printed Antenna Arrays With Wide Scanning Capability[END_REF], an inter-digitated capacitance is used at the end of the dipole arms. The antenna is connectorized with a single SMPM connector. The overall antenna thickness including the multilayer PCB and the metallic ground plane is 10 mm. Antenna measurements were performed in ONERA's anechoic chamber. Measurement results show good performances for both array antennas. The reflection coefficient of the antenna with one sub array is below -10 dB in the band of interest (Fig. 6). Good agreement between simulation and measurement can be observed, especially at the lowest frequencies.

Fig. 1 .

 1 Fig. 1. Unit cell of a single-polarized array with optimized radiating element (left) and active VSWR in the E-plane (right)

Fig. 2 .

 2 Fig. 2. 16x16 element array manufacturing with 50 ohm coaxial cables (left) and measured active VSWR (central element, beam at broadside) (right)

Fig. 3 .

 3 Fig. 3. Unit cell of the dual-polarized array (left) and active VSWR in several typical planes for the H-/ V-polarization (right)

Fig. 4 .

 4 Fig. 4. Front (left) and rear (right) views of the sub array A second antenna comprising eight sub arrays has been developed in a 4×2 configuration. It is referred in this paper as the antenna with eight sub arrays. Except for the number of sub arrays, identical elements and multilayer PCB stack have been used to design the antenna. Eight SMPM connectors are used to feed the antenna (one connector per sub array). The antenna with eight sub arrays provides the possibility to consider MIMO (Multiple Input Multiple Output) approaches while post processing the received signals. Figure 2 presents photos of the manufactured array antennas.

Fig. 5 .

 5 Fig. 5. Photo of the manufactured array antennas with their mechanical support. Antenna sizes: 142 mm × 142 mm × 10 mm for the antenna with one sub array (left), 400 mm × 200 mm × 10 mm for the antenna with eight sub arrays (right)

Fig. 6 .

 6 Fig. 6. Reflection coefficient of the antenna with one sub array Figure 7 presents the measured radiation pattern of the antenna with one sub array at 15.5 GHz in E and H planes. The measured gain of the antennas is comprised between 19.3 dB and 20 dB in the range [13.5 GHz -17 GHz].

Fig. 7 .

 7 Fig. 7. Measured radiation pattern of the antenna with one sub array at 15.5 GHz IV. CONCLUSION This paper presented two antenna arrays developed at ONERA: an ultrawideband antenna array dedicated to multifunctional RF systems and an antenna array for SAR. Both designs are based on the CSA concept with high coupling between radiating elements thanks to interdigital capacitors. Measurements results show a good agreement with simulations. Others examples of recent antenna array developments at ONERA will be given during the presentation.


Jérôme Sterpenich

Marie-Camille Caumon

Véronique Lachet

Benoit Creton

Mohamed El Jarmouni

Aurélien Randi

Pascal Robert

NO solubility in water and brine up to 60 MPa and 373 K by combining Raman spectroscopy and molecular simulation

Keywords: Nitrogen monoxide, solubility, water, molecular simulation, high pressure

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Introduction

In the context of Carbon Capture and Storage (CCS), the role of impurities likely injected with CO2 has to be tackled in order to assess the long term behaviour of the storage [START_REF] Ieaghg | Effects of impurities on geological storage of CO[END_REF][START_REF] Sterpenich | [END_REF][3][START_REF] Seevam | 2008 7th International Pipeline Conference[END_REF][START_REF] Liu | [END_REF][6][START_REF] Creton | Thermodynamic Study of Binary Systems Containing Carbon Dioxide and Associated Gases Using Molecular Simulation Techniques[END_REF] . As a function of the industrial process releasing CO2 in the fumes (power plant, cement plant, glass industry…) and depending on the capture and purification processes, the composition of the CO2-rich stream injected in geological storages can vary significantly. If gases such as Argon or Nitrogen can dominate the composition of impurities, other gases such as SOx or NOx can be minor but can cause the system to be chemically reactive. In the presence of water such gases can dissolve and produce strong acids that could react with storage components, such as reservoir and caprock, or well materials (cement and steel casing). If the thermodynamics of CO2 under the pressure and temperature conditions of a storage (>7.4 MPa and >304.25 K, over the critical point of CO2) is well known, this is not the case for sulphur and nitrogen oxides (SOx and NOx where x stands for the stoichiometric coefficient). As an example, the solubility data for NO are sparse and only atmospheric pressure is documented [START_REF] Armor | [END_REF][9][START_REF]Lange's handbook of chemistry[END_REF][START_REF] Zacharia | [END_REF][12] . However the solubility data are essential for the use of the geochemical codes in order to predict the physicalchemical evolution of the storage and the possible chemical reactions occurring between fluids and minerals [3,[START_REF] Corvisier | Considering Non-Ideal Gas Mixtures in Geochemical Modeling of Gas-Water-Salt-Rock Interactions: Application to Impure CO2 Geological Storage[END_REF] . The High Pressure Optical Cell (HPOC) is an experimental device combining a silica microcapillary, a heating-cooling stage, a pressurization device and a Raman microspectrometer [START_REF] Chou | Raman Spectroscopy Applied to Earth Sciences and Cultural Heritage[END_REF][START_REF] Chou | Advances in High-Pressure Technology for Geophysical Applications[END_REF] . The microcapillary is used as a sample cell whose pressure and temperature can be controlled accurately. As silica is transparent in the visible range, Raman spectra can be recorded through the capillary. This device has been widely used in a wide range of applications, mainly gas solubility [16- 18] , gas diffusion in aqueous solutions [19][20][21] , gas phase composition and density [22][START_REF] Le | XIII GeoRaman[END_REF][START_REF] Fall | [END_REF][25][26] or to follow reaction processes [27] . Raman spectroscopy is a semiquantitative technique that requires to calibrate the intensity of the signal to a standard. Previous studies of CO2 or CH4 solubilities were calibrated on wellestablished thermodynamic models and experimental data. Unfortunately there is neither data nor accurate thermodynamic models for NO solubility. This is also not possible to prepare standard solutions at known NO concentration as there is no stable salt species giving dissolved NO with a known equilibrium constant. In some previous studies, a Hg-plug were used to put water and gas inside the capillary at room temperature and pressure. The number of moles of each species was evaluated by measuring volume and using densities at room TP [28][29][30] . However, it was not possible to use the Hg-plug method in our lab because of safety policies regarding Hg. Moreover, this method is questionable with highly soluble gases at room temperature (SO2, H2S, etc.) because the aqueous phase can contain a large amount of dissolved gas at room conditions, affecting liquid density and global molal composition. In this study we propose an original combination of HPOC and Raman spectrometry with molecular simulation to determine NO solubility in water and 1M-NaCl solutions from 2 to 60 MPa and from room temperature to 373 K.

Materiel and methods

Pressurization device and Fused Silica Capillary

The determination of NO solubility was performed acquiring Raman spectra of aqueous solutions loaded in silica capillaries using the same device as in previous studies [START_REF] Caumon | [END_REF]17,31,32] . The experiments were performed at 295 K, 298 K, 308 K, 323 K, 333 K, and 373 ± 0.1 K and pressures ranging from 1 to 30 MPa (up to 60 MPa at 295 K), using a High Pressure Optical Cell. Experiments were performed in pure water (deionized water, 18.2 MΩ.cm) and at 298 K, 323 K and 373 K in 1M-NaCl solutions. After burning the polyimide coating, one end of the Fused Silica Capillary (FSC) tube was welded. The FSC was then filled with water or NaCl solution. It was then connected to the stainless tube of a pressurization device using epoxy glue. The FSC was gently evacuated under vacuum to be purged from atmospheric gases. The FSC was then filled with NO and then closed with a valve. Finally, the FSC was connected to the High Pressure device. Pressure was controlled to ± 0.1 MPa. The FSC was placed in a heating-cooling stage (CAP500, Linkam) under the microscope of the Raman spectrometer. Temperature was controlled to ± 0.1 K.

Raman spectra acquisition

Raman spectra were acquired using a LabRAM HR spectrometer (Horiba Jobin-Yvon) equipped with a 600 gr.mm -1 grating. Excitation was done by using the 514.53 nm line of an Ar + laser at about 200 mW (Stabilite 2017, Spectra-Physics) and focused inside the capillary tube using a 20× objective (Olympus, N.A. = 0.4). Spectral resolution was about 1.6 cm -1 . A neon (Ne) lamp was positioned below the capillary to record Ne emission line for wavelength calibration time to time. Neon reference lines were taken from the NIST Atomic Spectra Database [START_REF] Kramida | NIST Atomic Spectra Database (ver. 5.7.1)[END_REF] . The Raman spectra were acquired at each P-T step after 20-30 min of equilibrium checked by a constant Raman signal. As previously done in our work on the solubility and diffusion of CO2 [19] and CH4 [START_REF] Caumon | [END_REF] , measurements were done very close (< 50µm) to the liquid-gas interface. Each spectrum was the mean of 10 accumulations of 6-10 s. Six spectra were collected at each P-T step. The intensity of the signal of N2 from the atmosphere was checked by recording a defocused Raman spectrum with the same parameters (laser power, objective, acquisition time).

Data processing

Experimental data were processed using Labspec 6 software (Horiba). A third-order polynomial baseline was subtracted between 1200 and 2000 cm -1 . Water bending vibration peak (~1640 cm -1 ) and NO stretching vibration peak (~1867 cm -1 ) were fitted using Gaussian-Lorentzian function to determine peak position, intensity (height), width (FWHM), and area (integrated intensity). Data acquisition and data processing were carried out by two different operators at different times (over more than 1 year) to ensure reproducibility. No difference between operators for data at similar P-T conditions was observed. The ratio between the peak area of NO and H2O Raman signal (PAR: Peak Area Ratio) was selected as the most accurate parameter to follow NO solubility in water. Experimental uncertainty was calculated from the mean of the 6 repeated measurements. Uncertainty was expressed at 1σ. Molecular simulation data sets at 295 K, 333 K and 373 K (see below for simulation method description) were each fitted using a second-order polynomial using Weighted Least Squares method to interpolate the data simulated at 4 different pressures to any pressure up to 60 MPa (LNE-RegPoly 1.0 software [START_REF] Yardin | 16th International Congress of Metrology[END_REF] ). Data from molecular simulations were then used to calculate the molar fraction of NO (xNO) at all P steps of the experimental data in pure water at the same temperatures using LNE-RegPoly to propagate uncertainties. A linear correlation between PAR and xNO was then calculated using GLS-GGMR method to determine the fitting function considering uncertainty from PAR (experimental Raman uncertainty) and xNO (simulation uncertainty). The experimental data at the same temperature as simulation (295 K, 333 K, and 373 K) were selected for calibration. The two data points at higher pressure at 295 K were not included in calibration because of higher experimental uncertainty and the absence of such high-pressure points at other temperatures. xNO for all experimental data in the fitting range (PAR range ± 10 %) were finally determined using LNE-RegPoly to propagate uncertainties. xNO values from PAR out of the fitting range were estimated simply applying the fitting function with no possibility to propagate uncertainty.

Simulation method

Monte Carlo method

The solubility of NO in water was also investigated by means of molecular simulation techniques which have been proven as valuable complementary approaches to experimental measurements, especially when hazardous compounds and/or extreme pressure or temperature conditions are considered. Monte Carlo (MC) simulations were performed in the Gibbs NPT ensemble (constant number of particles N, constant pressure P and constant temperature T) using the GIBBS Monte Carlo code [START_REF] Ungerer | Applications of molecular simulation in the oil and gas industry: Monte Carlo methods[END_REF] . In such simulations, coexisting phases (in this study, a NO-rich phase and a H2O-rich phase) were simulated in individual boxes without an explicit interface, and particle transfers between boxes were performed in order to ensure phase equilibrium. The following three MC move types were used in order to sample the configurational space of the studied systems: (i) internal moves (rigid body translations and rotations of a molecule), (ii) volume changes, (iii) transfers between phases using a pre-insertion bias [START_REF] Bourasseau | [END_REF] . This pre-insertion bias algorithm, used to improve the efficiency of the sampling, involved two steps. The first step consisted in the selection of a suitable location for inserting a new molecule by testing several places with a simple Lennard-Jones particle. The second step involved the test of several orientations with the centre of mass of the inserted molecule at the location selected in the first step. The selected probabilities for the different MC move attempts were 0.3 for translations, 0.3 for rotations, 0.395 for transfers, and 0.005 for volume changes. A total number of 1000 water molecules and 100 NO molecules were considered in our MC simulations. For some conditions, simulations using a bigger system with 5000 water molecules were also performed in order to ensure that no size effect occurred. Three temperatures were investigated (295.15 K -323.15 K -373.15 K) for pressures ranging from 5-60 MPa. For each studied condition, a total number of at least 6.10 8 MC iterations were performed.

Macroscopic fluid properties were derived by calculating appropriate averages over generated configurations.

Interaction potentials and energy calculation

Nitric oxide and water molecules were represented using models proposed by Lachet et al. [37] and Abascal and Vega [38] , respectively. In these models, molecules were considered to be rigid, thus no intramolecular energy was accounted for. Intermolecular energy was calculated with the two following contributions: dispersion-repulsion and electrostatic. Dispersionrepulsion energy between two force centres was represented as a function of their separation distance with a Lennard-Jones (LJ) potential. In the case of binary interactions involving different force centres, the Lorentz-Berthelot combining rules were used. Electrostatic energy was computed from the Coulomb law, assuming that the molecules bear electrostatic point charges. In the model proposed by Lachet et al. [37] , NO was treated as a single LJ sphere and the dipole moment of the molecule was neglected, thus no partial charges were considered for this molecule. H2O was represented using the TIP4P/2005 model, i.e. a single LJ sphere located on the oxygen atom together with a distribution of three partial charges: two of them being located on the hydrogen atoms and the third one being shifted (0.1546 Å) from the oxygen nucleus toward an intermediate axial position. The distance between oxygen and hydrogen atoms was 0.9572 Å, and the HOH angle was 104.52 degrees.

The force field parameters corresponding to these two models are presented in Table 1.

Calculation of this intermolecular energy was done by applying periodic boundary conditions, following classical procedures of molecular simulations [START_REF] Allen | Computer simulation of liquids[END_REF] . Lennard-Jones interactions were computed by applying a cut-off distance set to half of the box length. A standard long distance correction was used to account for interactions beyond the cut-off distance. The calculation of electrostatic interactions was done using the Ewald summation method with 7 vectors in each space direction and a Gaussian width set to 2π/L, where L was the size of the simulation box.

Nitric oxide dimerization study

Special attention must be paid when studying nitric oxide containing systems because this compound can exist as a mixture of monomers (NO: nitrogen monoxide) and dimers (N2O2: dinitrogen dioxide).

The composition of the NO-N2O2 equilibrium mixture depends on pressure and temperature conditions: the dimer is favoured at high pressures and low temperatures [START_REF] Snis | [END_REF] . In order to assess the state of nitric oxide that must be considered in this study, a monophasic NPT simulation of the reacting NO-N2O2 system was first conducted at 295.15 K and 60 MPa using reaction ensemble Monte Carlo (ReMC). The ReMC method [41,42] allows the study of chemically reacting mixtures. During this simulation, an additional MC move, the reaction move, was used in order to account for the possible dimerization of two NO molecules into N2O2. This move consisted in firstly choosing a direction to perform the reaction, second in deleting a set of reactant molecules randomly chosen in the system, and finally inserting product molecules. In our case, the reaction move was: 2NO → N2O2, where two randomly chosen NO molecules were deleted and one N2O2 was inserted, or N2O2 → 2NO, where one N2O2 molecule randomly selected was deleted and two NO molecules were inserted. To model N2O2 molecules, we used two NO LJ sites separated by 2.237 Å; the individual LJ parameters for each NO site in the dimer being the same as those for the monomer. No detailed description of these calculations is proposed here and we invite interested readers to investigate the two articles cited above [41,42] for more details and the study of Lachet et al. [37] for specific application of this method to nitric oxide study.

The simulation performed at 295.15 K and 60 MPa (i.e. the lowest investigated temperature and the highest investigated pressure of the present work) showed a mole fraction of dimers of 2.10 -6 . This result is consistent with our previous results conducted at lower pressures [37] which showed that, for temperature above the critical temperature of the NO-N2O2 system (Tc = 180.15 K), associations fully disappeared. Only the monomer form of the nitric oxide (NO) was thus accounted for in this work.

Results

The Raman spectra of NO dissolved in water were recorded step by step at each pressure and temperature (Figure 1). The bending vibration mode of water is a large band around 1640 cm -1 [43] . The main peak of dissolved NO is visible at 1868 cm -1 (symmetric stretching). No literature data refereeing to the Raman spectrum of dissolved NO was found so the assignment was done by comparison with the position of the gaseous species at 1877 cm -1 [44,45] . The only other species is N2 with a signal of the same intensity as the one found in the atmosphere (2331 cm -1 ). The intensity of the signal of NO increases when pressure increases (Erreur ! Source du renvoi introuvable.). Peak position and shape are constant. Temperature does not affect band shape and band position (not shown here). Traces of the oxidized species were detected in some cases at the end of the experiments, with signals corresponding to nitrate (at 1041 cm -1 and 1410 cm -1 ). The PAR calculated from Raman data were plotted as a function of pressure, temperature and salinity (Figure 2). The PAR increases when pressure increases. PAR decreases when temperature increases. It means that NO solubility decreases from 295 K to 373 K. For the same temperature and pressure, PAR decreases when NaCl is added, i.e. NO solubility is affected by a salting out effect.

To calculate solubility from PAR, the experimental PAR data are calibrated on simulation data giving NO solubility as a function of pressure at 295 K, 323 K and 373 K (Figure 3) as there is only a few experimental data available in the literature and only at atmospheric pressure [START_REF] Armor | [END_REF][9][START_REF]Lange's handbook of chemistry[END_REF][START_REF] Zacharia | [END_REF][12] . As observed on Raman data, the solubility of NO increases when pressure increases and decreases from 295 K to 373 K. Molecular simulation data of xNO in pure water (Table 2) were interpolated by a polynomial function for each temperature in order to determine NO solubility at any pressure. A unique linear correlation

(1) was established between simulation data and all experimental Raman data at 295 K, 323 K and 373 K in pure water (Figure 4) as no temperature effect can be observed in the investigated ranges of P and T conditions. Based on previous studies, it was also supposed that low salinity (1 M) does not significantly affect the calibration line slope [17,[46][47][48] below 373 K. xNO = 0.09927 PAR R² = 0.999 (1)

Based on the relation derived from Figure 4, the Raman data in Figure 2 were then converted into molar fraction scale at all temperatures in pure water and in saline solutions (Figure 5). All numerical data are gathered in Table S1. S1.

Discussion

The Raman peak area of one vibration mode of a molecule is proportional to the number of molecules in the analysed volume [START_REF] Placzek | The Rayleigh and Raman Scattering[END_REF] . It means that the peak area ratio is proportional to concentration (moles per litre of solution). The linearity of this relation may be affected by a variation of the refractive index of the solution or of the cross-section (efficiency) of the considered vibration mode [START_REF] Schrötter | Raman Spectroscopy of Gases and Liquids[END_REF] . The linearity observed in Figure 4 demonstrated that these effects can be neglected in the PTX range of these experiments. The dissolution of NO in an aqueous solution follows the same rule as other non-polar gases (CH4, N2, O2, CO,…), i.e. an increase of solubility with pressure, a decrease of solubility with temperature between 295 K and 373 K then solubility increases at higher temperature [START_REF]Lange's handbook of chemistry[END_REF][START_REF] Zheng | [END_REF] . Solubility decreases when salinity increases [12] (salting out effect). This last point is in agreement with literature at room pressure [12] . No other species than dissolved NO was detected in the Raman spectra. Despite careful preparation of the samples and evacuation under vacuum of all the experimental setup before loading gas, oxidized ions (nitrate) appear in some cases at the end of the experiments. It could be due to the reaction of NO with residual gaseous O2 in the experimental device or dissolved O2 in water or due to NO disproportionation. Disproportionation reactions of NO to give NO2 and N2O were described at high pressure [52] or in the presence of catalyser [53] but should not occur in the investigated ranges of pressure and temperature. It was therefore considered that the main process generating oxidized species in these experiments was oxidation by residual O2.

Figure 6. Comparison of NO, SO2 and CO2 solubility in water as a function of pressure and temperature. Solubility data are from Rumpf et Maurer [START_REF] Rumpf | [END_REF] and Zhou et al. [30] for SO2 and from Corvisier et al. [START_REF] Corvisier | Rapport bibliographique pour les systèmes eau-gaz-sel d'intérêt pour le projet SIGARRR[END_REF] and references therein for CO2.

The solubility of NO in pure water determined in this study was compared to experimental data of CO2 and SO2 solubility from literature [30,[START_REF] Corvisier | Rapport bibliographique pour les systèmes eau-gaz-sel d'intérêt pour le projet SIGARRR[END_REF][START_REF] Rumpf | [END_REF] (Figure 6). NO is about 5-15 times less soluble than CO2 in pure water. The effect of pressure and temperature are similar but a change in the solubility slope curve is observed for CO2 at intermediate pressure (especially at low temperature). The CO2 behaviour could be linked to a change of CO2 from gas-like to liquid-like compound over critical temperature Tc whereas the Tc of NO is far from the studied temperature range (180 K). SO2 is quite more soluble than CO2 by about one order of magnitude and thus is about 50 to 100 times more soluble than NO at low pressure (<1.7 MPa). There is no reliable solubility data of SO2 at higher pressure [30,[START_REF] Corvisier | Rapport bibliographique pour les systèmes eau-gaz-sel d'intérêt pour le projet SIGARRR[END_REF] in this range of temperature because of complex phase changes.

Conclusion

For the first time, the solubility of NO under geological conditions of pressure and temperature was determined using a coupled approach of Raman spectrometry and Monte Carlo molecular simulation. The extrapolation of the range of calibration by simulation was possible in the limit of the linearity of the correlation between Raman data and simulation, at least in the range 295-373 K, 2-60 MPa and 0-1 M-NaCl-H2O. No chemical reaction was observed, NO being stable in the experimental ranges of P and T conditions for the time of the experiments. The new data of solubility in aqueous solutions can be used to fit standard equations of state and to implement the geochemical codes used to simulate water/gas/rock interactions in the case of the geological storage of CO2 with SOx-NOx impurities. These reactive gases found as impurities in fumes that could be stored underground in CCS projects show specific and different behaviours as a function of pressure, temperature and salinity. The understanding and thus the prediction of the behaviour of such complex mixtures will be addressed only if the thermodynamic properties of such gases are well known under the geological conditions of storage.

For that, the FSC technique appears as the more suitable technique to meet this challenge. The experimental device will be used in further studies to measure solubilities in extended ranges of pressure, temperature and salinity for pure gases but also for gas mixtures of non-reactive and reactive compounds such as CO2, NO, NO2, N2O or SO2, controlling phase transitions by optical microscopic observations as well as chemical speciation and equilibria by Raman spectroscopy.

Spectroscopy 1-9., which has been published in final form at https://doi.org/10.1002/jrs.6072. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.

Table 1. Force field parameters (σ and ε represent the diameter and the energetic parameter of the LJ potential, respectively and q - stands for the point charge) used to mimic NO and H2O molecule's behaviour.

Molecule

Figure 1 .Figure 2 .

 12 Figure 1. Raman spectra of NO dissolved in liquid water at 298 K as a function of pressure. N2 is from the air. * Ne lamp

Figure 3 .

 3 Figure 3. Simulation data of NO solubility (molar fraction, xNO) in pure water as a function of pressure and temperature.

Figure 4 .

 4 Figure 4. NO solubility (molecular simulation data) vs. PAR (Raman).

Figure 5 .

 5 Figure 5. Solubility of NO (molar fraction, xNO) in water (standard series are the ones used for calibration from molecular simulations, Figure 4) and brine (1M-NaCl-H2O) as a function of pressure and temperature, from Raman data. Error bars were calculated by propagation of PAR uncertainty and from the uncertainty of the GLS-GGMR fitting in Figure 4. Data provided in TableS1.

Table 2 .

 2 Molar fraction of NO (xNO) in water as a function of pressure and temperature from molecular simulation calculations TableS1. NO solubility (molar fraction xNO) in pure water and 1M NaCl solution calculated from Raman data. Data in italic are extrapolated out from the initial calibration range.

	Temperature / K	Pressure / MPa	xNO (× 10 3 )	u(xNO) (× 10 3 )
	295	5	1.2	0.3
		10	2.1	0.3
		20	3.4	0.7
		40	5.9	1.1
		60	6.4	0.9
	333	5	1.02	0.12
		10	1.65	0.14
		20	3.1	0.4
		40	5.3	0.5
		60	6.1	0.9
	373	5	0.79	0.05
		10	1.53	0.07
		20	2.74	0.19
		40	4.8	0.3
		60	6.0	0.5

Acknowledgments

This work was supported by the ANR grants ("GazAnnexes" ANR-06-CO2-005 and "SIGARRR" ANR-13-SEED-0006), INSU CESSUR grant and Carnot Institute Icéel.

This is the peer reviewed version of the following article: Sterpenich, J., Caumon, M.-C., Lachet, V., Creton, B., Jarmouni, M.E., Randi, A., Robert, P., 2021. NO solubility in water and brine up to 60 MPa and 373 K by combining Raman spectroscopy and molecular simulation. Journal of Raman