Méthodologies pour la modélisation des couches fines et du déplacement en contrôle non destructif par courants de Foucault (application aux capteurs souples)

Ce travail de thèse porte sur le développement d outils de modélisation pour le contrôle non destructif (CND) par courants de Foucault (CF). Il existe actuellement une tendance à la mise en œuvre de capteurs souples qui représentent une solution pertinente pour inspecter des pièces ayant une surface complexe. L objectif principal de cette thèse est l élaboration de techniques permettant la modélisation de ce type de capteurs au sein de la méthode des éléments finis (MEF).Lors de la modélisation d un capteur souple avec la MEF, trois problématiques se manifestent. La première concerne le maillage des milieux fins qui apparaissent dans ce type de configuration (distance capteur-pièce contrôlée, bobine plate, revêtement fin...). Le maillage de ces régions par des éléments simpliciaux peut poser des problèmes numériques (éléments déformés quand un maillage grossier est considéré et grand nombre d inconnues quand un maillage fin est utilisé). La deuxième problématique concerne le déplacement du capteur. Si les différents sous-domaines géométriques (air, pièce, capteur...) sont convenablement remaillés pour chaque position du capteur, le temps total pourra être pénalisant. La troisième problématique relative à la modélisation d un capteur souple porte sur l imposition du courant dans des bobines déformées.Une comparaison de différentes approches nous a conduit à retenir la méthode overlapping, qui permet de considérer simultanément des milieux fins avec maillages non-conformes. Cette méthode permet d effectuer le recollement de deux surfaces non planes et/ou de géométries différentes. La méthode overlapping a été implantée dans deux formulations duales (magnétique et électrique) en 2D et 3D intégrées dans le code de calcul DOLMEN (C++) du LGEP. La méthode overlapping a été validée pour la prise en compte de plusieurs types de régions minces (air, milieux conducteurs, milieux magnétiques, bobines plates...). La modélisation des capteurs souples nécessite aussi l implantation d une technique permettant d imposer correctement les courants dans un inducteur de forme arbitraire. Une technique a été sélectionnée et programmée, d abord pour des bobines classiques (volumiques) déformées puis pour des bobines plates flexibles. Afin de valider les développements réalisés, différentes configurations de test ont été traitées et les résultats comparés avec des solutions de référence analytiques ou expérimentales.The objective of this thesis is the development of modeling tools for eddy current testing (ECT). Currently there is a tendency to use flexible sensors which represent a viable solution for inspecting parts with a complex surface. The main objective of this thesis is the development of techniques for taking into account this kind of sensors within the finite element method (FEM).When modeling a flexible sensor with the FEM, three issues have to be considered. The first one is related to the mesh of thin regions that appear in this kind of configuration (sensor-inspected part distance, thin coating...). The meshing of these regions with simplicial elements can cause numerical problems (distorted elements when a coarse mesh is considered and high number of unknowns when a fine mesh is used). The second issue is related to the displacement of the sensor on the part surface. If the different subdomains (air, part, sensor ...) are properly remeshed for each position of the sensor, the required time can be penalizing. The third issue, related to the modeling of a flexible sensor, is the computation of the current in distorted sensor coils.A comparison of different approaches has led to select the overlapping element method, which allows to simultaneously consider the thin regions with nonconforming meshes. This method allows to perform the connection of two surfaces which can be non-planar and/or have different geometries. The overlapping method has been implemented in two dual formulations (magnetic and electric) in 2D and 3D and integrated in the computation code (C++) DOLMEN of LGEP. The overlapping method has been validated for several kinds of thin regions (air, conductive regions, magnetic regions, flat coils...). The modeling of flexible sensors also requires the establishment of a technique for properly imposing the current in an inductor of arbitrary shape. A technique has been selected and implemented for conventional (volumic) distorted coils but also for flexible flat coils. Different test configurations have been considered in order to validate the developments and the results have been compared with analytical references or experimental solutions.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Les sous-préfets de Bretagne sous la monarchie de Juillet (1830-1848) : une génération d’administrateurs à part ?

Cet article, fondé sur l’exploitation systématique des dossiers de carrière, tente de cerner l’action jouée par les sous-préfets nommés en Bretagne sous la monarchie de Juillet. Leur action est à première vue contrariée par leur grande mobilité, la plupart d’entre eux étant étrangers à la région et changeant fréquemment de résidence. Mais elle n’est pas moins bien réelle : souci de stabiliser l’ordre socio-politique et volonté d’inaugurer une ère de progrès apparaissent comme les deux dimensions, sans cesse intriquées, d’une politique locale originale, qui reflète l’esprit du nouveau régime. L’exemple du sous-préfet Auguste Romieu, exceptionnellement documenté, montre enfin qu’au moins dans certains cas, cette action tire sa justification d’un libéralisme hérité des Lumières, qui identifie liberté politique et intégration nationale.This article, based on the systematic study of the career files, proposes an analysis of the role of the sub-prefects appointed in Bittany during the July monarchy period. At first sight their important mobility appears as a real handicap for the development of their action. Indeed, most of them came from other regions and keep moving from one place to the other. Yet, their action is real: the concern for a stabilized social political order and the wish to inaugurate an era of progress are the two main dimensions, linked together, of an original local policy, reflecting the spirit of the new political system. Finally, the example of the sub-prefect Auguste Romieu, on whom we have many documents, shows that, at least in some cases, the justification of this action rests on a liberalism inherited from the Enlightenment, which identifies political freedom with national integration

L’espace de l’État

Cette communication aborde le thème, peu étudié, des transformations de l’espace administratif entre 1800 et 1914, l’objectif étant ici de s’interroger sur son éventuelle rationalisation. Pour cela, deux administrations – la Gendarmerie et le Trésor Public – et un département – l’Ille-et-Vilaine – ont été choisis à titre de tests. Au vu des résultats, il apparaît que le territoire administratif se « cantonalise » progressivement au cours de la période, sous l’effet de deux logiques, en rien contradictoires : une volonté de rationalisation d’une part, un certain pragmatisme d’autre part.This paper deals with the nearly unstudied subject of the changes in the administrative areas between 1800 and 1914. Its main aim is to wonder about its possible rationalization. Two civil services (the Gendarmerie and the Treasury department) as well as a département have been chosen and studied. According to the results, it seems that the administrative area has gradually undertaken the role of cantons during the studied period because of two different but not conflicting hings: on the one hand a real will of rationalization and on the other hand a certain pragmatism

Equivalent input and output impedances in HF RFID system including resonator

High Frequency Radio Frequency Identification (HF RFID) system based on Magnetically Coupled Reader Resonator Coils (MCRRC) is reported. The proposed system consists of reader antenna including small resonant coil operating by magnetic coupling with the tag coil. In the proposed system, the reader and tag impedances are modified. The equivalent electrical model is used to express the equivalent impedance matrix and used to express the equivalent input and output impedances of the system. The formulas are confirmed by comparison between High Frequency Structure Simulator (HFSS) results and measures

Improvement of HF RFID detection for small and misaligned tag

A design of a reader antenna is proposed to optimize HF RFID range detection in parallel and perpendicular configuration. The reader antenna has a surface of 500 cm2, the tag corresponds to 0.7% of the reader surface. For passive RFID system, if the reader antenna does not provide the threshold energy to the tag, this one will not be detected. This is the case of the misalignment systems with great difference size antenna. Another problem limiting RFID detection is the different possible tag orientations. In perpendicular configuration, the detection is weak, the tag can only be detected above the edges of the antenna. These limits are minimized in this work by using a multiple loop antenna including resonators. Electrical model is developed to calculate the equivalent mutual inductance of the system from the impedance matrix: the measured results confirm the simulated ones. The detection measurements validate the improvement

Antenna array in 3D to improve tracking of small HF RFID tag

This paper presents an improvement of small RFID tags detection in HF near field, whatever their lateral and angular misalignments, using a complementary sub-coils reader antenna, enhanced by coplanar weakly-coupled resonators, and conformed on a 3D tube. The key ideas of detection improvement are: (i) modification of B -field vector distribution with the complementary coils above the common edge of consecutive loops; (ii) increase of B -field vector diversity and magnitude distribution by a 3D structure conformed on the tube, by realising 2 pairs of Identical Coaxial Loops (ICLs) with face-to-face sub-coils in forward current, and (iii) enhancement of B -field magnitude distribution by resonators included in the complementary sub-coils. Numerical simulations are carried out using High Frequency Structure Simulator (HFSS). The studied figure-of-merit is the mutual inductance between the tag and the reader coil. Results are reported for the 4 planar complementary sub-coils, the previous structure conformed on the tube and for the structure in which RCL resonators are added in the 3 planar complementary sub-coils. Experimental detection range measurements of each fabricated structure drives to the enhancement of the 3D complementary 4 × 3 sub-coils structure with weakly-coupled RLC resonators in each-sub-coil in terms of read-out distance and detection surface area

Array sub-loops reader antenna for HF RFID tracking

This paper focuses on tracking and objects identification by means of High Frequency magnetic coupling RFID (Radio Frequency IDentification) at 13, 56 MHz. The coil of the used RFID tags corresponds to 1.9% of the reader coil surface (120×160 cm 2 ). To increase the size ratio between the two coils, we proposed the use of multiple twisted loops antenna. The reader antenna is consequently divided into four sub-loops, corresponding to 8% of the surface of each one of the sub-loops area. According to the principle of twisted loop antenna, the nearest sub-loops are feed by current in opposite phase (complementary loops principle), and. This structure creates a strength curvature of magnetic field lines between each two of them, improving the magnetic coupling for vertical magnetic dipoles. In contrast, the structure presents at its center a null of magnetic field intensity due to the symmetry. To avoid this inconvenient a resonator is added to the structure to broke the symmetry and modify the magnetic field distribution. Its positioning is studied to optimize RFID detection in different angular and lateral positioning of the tag. Simulations and measurements of the proposed design with and without resonator are presented in the different parts of this paper

3D HF RFID reader antenna for tag detection in different angular orientations

Herein, a 3D 13, 56 MHz (HF) RFID reader antenna is proposed in order to optimize detection performance whatever the tag angular positioning. The design is made of a multi-loop structure, based on serial complementary antennas, as said “twisted” antennas. The RFID tag detection is optimized by two factors which rely on the modifications of the magnetic field (i) vectorial distribution and (ii) magnitude density. The reader antenna design is analyzed with electromagnetic simulation under HFSS (High Frequency Electromagnetic Field Simulation), and validated by detection measurements, in coplanar mode. A multi-loop structure, composed by 4 sub-loops, is then conformed onto a tube surface to provide the 3D structure. The goal of this improvement is to provide tag detection for any angular positions. At the center of the tube (3D reader structure), the detection of the tag is performed whatever its angular orientation, that is to say for any radial orientation

Effect of added resonators in RFID system at 13.56 MHz

In this study, a reader antenna including resonators is proposed to improve detection of a small moving tag in the case of tracking a radiofrequency identification (RFID) system. The near-field RFID technology is based on load modulation, the input impedance on the reader coil and the mutual inductance between the reader and tag coils are the main parameters for performing detection. They are calculated from the impedance matrix parameters. The added resonators change all the parameters of the impedance matrix consequently the input impedance and mutual inductance are also changed. In this study, analytical formulation defining the equivalent impedance matrix parameters is developed. These formulae are used to evaluate the performance of the proposed design according to the tag misalignment (lateral and angular). From the calculation and simulation results, a frequency shift in the equivalent input impedance is found. To avoid this problem, optimising the positioning of the resonators on the reader coil is performed. This study is confirmed by measures of RFID detection for a reader prototype (with and without resonators) and a small commercial tag. Both the surface and volume of detection of the small moving tag (lateral and angular misalignment) are improved by the principle of added resonators

A Twisted Loop Antenna to enhance HF RFID detection for different tag positioning

In this paper, a new LF/HF RFID reader loop antenna design is proposed and tested, in order to increase detection areas of the tags. The studied structure is a Twisted Loop Antenna (TLA) which is based on a modified distribution and orientation of the magnetic field lines. Our structure fruitfully uses the complementary antenna principle in a co-planar configuration. This offers more possibilities of tag detection whatever the tag position and orientation. The antenna performances are evaluated by optimizing the equivalent mutual inductance between reader antenna and tag antenna. Results are presented firstly in simulation (MATLAB and HFSS electromagnetic calculator) and secondly by experimental tests at different distances and misalignments, for the two possible tag orientations: parallel and perpendicular