Xavier Faget, Ph.D.

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Xavier Faget will defend his Ph.D. thesis entitled : "Application expérimentale de méthodes inverses avancées pour l’imagerie des propriétés électromagnétiques d’un matériau magnéto-diélectrique" on Wednesday, January 31, at 2:00 p.m. in Pierre Cotton Room, Institut Fresnel.

Jury Members :

- Ronan SAULEAU - IETR, Rapporteur
- Yann LE BIHAN - GEEPS, Rapporteur
- Claire MIGLIACCIO - LEAT, Examinator
- Stefan ENOCH - Institut Fresnel, Examinator
- Juan Carlos CASTELLI - ONERA, Examinator
- Nicolas MALLÉJAC - CEA, le Ripault Thesis co-Director
- Amélie LITMAN - Institut Fresnel, Thesis Director

Abstract :

The subject of this thesis is the non-destructive characterization of complex inhomogeneous magneto-dielectric structures. Successively, the experimental developments, the modelling and the data treatments stages are addressed. A forward model that links the scattered field to the electromagnetic properties is established. This model requires some finite element computations in order to estimate the propagation of the electromagnetic wave in presence of the magneto-dielectric object which is glued on a metallic support. A multistatic bench has been designed and constructed in order to collect measured scattered fields. Several adjustments and calibration procedures have been carried out to reduce the measurement noise and biases. Next, the inverse problem has been dealt with, in order to retrieve the electromagnetic properties of the samples, from the measured scattered field. The inverse problem is mainly solved with a linear approach, with a careful selection of the hyperparameters. Once the system has been fine tuned, six studies have been realized to validate our 2D imaging system. The assessment of the measurement uncertainty, the evaluation of the spatial resolution, the characterization of various magnetics materials and the use of different supports with variable geometries have been performed. So far, all the developments were done under a 2D hypothesis. That is why, we have then focused our research on the design of a 3D innovative imaging setup. To this end, a secondary source moving close to the target has been added in order to gain information in the third direction. A numerical study has been performed to assess the expected performances of this new setup.

Keywords : permeability, microwave tomography, magnetic materials, radiofrequency, free-space measurement, inhomogeneous medium, non destructive chacaterization, hyperfrequency.