Une nouvelle méthode d'inversion pour les problèmes de synthèse de Fourier en imagerie

- La plupart des méthodes classiques d'inversion en synthèse de Fourier sont basées sur l'interpolation et la Transformée de Fourier (TF) inverse rapide. Mais, lorsque les données ne remplissent pas d'une manière uniforme le domaine de Fourier, ce qui est le cas dans grand nombre d'applications en imagerie, ou lorsque la phase du signal n'est pas accessible, comme en interférométrie non cohérente, ces méthodes ne fournissent pas de résultats satisfaisants. La méthode proposée est une méthode de régularisation basée sur l'estimation bayésienne. Une modélisation appropriée de l'image permet de remédier, d'une manière simple, au manque d'information lié aux données et de fournir des résultats satisfaisants. Notre objectif ici est de fournir une méthode utilisable en pratique en faisant un compromis entre complexité de mise en oeuvre et performances. La méthode proposée est testée sur des données expérimentales en imagerie microonde

Detecting range and coupling coefficient tradeoff with a multiple loops reader antenna for small size RFID LF tags

International audienceThis paper summarizes some tests with Low Frequency (LF, 125 kHz) RFID tags of two types: Card and Token. These tests were done in order to evaluate the feasibility of an identification/traceability of tags which size is constrained and supposed to be detected inside a delimited volume of 40×40×10 cm 3 . As the size of the antenna tag is supposed to be very small, we improve the detection range and volume of definition by designing different reader antennas. Reader antennas presented are of two types whether they are based on single (SL) or multiple loops (ML). Detection range was evaluated for planar antennas (3 SL and one ML). Volume of definition for the detection was estimated by designing two-level prototypes of ML antennas. Results are discussed about the optimization possibility of detection range and volume thanks to ML

Active wideband antenna for underwater tomography (1 GHz)

International audienceA new active antenna has been designed to measure electromagnetic fields in water. It combines a differential wideband amplifier and a dipole, the characteristics of which have been designed to provide a constant gain on the bandwidth of the antenna. The small size of the dipole reduces the mask effect. The designed antenna is a symmetrical reception antenna for the electromagnetic field measurement in water in the frequency range of 100 MHz to 1 GHz and it introduces few disturbances. A possible application will be the microwave imaging of immersed objects

Antenne active et retournement temporel pour l'imagerie micro-onde sous-marine

Le système d'imagerie micro-onde d'objets immergés du laboratoire des signaux et systèmes (L2S) a été récemment perfectionné sur deux points. La conception d'une antenne active large bande spécifique a permis de réduire sensiblement les perturbations dues au système de mesures. En outre, une méthode originale basée sur le principe du retournement temporel permet d'estimer rapidement la position de l'objet immergé et est en cours de validation expérimentale

Antenne active et retournement temporel pour l'imagerie micro-onde sous-marine

Le système d'imagerie micro-onde d'objets immergés du laboratoire des signaux et systèmes (L2S) a été récemment perfectionné sur deux points. La conception d'une antenne active large bande spécifique a permis de réduire sensiblement les perturbations dues au système de mesures. En outre, une méthode originale basée sur le principe du retournement temporel permet d'estimer rapidement la position de l'objet immergé et est en cours de validation expérimentale

A UWB micro-strip antenna design and simulation

International audienc

Nonlinear inversion of immersed objects from laboratory controlled data

International audienceThe paper is focused on the characterization of objects immersed in water using laboratory-controlled data obtained in the microwave frequency range. Experiments performed at the laboratory represent, at a reduced scale, the electromagnetic characterization of objects buried at a shallow depth in the sea, with the objects and the emitting and receiving antennas being immersed. Characterization is taken here as an inverse scattering problem whose data, whilst limited in aspect, consist of the values of the time-harmonic scattered electric fields measured at several discrete frequencies on a single line of a few receivers. The modelling of the wave–object interaction is performed through a domain integral representation of the fields in a two-dimensional transverse-magnetic configuration. The inverse scattering problem is solved by means of two iterative algorithms tailored for homogeneous objects: the so-called level-set method and a binary specialized contrast source inversion method. Emphasis is put both on the experimental features and their modelling, and the results obtained for different types of objects are presented

Comparison between a 2.45 GHz planar and circular scanners for biomedical applications

International audienceMicrowave imaging is an efficient technique to non-invasively visualizing dielectric properties of non-metallic bodies. One potential of the technique is the high contrast in dielectric properties between biological tissues. In the 80’s, Supélec developed a 2.45 GHz planar microwave camera, in the 90’s the group developed algorithms for quantitative microwave imaging. The purpose of this study is to investigate the capability of these existing materials, or an extended version of them, in terms of quantitative imaging of high-contrast inhomogeneous object for application of breast cancer detection. A two-dimensional formalization is considered to be followed up with future three-dimensional investigations