Search

International audience; For foliage penetrating (FoPen) radar development, we previously developed a hybrid volume-surface model, named Domain dEcomposition Model (DEMOS), to evaluate the electromagnetic scattering from large scenes composed by targets (metallic objects) placed in a natural environment (dielectric object). In this letter, we compare the scattered field obtained by DEMOS with the quasi-monostatic measurements done in an anechoic chamber on scaled models composed of dielectric and metallic structures. For all measurements, we consider both polarizations, HH and VV. Our final objective is to determine the optimal configurations for the detection of a target placed in a forest environment in the very high-frequency (VHF)-UHF frequency bands.

International audience; This paper focuses on the role of polarization-and more specifically, the effect of its selection-in 3D quantitative imaging obtained from scattered field measurements. Although polarization is now commonly used in linear imaging procedures (when unknowns are linked by a linear relationship to the measured signal), the influence of polarization choice is generally ignored in nonlinear imaging problems. In this paper, we propose a formulation to obtain the 3D permittivity map, by a nonlinear imaging procedure, from the scattering matrix. This allows one to select, from the same data set, the desired polarization case as input data for the imaging algorithm. We present a study of the influence of the input data polarization choice on the reconstructed per-mittivity map. This work shows that a suitable basis choice for the description of the scattering matrix and an appropriate selection of the element of this scattering matrix can greatly improve imaging results.

International audience; This paper presents an attempt to optimize the technical settings of the experimental setup of the CCRM in Marseille in order to reduce the experimental noise and test its influence on inverse scattering reconstructions. This work has been done with the constraint of keeping a Gaussian noise distribution. The reconstructions, obtained from both simulation and measurements of the field scattered by the target under study, a spiral, were obtained with an inversion algorithm based on a Bayesian approach. Moreover, two different reconstructions from measurements are discussed here, with and without taking into account in the inversion algorithm the distribution of the noise affecting the measurements. Some preliminary conclusions are drawn.

Semiconductors like Si, Ge (and other compounds like GaAs, GaP, etc) show high values of their refractive index and low absorption in the visible (VIS) and near-infrared (NIR) ranges. Nanoparticles made of these high refractive index (HRI) materials have been recently proposed as an alternative to metallic ones to overcome their inherent ohmic losses. In addition, the excitation of coherent electric and magnetic resonances makes these HRI nanoparticles to become basic to build multifunctional elements in optical devices for controlling the directionality of the scattered radiation. Here, we present unambiguous experimental evidence in the microwave range that a dimer of spherical High Refractive Index dielectric particles behaves as an elementary block for building switching devices whose binary state only depends on the polarization of the incident radiation. The corresponding analysis has been carried out by means of the linear polarization degree of the scattered radiation at the right angle scattering configuration.

International audience; This paper describes how the bistatic radar cross section (RCS) experimental setup of the “Centre Commun de Ressources en Microondes” (CCRM) was used to precisely determine various scattering quantities and how we took profit of the large scattering angular range available with this setup. Results on extinction cross section, linear degree of polarization and other scattering quantities of interest are presented. We also show how those results are interesting in different domains where scattering phenomena are studied thanks to the scale invariance properties of the Maxwell equations using the so called microwave analogy.

International audience; In this paper, our particular focus is on the uncertainties impact on scattered field measurements. These uncertainties can be due to a non perfect knowledge on the object parameters or to the measurement procedure itself. The influence of these uncertainties is of great importance when one want to perform comparisons between EM experimental fields and simulated fields.

International audience; For the development of millimeter wave imaging systems, it is important to be able to simulate some representative scattering configurations. Typically, Gaussian beams are used in active imaging systems. Since these beams only illuminate a spatially limited region, many objects can be treated as infinitely long 2D (in)homogenous cylinders. However, the incident Gaussian beams have a 3D character. Therefore, a dedicated 2.5D scattering simulator was developed. In this paper, simulation results obtained with this simulator are compared to measurements obtained from a bi-static microwave set-up and from a W-band millimeter wave set-up. Comparison of simulations and measurements proves that the 2.5D algorithm is a good simulation tool to study scattering of long inhomogeneous cylinders, illuminated by 3D plane waves or 3D Gaussian beams under different elevation angles.

Thanks to the success of the 2D scattering fields databases that we have measured in the anechoic chamber of the Institut Fresnel and proposed to the inverse problem community, we are now extending these studies to 3D configurations. This introduces new challenges due to the low level of signal as well as its sensitiveness to small disturbances. A careful characterization of the experimental errors is therefore necessary and we focus therein on drift errors, as they are mainly responsible for the scattered field variations. The objective is double: improve scattered field measurement accuracy and reduce acquisition time as it can take several hours for one incident illumination for 3D inverse scattering applications. To compensate for this drift error, we propose a fast correction based on a limited spectral bandwidth criteria, with the benefit of no loss of information and no need of a priori knowledge on the scatterer. After introducing the measurement setup and describing this correction protocol, we highlight its influence on the acquisition process