Christelle Eyraud
Aix-Marseille University
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Publication
Featured researches published by Christelle Eyraud.
Science | 2015
Wlodek Kofman; Alain Herique; Yves Barbin; Jean Pierre Barriot; Valérie Ciarletti; S. M. Clifford; P. Edenhofer; Charles Elachi; Christelle Eyraud; Jean Pierre Goutail; Essam Heggy; L. Jorda; J. Lasue; Anny Chantal Levasseur-Regourd; E. Nielsen; Pierre Pasquero; Frank Preusker; Pascal Puget; Dirk Plettemeier; Yves Rogez; H. Sierks; Christoph Statz; I. P. Williams; Sonia Zine; Jakob J. van Zyl
The Philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus, providing information about its formation and evolution in the early solar system. We present Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) measurements of the interior of Comet 67P/Churyumov-Gerasimenko. From the propagation time and form of the signals, the upper part of the “head” of 67P is fairly homogeneous on a spatial scale of tens of meters. CONSERT also reduced the size of the uncertainty of Philae’s final landing site down to approximately 21 by 34 square meters. The average permittivity is about 1.27, suggesting that this region has a volumetric dust/ice ratio of 0.4 to 2.6 and a porosity of 75 to 85%. The dust component may be comparable to that of carbonaceous chondrites.
Scientific Reports | 2015
Michael I. Tribelsky; Jean-Michel Geffrin; Amelie Litman; Christelle Eyraud; F. Moreno
The future of ultra-fast optical communication systems is inevitably connected with progress in optical circuits and nanoantennas. One of the key points of this progress is the creation of elementary components of optical devices with scattering diagrams tailored for redirecting the incident light in a desired manner. Here we demonstrate theoretically and experimentally that a small, simple, spatially homogeneous dielectric subwavelength sphere with a high refractive index and low losses (as some semiconductors in the visible or near infrared region) exhibits properties allowing to utilize it as a new multifunctional element for the mentioned devices. This can be achieved by taking advantage of the coherent effects between dipolar and multipolar modes, which produce anomalous scattering effects. The effects open a new way to control the directionality of the scattered light. The directional tuning can be obtained in a practical way just by a change in the frequency of the incident wave, and/or by a well-chosen diameter of the sphere. Dielectric nanoparticles with the required optical properties in the VIS-NIR may be now readily fabricated. These particles could be an efficient alternative to the widely discussed scattering units with a more complicated design.
Applied Physics Letters | 2008
Jean Michel Geffrin; Patrick C. Chaumet; Christelle Eyraud; Kamal Belkebir; Pierre Sabouroux
This paper deals with the problem of reconstructing the relative permittivity of three-dimensional targets using experimental scattered fields. The fields concerned were measured in an anechoic chamber on the surface of a sphere surrounding the target. The inverse scattering problem is reformulated as an optimization problem that is iteratively solved thanks to a conjugate gradient method and by using the coupled dipoles method as a forward problem solver. The measurement technique and the inversion procedure are briefly described with the inversion results. This work demonstrates the reliability of the experiments and the efficiency of the proposed inverse scattering scheme.
IEEE Transactions on Antennas and Propagation | 2011
Christelle Eyraud; Jean-Michel Geffrin; Amelie Litman
We present reconstructions of an aggregate of small spheres from experimental scattered fields using a working frequency of 18 GHz. This target presents at the same time a complex 3D shape and a low-contrast permittivity. Concerted experimental and numerical efforts have enabled to obtain accurate reconstructions. In particular, we took into account the real random noise via a Bayesian framework. Reconstructions have been realized with scattered fields measured in different polarization cases: the results are compared and discussed.
IEEE Antennas and Wireless Propagation Letters | 2015
Christelle Eyraud; Jean-Michel Geffrin; Amelie Litman; Hervé Tortel
An accurate knowledge of the complex permittivity value of materials is compulsory when performing experimental electromagnetic applications. Unfortunately, these values are not so obvious to determine in practice. In this letter, we propose a novel approach for determining the complex dielectric constant of materials. This method combines free-space far-field scattering pattern measurements with a Bayesian procedure, which fully exploits the measurement uncertainties. Therefore, the measured values weighted according to their experimental accuracy are incorporated in the permittivity determination algorithm. In this letter, the samples are all shaped as spheres in order to benefit from efficient Mie scattered field computations. The dielectric properties of typical plastic samples are first determined and compared to values found in the literature in order to assess the validity and the accuracy of the proposed methodology. A more “exotic” sample extracted from a microwave absorber, which is a polyurethane foam charged with carbon particles, is also analyzed.
Journal of The Optical Society of America A-optics Image Science and Vision | 2013
Christelle Eyraud; Rodolphe Vaillon; Amelie Litman; Jean-Michel Geffrin; Olivier Merchiers
In tomography algorithms, the complex amplitude scattering matrix corresponds to the input parameter. When considering 3D targets, the scattering matrix now contains vectorial information. Thus, this scattering matrix might be calculated with various polarization projections. Moreover, when dealing with experimental data, we are almost every time faced with truncated data. We focus here on the impact of selecting parts of the amplitude scattering matrix elements versus others and in particular on the influence of the polarization choices on the imaging results. In order to better apprehend the physical content associated to each polarization term, the study is conducted with a simple vectorial-induced current reconstruction algorithm allowing reconstruction of qualitative maps of the scene. This algorithm is applied on scaled models of aggregates combined with experimental scattered fields acquired in the microwave frequency range.
ieee conference on antenna measurements applications | 2014
J-C Castelli; F. Comblet; F. Daout; Christelle Eyraud; S. Fargeot; R. Guillerey; J-M Geffrin; S. Leman; P. Massaloux; G. Mazé-Merceur; G-P Piau
A national comparison of RCS measurement results between national measurement laboratories has been organized in the framework of a French Working Group (Groupe de Travail incertitudes: GTi), dealing with measurement uncertainties in anechoic chamber. This Working Group involves 22 laboratories that are either industrial or academic research ones, or laboratories depending on governmental organisms. Three tasks have been defined: 1/ State of the art, 2/ Comparisons of RCS measurements, 3/ Comparisons of Antenna Measurements. This paper deals with the second task, in which 8 laboratories are engaged. The motivations and the scheduled tasks are described.
Near Surface Geophysics | 2014
Soufiane Nounouh; Christelle Eyraud; Amelie Litman; Hervé Tortel
Probing the near-subsurface in the presence of absorbing media is a very challenging problem. Within that framework, we analyse the capabilities of a mono-frequency/multistatic set-up for detecting shallowly buried targets. As the antennas constitute an important part of the probing device, an accurate method for modelling the antennas behaviour is proposed. This modelling, performed thanks to a correct balanced set of elementary sources, is then incorporated in the calculation of the scattered field, performed with a home-made Finite Element Method software. Efforts have also been put into the measurement procedure. The measured fields are thus post-processed with an efficient method which takes profit of the spectral bandwidth properties of the scattered field. These fields serve as input data for the inversion algorithm, an extension of the DORT method to elongated targets. This qualitative and fast imaging procedure, which exploits the spectral properties of the multistatic scattering matrix, has been adapted to the present stratified configuration. Imaging results of shallowly buried targets embedded in a high losses medium are presented to assess the well-behaviour of the proposed methodology.
IEEE Microwave and Wireless Components Letters | 2015
Jean-Michel Geffrin; Christelle Eyraud; Amelie Litman
The internal structure of a sample of an absorber is retrieved from its measured scattered field. By its very nature, this target is a very weak-scatterer as it is used to cover the walls in anechoic chambers. The real part of its permittivity is rather small but its dielectric losses are non negligible. Quantitative maps of the complex permittivity of the sample were obtained from monochromatic scattered fields measured inside an anechoic chamber in a multistatic configuration. An imaging procedure taking into account the noise characteristics disturbing the measurements was used for this purpose.
Physical Review B | 2016
Michael I. Tribelsky; Jean-Michel Geffrin; Amelie Litman; Christelle Eyraud; F. Moreno
We report the experimental evidence of directional Fano resonances at the scattering of a linearly polarized electromagnetic plane wave by a homogeneous dielectric sphere with a high refractive index and low losses. We observe a typical asymmetric Fano profile for the intensity scattered in practically any given direction, while the overall extinction cross section remains Lorentzian. The phenomenon originates in the interference of the selectively excited electric dipolar and quadrupolar modes. The selectivity of the excitation is achieved by the proper choice of the frequency of the incident wave. Owing to the scaling invariance of the Maxwell equations, in these experiments we mimic the scattering of the visible and near IR radiation by a nanoparticle made of common semiconductor materials (Si, Ge, GaAs, GaP) by the equivalent scattering of a spherical particle of 18 mm in diameter in the microwave range. The theory developed to explain the experiments extends the conventional Fano approach to the case when both interfering partitions are resonant. A perfect agreement between the experiment and the theory is demonstrated.