Pierre Sabouroux

A metallic Fabry-Perot directive antenna

We report the design of a directive antenna using the electromagnetic resonances of a Fabry-Perot cavity. The Fabry-Perot cavity is made of a ground plane and a single metallic grid. The resonance is excited by a patch antenna placed in the cavity at the vicinity of the ground plane. The two remarkable features of Fabry-Perot cavity antennas are, first, that they are very thin and second that only one excitation point is needed. A directivity of about 600 is measured at f=14.80 GHz which is to our knowledge one of the highest directivities reported for an antenna using Fabry-Perot resonances.

Continuing with the Fresnel database: experimental setup and improvements in 3D scattering measurements

In this paper, the experimental setup and the improvements required to obtain further measurements for the third opus of the Fresnel Database are presented. The most original feature of those new datasets is the fact that they were obtained with three-dimensional targets instead of the two-dimensional ones used in the two previous opuses. The measurements were performed all around the targets under test to collect enough information about the objects to be able to perform inversion on their scattered fields. As the targets were small in comparison with the wavelength, the challenge here was to extract these small scattered fields from the measurements, and a specific post-processing procedure had to be designed to compensate for the drift errors. The five targets selected for the database are presented, including the Myster target, a hitherto undivulged target that is presented in this paper for the first time, i.e., at the same time as the submissions of all the other contributors to this special section. Some scattered field comparisons are also presented.

Electromagnetic three-dimensional reconstruction of targets from free space experimental data

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.

Molding acoustic, electromagnetic and water waves with a single cloak

We describe two experiments demonstrating that a cylindrical cloak formerly introduced for linear surface liquid waves works equally well for sound and electromagnetic waves. This structured cloak behaves like an acoustic cloak with an effective anisotropic density and an electromagnetic cloak with an effective anisotropic permittivity, respectively. Measured forward scattering for pressure and magnetic fields are in good agreement and provide first evidence of broadband cloaking. Microwave experiments and 3D electromagnetic wave simulations further confirm reduced forward and backscattering when a rectangular metallic obstacle is surrounded by the structured cloak for cloaking frequencies between 2.6 and 7.0 GHz. This suggests, as supported by 2D finite element simulations, sound waves are cloaked between 3 and 8 KHz and linear surface liquid waves between 5 and 16 Hz. Moreover, microwave experiments show the field is reduced by 10 to 30 dB inside the invisibility region, which suggests the multi-wave cloak could be used as a protection against water, sonic or microwaves.

Microwave analog to light scattering measurements on a fully characterized complex aggregate

We present experimental measurements of three-dimensional electromagnetic wave scattering in the microwave frequency range, by a complex aggregate consisting of 74 primary spheres with fully known optical and geometrical properties. We measured the complete amplitude scattering matrix (or Jones matrix), from which the electric fields (amplitude and phase) with arbitrary polarization can be obtained. These results offer the opportunity to test approximate computational methods against experiments.

Permittivity measurements of porous matter in support of investigations of the surface and interior of 67P/Churyumov-Gerasimenko

Permittivity measurements on porous samples of volcanic origin have been performed in the 0.05–190 GHz range under labo- ratory conditions in support of the Rosetta mission to comet 67P/Churyumov–Gerasimenko, specifically with the MIRO radiometric experiment and CONSERT radar experiment. Methods. The samples were split into several subsamples with different size ranges covering a few μm to 500 μm. Bulk densities of the subsamples were estimated to be in the 800 to 1500 kg/m3 range. The porosities were in the range of 48% to 65%. From 50 MHz to 6 GHz and at 190 GHz, permittivity has been determined with a coaxial cell and with a quasi-optical bench, respectively. Results. Without taking into account the volume-scattering effect at 190 GHz, the real part of the permittivity, normalized by the bulk density, is in the range of 2.1 to 2.6. The results suggest that the real part of the permittivity of an ice-free dust mantle covering the nucleus is in the 1.5−2.2 range at 190 GHz. From these values, a lower limit for the absorption length for the millimeter receiver of MIRO has been estimated to be between 0.6 and 2 cm, in agreement with results obtained from MIRO in September 2014. At frequencies of interest for CONSERT experiment, the real part of the permittivity of a suspected ice-free dust mantle should be below 2.2. It may be in the range of 1.2 to 1.7 for the nucleus, in agreement with first CONSERT results, taking into account a mean tem- perature of 110 K and different values for the dust-to-ice volumetric ratio. Estimations of contributions of the different parameters to the permittivity variation may indicate that the porosity is the main parameter.

Analytical, Simulation and Measurement Studies of a Dual-Band Open-Sleeve Curved Meander Line Antenna on a Flexible Substrate

An innovative antenna on flexible substrate with two resonators is presented. The antenna is composed of a metallic wire sewn on the substrate. Two dipolar modes in far field are radiated. To understand the interaction of the resonators with the principal antenna, studies with and without the sleeves are done in near field and far field.

Compressed perovskite aqueous mixtures near their phase transitions show very high permittivities: New prospects for high-field MRI dielectric shimming

Perovskites are greatly used nowadays in many technological applications because of their high permittivity, more specifically in the form of aqueous solutions, for MRI dielectric shimming. In this study, full dielectric characterizations of highly concentrated CaTiO3/BaTiO3 water mixtures were carried out and new permittivity maxima was reached.

Cyclic concentrator, carpet cloaks and fisheye lens via transformation plasmonics

We first review basic equations of plasmonics in anisotropic media. We recall the origin of Maxwell’s gradient index fisheye lens. We then apply tools of transformation optics to the design of a cyclic concentrator and a variety of plasmonic carpet-cloaks. We further give a brief account of the discovery of spoof plasmon polaritons (SfPPs) by Pendry et al (2004 Science 305 847–8) 150 years after Maxwell invented the fisheye lens. Finally, we experimentally demonstrate a concept of a fisheye lens for SfPPs at microwave frequencies. We stress that perfect metal surfaces perforated with dielectrics offer a playground for moulding surface waves in many areas of physics

Characterization of the permittivity of controlled porous water ice-dust mixtures to support the radar exploration of icy bodies

The internal properties of porous and icy bodies in the Solar System can be investigated by ground-penetrating radars (GPRs), like the CONSERT instrument onboard the Rosetta spacecraft which has sounded the interior of the nucleus of comet 67P/C-G. Accurate constraints on the permittivity of icy media are needed for the interpretation of the data. We report novel permittivity measurements performed on water ice samples and icy mixtures with porosities in the 31–91% range. The measurements have been performed between 50 MHz and 2 GHz with a coaxial cell on a total of 38 samples with a good reproducibility. We used controlled procedures to produce fine-grained and coarse-grained ice samples with a mean diameter of 4.5 μm and 67 μm, respectively, and to prepare icy mixtures. The JSC-1A Lunar regolith simulant was used as the dust component in the mixtures. The results are focused on the real part e′ of the permittivity, which constrains the phase velocity of the radio waves in low-loss media. The values of e′ show a non-dispersive behavior and are within the range of 1.1 to 2.7. They decrease with the increasing porosity Φ according to E(1 − Φ), with E equal to about 3.13 for pure water ice, and in the 3.8–7.5 range for ice-dust mixtures with a dust-to-ice volumetric ratio in the 0.1–2.8 range, respectively. These measurements are also relevant for radiometers operating in the millimeter-submillimeter domains, as suggested by the non-dispersive behavior of the mixtures and of the pure components.