Kerker Effect with Hybridized Radiofrequency Resonators

International audienc

Controllable emission of a dipolar source coupled with a magneto-dielectric resonant subwavelength scatterer

We demonstrate experimentally and theoretically that a local excitation of a single scatterer of relative dielectric permittivity {\epsilon} = 6 permits to excite broad dipolar and quadrupolar electric and magnetic resonances that shape the emission pattern in an un- precedented way. By suitably positioning the feed with respect to the sphere at a ?=3 distance, this compact antenna is able to spectrally sort the electromagnetic emission ei- ther in the forward or in the backward direction, together with a high gain in directivity. Materials with {\epsilon} = 6 can be found in the whole spectrum of frequencies promising Mie antennas to become an enabling technology in numbers of applications, ranging from quantum single photon sources to telecommunications

Single frequency microwave cloaking and subwavelength imaging with curved wired media

International audienceWe consider the cloaking properties of electromagnetic wired media deduced from arbitrary coordinate transformations. We propose an interpretation of invisibility via sub-wavelength imaging features. The quality of cloaking is assessed by the level of deformation of the image of a P-shaped source through the stretched wired media: the lesser the image deformation, the more effective the cloaking. We numerically and experimentally demonstrate a tetrahedral wired cloak with longer edge length about 7cm at a frequency of 1GHz (the cloak is thus subwavelength). The wired cloak has two functionalities: it can serve as a high-resolution imaging system over long distances, and it can also perform space transformations such as, but not limited to, cloaking at a single operation frequenc

Improving B1 homogeneity in abdominal imaging at 3 T with light and compact metasurface

Radiofrequency field inhomogeneity is a significant issue in imaging large fields of view in high- and ultrahigh-field MRI. Passive shimming with coupled coils or dielectric pads is the most common approach at 3 T. We introduce and test light and compact metasurface, providing the same homogeneity improvement in clinical abdominal imaging at 3 T as a conventional dielectric pad. The metasurface comprising a periodic structure of copper strips and parallel-plate capacitive elements printed on a flexible polyimide substrate supports propagation of slow electromagnetic waves similar to a high-permittivity slab. We compare the metasurface operating inside a transmit body birdcage coil to the state-of-the-art pad by numerical simulations and in vivo study on healthy volunteers. Numerical simulations with different body models show that the local minimum of B1+ causing a dark void in the abdominal domain is removed by the metasurface with comparable resulting homogeneity as for the pad without noticeable SAR change. In vivo results confirm similar homogeneity improvement and demonstrate the stability to body mass index. The light, flexible, and cheap metasurface can replace a relatively heavy and expensive pad based on the aqueous suspension of barium titanate in abdominal imaging at 3 T.Comment: 18 pages, 6 figures, 4 supplementary figure

Photosensitive chalcogenide metasurfaces supporting bound states in the continuum

International audienceWe study, both theoretically and experimentally, tunable metasurfaces supporting sharp Fano-resonances inspired by optical bound states in the continuum. We explore the use of arsenic trisulfide (a photosensitive chalcogenide glass) having optical properties which can be finely tuned by light absorption at the post-fabrication stage. We select the resonant wavelength of the metasurface corresponding to the energy below the arsenic trisulfide bandgap, and experimentally control the resonance spectral position via exposure to the light of energies above the bandgap

Anomalous Reflection From Hyperbolic Media

Despite the apparent simplicity, the problem of refraction of electromagnetic waves at the planar interface between two media has an incredibly rich spectrum of unusual phenomena. An example is the paradox that occurs when an electromagnetic wave is incident on the interface between a hyperbolic medium and an isotropic dielectric. At certain orientations of the optical axis of the hyperbolic medium relative to the interface, the reflected and transmitted waves are completely absent. In this paper, we formulate the aforementioned paradox and present its resolution by introduction of infinitesimal losses in a hyperbolic medium. We show that the reflected wave exists, but became extremely decaying as the loss parameter tends to zero. As a consequence, all the energy scattered into the reflected channel is absorbed at the interface. We support our reasoning with analytical calculations, numerical simulations, and an experiment with self-complementary metasurfaces in the microwave region. In addition to the great fundamental interest, this paradox resolution discovers a plethora of applications for the reflectors, refractors, absorbers, lenses, antennas, camouflage and holography applications.Comment: 16 pages, 4 figure

Développement de méthodologies de caractérisation électromagnétique des matériaux et métamatériaux, approche de la fonction d absorption

La généralisation de l utilisation des matériaux composites a rendu indispensable la connaissance de leurs propriétés électromagnétiques. Celles ci sont définies à partir des valeurs de leurs paramètres intrinsèques. Au cours de cette thèse, nous avons étudié les matériaux composites à indice de réfraction négatif. Nous avons développé des méthodes de calcul théoriques capables de traduire correctement leurs paramètres intrinsèques. Ensuite, nous avons mis en place des modèles électriques basés sur des résultats expérimentaux issus de bancs de mesure que nous avons conçus. Ces modèles nous ont permis de décrire la participation de chacun des composants d un métamatériau à la réponse globale du système. Enfin, nous avons vérifié la faisabilité de systèmes à base de métamatériaux réalisant une fonction d absorption. Pour cela, nous avons réalisé des structures à base de résonateurs fendus dissymétriques électriquement résonants, puis dans un souci de performance, nous avons évolué vers des structures à base de surfaces fractales.The knowledge of the electromagnetic properties of composite materials has become indispensable since their use was generalized. These electromagnetic properties are defined with their intrinsic parameter values. In this thesis, we have studied composite materials with a negative refractive index. We have developed theoretical methods capable of correctly translating their intrinsic parameters. Then, we have set up theoretical models based on experimental results obtained from experimental benches realized in our lab. These models have led to the description of the participation of each of the material components to the global response of the system. Finally, we have verified the feasibility of metamaterial based systems in order to realize an absorbing function. To do so, we have realized structures basedNANTERRE-BU PARIS10 (920502102) / SudocSudocFranceF

A quasi-universal method to measure the electromagnetic characteristics of usual materials in the microwave range

International audienceKnowing the electromagnetic characteristics of differen material has become a major topic with the growing of wireless communications. The actual tools to perform this characterization have some limits, either in terms of limited frequency band, or in terms of inconstancy according to the different kinds of materials. On the basis of well-known procedures in the microwave domain, we present a new measurement cell equipped with a sample holder that can contain any kind of materials: solids, semi-solids (granular or powder materials), liquids. This technique can also characterize materials of thin thickness that are also more and more used in the RFID domain or in the realization of antennas on flexible substrates