Homogenization of Thin and Thick Metamaterials and Applications

The wave propagation in structures involving metamaterials can be described owing to homogenization approaches which allow to replace the material structured at the subwavelength scale by an equivalent and simpler, effective medium. In its simplest form, homogenization predicts that the equivalent medium is homogeneous and anisotropic and it is associated to the usual relations of continuity for the electric and magnetic fields at the boundaries of the metamaterial structure. However, such prediction has a range of validity which remains limited to relatively thick devices and it is not adapted to more involved geometries (notably three-dimensional). The following two aspects are considered: (i) we study how the homogenization at the leading order can be improved when the thickness of the device becomes small and (ii) we propose a heuristic extension of the solution given by the leading order homogenization in order to deal with a complex geometry; in the latter case, an application to a demultiplexer device is proposed

Iterative Interference Cancellation for Time Reversal Division Multiple Access

Time Reversal (TR) has been proposed as a competitive precoding strategy for low-complexity devices, relying on ultra-wideband waveforms. This transmit processing paradigm can address the need for low power and low complexity receivers, which is particularly important for the Internet of Things, since it shifts most of the communications signal processing complexity to the transmitter side. Due to its spatio-temporal focusing property, TR has also been used to design multiple access schemes for multi-user communications scenarios. However, in wideband time-division multiple access schemes, the signals received by users suffer from significant levels of inter-symbol interference as well as interference from uncoordinated users, which often require additional processing at the receiver side. This paper proposes an iterative TR scheme that aims to reduce the level of interference in wideband multi-user settings, while keeping the processing complexity only at the transmitter side. The performance of the proposed TR-based protocol is evaluated using analytical derivations. In addition, its superiority over the conventional Time Reversal Division Multiple Access (TRDMA) scheme is demonstrated through simulations as well as experimental measurements at $2.5$ GHz carrier frequency with variable bandwidth values.Comment: 7 pages, 8 figures, published in an IEEE Journa

Directive metamaterial-based subwavelength resonant cavity antennas – Applications for beam steering

International audienceThis article presents the use of composite resonant metamaterials for the design of highly directive subwavelength cavity antennas. These metamaterials, composed of planar metallic patterns periodically organized on dielectric substrates, exhibit frequency dispersive phase characteristics. Different models of metamaterial-based surfaces (metasurfaces), introducing a zero degree reflection phase shift to incident waves, are firstly studied where the bandwidth and operation frequency are predicted. These surfaces are then applied in a resonant Fabry-Perot type cavity and a ray optics analysis is used to design different models of ultra-compact high-gain microstrip printed antennas. Another surface presenting a variable reflection phase by the use of a non-periodic metamaterial-based metallic strips array is designed for a passive low-profile steering beam antenna application. Finally, the incorporation of active electronic components on the metasurfaces, allowing an electronic control of the phase responses, is applied to an operation frequency reconfigurable cavity and a beam steering cavity. All these cavity antennas operate on subwavelength modes, the smallest cavity thickness being of the order of lambda/60. To cite this article: A. Outir et al., C R. Physique 10 (2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Applications de matériaux à bandes interdites photoniques et de métamatériaux en télécommunications

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Homogenization of ultrathin metallo-dielectric structures leading to transmission conditions at an equivalent interface

International audienceWe present a method of homogenization of thin metallo-dielectric structures as used in the design of artificial surfaces , or metasurfaces. The approach is based on a so-called matched asymptotic expansion technique, leading to parameters being characteristic of an equivalent interface associated to jump conditions. It is applied to an array of metal strips on top of a metal-backed dielectric slab, with the strips having a small but possibly finite thickness. Solving the equivalent problem provides explicit expressions (i) of the reflection coefficient for a wave at oblique incidence and (ii) of the dispersion relation of the surface waves. The results are shown to be in agreement with results coming from the transmission line theory in the limit of vanishing thickness of the metallization and for normal incidence of the wave. The influence of the finite thickness of the metallization is exemplified and validated by comparison with full wave simulations

Light scattering by periodic rough surfaces: equivalent jump conditions

International audienceWe present an interface model based on two-scale homogenization to predict the coherent scattering of light by a periodic rough interface between air and a dielectric. Contrary to previous approaches where the roughnesses are replaced by a layer filled with an equivalent medium, our modeling yields effective jump conditions applying across the region containing the roughnesses. The validity of the model is inspected by comparison with direct numerics and with experimental measurements on a air/silicium rough interface near the Brewster angle. It is shown that the interface model reproduces accurately the shift in the Brewster phenomenon without any ajustable parameter, which is of practical importance in retrieval methods to get thickness or filling fraction with reliable physical values

Usual Anderson localization restored in bilayered left- and right-handed structures

6 pagesInternational audienceWe present a study of the attenuation length in a one-dimensional array of alternating left- and right-handed materials in which both the permittivities and the permeabilities are disordered. This type of structure has been shown to present an anomaly in the attenuation length when only permeabilities are disordered. We derive a simple analytical expression of the attenuation length, when the disorder in the refraction index is due to perturbations in both the permeability and the permittivity. Our expression is able to explain the transition to the anomalous behavior when perturbation only in the permeability or only in the permittivity is considered. Besides, we show that the anomaly is dramatically affected when considering perturbations in permeability and permittivity. The coupling effects are able to restore the ordinary localization length. © 2012 American Physical Society

Étude de la transmission du son par une lame perforée de trous sub-longueur d'onde

International audienceWe analyze the transmission of sound through a sound hard film or layer with periodic subwavelength slits. For wavelength comparable to or larger than the slit spacing, the transmission spectra are revisited in terms of the transmission through an equivalent birefringent layer. It is shown that the Fano-type resonances can be understood by means of the dispersion relations of guided waves within the birefringent layer in the homogenized problem, equivalent to spoof plasmons for gratings. This is done by extending the homogenization to the evanescent waves being excited in the near field of the actual perforated layer.Nous analysons les spectres de transmission par une lame rigide perforée périodiquement de trous sub-longueur d'onde. Pour des longueurs d'onde comparables ou plus grandes que l'espacement des perforations, les spectres de transmission sont revisités en termes de transmission par une lame équivalente biréfringente. Nous montrons que les résonances de Fano se comprennent au vu des relations de dispersion d'ondes guidées par la couche biréfringente, similaires aux spoof plasmons dans les réseaux en réflexion. Ces relations de dispersion sont obtenues en étendant l'homogénéisation aux ondes évanescentes excitées en champ proche dans le problème réel