Problématique de l'homogénnéisation des matériaux artificiels et résonnants présentant un indice de réfraction négatif

Cette étude traite de métamatériaux à indice de réfraction négatif constitués d'une répartition périodique de tiges et anneaux résonants (aussi appelés Split Ring Resonators ou SRRs). Ces structures ayant des dimensions électriques voisines d'un dixième de la longueur d'onde, l'approximation des milieux effectifs est généralement faite et la permittivité et la perméabilité effectives sont calculées au sens de Fresnel. En effet, malgré la nature composite du milieu, nous l'assimilerons à un matériau homogène auquel nous affecterons des grandeurs macroscopiques identiques matériaux classique. Cependant, des auteurs ont démontré l'existence d'une bande de fréquence où la partie imaginaire de la permittivité est positive. Cette observation contredit notre intuition physique car cette partie imaginaire, représentant des pertes, devrait être négative quel que soit le signe de la partie réelle. La procédure d'homogénéisation de tels milieu semble donc avoir des limites. L'objectif de notre étude est d'interpréter les paramètres effectifs dans cette bande de fréquence anormale. Nous démontrons que leur validité au sens des équations de Fresnel est contestable. La participation d'onde évanescente à la propagation au sein de la structure périodique rend sa description macroscopique difficile. Dans la bande de fréquence où ces paramètres sont définis correctement, l'indice effectif atteint une valeur maximale dictée par la structuration du métamatériau

Electromagnetic Wave Propagation Modeling for Finding Antenna Specifications and Positions in Tunnels of Arbitrary Cross-Section

This chapter is organized as follows : Section II introduces the modal approach for guiding structures. It is based on a full-wave method, namely the Transmission Line Matrix (TLM) method. These methods has been hampered by their large computational time when compared to asymptotic methods when large size environments are considered. Thus, a suitable 2.5 D TLM implementation to reduce the computational time and to include lossy dielectric walls of tunnels is briefly presented [2]. The computation cost is reduced compared to typical solutions by using the concept of Surface Impedance Boundary Condition (SIBC). Section III is devoted to the description of a methodology for the determination of antenna field specifications and positioning in operational scenarios at high frequencies. Section IV presents the validation of this methodology for a simple canonical case. Lastly, section V describes the analysis and results for a real scenario representative of tunnel environments. Finally, discussions and conclusions are developed

Time-Domain Electromagnetic Wave Propagation in Confined Environments

International audienceConfined environments like tunnels are electrically large structures for guided wave propagation. They can have arbitrary cross sections, and the design and optimization of antenna for communication system requires the knowledge of a "full-wave" solution in nearby zones. Current models based on asymptotic approaches do not describe adequately the wave propagation under the above conditions. In addition, a complete "full-wave" analysis of the tunnel propagation performances is not feasible in terms of computer expenditure. After a survey of the most commonly used techniques for propagation in tunnels, some investigation regarding an appropriate approach to find the fields is proposed. It is based on a modal decomposition of the wave propagation that allows an optimization of the coupling with the antenna. To find the mode characteristic for arbitrary cross section, a full-wave method, namely, the transmission-line matrix (TLM), is modified to a so-called 2.5-dimensional TLM algorithm and presented in details. This approach is validated for a canonical structure. Then, it is applied to study the wave propagation in a realistic rectangular tunnel. The concept of surface impedance boundary condition (SIBC) is introduced to reduce the TLM computational domain and model the tunnel walls that can be considered as lossy dielectric. Results show that guided structures with lossy dielectric walls of arbitrary cross section can be studied with this approach

Real-time 3D electromagnetic field measurement instrument with direct visualization

Nowadays, a wide variety of terminals are proposed to nomadic users. Generally these terminals provide wireless communication operating at frequencies between one and a few GHz. For technical reasons, including multiple access to the communication channel and battery autonomy, these terminals transmit only during very short periods i.e. transmission bursts. For a direct observation of certain characteristics of the transmitted signals radiated by such terminals, only a few measurement setups exist. This article proposes such a novel real-time 3D electromagnetic field measurement instrument with direct visualization. The prototype used for validation is based on an array of probes regularly attached on a non-conductive rigid loop which is put into fast rotation around the terminal under test. To cite this article: J. Rioult et al., C. R. Physique 10 (2009). (C) 2008 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved

Miniaturized CPW-Fed Planar Monopole Antenna for Multi-band WLAN/WiMAX Wireless Applications

To incorporate two different communication standards in a single device, a miniaturized dual-band planar monopole antenna is presented in this paper. The proposed antenna is formed by a CPW feed line and a rectangular ring monopole with a vertical strip. The designed antenna has a small overall size of 19 mm 36 mm 1.6 mm. A prototype of the proposed antenna which was fabricated and measured to validate the design shows a good agreement between the simulation and the experiment. The measured results indicate that the antenna has the impedance bandwidths of 650 MHz (2.30-2.95 GHz) and 2460 MHz (3.40-5.86 GHz) at the first and second bands, respectively with a reflection coefficient less than – 10 dB covering all the WLAN bands (2.4/5.2/5.8 GHz) and WiMAX bands (2.6/3.5/5.5 GHz). In addition, the nearly omni-directional and bi-directional radiation patterns are also achieved in both H- and E-planes, respectively. It is also noticeable that a good antenna gain over both operating bands has been obtained. Therefore, this simple compact planar monopole antenna with multi-band characteristics is well suitable for WLAN and WiMAX wireless communication applications. Details of the proposed antenna design and both simulated and experimental results are analyzed and discussed

Etude de métamatériaux à indice de réfraction négatif

1 Volume; Diffusion restreinte; 87 page

Metamaterials for non-radiative microwave functions and antennas, in Metamaterials and wave control

International audienceCurrent and future wireless communications systems have to be smart while proposing an acceptable quality of service for given applications and optimized resource management in terms of energy consumption and spectral occupation. Moreover, the demand for nomadic devices is growing, thus requiring light, low profile and miniaturized microwave components which can easily integrate into complex systems. All these requirements can be contradictory for the conventional microwave engineer since for instance, miniaturization is usually achieved with a non-negligible impact on overall performances. Since metamaterials can be tailored to present required electromagnetic properties, it should definitely provide a higher degree of freedom in the design of both radiative and non-radiative components for wireless systems. The potential of metamaterial to improve the performances of microwave devices should also be considered. This chapter is divided in two main parts: the first one deals with metamaterial applications for non-radiative microwave components and the second one describes the potential and applications of metamaterials to microwave antennas

Reflection ellipsometry for in-situ measurements of complex permittivity and thickness of a single-layer material at microwave frequencies : Theory and Experiments

International audienc

Étude des métamatériaux à indice de réfraction négatif (paramètres effectifs et applications antennaires potentielles)

Les métamatériaux à indice de réfraction négatif (MIRN) étudiés sont des composites artificiels assimilables à un milieu continu présentant des caractéristiques inédites. Ce mémoire est divisé en trois parties. La première partie traite de l'homogénéisation de composites constitués d'inclusions métalliques dans un diélectrique. L'originalité de notre travail réside dans l'extension des techniques d'homogénéisation classiques aux MIRN. Les limites pour lesquelles les MIRN peuvent être considérés comme des milieux continus sont établies. Une bande de fréquence anormale est mise en évidence. Dans la deuxième partie, des critères de conception ainsi que des règles de dimensionnement de composites magnétiques artificiels sont établies. Nous proposerons ensuite un milieu plus performant. Finalement, nous appliquerons une particularité des MIRNaux antennes : la résonance d'ordre zéro. Le passage du concept à la mise en œuvre sera démontrée à l'aide des résultats dégagés précédemment.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF