Showing papers by "Hossein Mosallaei published in 2001"
17 Apr 2001
TL;DR: In this paper, a computational engine utilizing finite difference time domain (FDTD) technique integrated with the Prony method is presented to analyze and understand the unique propagation characteristics of different classes of complex EBG structures such as, (a) FSS structures, (b) PBG crystals, (c) smart surfaces for communication antenna applications, (d) surfaces with perfectly magnetic conducting properties (PMC), creation of materials with negative permittivity and negative permeability, surfaces with reduced edge diffraction effects, and (g) the notion of equivalent media.
Abstract: When periodic structures interact with electromagnetic waves amazing features result. In particular, characteristics such as frequency stop-bands, pass-bands and band-gaps could be identified. Surveying the literature, one observes that various terminology have been used depending on the domain of the applications. These applications are seen in filter designs, gratings, frequency selective surfaces (FSS), photonic crystals and band-gaps (PBG), etc. We classify them under the broad terminology of "electromagnetic band-gaps (EBG)". The focus of this paper is to present a powerful computational engine utilizing finite difference time domain (FDTD) technique integrated with the Prony method to analyze and understand the unique propagation characteristics of different classes of complex EBG structures such as, (a) FSS structures, (b) PBG crystals, (c) smart surfaces for communication antenna applications, (d) surfaces with perfectly magnetic conducting properties (PMC), (e) creation of materials with negative permittivity and negative permeability, (f) surfaces with reduced edge diffraction effects, and (g) the notion of equivalent media. The performance of two types of the EBG structures namely, single and multi-layered tripod FSS, and rectangular, triangular and woodpile PBG crystals is detailed. Some of the potential applications of these structures are highlighted.
192 citations
TL;DR: In this paper, a GA with adaptive cost function is implemented to obtain the optimal design of a non-uniform Luneburg (1964) lens antenna, where the GA optimizer simultaneously determines the optimal material and its thickness for each shell by controlling the gain and sidelobes envelope of the radiation pattern.
Abstract: Design optimization of radially nonuniform spherical lens antennas is the focus of this paper. In particular, special attention is given to the optimal design of nonuniform Luneburg (1964) lens antennas. One of the important engineering objectives of designing an optimal Luneburg lens antenna is to use as small number of shells as possible while maintaining an acceptable gain and sidelobe performance. In a typical radially uniform design, by reducing the number of shells, the gain is decreased and the grating lobes are increased. This deficiency in the radiation performance of the uniform lens antenna can be overcome by designing the nonuniform lens antenna. This necessitates the optimum selection of each layer thickness and permittivity. A genetic algorithm (GA) optimizer with adaptive cost function is implemented to obtain the optimal design. In this manner, the GA optimizer simultaneously determines the optimal material and its thickness for each shell by controlling the gain and sidelobes envelope of the radiation pattern. Various lens geometries, including air gaps and feed offset from the lens surface, are analyzed by using the dyadic Green's functions of the multilayered dielectric sphere. Many useful engineering design guidelines have been suggested for the optimum construction of the lens. The results have been satisfactory and demonstrate the utility of the GA/adaptive cost-function algorithm. Additionally, the radiation characteristics of a novel two-shell lens antenna have been studied, and its performance is compared to the Luneburg lens.
138 citations
08 Jul 2001
TL;DR: In this article, a composite material of periodic conducting straight wires/split ring resonators is presented to introduce a left-handed (LH) material with simultaneously negative permittivity/permeability.
Abstract: A novel composite material of periodic conducting straight wires/split ring resonators is presented to introduce a left-handed (LH) material with simultaneously negative permittivity/permeability. A powerful computational technique utilizing FDTD analysis with the Prony method is applied to characterize and demonstrate the unique electromagnetics phenomena of the complex structure. The results presented in this paper are a basis for the further investigations of the fascinating electrodynamics effects anticipated for such composite material in order to incorporate it into some potential applications.
17 citations
08 Jul 2001
TL;DR: In this article, an efficient and powerful computational engine utilizing the FDTD/Prony method was developed to obtain the electromagnetic characteristics of the periodic structures composed of complex scatterers of dielectrics and conductors of arbitrary shape.
Abstract: The finite difference time domain (FDTD) technique is an approach to efficiently investigate the broadband characteristics of periodic structures. The challenge in this paper is to develop an efficient and powerful computational engine utilizing the FDTD/Prony method to obtain the electromagnetic characteristics of the periodic structures composed of complex scatterers of dielectrics and conductors of arbitrary shape. It is demonstrated that the FDTD/Prony technique is a powerful engine in the characterization of complex electromagnetic structures.
8 citations