INTERACTION OF ELECTROMAGNETIC WAVES WITH DIELECTRIC DISKS AND RODS

Abstract

In this dissertation, the interaction of electromagnetic waves with dielectric disks and rods are investigated. The challenging objective of this study is to investigate the enhancements and reductions of the scattered electric field from these targets using the well known existing models. The reduction in the radar cross section (RCS) from these targets is extremely important in designing of the modern remote sensing sys tems i.e., radar and stealth technologies. This dissertation is divided into two parts. In the first part of the dissertation, an analytical solution is provided to investigate the effects of tilt angles upon the back-scattering cross section of a thin dielectric circular disk. This analytical solution is based upon three different scattering approxima tions such as Rayleigh-Gans, Volume Integral Physical Optics and Koh-Sarabandi by considering both types of incident polarization i.e., horizontal and vertical. It is investigated that by varying the orientation of the disk, the back-scattering cross section can be enhanced or diminished as compared to the disk having no tilt. It is further studied that for the specific tilt and size parameter of a low loss Gallium Arsenide (GaAs) disk, the back-scattering cross sections can be made almost equal to zero for both types of incident polarizations. Later on, the disk-shape effects of a thin dielectric disk upon the back-scattering cross sections for both types of incident polarizations have been studied. For the solution of this problem, an analytic theory for the scattering of electromagnetic waves from various shapes of thin dielectric disks is developed. This proposed theory is based on the Koh-Sarabandi (KS) approxima tion for the electromagnetic wave scattering from a thin dielectric disk along with the spectral representation of the dyadic Green’s function. The considered disk shapes ii are triangular, elliptical, circular, semi-circular and square disks having same elec tromagnetic and geometrical parameters. It is studied that the back scattering cross sections for a low loss Gallium Arsenide (GaAs) triangular disk at a specific incidence angle can be made almost zero for both types of incident polarizations is the lowest for both types of incident polarizations. Attention is then focused upon the computation of the coherent electromagnetic wave scattering from a sparsely distributed N-tilted thin circular disks. The influences of the various parameters including incident angle, size parameter of the disk, relative permittivity of the disk and spacing among disks upon the back-scattered cross sections have been studied for incident horizontal and vertical polarizations. Some conditions are discussed where a pair of sparsely located tilted low loss Gallium Arsenide disks significantly reduced the back-scattered cross section as a compared to a single tilted Gallium Arsenide disk. In the second major part of this dissertation, I primarily focused on the scattering characteristics of the electromagnetic Metamaterials. Firstly, an analytical theory is developed and studied for the scattering characteristics of an isolated dielectric and dielectric coated conducting rods. The types of dielectric materials considered are Barium Strontium Titanate (BST) Ba0.5Sr0.5T iO3, Magnetodielectric, Gallium Arsenide (GaAs) and Silicon Carbide (SiC). It is found that the gallium arsenide coating can be used to significantly reduce the scattering width from a thin perfectly electric conducting cylindrical rod at specific observation angles. Later on, the ef fective permittivity and permeability of metamaterials composed of two dimensional periodic arrangements of these dielectric coated cylindrical rods have been studied. An increase in the double negative bandwidth of a metamaterial composed of barium iii strontium titanate coated conducting rods has been observed in contrast to the corre sponding bandwidth of a metamaterial composed of only barium strontium titanate Ba0.5Sr0.5T iO3 (BST) material rods. Also an additional plasmonic epsilon negative bandwidth has been found in case of a metamaterial composed of barium strontium titanate coated conducting rods. It is further observed that the widest epsilon nega tive, mu negative and double negative bandwidths exist for a metamaterial composed of gallium arsenide rods