PLANE-WAVE SCATTERING BY SPHERICAL OBJECT COMPOSED OF AN ORTHORHOMBIC DIELECTRIC-MAGNETIC MEDIUM

Abstract

The scattering of electromagnetic waves from an anisotropic object may provide unique features that are not provided by the isotropic one. The electromagnetic properties of anisotropic mediums can be thus useful in designing structures for many applications, for example, low scattering and high absorption etc. The objective of this dissertation is to theoretically investigate scattering of plane wave by the spher ical structure composed of an orthorhombic dielectric–magnetic medium (ORDM) when coated with different materials. The permittivity dyadic of the medium is a scalar multiple of its permeability dyadic to make it unirefringent. By utilizing the recently derived spherical vector wavefunctions in closed form for an ORDM medium, the fields induced were represented as superposition of these wavefunctions. We then solve boundary-value problems in framework of the T matrix Method. Firstly, we examined scattering of Beltrami waves by an ORDM sphere embedded in chiral medium by the above procedure. Beltrami waves are circularly polarized plane waves that can propagate inside an infinite chiral medium without changing their state of polarization. A chiral medium is, therefore, birefringent. Numerical results were obtained. Then, the extinction, total scattering, forward scattering, and backscattering efficiencies were calculated in regard to: (i) the chirality parameter of host medium, (ii) the constitutive-anisotropy parameters of the permittivity and permeability dyadic. The effect of chirality parameter of surrounding medium is found noticeable on the efficiencies, when size parameter is increased to a value which make the wavenumbers representing left- and right-circularly polarized wave different from each other appreciably. Regardless of the choice of value of chirality parameter and the incident wave polarization-state, the back scattering efficiency shows an oscillating behavior. Thereafter, plane-wave scattering by the ORDM sphere when coated concentri cally with a chiral layer of finite thickness was explored. Due to chiral/ free-space ii and chiral/ ORDM interfaces, the complexity in the boundary-value problem was increased. In particular, role of the chirality of coating is prominent on the forward scattering efficiency. As the electrical size of sphere was increased, the backscattering efficiency exhibited undulating behavior. Although the total scattering efficiency ex ceeds absorption efficiency, however, presence of chirality tends to enhance absorption. Several lobes with much sharp resonance are seen in the scattering patterns of the coated sphere. The plane wave response of the dielectric-coated ORDM sphere were also examined, numerically as well as analytically. The radar cross sections of ORDM sphere when coated with the electrical insulating materials of different permittivity were computed and characterized. From computer results, it revealed that the mag nitude of scattering cross sections can be modified by changing the strength of the dielectric constant of coating. A particular case of an impedance-matched uniaxial sphere was also considered. The resonances appeared in the profile of radar cross sections of the sphere