Electromagnetic Scattering From Chiral Media

Time and frequency domain analysis of electromagnetic plane wave scattering from chiral media are presented. The frequency domain solution deals with two-dimensional scatterers using a boundary value and an iterative techniques for the scattering from a number of parallel circular cylinders forming a scatterer of arbitrary cross-section. The time domain solution is based on a scattered field finite difference time domain (FDTD) formulation developed with plane wave excitation. Applications are presented to show the flexibility of the developed techniques in changing the parameters of composite scatterers with inhomogeneous chirality distribution. Parametric studies are investigated for the problem of scattering from an inhomogeneous chiral slab to show the appropriate values, where the slab can act as a focusing lens by increasing the value of the forward wave and reducing the backward scattered field. Introduction The interaction of electromagnetic fields with chiral matters has been studied over the years. Chiral media were used in many applications involving antennas and arrays, antenna radomes, microstrip substrates and waveguides. A chiral object is, by definition, a body that lacks bilateral symmetry, which means that it cannot be superimposed on its mirror image neither by translation nor rotation. This can also be known as handedness. Objects that have the property of handedness are said to be either right-handed or left-handed. Chiral media are optically active – a property caused by asymmetrical molecular structure that enables a substance to rotate the plane of incident polarized light, where the amount of rotation in the plane of polarization is proportional to the thickness of the medium traversed as well as to the light wavelength [1-5]. Thus chiral medium has an effect on the attenuation rate of the right hand and left hand circularly polarized waves. Unlike dielectric or conducting cylinders, chiral scatterers produce both co-polarized and cross-polarized scattered fields. Coating with chiral material is therefore attempted for reducing radar cross-section of targets. In this paper, the scattering of electromagnetic plane wave from two and three-dimensional chiral scatterers as well as the reflection and transmission from one-dimensional slab are presented. The computed data for the two-dimensional problems were implemented using two different techniques, a boundary value solution and an iterative scattering technique, while for the three and one dimensional problems, a finite difference time domain (FDTD) formulation was developed with plane wave excitation using a scattered field formulation. A comparison between the fields of the transmitted and reflected waves from a one-dimensional chiral slab as well as the far field of a chiral sphere based on the exact solution and the developed FDTD formulation is presented as a verification of the developed formulations for a wide band frequency range. Applications are presented for scattering from homogeneous, inhomogeneous chiral slabs, and homogeneous chiral spheres. In one application, the slab is designed to acts as a focusing lens by increasing the value of the forward scattered field and reducing the backward scattered field. Progress in Electromagnetic Research Symposium 2004, Pisa, Italy, March 28 31 800 Formulation Chiral medium is characterized by the following constitutive relations for electromagnetic field with j t e ω time-harmonic dependence [6] c D E j B ε ξ = − , 1 c H B j E ξ μ = − (1) The chiral media has two different phase velocities for right-hand circularly polarized waves (RCP) and left-hand circularly polarized waves (LCP) leading to two different bulk wave numbers + k and − k , which are given by 2 [ 1 ] k k χ χ ± = + ± (2) where k ω με = and the chirality parameter / c χ μ εξ = , and c ξ is the chiral admittance [6]. Waves in a chiral medium can be expressed as a superposition of RCP and LCP waves [3, 4] such that,