Affiliated with the
Communication & Space
Sciences Laboratory

Computational EM Modeling Techniques

Scattering from Chiral Objects

Normalized scattering cross section of a chiral sphere in free space characterized
by εcr = 3.0, μcr = 1.0 and ξr = 0.0, 0.1, 0.3, 0.8 for co-polarized components.

Bistatic scattering cross section of a homogeneous chiral sphere of radius 0.3 m
located at 0.4 m above a lossy half space characterized by ξgr = (5.0, 0.2) and σg = 0.01 S/m for φφ-polarization.

    The interaction of electromagnetic waves with artificial microwave chiral materials has drawn considerable attention in recent years. Since the chirality parameter provides an extra degree of freedom to control the scattering properties of targets, there have been many potential applications suggested for chiral materials. At microwave frequencies, it may be possible to use chiral materials to coat an object to achieve more effective control of its scattering properties. Moreover, chiral material has been considered for use in other applications including as substrates in microstrip antennas to reduce the resonance frequency and as polarization transformers.

    Here, a set of mixed potential integral equations has been developed for computing the electromagnetic scattering of 3D arbitrarily shaped homogeneous chiral targets in free space and located above a lossy half space. The effects of the relative chirality parameter on the scattering cross section are examined by considering several canonical examples. Scattering from multiple chiral targets in the presence of a lossy half space was also investigated. These results indicate that the relative chirality can significantly change the scattering behavior of objects. This work represents an important step toward the fundamental understanding of how the scattering cross sections of chiral objects located above a half space can be controlled via the chirality parameter.

..: References :..

1 -) Interaction of Electromagnetic Waves With 3-D Arbitrarily Shaped Homogeneous Chiral Targets in the Presence of a Lossy Half Space
by Xiande Wang, Douglas H. Werner, Le-Wei Li, Yeow-Beng Gan
IEEE Transactions on Antennas and Propagation, Vol. 55, No. 12, December 2007

ABSTRACT: The interaction of electromagnetic waves with an arbitrarily shaped three-dimensional (3-D) homogeneous chiral object located above a lossy half space is investigated using the method of moments (MoM) via the coupled mixed potential integral equations (MPIEs). Based on the surface equivalence principle, the equivalent surface electric and magnetic currents are used to replace the homogeneous chiral target in the presence of the half space. Two coupled MPIEs are developed for the unknown equivalent surface electric and magnetic currents by utilizing the continuity condition of the tangential total electric and magnetic field components on the chiral body’s surface. The well-known Galerkin procedure with Rao-Wilton-Glisson (RWG) basis functions is applied to solve this problem. The spatial domain half-space Green’s functions are obtained from the corresponding spectral domain Green’s functions via the discrete complex image method (DCIM) combined with the generalized-pencil of function (GPOF) technique. The reciprocity theorem is employed to calculate the far-zone scattered field. Numerical results are presented for characterizing electromagnetic scattering by a 3-D arbitrarily shaped homogenous chiral object located above a lossy half space so as to demonstrate the accuracy and efficiency of the proposed technique.

2 -) Novel BI-FDTD Approach for the Analysis of Chiral Cylinders and Spheres
by Andrey Semichaevsky, Alkim Akyurtlu, Douglas Kern, Douglas H. Werner, and Matthew G. Bray
IEEE Transactions on Antennas and Propagation, vol. 54, No. 3, pp. 925-932, March 2006

ABSTRACT: A versatile time-domain technique, known as bi-isotropic finite difference time domain (BI-FDTD), has recently been introduced for the numerical analysis of electromagnetic wave interactions with complex bi-isotropic media. However, to date only one-dimensional BI-FDTD schemes have been successfully implemented. This paper presents novel two-dimensional (2-D) and three-dimensional (3-D) dispersive BI-FDTD formulations for the first time. The update equations for these new 2-D and 3-D BI-FDTD approaches are developed and applied to the analysis of electromagnetic wave scattering by chiral cylinders and spheres in free space. The distinctive feature of this technique is the use of two independent sets of wavefields representing the left- and right-polarized waves in the chiral medium. This wave-field decomposition approach allows dispersive models for the chirality parameter as well as the permittivity and permeability of the medium to be readily incorporated into an FDTD scheme. The 2-D and 3-D BI-FDTD simulation results are compared with available analytical solutions for the scattering from a circular chiral cylinder and a chiral sphere respectively.

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