International Journal of Applied Electromagnetics and Mechanics - Volume 9, issue 2

Authors: Weiglhofer, Werner S.

Article Type: Research Article

Abstract: An introduction to this special issue devoted to Bianisotropics’97 is given by providing a perspective on the concept of bianisotropy in the context of electromagnetics. The scene is set via a discussion of constitutive relations for frequency‐dependent as well as time‐dependent fields, constraints and conditions on the parameters describing a material medium. A brief delineation of a coherent terminology for different types of media is attempted.

DOI: 10.3233/JAEM-1998-107

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 93-101, 1998

Authors: Cloete, J.H. | Kuehl, S.A. | Bingle, M.

Article Type: Research Article

Abstract: Physical principles are discussed which may improve the absorption of electromagnetic waves, especially in the microwave regime, by synthetic chiral and racemic materials. These principles are used to design a chiral composite for enhanced electromagnetic wave absorption at about 14 GHz. The chiral absorber consists of single‐turn copper helices, each wound on a ferrite core and randomly dispersed in a dielectric absorber made of tiny spheres of graphite‐coated expanded polystyrene. Its constitutive parameters, and those of some related dielectric, chiral, non‐chiral (bihelix) and racemic absorbing composites, are studied in the 10 to 18 GHz band. The materials are analyzed as …third‐order Dällenbach layers to compare their ability to reduce normal incidence specular reflection by a flat metal plate. The presence of half‐wave resonant helices moderately increases the absorption bandwidth of the dielectric host. A chiral composite and its racemic counterpart have essentially identical properties as absorbers of specular reflection. Show more

DOI: 10.3233/JAEM-1998-108

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 103-114, 1998

Authors: Busse, G. | Jacob, A.F.

Article Type: Research Article

Abstract: A key to expand the range of waveguide measurement setups for chiral materials is to introduce step discontinuities. Therefore, in this paper the discontinuity of a chiral section of differing diameter in an otherwise empty circular waveguide is analysed by means of a mode‐matching technique. The frequency‐dependent scattering parameters are calculated for some typical constitutive parameters and geometries. The validity of this concept is confirmed by the inversion of these results.

DOI: 10.3233/JAEM-1998-109

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 115-121, 1998

Authors: Athanasiadis, Christodoulos | Stratis, Ioannis G.

Article Type: Research Article

Abstract: This paper deals with the inverse scattering problem to determine the shape of a chiral obstacle immersed in achiral free space from the knowledge of the scattered wave. A variational equation is established for the corresponding direct scattering problem. Then, under appropriate assumptions, it is shown that the chiral obstacle is uniquely determined by the far field patterns of all incident waves with a fixed wave number.

DOI: 10.3233/JAEM-1998-110

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 123-133, 1998

Authors: Altman, C. | Suchy, K.

Article Type: Research Article

Abstract: Useful information on the solutions to the Maxwell system of first order linear differential equations may be obtained with the aid of two distinct, but not independent, sets of adjoint equations, the formally adjoint system which reduces to the complex conjugate equations in loss free media, and the Lorentz adjoint system which reduces to the time reversed equations in loss free media. The formally adjoint system is used to define a generalized energy flux vector, to decompose wavefields into constituent modes and to define their amplitudes. The Lorentz adjoint system is used to construct time reversed, “complementary” media, and time …reversed wavefields and sources that are Lorentz reciprocal to the given wavefields and sources. In some problems, such as the determination of reciprocal scattering matrices or reciprocal modal Green’s functions, it is necessary to employ both adjoint systems. Show more

DOI: 10.3233/JAEM-1998-111

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 135-142, 1998

Authors: Borzdov, George N.

Article Type: Research Article

Abstract: New types of parametric representations of the wavevector surface in a biaxial crystal, which are based on the use of orthogonal curvilinear coordinates making possible to obviate the need for solving algebraic equations, are presented. By making use of them, the basic quadratic forms, the asymptotic directions, the asymptotic and parabolic curves are calculated, the excitation conditions of associated modes are found. It is shown that the presented coordinate systems can be used for the description of field vectors of eigenwaves and light beams and that similar systems can be introduced on some other surfaces.

DOI: 10.3233/JAEM-1998-112

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 143-156, 1998

Authors: Arnold, J.M. | Hutchings, D.C.

Article Type: Research Article

Abstract: Nonlinear electromagnetic propagation in materials having anisotropic nonlinear susceptibilities induces complex dynamical phenomena which can be controlled by appropriate engineering of the material. Two optical examples are studied, of second‐harmonic generation and third‐order polarisation instabilities in cubic semiconductors, exemplified by gallium arsenide.

DOI: 10.3233/JAEM-1998-113

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 157-165, 1998

Authors: Michel, Bernhard | Lakhtakia, Akhlesh | Weiglhofer, Werner S.

Article Type: Research Article

Abstract: We present here the application of the Maxwell Garnett (MG) and the Bruggeman (Br) formalisms to homogenize very general linear bianisotropic‐in‐bianisotropic particulate composite media with ellipsoidal inclusions. Both formalisms involve the calculation of certain depolarization dyadics, which generally amounts to the numerical evaluation of several two‐dimensional integrals. The MG estimate of the constitutive dyadic of the homogenized composite medium can then be obtained by straightforward matrix manipulations. The Br estimate, however, involves nonlinear equations which have to be solved iteratively. We present an iteration scheme that converged rapidly in most cases tested. Numerical results are given for those composite media …for which the Bruggeman formalism so far has not been implemented: spherical chiral inclusions in a uniaxial dielectric host medium, spheroidal chiral inclusions in free space, spherical chiral inclusions in a biaxial dielectric host medium, and spherical voids in a gyrotropic dielectric host medium. Show more

DOI: 10.3233/JAEM-1998-114

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 167-178, 1998

Authors: Vegni, L. | Toscano, A.

Article Type: Research Article

Abstract: The general theory of the propagation of the electromagnetic field in Omega media with cylindrical symmetry where the density of the Ω-shaped conducting microstructures drops as a function of 1/\rho fed by extended electric cylindrical sources is addressed, and it is established that the wave phenomena can be modeled in terms of the Kummer differential equation. This model leads to closed form analytical expressions in terms of the confluent hypergeometric functions for all the components of the electromagnetic field in far zone.

DOI: 10.3233/JAEM-1998-115

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 179-190, 1998

Authors: Yatsenko, V.V. | Tretyakov, S.A. | Sochava, A.A.

Article Type: Research Article

Abstract: Complex three-dimensional grids formed by parallel conductive spirals are considered using a homogenization procedure. Spirals are replaced by straight wires with periodically inserted loops. Averaged electric and magnetic currents are determined which allows to calculate the reflection and transmission coefficients. Numerical examples for co‐ and cross‐polarized reflection and transmission coefficients are given.

DOI: 10.3233/JAEM-1998-116

Citation: International Journal of Applied Electromagnetics and Mechanics, vol. 9, no. 2, pp. 191-200, 1998