MATERIAL EFFECTS IN BI-ANISOTROPIC ELECTROMAGNETICS

The emphasis on nonisotropic media in the electromagnetics research co mmunity has recently brought forward a large amount of new literature on the material effects. The material phenomena affecting the electrom agnetic characterization are contained in the constitutive relations b etween an electric and a magnetic excitation and an electric and a mag netic response. Starting from the constitutive equations, this article is an attempt to cast light on the labels, terms, notation, and class ification of linear electromagnetic materials. Using dyadic analysis a nd physical concepts like reciprocity and magnetoelectric coupling, th e different classes within bi-anisotropic media are presented in syste matic form. Simple isotropic media can be characterized by two materia l parameters: the electric polarizability is measured by permittivity epsilon, and the magnetic polarizability by the permeability mu. For b i-isotropic media, there exists magnetoelectric coupling, but due to i sotropy (independence of the direction of the field vectors) the two a dditional material parameters are scalars. The physical interpretation to these two parameters are chirality and nonreciprocity. The two sub classes of bi-isotropic materials are Pasteur and Tellegen media. If t here is direction dependence in the medium, we carl the material aniso tropic, and a scalar quantity has to be described by a dyadic with nin e components. Finally, the most general material is called bi-anisotro pic, which means that in addition to a dyadic permittivity and permeab ility, the two magnetoelectric material parameters are dyadics. The es sential feature in the classification of the present paper is the sepa ration of all the four material parameter dyadics into symmetric and a ntisymmetric parts. For permittivity and permeability, the symmetric p arts correspond to reciprocal media and the antisymmetric parts are no nzero for nonreciprocal media. In the cross-coupling dyadics the decom position into symmetric and antisymmetric parts discriminates chiral m edia, omega media, classical magnetoelectric media, and moving media. Finally, possible alternative characterizations of bi-anisotropic mate rials are discussed.