A Brief Review of a New Development for Constitutive Relations of Linear Bi-anisotropic Media

While physical restrictions on the constitutive parameters of linear bi-anisotropic media are well known, attention has been meager on the issue of mathematical consistency, when specializing the Maxwell equations for material media. We show here that such a consistency requirement results in a mathematical constraint: an algebraic relation between the constitutive parameters. Repercussions for specific types of linear media are discussed, most importantly, the consequence that bi-isotropic media must be reciprocal.