Classifications of electromagnetic media

Applying four-dimensional differential-form formalism, the Maxwell equations are known to obtain a compact form in which the electromagnetic fields are represented by two two-forms, each of which has six components. The mapping between the field two-forms in a linear medium can be expressed in terms of a medium bidyadic which in the general case involves 36 scalar parameters. Handling the most general medium appears quite troublesome. This makes it necessary to define special classes of media definable by a smaller number of parameters. In the present paper a few possible definitions are considered and some properties of the medium classes are discussed.