On electromagnetic fields in skewon-axion media

Applying four-dimensional formalism for the electromagnetic fields, the electromagnetic medium can be characterized by a dyadic involving 36 parameters in the general case. A subclass “skewon-axion media” with 16 parameters can be defined independent of any basis system. Since it is known that the interface of some skewon-axion media acts as an electromagnetic boundary, it is attempted to find more general cases by varying the form of the medium dyadic. As a result, novel SHDB boundary conditions are arrived at, which generalize those of the soft-and-hard surface and DB boundary.