Onsager-Casimir principle and reciprocity relations for bianisotropic media

To use the general reciprocity theorem for bianisotropic media, the physical basis should be established. There is the Onsager-Casimir principle that shows how the time-reversal invariance of microscopic equations of motion gives certain relations for macroscopic susceptibilities of a causal linear bianisotropic medium. In this paper, we show that in a general case of a bianisotropic medium, the Onsager-Casimir principle is not the same as the Lorentz reciprocity. We discuss the fact that one cannot use the Onsager-Casimir principle to "ensure the physicality" of the known microwave chiral and Ω-media. At the same time, we show that the Onsager-Casimir principle is applicable to new particulate bianisotropic composites - the MCBMs. The MCBMs give an example of nonreciprocal bianisotropic media with dynamical constitutive symmetry.