Nonreciprocal microwave bianisotropic materials: reciprocity theorem and network reciprocity

There are many attempts to generalize the reciprocity theorem for bianisotropic media. With formal introduction of notion of reaction for bianisotropic media, we can formulate reciprocity conditions for the medium parameters. We can also extend the procedure used for a gyrotropic medium and consider the complementary, or the Lorentz-adjoint, bianisotropic medium, which satisfies the reciprocity theorem. Definition of the notion of reaction in bianisotropic media is, however, not so trivial. We consider some important aspects of the physical admissibility to use the notion of the reaction as a "physical observable" in bianisotropic media. The questions also arise: for what kinds of the known bianisotropic media is the reciprocity theorem physically applicable? Based on what kind of bianisotropic media, can nonreciprocal microwave devices be realized? We show that a novel class of microwave bianisotropic materials-magnetostatically controlled bianisotropic materials (the MCBMs)-are "physically justified" materials. The Onsager-Casimir principle and the notion of reciprocity are applicable in this case. New nonreciprocal microwave devices based on the MCBMs can be realized.