Backward waves in magnetoelectrically chiral media: Propagation, impedance, and negative refraction

Magnetoelectrically chiral media are studied in this paper as potential materials to realize double negative materials and negative refractive characteristics. The behaviors of the negative refractive index, the backward eigenwaves, and the impedance of these eigenmodes of this particular type of chiral media are examined in detail. We consider longitudinal and transverse propagation separately. Among the wave numbers obtained, we find that two of them are backward propagating waves in certain frequency bands. The helicity and polarization states are shown. We further study the impedance of these backward eigenmodes, which have potential applications in impedance matching, subwavelength resonator cavities and high-directivity antennas. Due to the off-diagonal gyrotropic parameters, a negative refractive index can be achieved when the material parameters and frequency are properly chosen. A study of the zero index of refraction for magnetoelectrically chiral media is carried out, and potential applications are proposed.