Backward wave propagation in anisotropic metamaterials

In this paper, we study the backward wave propagation phenomenon in completely anisotropic metamaterials. The formation conditions for backward wave propagation under an arbitrary angle between the metamaterials' intrinsic coordinate axis and transmission axis are obtained. The influences of permittivity and permeability tensors and polarization on the backward wave formation and propagation are analyzed. On this basis, we further analyze the situation of backward wave in anisotropic metamaterials with different dispersion relations, and the angle between wave vector and Poynting vector, and the general conclusion of backward wave propagation are obtained. In addition, we studied the propagation characteristics of backward wave in epsilon-near-zero metamaterials, and discovered that the backward wave in these metamaterials is a perfect backward wave.