Phase and group velocities of bulk optic and acoustic waves in crystals, periodic structures and metamaterials.

The paper considers regular trends of propagation of plane optic and acoustic waves in crystals, periodical structures and metamaterials. It is stated that mutually opposite directions of wave vectors and Poynting vectors are typical of plane waves in «metamaterials» and «negative media». It is also demonstrated that in crystals with a strong anisotropy of optic and elastic properties, a wave vector and a Poynting vector may be directed with respect to each other at angles as wide as ψ = 740. It is proved that the anisotropy of materials may result in unusual propagation and reflection of plane waves in these media. A few examples of peculiar wave behavior in the crystalline materials are described in the presentation. A diagram is proposed showing possible orientations of group velocity vector relatively to the phase velocity vector of waves in the anisotropic media. [ABSTRACT FROM AUTHOR]