Transverse elastic waves in superlattices: The Brewster acoustic angle

We use a plane wave basis to study the transverse acoustic waves in elastic superlattices-artificial binary structures of periodic mass density rho(z) and periodic transverse elastic velocity c(t)(z). The bulk frequency bands for oblique propagation support minigaps that can close due to the edge cr ossing of subsequent bands. Some of these crossings are explained in terms of the acoustic Brewster angle theta(aB) that is a function of the material parameters only. A second condition for the complete shrinking of the gaps that involves the structural parameters is also discussed. The surface wav es in the corresponding truncated superlattices are obtained by use of the supercell method. The dispersion curves of these waves are strongly depende nt on the material of the layer at the surface-the surface waves that appea r for a selected layer at the surface can completely disappear when the las t layer is the other one. Specific applications are given for Zn/Fe, Pb/Ge, and Si/Au superlattices.