ACOUSTIC AXES FOR ELASTIC-WAVES IN CRYSTALS - THEORY AND APPLICATIONS

The purpose of this paper is to present, a simple and direct way of fi nding the number of acoustic axes and their locations for all crystals of orthorhombic, tetragonal, hexagonal or cubic symmetry ('RTHC cryst als'). The procedure is based upon a decomposition of the acoustical t ensor due to Fedorov & Fedorov. Excepting cases for which there may be an infinity of acoustic axes (for instance, the case of hexagonal cry stals), it is shows that RTHC crystals may have at most 16 acoustic ax es, four in each coordinate plane, and four out of coordinate planes. Very simple equations are presented for the explicit determination of these acoustic axes. Then, these results are applied in turn to each o f the RTHC crystal systems. In each case the possible numbers of acous tic axes are easily obtained. Explicit numerical examples are presente d for several specific crystals.