Types of leaky SAW degeneracy in crystals

Various types of leaky surface acoustic wave (SAW) degeneracies in crystals are considered and systematically classified, Concrete examples of these degeneracy types are given. The possibility of existence of subsonic leaky SAWs is numerically predicted. New correct equations for acoustic axes oblique to symmetry planes in trigonal crystals are derived. It is found that the maximum number of acoustic axes in trigonal crystals is equal to 16 rather than 10 as was previously stated in the literature.