Head waves in a piezoelectric-half-space

Head waves are an interesting phenomenon that is often ignored in piezoelectric harmonic wave study. They affect fields in the interior as well as those on the surface. Using the exact algebraic expressions for transient fields [Liu et al., 1991 IEEE Ultrason. Symp. Proc., p.377-81], we find that their directivity depends only on critical angles and can be given as a simple formula, while the intensity depends on material parameters as well as on the kind of the source that excites it. Their polarization, on the other hand, is independent of the observation angle and of the kind of the excitation source. A metallized surface reduces the number of head waves in a piezoelectric medium and affects the intensity of existing head waves, but does not change their propagation. Numerical examples are given for all three types of head waves, namely electromagnetic electromagnetic (EMEM) head waves, electromagnetic acoustic (EMAC) head waves and acoustic acoustic (ACAC) head waves, for both mechanical and electrical sources, and with both free and metallized surfaces