ENERGY FLOWS OF DIRECT AND INVERSE NORMAL TRANSVERSE ACOUSTIC-WAVES IN PIEZOELECTRIC PLATES

Energy flows carried by normal transverse acoustic waves propagating i n piezoelectric plates with frequencies close to critical, i.e., under the conditions allowing the existence of inverse waves, are studied t heoretically. The energy flows related to the elastic displacements an d the electric fields accompanying such acoustic waves are calculated. It is demonstrated that the energy flow related to the electric field in vacuum is directed oppositely to the wave vector, and, in the case of antisymmetric waves in the vicinity of critical frequencies, it ex ceeds in magnitude the energy flow related to the elastic displacement s. This effect is responsible for the existence of inverse transverse acoustic waves in piezoelectric plates.