COUPLING OF SURFACE BOUNDED ACOUSTIC MODES TO PLATE MODES IN PIEZOELECTRIC MEDIA

A new approach is made to study the propagation of pseudo surface acoustic waves (PSAW) in piezoelectric media. Thick plates instead of half-spaces are treated by numerical methods. In this case the energy leaking of PSAW typical for half-spaces is replaced by coupling to plate modes. The dispersion anomalies due to this coupling enable to derive details of PSAW propagation depending on the crystal orientation. Thus, orientations are found without partial waves radiated from the surface. At stress free surface the PSAW agrees in this case with the fast shear bulk wave of same propagation direction. If the surface is electrically shortened the PSAW is trapped within a depth of about one wavelength. Details of this behavior are calculated for LiNbO3 and LiTaO3 and are new with respect to published data.