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

A new approach is made to study the propagation of pseudo surface acou stic waves (PSAW) in piezoelectric media. Thick plates instead of half -spaces are treated by numerical methods. In this case the energy leak ing of PSAW typical for half-spaces is replaced by coupling to plate m odes. The dispersion anomalies due to this coupling enable to derive d etails of PSAW propagation depending on the crystal orientation. Thus, orientations are found without partial waves radiated from the surfac e. At stress free surface the PSAW agrees in this case with the fast s hear bulk wave of same propagation direction. If the surface is electr ically shortened the PSAW is trapped within a depth of about one wavel ength. Details of this behavior are calculated for LiNbO3 and LiTaO3 a nd are new with respect to published data.