A General Theory for the Interaction of Bulk and Surface Acoustic Waves on Piezoelectric Substrates

Abstract

A general theory appropriate to describing the excitation of both bulk and surface acoustic waves in piezoelectric media is presented. In particular, the theory is capable of treating those orientations in which propagating bulk wave and SAW velocities are in close proximity. It is shown that under such conditions the well known parameter, Avlv, is no longer a valid measure of the coupling coefficient for the surface wave. Closed form expressions are derived for the transducer radiation resistance, surface potential, and insertion loss in terms of transducer geometry and only four substrate parameters, the bulk wave cutoff velocity, the free and metallized surface SAW velocities, and the off-resonance substrate dielectric constant The theory is compared to experimental measurements of energy trapping effects made on rotated Y-cut quartz.