SAW and pseudo-SAW properties using matrix methods

摘要

Pseudo-surface-waves (PSAW's), or leaky SAW's, were first recognized over 25 years ago and the phase velocity (v/sub p/) and attenuation per wavelength (/spl alpha//spl lambda/) of PSAW modes for nonpiezoelectrics were calculated soon after. Since the seventies progress has been made in exploiting the higher velocities and electromechanical coupling constants (K/sup 2/=2/spl Delta/v/v) achievable with PSAW's for piezoelectric device applications; this has stimulated new interest in the search for piezoelectric materials with orientations which have low /spl alpha//spl lambda/, high K/sup 2/, high v/sub p/. Procedures for calculating the PSAW properties (v/sub p/, /spl alpha//spl lambda/, and K/sup 2/) are not very explicitly given. In light of the preceding we present in this paper a review of the basic features of SAW and PseudoSAW's using the matrix method. In this paper: the mechanically free open-circuited and short-circuited surface wave boundary value problems for piezoelectrics are formulated using the matrix method; two types of modes (SAW and PSAW) are described; and a number of computationally simple, frequency independent analytical functions are derived, from which /spl alpha//spl lambda/, v/sub p/, and K/sup 2/ are calculated for any direction on any material plane using commercially available PC software. The relationship of these functions to the effective permittivity concept, favoured by many researchers, is demonstrated and illustrative numerical examples for the PSAW's reveals that low-loss orientations are quite sensitive to material constant values.