SAW AND PSEUDO-SAW PROPERTIES USING MATRIX-METHODS

Pseudo-surface-waves (PSAW's), or leaky SAW's, were first recognized over 25 years ago and the phase velocity (upsilon(p)) and attenuation per wavelength (alpha 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 (K2 = 2DELTAupsilon/upsilon) achievable with PSAW's for piezoelectric device applications; this has stimulated new interest in the search for piezoelectric materials with orientations which have low alpha lambda, high K2, high upsilon(p). Procedures for calculating the PSAW properties (upsilon(p), alpha lambda, and K2) are not very explicitly given. In light of the preceding we present in this paper a review of the basic features of SAW and Pseudo-SAW'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 alpha lambda, upsilon(p), and K2 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.