Acoustic Surface Wave Excitation in Layered Structures

Abstract

An analytical and computational procedure for the study of acoustic surface wave excitation in anisotropic layered structures has been developed. The analysis is based upon solution of the coupled wave equations in both layer and substrate and is directed toward materials which can be oriented such that the particle displacements are in the sagittal plane. The admittance characteristics (complex) of interdigital transducers, as used to excite surface waves in such structures, are calculated and found to be in excellent agreement with experimental results. ducers in such structures (g) , ( 181 . However, a basic theoret- ical study of surface wave excitation in layered structures has not yet been published.' This paper attempts to fill this ap- parent gap and to show that the admittance characteristics of the ID transducers used to launch surface waves in layered structures can be accurately predicted from the material con- stants which are determined from bulk wave measurements. The intent of this study is to concentrate on low coupling materials, such as CdS and ZnO, in conjunction with nonpie- zoelectric materials for the layer and substrate, respectively. Thus the analysis is based on a low-coupling approach, and certain crystalline symmetry restrictions are imposed to reduce the mathematical complexity. Nevertheless, the analysis pre- sents a method which could be used for a more general situa- tion if so desired. 11. THEORY