A simple determination of first order velocity shifts and reflection coefficients for periodic IDTs

The design and fabrication of interdigital transducers with metallic fingers on piezoelectric substrates requires accurate values of velocity shifts and reflection coefficients caused by the mechanical and electrical loading of the fingers. We describe a simple and reliable method of determining electric reflection and velocity shifts as well as mechanical velocity shifts to first order in h/λ for transducers with an anisotropic substrates. We calculate SAW velocities and wavefunctions (displacements and potential) for various substrates with one thin metallic layer. A simple multiplication of the resulting material constants with the appropriate geometrical factor yields the desired SAW parameters. An analogous procedure for the mechanical reflection coefficient is being sought. We present results for many standard SAW substrates and crystal orientations with a metallic overlay, and compare with other first order treatments and some experimental results presently available