Research to Provide a Theoretical Determination of Surface Acoustic Wave Velocity and Impedance Differences between Metal Strips and Free Surface Regions of Metallic Gratings

摘要

With the advent of surface acoustic wave resonators and withdrawal weighted filters, quantitative knowledge of the velocity and acoustic impedance differences between metal strips and free surface regions in metallic gratings used for these structures has become necessary. During the course of this program mass loading, topographical effects, electrical loading, and energy storage have been considered and the surface acoustic wave velocity and impedance differences (DELTERV and DELTERZ) have been theoretically determined for shorted arrays, single electrode transducers and double electrode transducers at center frequency. Buried electrodes are also considered. It was an objective to find the electrode structure that produced the minimum impedance and velocity perturbation. It has been found that acoustic impedance mismatch and velocity shift, unlike in a transmission line, are not minimized simultaneously. Combinations of electrode metals are suggested for minimizing each of the perturbations. The results are presented in a form that is useful in the transmission line model analysis of SAW devices. (Author)