Acoustic Surface Waves in Split Strip Periodic Metal Gratings on a Piezoelectric Surface

Abstract

Ahrruct-The propagation of acoustic surface waves in configurations of split periodic metal gratings on the surfaces of piezoelectric materials is analyzed. The analysis is based on analytic solutions for the electric field distribution. Particular attention is paid to the details of the dis- persion relations near the resonances, where the stopband frequencies for various combinations of externally interconnected or disconnected strips are calculated as functions of strip geometry for stopbands of various order. several wavelengths is frequently used either to create multiple passbands or to minimize phase errors and bulk wave conver- sion which may be a problem, especially at high frequencies. So far the models used to analyze these transducers have been equivalent circuits with adjustable empirical parameters for the effective coupling coefficient, as well as for the electrostatic coupling between distantly spaced neighboring taps. The subject of the present paper is a field analysis of split strip periodic gratings with two metal strips per period. The analysis leads to analytic expressions for the dispersion rela- tions. Particular emphasis is paid to the behavior around the stopbands where the period of the structure is close to an in- tegral number of half wavelengths. From the dispersion rela- tion one can easily derive the decay of waves in the stopbands, a figure which is of central importance in the design of surface wave resonators. Numerical results are given for the promi- nent cases with one half wavelength between neighboring strips to show the effect of thinning as well as for a regular array with four strips per wavelength corresponding to the split finger transducer. models can be derived from the dispersion relations and the field solutions without the necessity of empirically adjustable parameters. In an accompanying paper, it is shown that equivalent circuit