Finite-Element Analysis of Periodic Surface Acoustic Waveguides

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Abstract
A numerical approach based on the three-dimensional finite-element method is developed for the analysis of periodic surface acoustic waveguides. Only a region corresponding to one period of the waveguide is discretized using three-dimensional elements of hexahedral form with 20 nodal points, and cutoff frequencies of a stop band and standing-wave distributions at these frequencies are calculated. These data are used for determining the self- and mode-coupling coefficients of coupled-mode equations with which the reflection characteristics of finite periodic surface acoustic waveguides are easily estimated. In this method, all the effects of piezoelectric perturbation, mechanical perturbation, energy storage due to nonradiated bulk waves, and three-dimensional field distributions are automatically taken into account. Using this method, aluminum strip gratings on an Al/45° X-Z Li2B4O7 or 128° Y-X LiNbO3 substrate are analyzed, and the effects of strip width in the aperture direction on the reflection characteristics are investigated.

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