A unified analysis of SAW reflection and mode conversion in layered systems using Green´s functions

First-order expressions are derived using Green´s functions to calculate scattered waves for the case when a surface acoustic wave (SAW) interacts with arbitrarily shaped perturbations in a layered system of any material symmetries on a piezoelectric substrate. SAW reflection coefficients of rectangular strips are calculated using special solutions of the scattering problem. In comparison with data from the literature based on the perturbation theory, some deviations exist for the systems Al on ST-quartz and Al on Y-LiTaO₃. From the phase of the reflection coefficient for the electric potential, NSPUDT behavior can be derived. The energy loss due to mode conversion is calculated by the same description of the scattering process used for the reflection problem. Based on this theory, the demands on the shape of ZnO layer edges are investigated in order to guarantee sufficient small insertion losses, if SAWs are crossing the edges. In a special case, the insertion loss is reduced from 8 dB to less than 1 dB, replacing a sharp edge by a slanted edge with a width of 2λ. This theoretical result has been confirmed qualitatively by experiments