Determination of SAW velocity shift and reflection coefficients for SPUDT structures

Design of SPUDT type SAW devices requires accurate values or velocity shifts and reflection coefficients associated with asymmetric finger overlays in each unit cell. Until now, these parameters have been deduced experimentally since accurate theoretical models are not available. Previous work has been limited to symmetric and periodic structures. We report extension of the model to analyses of EWC and DART. The first-order reflection coefficients r₁ and velocity shift s₁ are computed for several standard SAW materials and cuts. The sensitivity of r and s to variations in the finger geometry is determined for the SPUDT structure. Comparison between theoretical and experimental results for 34°-quartz and 112° LiTaO₃ are presented. The second order effects of evanescent and bulk waves of higher harmonics coupled to the fundamental components are expected to be important for thicker fingers