Quasi-static analysis of floating-electrode unidirectional SAW transducers

The quasi-static theory of SAW transducers is a simplified Green's function analysis that has previously been shown to be effective for transducers in which short-circuit reflections are negligible. Here, the theory is extended to allow for floating electrodes, which occur in floating-electrode unidirectional transducers (FEUDTs). An analysis for the coupled-mode (COM) parameters of FEUDTs is developed, giving the capacitance, transduction, and reflection parameters and the locations of the transduction and reflection centers. For a FEUDT with six electrodes per period, algebraic results are obtained in terms of Legendre function expressions, giving the COM parameters as functions of metalization ratio. These results agree with earlier derivations by other authors, but they are obtained much more simply. Numerical results are straightforward to obtain. A FEUDT with five electrodes per period is also analyzed, showing that it performs similarly to the six-electrode type.