Fast COM parameter extraction from theoretically derived dispersion relations for SAWs propagating in periodic metallic gratings

We present a method of theoretically calculating COM parameters for SAW substrates using a modified version of the hybrid finite element method and spectral domain analysis (FEM/SDA) introduced by K. Hashimoto et al. We review how the COM parameters for a SAW substrate can be calculated from the open and short circuit stop band edge frequencies of a periodic grating. We then demonstrate how the FEM/SDA formalism can be modified to calculate SAW dispersion at the stop band edges, allowing for quick calculation of the COM parameters. To demonstrate the method we calculate the COM parameters for reflecting DART cells on 112° LiTaO₃ as a function of metal thickness and compare with available experimental data.