Scattering matrix approach to SHAPM delay line with long interdigital transducers on BT-cut quartz

Transfer function of a shear horizontal acoustic plate mode (SHAPM) delay line with long interdigital transducers (IDTs) was derived using the scattering matrix method. Analytical expressions for the admittance, scattering coefficients, and reflection coefficient of the periodic electrodes of the IDT, derived previously for SAWs, were used for numerical calculations. By matching the measured and calculated amplitude responses, the velocity, electromechanical coupling coefficient, and reflection coefficient of an aluminum electrode on BT-cut quartz were determined. It was shown that for a sufficiently thick aluminum layer, a reasonable insertion loss could be achieved in spite of a very small electromechanical coupling coefficient.