Analysis of thin-film-dielectric decoupling of interdigital transducers

A perturbation analysis is presented for the reduction in the coupling coefficient ¿V/V of an interdigital transducer that is spaced away from the surface of a piezoelectric substrate by a thin isotropic nonpiezoelectric dielectric film. The analysis shows that the static capacitance and coupling ¿V/V are reduced rapidly by the addition of thin dielectric films, while the series radiation resistance is relatively insensitive to film thickness for films less than approximately 0.03 wavelengths.