Propagation of leaky surface acoustic waves under thin periodic metal electrodes

Leaky surface acoustic waves (LSAWs) propagating under thin periodic metal gratings on anisotropic and piezoelectric substrates are investigated. The inherent physical behavior of LSAWs, consisting of coupled modes including terms decaying into the substrate and a term representing a radiating bulk wave, under thin metal strips is explained. A field theoretical analysis that fits both the mechanical and electrical periodic boundary conditions is developed. Four types of electrically connected metal strips are discussed. The dispersion relation for LSAWs is computed for different normalized metal strip thicknesses. The frequency dependence of the LSAW attenuation constant is analyzed, and bulk wave scattering is studied. It is found that both the mechanical surface perturbation and the type of electrical connection between metal strips can strongly influence LSAW propagation behavior. Numerical results are given for aluminum electrodes on 36 YX LiTaO₃ substrate