Leaky SAW in an isotropic substrate with thick electrodes

It has previously been found that "leaky longitudinal" (LL) wave with low attenuation exists in LiNbO₃ and LiTaO₃ substrates with relatively thick electrodes. Using numeric FEM simulations, we show that similar wave can exist in an isotropic material covered by a system of rather thick electrodes. In this paper, a simple model is proposed, which shows how the radiation of the slow shear component, inevitably accompanying a longitudinal wave skimming along the surface of an isotropic substrate, can be suppressed due to the presence of the electrodes. The main feature of the model is that the electrodes are treated as resonators, as far as their reaction to horizontal (σ_yz) stresses is concerned. The thickness of the resonators must be close to the λ_Al/4 condition (where λ_Al is the shear wavelength in Al-the material of the electrodes), which explains why a "magic" thickness of h/λ about 9% is always necessary (here λ is the LL wavelength in the substrate, close to the longitudinal bulk wavelength). The role of the fingers is only to create the condition for the suppression of the slow shear bulk wave radiation, while the main energy of the wave is concentrated inside the substrate and propagates in the form of a longitudinal surface wave