Analytical solutions for sagittal plane plate waves in composites

Propagation characteristics of sagittal plane plate waves in a composite plate loaded by a liquid of finite thickness are presented. The composite consists of a solid isotropic plate sandwiched between two acoustically thin (≪λ) isotropic solid films, where λ is the acoustic wavelength. The solutions are separately derived for the symmetric and antisymmetric modes. For each type of mode, an approximately analytical dispersion equation is given. Numerical calculations for the lowest symmetric and antisymmetric modes of such a structure are shown. The phase velocity of sagittal plane plate waves changes with the thickness of the thin solid films and that of the liquid, and significantly for the lowest symmetric mode when the liquid thickness is around 0.25 liquid wavelength. Applications pertinent to sensors such as mass sensitivity variation due to the presence of thin solid films and liquids are presented