Mass sensitivities of shear horizontal waves in three-layer plate sensors

Explicit velocity and mass sensitivity formulas for shear-horizontal (SH) plate wave sensors loaded symmetrically on both sides of a plate are presented. The sensor geometry is a composite plate which consists of a central isotropic plate sandwiched symmetrically between two identical layers of isotropic solids. It is demonstrated that if the side layers are considered as the mass loading, for the lowest SH mode (SSo) the sensitivity decreases by a factor of (1-(/spl mu//sub 2///spl rho//sub 2/)/(/spl mu//sub 1///spl rho//sub 1/)) due to the elasticity and by a factor of (1+/spl rho//sub 2/h//spl rho//sub 1/d)/sup -1/ due to the inertia of the mass loading layers, where /spl mu//sub 1/,/spl mu//sub 2/; /spl rho//sub 1/, /spl rho//sub 2/ and 2d, h are the shear moduli, densities and thickness of the central plate and of the side layers, respectively. For higher order modes, the behavior of sensors which are operated near cutoff frequency is analyzed. The mass loading decreases the cutoff frequencies of the higher order modes and near the cutoff frequencies the mass sensitivities are very high but decrease dramatically as the mass loading increases. Specific examples are given for the case of a fused silica plate sandwiched between two thin lucite layers.< >