Modelling of the mass sensitivity of the Love wave device in the presence of a viscous liquid

This paper describes a new theoretical model for the analysis of the mass sensitivity of the Love wave device. We use this model along with calculations from perturbation theory to calculate sensitivity. The model is based on Love wave propagation in an isotropic, non-piezoelectric quartz substrate over-layered by a silica waveguiding layer and immersed in a viscous liquid. The analysis considers power flow in the three-layered system, comprising the quartz substrate, the silica over-layer and the viscous liquid. The model fully accounts for the first time for the power that hows through the liquid phase and assesses its effect on mass sensitivity. Mass sensitivity values were obtained by determining the displacement field throughout the viscous liquid and the Love waveguide device. The resulting velocity field was used to generate a number of trial functions that had solutions assuming stress and strain continuity at the boundaries, and the complex dispersion relation was evaluated numerically. The resulting wavevector k and propagation constant beta values were used to calculate the power in both the Love wave device and the liquid layer and the velocity amplitude at the surface. The model predicts that the mass sensitivity of the Love wave device will increase in the presence of a viscous solution due to power flow into the liquid.