4-LAYER THEORY FOR THE ACOUSTIC SHEAR-WAVE SENSOR IN LIQUIDS INCORPORATING INTERFACIAL SLIP AND LIQUID STRUCTURE

A theory is developed which describes the behavior of thickness shear mode acoustic wave sensors in liquids. The arguments presented allow the introduction of solid sensor, surface-adjacent liquid, transition, and bulk liquid layers. The rigorous linear theory for piezoelectricity is coupled to a treatment which describes interfacial viscosity in terms of an activation energy barrier to interfacial flow. Surface free energy reflected in contact angle values can be correlated with the interfacial slip characteristics. Calculations of series resonance frequency, impedance, and phase angle are presented for various conditions.