Characterization of SH acoustic plate mode liquid sensors

Abstract

Two-port acoustic wave sensors have been fabricated, which utilize shear horizontal (SH) acoustic plate modes (APMs) to probe a solid/liquid interface. These modes, excited and detected by interdigital transducers on thinned quartz plates, propagate efficiently with liquid contacting the device and allow sensing to be performed on the side of the device opposite the transducers. A number of sensing mechanisms have been discovered, including mass loading, viscous entrainment of the contacting liquid, and acoustoelectric coupling between evanescent plate mode electric fields and ions and dipoles in solution. The mass sensitivity of the APM device enables it to function as a microbalance in a number of sensing applications. A chemical sensor capable of detecting low concentrations of Cu²⁺ ions in solution has been constructed by chemically modifying the device surface with ethylenediamine ligands. The treated devices bind Cu²⁺ ions in a manner that can be reversed by the addition of acid to the solution.