PERTURBATION OF THE ELECTRIFIED INTERFACE AND THE RESPONSE OF THE THICKNESS-SHEAR MODE ACOUSTIC-WAVE SENSOR UNDER CONDUCTIVE LIQUID LOADING

The behavior of the thickness-shear mode (TSM) acoustic wave sensor under conductive liquid loading has been examined by acoustic network analysis. The response of the TSM sensor arises from the perturbation of the electrified interface, including the acoustoelectric coupling of the surface potential with ionic species and the formation of the electrical double layer. In dilute solutions, dissipation of acoustic energy resulting from acoustoelectric coupling dominates the complete energy-transfer process, which leads to a rapid decrease of the series resonant frequency and an increase in the motional resistance. In concentrated solutions, energy transfer from the quartz dielectric to the interface becomes more important due to increasing energy storage of the double layer, as shown by the continuing increase of the static capacitance and steady decrease of the parallel resonant frequency. In addition, the overall energetics of the dissipation and transfer processes at the interface are reflected in the measurement of the quality factor.