Transverse bulk wave reflection at a piezoelectric crystal-viscous conductive liquid interface [RBW sensors]

The reflection of obliquely incident shear horizontal (SH) waves at the interface of a piezoelectric crystal and a viscous conductive liquid is investigated theoretically. In addition to viscous entrainment and mass loading effects, it is shown that the presence of a reflection-generated external electric field offers the possibility of acoustoelectric interaction with charged particles in the solution, which, in turn, could be exploited for liquid chemical analysis and biosensor applications. Closed-form expressions are obtained for the reflection coefficients (amplitude and energy) and phase shift upon reflection in terms of the angle of incidence, wave frequency, crystal parameters and liquid properties. It is shown that the sensitivity of such reflected-bulk-wave detectors could be tailored by properly choosing the interdigital-transducer periodicity, separation, crystal thickness, and the number of bounces