Contents I. Introduction
Acoustic-wave devices have been applied as chemical and physical sensors for gas and liquid phases. The acoustic wave sensors are classified on the bases of their vibration and wave modes [1], [2]. All acoustic wave devices can be applied as gas sensors, whereas acoustic wave devices with a shear horizontal mode (SH mode) or 0th antisymmetric Lamb wave, namely, a flexural plate wave (FPW), are applied as liquid-phase sensors. For liquid-phase sensor applications using acoustic wave sensors, the detection mechanisms are based on mechanical and electrical perturbations. Mass loaded onto the acoustic wave sensors, and density and viscosity products of the adjacent liquid are detected by the mechanical perturbation (or mechanical interaction), whereas the conductivity and the dielectric constant of the adjacent liquid are detected by the electrical perturbation (or an acoustoelectrical interaction).
