Surface shear horizontal wave propagation at the boundary of a piezoelectric substrate with a viscous fluid is theoretically analyzed. The analytical solution clearly shows the dependence of the velocity change, the wave propagation loss, and the wave amplitude profile (thus the energy confinement near the surface), in terms of the liquid viscosity and density, the layer thickness, and the wave frequency. It is shown that the viscous fluid loading produces some guidance near the surface but also some damping of the wave. The propagation loss is due only to viscous coupling and not to a mode conversion and viscous coupling as is the case with Rayleigh surface acoustic waves (SAWs). Closed-form expressions are derived for the attenuation coefficient and the fractional velocity change (thus the frequency change) in terms of the piezoelectric crystal and viscous liquid parameters. The theory, applicable to both a Bleustein–Gulyaev (BG) wave and a surface skimming bulk wave (SSBW), indicates that surface shear waves could be used in the implementation of sensitive acoustic wave liquid-phase-based detectors, viscosity sensors, and/or biosensors. These sensors will not experience the high propagation loss associated with Rayleigh SAWs.
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Josse et al. (1988) studied this question.