Acoustic Love plate sensors: comparison with other acoustic devices utilizing surface SH waves

Abstract

Acoustic sensors based on shear-horizontal (SH) waves have become very popular in recent years due to their ability to operate in liquid media. SH waves can propagate in the presence of aqueous solutions with minimum losses, since they do not possess a vertically polarized displacement component. Three acoustic geometries based on pure SH waves have appeared in the literature: the bulk acoustic wave (BAW) device, the acoustic plate mode @PM) device and the Love waveguide device [l] (Fig. 1). The BAW device utilizes a crystal resonator to generate shear acoustic waves, confined between the vibrating surfaces in the bulk of the crystal. APMs and Love waves are surface-generated bulk acoustic waves, since they utilize a surface acoustic wave (SAW) device to excite mainly SH bulk waves. APMs exist in thin piezoelectric plates and energy is confined mainly in the bulk of the plate as the wave propagates through multiple reflections, while generating a displacement at the upper and lower surface. The Love plate sensor is a waveguide structure where the SH wave is confined within an elastic layer deposited on a SAW substrate that supports SH waves. Due to the excitation and propagation differences of the above SH waves, the sensitivity of each device to mass deposition is expected to vary considerably, making some geometries more attractive than others for sensing applications. In this paper the performance of the three SH wave devices is evaluated in terms of the mass-tofrequency sensitivity of each sensor. Calculations are