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- Bulk acoustic wave (BAW): wave travels through the piezoelectric substrate
- Thickness shear mode resonator (TSM)
- Shear-horizontal acoustic plate mode sensor (SH-APM)
- Surface acoustic wave (SAW): wave travels on the surface of the substrate
- Rayleigh surface waves sensor (generally known as a SAW sensor)
- Shear-horizontal surface acoustic wave sensor (SH-SAW), also known as the surface transverse wave sensor (STW)
SAW devices are particular among this group since surface acoustic waves include a vertical shear component, which greatly affects the velocity and amplitude of the wave along the delay line. This results in higher sensitivity among SAW devices than shear-horizontal wave sensors.
Propagation of a Rayleigh SAW with shear vertical component vs a Love SAW with shear horizontal component. Consider state of environment above the waves, e.g. if medium were air or water and their relative damping effects on the waves. Source: http://www.tjhsst.edu/~jlafever/wanimate/Wave_Properties2.html
However, this vertical shear component also undergoes severe damping when placed in a liquid medium, rendering SAW devices best suited for only gaseous and vacuum environments. TSM, SH-APM, and SH-SAW devices are better suited for operation in liquid environments since their shear horizontal waves do not lose much energy into liquids.
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