Attenuation of acoustic normal modes in piezoelectric plates loaded by viscous liquids

Attenuation alpha_n versus viscosity eta of adjacent liquid is measured for each normal mode n generated in 30 different plates of commercially available, piezoelectric crystals with thickness-to-wavelength ratio in the range h/lambda = 0.6-2.5. Two modes with an optimal combination of sensitivity (0.1 dB/mmmiddotcP), insertion loss (<35 dB), and stop-band rejection (>15 dB) are found in liquid-loaded 128degY, X + 90deg-LiNbO₃ with h/lambda = 1.67. Both modes are suited for viscosity measurements and other sensing tasks in viscous liquids. They have predominantly longitudinal displacement and large propagation velocity v_n about 15,000 m/s