ABSTRACT Attenuation αn versus viscosity η 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/λ = 0.6 - 2.5. Two modes with an optimal combination of sensitivity (0.1 dB/mm·cP), insertion loss (<35 dB), and stop-band rejection (>15 dB) are found in liquid-loaded 128° Y,X+90°-LiNbO3 with h/λ = 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 vn about 15,000 m/s.
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