VISCOSITY SENSOR UTILIZING A PIEZOELECTRIC THICKNESS-SHEAR SANDWICH RESONATOR

This paper describes a novel quartz crystal sensor for measurement of the density-viscosity product of Newtonian liquids, The sensor element consists of two piano-convex AT-cut quartz crystals vibrating in a th ickness-shear mode with the liquid sample in between. This special set -up allows suppression of disturbing resonances in the liquid layer. S uch resonances are generated in the common single-plate arrangements d ue to compressional waves caused by spurious out-of-plane displacement s of the shear vibrating finite plate. The primary measurands of the s ensor are the fundamental resonance frequency and the associated reson ance Q-value, which are influenced by the viscously entrained liquid c ontacting the quartz surface. The sensor allows the measurement of sam ples with viscosities from almost zero (air!) up to 200 cP with a samp le volume of 130 mu l.