Ultrasonic shear viscometer for liquid droplets and its applications

An ultrasonic viscometer, capable of measuring small liquid volumes such as drops, was developed by utilizing the short effective path length of shear waves in liquids. The viscometer consists of an unplated quartz crystal excited to shear vibrations with the liquid drop to be tested placed on its surface. The vibrations of the natural modes of the quartz plate were represented by a mass-point compliant equation, and the viscosity equation was derived from the knowledge of the energy loss. Suitable electronics was built to drive the crystal and to record the decaying vibrations. A crystal orientation analysis insured a dominant thickness-shear mode not coupled to flexure and face-shear motion. The amount of sound radiated was determined from the change in the quality factor when the crystal was vibrating alone in air and under vacuum.