Acoustic wave viscosity sensor

An acoustic wave device utilizing plate modes having components of displacement parallel to a crystal surface has been demonstrated to be an effective sensor of liquid shear viscosity (η) over a wide viscosity range. When a liquid is present on the sensor surface, the propagation loss of the acoustic wave depends upon η in a calculable fashion. Because the device functions at 159 MHz, liquid relaxation effects occur with high viscosity liquids, causing the propagation loss to saturate. Viscosity is sampled in the 50-nm-thick liquid layer which couples to the acoustic wave, so that only a single drop of liquid is required for measurement.