Shear-wave corner retroreflector device for ultrasonic measurement of viscosity

Abstract

This work shows a novel ultrasonic viscosity measurement device with increased sensitivity. The measuring principle is based on the determination of the complex reflection coefficient of shear-waves at the solid-liquid interface. But the proposed approach is the replacement of the flat surface at the measurement interface with a grooved surface, which works in a similar way to an optical retroreflector. The complete reflection of the waves involves a double reflection with oblique incidence, where both phenomena increase sensitivity, in comparison with a plane surface. It is shown that a set of orthogonal flat interfaces reflects a well-defined ultrasonic pulse. The sensitivity is enough to measure the change in the magnitude and phase of the reflection coefficient even for the small portion of the energy transmitted to water. A model for calculating the viscosity and a calibration approach for the measurement were proposed. Results with samples of corn syrup-water mixture are reported.

Keywords: Acoustic retroreflector; Reflection coefficient; Shear waves; Viscosity.