Self-calibrating measurements of the density and velocity of sound from the reflection of ultrasound at two solid-liquid interfaces

This report describes a method to measure the density of a liquid and velocity of sound by observing two reflections of ultrasound from a solid-liquid interface: one for perpendicular incidence of a longitudinal wave and the second for incidence of a shear wave at an angle of 45 deg. In previous research [J. Fluids Eng. 126, 189 (2004)], transducers were mounted on the outside of a stainless steel pipeline, 6 mm thick. Multiple reflections within the wall yielded the acoustic impedance. This method is self-calibrating because each echo is affected in the same way by any change in transducer voltage. The velocity of sound was obtained from the time-of-flight (TOF) across the pipeline. The current research replaces the TOF measurement by using a triangular stainless steel wedge (45, 90, 45 deg). A 1-MHz shear wave transducer is mounted on a short side of the wedge, with the longer side immersed in the liquid. Multiple reflections from the opposide of the wedge are obtained. The two reflection coefficient can be used to solve for the density and velocity of sound. Greater precision can be obtained by using fused quartz instead of stainless steel.