Oil viscosity measurement by ultrasonic reflectance

Pulses of shear‐mode ultrasound (center frequency 10 MHz) are reflected from the surface of a series of vegetable and synthetic high‐viscosity calibration oils at a range of temperatures (5–50°C). For all samples and temperatures there is a single negative correlation between the magnitude of the echo from the interface between the delay‐line and the sample and the viscosity of the sample. Similar experiments with longitudinal ultrasonic waves show the amount of sound reflected decreased with increasing viscosity, but there is no single correlation for all samples.