Measurements of Normal Incidence Reflection Loss as a Function of Temperature at the Water-Castor Oil Interface †

Reflection loss at the water-castor oil interface as a function of temperature was measured in a direction normal to the interface using a 200-kHz acoustic signal. The acoustic impedance of water increases with temperature, whereas that of castor oil decreases. The measured reflection losses varied from 30 to 65 dB, and a sharp rising peak in reflection loss was observed at the temperature at which the acoustic impedance of water became equal to that of castor oil. This temperature is called the temperature of intromission in this paper. These measurements were compared with the model predictions based on a Rayleigh-reflection model using the measured sound speeds of both fluids. The sound speeds in water and castor oil as functions of temperature are the input parameters of the Rayleigh-reflection model, and were measured directly using an arrival time difference method in the temperature range of 5 to 30 °C. The comparison results imply that temperature is an important factor affecting the reflection at the interface separating the two fluids.