Transient surface velocity measurements in a liquid by an activeultrasonic probe

摘要

A high sensitive ultrasonic method for measuring the surfacenvelocity in a liquid is described. This method is based on the detectionnof the phase of a high frequency continuous ultrasonic wave (probe beam)nreflected from the moving surface. The analysis shows that the mainnphenomenon is the interaction, through the acoustic nonlinearitynparameter B/A of the fluid, between the reflected carrier wave and thenlow frequency pressure wave transmitted by the moving surface in thenliquid. This interaction produces a phase-shift of the carriernproportional to the surface velocity and to the time delay undergone bynthe probe beam. Results of experiments carried out in water with an30-MHz focused transducer probe are in good agreement with the analysis.nSurface velocity smaller than 0.04 mm/s (i.e., mechanical displacementsndown to 3 pin) can be detected in a 5 MHz bandwidth. Lateral resolutionnof 0.5 mm has been achieved. Compared to optical techniques, this methodnhas the advantages of compactness and of a low sensitivity to surfacenroughness