Absolute measurement of acoustic particle velocity

Abstract

A method for the absolute measurement of acoustic particle velocity is described. The technique uses the Doppler shift in frequency of laser light scattered from small particles suspended in the medium and vibrating with sensibly the same amplitude as the surrounding molecules. The measurement is made over a small volume at the intersection of two focused laser beams and since no transducer is required the sound field is not disturbed. Some typical data are presented illustrating its use over the range of particle velocities 0.5–50 mm sec−1 rms and it is shown that the results should be reliable at frequencies up to 50 kHz in air and higher frequencies in more dense media. Subject Classification: [43]85.22; [43]35.65.