Acoustic shock-wave induced cavitation: A comparison of theory and experiment

Abstract

A calibrated membrane hydrophone has been used to make measurements of pressure in a cavitating field generated in water by a single 30-μs duration ultrasound pulse with a 0.2-MHz center frequency and a peak negative pressure (p−) variable from 0.5 to 5 MPa as employed in clinical lithotripsy. The acoustic emission from cavitation in the vicinity of the hydrophone is identified as the high-frequency (>1 MHz) component of the waveform. This ‘‘cavitation component’’ is compared with theoretical predictions of the pressure radiated by a bubble made using the Gilmore model [C. C. Church, J. Acoust. Soc. Am. 86, 215–227 (1989)]. The model was run for initial bubble radii of 1–100 μm using the measured pressure waveform to drive the radial dynamics of the bubble. The theory predicts a transition from completely driven dynamics at p− below 3 MPa to largely undriven dynamics above 3 MPa. This transition, which is substantially independent of bubble size, is experimentally observed and occurs at a measured p− of 3±0.4 MPa. The time between the pressure pulse and the first undriven inertial collapse is predicted to increase approximately twice as rapidly with increasing amplitude as is measured. A mechanism resulting in shorter than predicted collapse times is discussed. [Work supported by the Medical Research Council, UK.]