The detection of microbubble radius versus time and some comparisons with theoretical results

Abstract

Based on the fact that the scattering strength of both a gas bubble and a void is proportional to the ka, where k is the acoustical wavenumber and a is the radius of the scatterer, a driving transducer with 755-kHz frequency was used to produce cavitation in water, and a transducer with a 30-MHz center frequency worked as an active detector (pulse-echo). The active detector sends a series of the tone bursts and receives the signal backscattrered by transient cavitation produced by the 755-kHz transducer. Bubble radius versus time from which the duration of the bubble's growing can be extracted can be estimated by demodulating the backscattered signal. Using the model of the gas-filled cavity, the collapse time τ for the model will be [E. A. Neppiras, Phys. Rep. 61(3), 159—251 (1980)] τ = 0.915Rmax (ρ/Pm) (1 + Q/Pm), where Pm and ρ are the pressure and density in the liquid and Q is the pressure in the bubble at the maximum bubble size. The maximum bubble radius Rmax was estimated using the measured value of τ and was compared with earlier numerical results [H. G. Flynn and C. C. Church, J. Acoust. Soc. Am. 84, 985–998 (1988)] for the same peak acoustic pressure as in the experiment. [Work supported by NIH through Grant No. 5-RO1-CA39374.]