Measurements of the acoustic emission from glowing bubbles

Abstract

A single bubble trapped in an acoustic standing wave can be made to undergo highly nonlinear volume mode pulsations resulting in inertial cavitation—the expansive growth and violent collapse of bubbles. Under certain conditions the collapse results in light emission called sonoluminescence (SL). Though much has been studied regarding properties of the emitted light, little work has been done on the acoustic emission from such a bubble. Previous measurements [Cordry et al., J. Acoust. Soc. Am. 98, 2921(A) (1995)] using a needle hydrophone show only a general low-level acoustic signature. In the present study, a broadband, nonfocused transducer is used to record the acoustic emission from single bubbles at various acoustic drive amplitudes in the SL and non-SL producing regions. The typical acoustic signature includes a large amplitude pulse corresponding to the initial collapse followed by smaller amplitude pulses corresponding to the rebounds. The rebounding bubble essentially oscillates at its resonance frequency so that the simple measurement of the time interval between rebounds makes it relatively easy to measure one of the fundamental unknowns of a sonoluminescence bubble—its equilibrium radius. [Work supported by NSF and ONR.]