Abstract:

The acoustic emissions from single cavitation bubbles have been measured with a state-of-the-art needle hydrophone. The measurements correspond to a stable cavitation bubble driven below and above the sonoluminescence threshold. Previous measurements above this threshold indicated that the lower-bound peak pressure at a distance of 1 mm from the bubble was nearly 2 bar [I. M. Hallaj et al., J. Acoust. Soc. Am. 100, 2717(A) (1996)]. The measured pressure amplitude below the sonoluminescence threshold is much weaker. Comparisons of the measured amplitudes with calculations are considered. In one case the acoustic emission mechanism is considered as being due to internal shock waves diverging into the fluid. In a second case the acceleration of the bubble wall is considered as the mechanism for the acoustic pulse, assuming a spatially uniform gas pressure in the bubble. Both methods are consistent with the measured values. However, neither method agrees well with the measured pulse amplitudes of the afterbounces. The addition of damping mechanisms not currently considered in the theories should provide better agreement. [Work supported by NSF. WCM's work was performed under the auspices of the U. S. Department of Energy at Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.]