Studies of non-linear bubble oscillations in a simulated acoustic field

Abstract

Gas bubbles in liquids are capable of forced oscillations in a sound field. Photographic study of these non-linear oscillations is difficult. It is technically most feasible at low acoustic frequencies, where lower framing rates are required, and where the resonance bubble size is larger. However, the acoustic pressures required to elicit a non-linear response from the bubble might, if generated at audible frequencies, be damaging to the hearing. This paper outlines an experimental solution to the problem, whereby a volume of liquid containing bubbles is vibrated vertically. The oscillating pressure in the water mimics an acoustic field at the vibration frequency and the bubble responds to it as such. The apparatus has minimal audible emissions, yet the oscillating pressure is of such an amplitude as to generate highly non-linear oscillations in the bubble. The experiment provides a good example of forced oscillation, as well as illustrating a subtle solution to a difficult experimental problem. Radius-time data from a given bubble were obtained using high-speed and stroboscopic photography, and were compared with the numerical predictions obtained from the Rayleigh-Plesset equation.