D. Felipe Gaitan

High-amplitude radial pulsations of a single gas bubble in several glycerine and water mixtures have been observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa (1.5 atm) at 21–25 kHz. Sonoluminescence (SL), a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring once every acoustic period. These emissions can be seen to originate at the geometric center of the bubble when observed through a microscope. It was observed that the light emissions occurred simultaneously with the bubble collapse. Using a laser scattering technique, experimental radius-time curves have been obtained which confirm the absence of surface waves, which are expected at pressure amplitudes above 100 kPa. [S. Horsburgh, Ph.D. dissertation, University of Mississippi (1990)]. Also from these radius-time curves, measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds were made and compared with several theories. The implications of this research on the current understanding of cavitation related phenomena such as rectified diffusion, surface wave excitation, and sonoluminescence are discussed.

The region of parameter space (acoustic pressure ${P}_{a}$, bubble radius ${R}_{0}$) in which stable single bubble sonoluminescence (SBSL) occurs in an air-water system is a small fraction of that which is accessible. This is due to the existence of an island of dissolution at high ${P}_{a}$ and small ${R}_{0}$. For dissolved gas concentrations above 50% of saturation, the region lies above the threshold for shape oscillations and is unobservable. Below 50%, an oscillating bubble is stabilized on the boundary of the island which lies below the shape threshold. SBSL is shown to exist exclusively along this boundary.

Sonoluminescence (SL) is generated from single, stably oscillating bubbles in a stationary, time-periodic acoustic field. By measuring the time dealy between flashes, the dynamics of the phenomenon has been investigated. While other researchers have concentrated on the remarkable periodic stability of the system, present results indicate that, for small variations in the governing parameters, period doubling, chaos, and quasiperiodicity can occur. The implications of the complex temporal behavior for the problem of determining the mechanism(s) for production of SL are discussed.

Single bubble sonoluminescence in an air-water system has been shown to occur along a unique surface in the acoustic pressure-ambient radius-gas concentration parameter space where the bubble is stable both in shape and in (average) size. In this paper, we show how the bubble deviates from the expected path (traced by the shape-instability threshold as a function of pressure) in order to reach the observed stability. We also present measurements of the expansion ratio (R(max)/R(0)) for bubbles near the threshold for light emission. The results suggest that maximal bubble radial response is an insufficient criterion for the onset of light emission, and we present data for the dependence of the emitted light on several parameters.

Finite amplitude standing waves have been studied in closed tubes filled with air and driven by a piston at frequencies near 200 Hz. The tubes were driven at resonance generating standing waves with amplitudes of up to 160 dB re: 20 μPa. The main objective was to measure the dissipation of energy by the fundamental frequency and the higher harmonics, as well as by other nonacoustic mechanisms. A formulation developed by Coppens and Sanders [J. Acoust. Soc. Am. 58, 1133–1140 (1975)] using a single nonlinear equation to describe standing waves in cavities of arbitrary resonance frequencies and quality factors was used successfully to predict the higher harmonics. In addition, the effect of detuning the tubes on the energy dissipation was measured in tubes with variable cross sections. It was found that the detuned tubes effectively suppress the energy transfer into (and energy dissipation by) the higher harmonics. It was also found that expanding rather than contracting the cross section of the tubes minimized the dissipation of energy through nonacoustic mechanisms.