気泡核の成長に及ぼす圧力波形の影響

抄録

The present study deals with the growth of bubble nuclei in a pressure field formed by high-intensity focused ultrasound using the equation of motion for a spherical bubble. In the analysis, two kinds of waveforms are used: one is a pressure waveform measured in an experiment for cavitation inception pressure by the backscattering of focused ultrasound from the interface of a laser-induced bubble, and the other is a sinusoidal wave. The analysis with the former waveform shows that once bubble nuclei of a few nanometers in radius grow explosively lager than about 40 microns by a negative pressure of the pressure wave, they grow gradually without showing oscillatory motions as the wave is continuously applied to the nuclei. On the other hand, when a sinusoidal wave is applied to bubble nuclei, they show periodic oscillations taking the period-doubling bifurcation with increase in the initial nuclei radius. These differences in bubble growth between them are due to the differences of pressure waveforms: the gradual increase in radius for the former waveform is caused by its nonlinear waveform in which the negative pressure amplitude is larger than the positive one.