Cavitation phenomena in pulse modulated ultrasound fields

Sonoluminescence (SL), subharmonic generation (SH) and ultrasound absorption in a cavitation zone generated by pulse modulated fields were studied. It has been shown that SL intensity may be increased due to pulse modulation of an ultrasound field by more than two orders of magnitude as compared to the SL intensity obtained by continuous irradiation. The achieved increase in the erosion rate is smaller with pulse modulation. The ultrasound absorption decreases with the inverse pulse duty ratio (or off/on factor), i.e. clarification effect is found to exist in pulsed fields. The thresholds of studied phenomena increase with inverse pulse duty ratio. The intensity of the subharmonic and of other low-frequency components of the cavitation noise decreases; this allows us to conclude that the decreased bubble volume concentration is mainly caused by a decrease of the large bubbles that have low energy concentration efficiency and make little contribution to the cavitation effects.