High-speed photography and acoustic emission synchronized observation of ultrasound induced acoustic cloud cavitation

Though the violent collapse of the acoustic cavitation during ultrasound therapy may cause tissue traumas, it has a potential for therapeutic benefits if it is carefully controlled. The investigation of a two-frequency focused ultrasound method for the acoustic cloud cavitation control for lithotripsy is discussed. In the forcing cycle, cavitation is controlled by generation, growth, and shape stabilization during a high-frequency (1–4 MHz) phase, and a violent forced collapse that produces very high pressure during a low-frequency phase (400–550 kHz). Ultra high-speed photography for various conditions, gas concentration in the media and the acoustic field properties, are conducted. The photography (up to 200 MHz) framing rate is synchronized with the measurement of the acoustic emission from the cavitation bubbles by a concave PVDF hydrophone with a high directivity and a broadband response up to 10 MHz. The behavior of the cloud cavitation during the two-frequency cavitation control cycle is investigated with respect to the acoustic emission of the cavitation bubbles. The shape stabilization of the cloud cavitation and the high-pressure concentration on the solid surface by the forced collapse of the bubble cloud are discussed.