Acoustic microcavitation: its active and passive acoustic detection

Area of Science:

• Acoustics
• Fluid Dynamics
• Materials Science

Background:

• Acoustic microcavitation is a phenomenon involving the formation and collapse of bubbles in a liquid under acoustic waves.
• Understanding the initiation and behavior of acoustic microcavitation is crucial for various applications, including sonochemistry and medical ultrasound.

Purpose of the Study:

• To investigate the conditions necessary for acoustic microcavitation in water at 0.75 MHz.
• To evaluate the role of microparticles and acoustic fields in initiating and influencing cavitation.

Main Methods:

• Utilized two acoustic detectors: a passive 1-MHz receiver and an active 30-MHz focused transducer in pulse-echo mode.
• Generated cavitation using a focused PZT-8 crystal transducer driven in pulse mode, confocally aligned with the active detector.
• Tested cavitation initiation in clean water and in water with polystyrene microparticles.

Main Results:

• No cavitation was observed in clean water, even at peak negative pressures of 22 bar.
• Cavitation was successfully induced when polystyrene microparticles were introduced into the water.
• The active detector's acoustic field was found to influence the cavitation process.

Conclusions:

• Polystyrene microparticles act as nucleation sites, enabling acoustic microcavitation in water.
• The presence of microparticles is essential for cavitation initiation under the tested conditions.
• Acoustic fields, particularly from the active detector, can modify cavitation thresholds and behavior.