A novel measurement method to investigate dynamics of single acoustic bubble near a rigid wall

Abstract

This paper proposes a non-invasive method to research on the dynamic behaviors of a micrometer scale air-bubble near a rigid boundary in ultrasound field. As the rapid change and tiny size of the acoustic bubble near rigid wall, it is very hard to record the dynamic behaviors of acoustic bubbles, which is one of the key fundamental problems in the application of ultrasonic cavitation. In this paper, a new method combining microscope, high speed photography and synchronous technology is proposed to noninvasively and accurately record the dynamic behaviors of a single bubble in ultrasound field. By this method, a single air bubble in tiny size can be created in water whose inner composition is almost the same as acoustic cavitation bubbles, and the relative position of the generated bubble near rigid wall can be controlled. In the experiment, the temporal evolution of the bubble is recorded by the high-speed camera at 300,000 frames per second, as well as the corresponding data, such as volume of the bubble and the velocity of the farthermost point on the bubble from the rigid boundary, is recorded. Results are demonstrated for a single bubble generated over a rigid wall under a certain standoff distance (1.85) in an ultrasound field with frequency of 20.47 kHz. The results show that the dynamics of a single bubble near the rigid wall in ultrasonic field can be divided into four parts: oscillation, movement, collapse and rebound. The maximum velocity of the bubble boundary, which is due to the formation of the high speed liquid jet, is around 11.3 m/s. Furthermore, the dynamic behaviors of a single bubble in the experiment of this paper have a good agreement with the corresponding numerical results.