Fine Droplets Generation Induced by Interactions between Focused Ultrasound and a Liquid Surface

Abstract

When the focused ultrasound of sufficient acoustic intensity in liquid interacts an air-liquid interface, atomization of the liquid occurs. This atomization process is well known that droplets are generated from the apexes of standing capillary waves with a wavelength that can be related to ultrasonic frequencies. In addition, there is a hypothesis that cavitation bubble oscillations can play a significant role in the pinch-off of droplets from capillary wave. The aim of this study is to clarify the influence of bubbles on the atomization of liquid. In this paper, we used the focused ultrasound with a frequency of 1 MHz; then, we observed the atomization process by using a high-speed photography. Also, we added the microbubbles to enhance the atomization of liquid. We found that threshold acoustic intensity of generating fine droplets becomes smaller. This result indicates that bubbles contribute significantly to the atomization of the liquid.