Propulsion of water-floating objects by acoustically oscillating microbubbles

In this paper, novel propulsion of micro/millimeter-sized water-floating objects has been experimentally demonstrated. When an acoustic wave propagates onto air bubbles in a liquid medium, the bubbles oscillate and generate cavitational microstreaming flows; this can be used to propel small water-floating objects. This propulsion concept is simple, but the propulsion can provide sufficient force to propel the water-floating objects without electrical connecting wires and mechanical moving parts. In this study, we prepared open-box-type micro/millimeter-sized objects using a thin Al film. We then experimentally realized linear and rotational motions and two-dimensional maneuvers on the surface of water. The effects of the frequency of the acoustic wave and the applied voltage on the motions are quantified with the bubble oscillation amplitude using high speed images. Such water-floating objects propelled by oscillating microbubbles can be integrated with cameras and sensors and used in environment monitoring systems or surveillance security systems.