Simulation for Forces on Levitated Droplet in Ultrasonic Standing Wave

Under the micro-gravity environment, holding technology of liquid is important to manufacture new materials and noncontact material property measurement methods. There are previous studies about droplet levitation by the ultrasonic standing wave for the holding technology. However it is still unknown experimentally and analytically how the ultrasonic standing wave acts on the levitated droplet. In the present study, the technology to handle the material in space by the ultrasonic wave is developed and the simulation technique to evaluate the ultrasonic standing wave field and the movement of the droplet in the ultrasonic standing wave. At first, the characteristics of droplets holding by the ultrasonic standing wave under normal gravity environment and micro-gravity environment are investigated experimentally. Secondly, pressure field by ultrasonic standing wave is measured with probe microphone. The measurement shows that 2-dimensional pressure distribution is arisen between the horn and the reflector, and positions where droplets are held are near nodes of the ultrasonic standing wave. Thirdly, numerical simulation considered for compressibility of gas is conducted to clarity the characteristics of ultrasonic standing wave. The 2-dimensinal pressure distribution obtained by this simulation agrees with the measurement result by probe microphone quantitatively. Finally, droplet movement is solved using results of pressure field simulation. It is shown that 2-dimensinal pressure distribution causes horizontal holding force.