Experimental consideration of droplet manipulation mechanism using surface acoustic wave

A longitudinal wave is radiated from a surface acoustic wave (SAW) when a liquid is loaded onto a SAW-propagating surface. Radiated longitudinal wave causes nonlinear phenomena, which is called SAW streaming. The SAW streaming phenomena depend on the applied electrical power. A droplet on the SAW-propagating surface vibrates, moves in the SAW-propagating direction, and ejects small droplets with increasing the applied power. The moving of a droplet is also named droplet manipulation. However, the mechanism of droplet manipulation using SAWs has not been clarified. It is important to understand the manipulation mechanism of droplets using a SAW to enable actual applications. To understand droplet manipulation, measurements of the radiation force in the droplet are necessary. In this study, we first observed streaming in a droplet during manipulation and found that the particles in the droplet accumulated at the front of the droplet. Then, we proposed the use of a flat spring with a strain gage to measure the radiation force in a water vessel. Fundamental characteristics of the force radiated from the SAW device were obtained experimentally. (C) 2015 The Japan Society of Applied Physics