Streaming phenomena in microdroplets induced by Rayleigh surface acoustic wave

This paper reports the numerical simulation and experimental characterization of three-dimensional acoustic streaming behavior of a liquid droplet subjected to a Rayleigh surface acoustic wave. The streaming behavior of the droplet was studied as a function of radio-frequency (RF) power, aperture of the interdigitated transducer, and size of the liquid droplet. The hydrodynamic flow field within the droplet was determined by solving the laminar incompressible Navier-Stoke's equations. The numerical and experimental results are shown to be in good agreement over the range of parameters examined. The ratios of the position of butterfly central line (axis of rotation) to radius of the droplet are demonstrated to be fairly constant for moderate droplet volumes and to vary by less than 12% at large droplet volumes. Besides that, an increase in the RF power and a decrease in the droplet size result in an increased surface acoustic wave (SAW) streaming velocity. The numerical results also suggest that a maximum streaming velocity is achieved when the SAW width is approximately half of the droplet radius. (C) 2011 American Institute of Physics.