Micromixing using swirling induced by three-dimensional dual surface acoustic waves (3D-dSAW)

Efficient mixing in a microfluidic system is difficult to achieve, since it is dependent solely on molecular diffusion due to low Reynolds number. In this paper, we newly propose a novel mixing technique using three-dimensional dual surface acoustic waves (3D-dSAWs) generated from two interdigitated transducers of top and bottom piezoelectric substrates. By using the 3D-dSAW, internal swirling in a single direction is induced, which can facilitate more efficient mixing of a fluorescent particle suspension and deionized water. Therefore, by using the 3D-dSAW mixer, higher efficiency mixing performance can be achieved compared to the single SAW mixer at the same flow rate and applied voltage. With the applied voltage of 14 V, 3D-dSAW mixing device could achieve 100% mixing efficiency at the flow rate of 50 μl/min, while the mixing efficiency of the traditional single SAW mixer was approximately 38%. Moreover, the throughput of 3D-dSAW mixing device could be enhanced up to 120 μl/min with the applied voltage of 18 V, at which the measured temperature was lower than 40 °C and the efficiency could reach approximately ∼95.6%.