High frequency travelling surface acoustic waves for microparticle separation

In this study, we have demonstrated a particle separation device taking advantage of the high frequency sound waves. The sound waves, in the form of surface acoustic waves, are produced by an acoustofluidic platform built on top of a piezoelectric substrate bonded to a microfluidic channel. The particles’ mixture, pumped through the microchannel, is focused using a sheath fluid. A Travelling surface acoustic wave (TSAW), propagating normal to the flow, interacts with the particles and deflects them from their original path to induce size-based separation in a continuous flow. We initially started the experiment with 40 MHz TSAWs for deflecting 10 µm diameter polystyrene particles but failed. However, larger diameter particles (~ 30 µm) were successfully deflected from their streamlines and separated from the smaller particles (~ 10 µm) using TSAWs with 40 MHz frequency. The separation of smaller diameter particles (3, 5 and 7 µm) was also achieved using an order of magnitude higher-frequency (~ 133 MHz) TSAWs.