Droplet translocation by focused surface acoustic waves

This paper presents the experimental investigations of droplet movement driven by focused surface acoustic waves (SAWs) generated by a circular-arc interdigital transducer (CIDT). Surface acoustic waves propagating through a droplet in contact with the substrate exerted an acoustic streaming force on the droplet, as demonstrated by numerical modeling in this study. Different from the straight droplet movement driven by a straight interdigital transducer (SIDT), the droplets were focused to the center region of the CIDT. In addition, the droplets driven by the CIDT moved much faster than those driven by the SIDT with an identical input power because of the concentrated acoustic energy in the CIDT. Merging of two moving droplets using the CIDT was also demonstrated. The present results show that focused SAWs can be more efficient than uniform SAWs for droplet and fluid actuation in microfluidics.