Droplet displacements and oscillations induced by ultrasonic surface acoustic waves: A quantitative study

We present an experimental study of a droplet interacting with an ultrasonic surface acoustic wave. Depending on the amplitude of the wave, the drop can either experience an internal flow with its contact line pinned, or (at higher amplitude) move along the direction of the wave also with internal flow. Both situations come with oscillations of the drop free surface. The physical origins of the internal mixing flow as well as the drop displacement and surface waves are still not well understood. In order to give insights of the underlying physics involved in these phenomena, we carried out an experimental and numerical study. The results suggest that the surface deformation of the drop can be related to a combination between acoustic streaming effect and radiation pressure inside the drop.