  We present an experimental study of a droplet interacting with an ultrasonic
surface acoustic wave (SAW). 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 appear together 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 as a combination between acoustic
streaming effect and radiation pressure inside the drop.
