Wave-propelled capillary spinners*

When a millimetric body is pinned at the interface of a vibrating liquid bath, the relative motion between the object and interface generates outwardly propagating capillary waves. It has recently been demonstrated that objects with a fore-aft mass asymmetry generate an asymmetric wavefield and consequently self-propel in unidirectional motion.  In this work, we demonstrate that chiral objects resting at a vibrating fluid interface can steadily spin, with their angular speed and direction of rotation controlled by the object size and driving parameters.  Scaling laws and a simplified model of the wavefield reveal the underlying physical mechanism of rotation while collapsing experimental data across parameters.  Guided by this discovery, we further demonstrate that bodies with multiple asymmetries can be remotely steered along 2D trajectories via modulation of the driving frequency.  This highly accessible and tunable macroscopic system may further serve as a novel platform for explorations of chiral active and driven matter.