Bidirectional wave-propelled capillary spinners

Abstract

When a solid body floats at the interface of a vibrating liquid bath, the motion of the object generates outwardly propagating surface waves. We here demonstrate that chiral objects on a vibrating fluid interface are set into steady rotation, with the angular speed and direction of rotation controlled by the interplay between object geometry and driving parameters. Scaling laws and a simplified model of the wavefield reveal the underlying physical mechanism of rotation, while collapsing measurements of the angular velocity across parameters. Leveraging the control over the chiral object’s direction of rotation, we demonstrate that a body with an asymmetric mass distribution and chirality can be remotely steered along two-dimensional trajectories via modulation of the driving frequency. This accessible and tunable macroscopic system serves as a potential platform for explorations of chiral active and driven matter, and demonstrates a mechanism by which wave-mediated forces can be manipulated for directed propulsion.

The design of novel and tunable experimental systems for synthetic active materials is of immense interest. The authors present one such design that uses the physics of self-generated waves to realize a tunable active spinner system.