Propulsion and interaction of wave-propelled interfacial particles*

When an asymmetric floating body is internally or externally vibrated, the self-generated capillary wavefield can lead to steady propulsion or rotation. In this talk, I will discuss several related and recently discovered systems that leverage this propulsion mechanism. On a vibrating fluid substrate, freely floating particles are shown to self-propel along straight paths or rotate in place, depending sensitively on the particle asymmetries and driving parameters. By combining multiple asymmetries, particles can be remotely steered along curvilinear trajectories via modulation of the driving frequency alone. Such surfing particles interact at a distance through their mutual wavefield, and exhibit a rich array of collective dynamics. Particle-level actuation can also lead to propulsion as realized by the "SurferBot": an untethered centimeter-scale vibrobot that self-propels along a fluid interface using an onboard vibration motor and battery. Overall, these highly accessible and tunable macroscopic systems serve as novel platforms for exploring active and driven matter interacting in fluid environments, as well as other fundamental concepts in physics more generally.