Self-propulsion of a grain-filled dimer in a vertically vibrated channel

Abstract

Steady dissipation of energy is a crucial property that distinguishes active particles from Brownian particles. However, it is not straightforward to explicitly model the dissipative property of existing active particles driven by a vibrating plate. We present a novel active particle that can be explicitly modeled by Newtonian dynamics of a conservative force field plus two asymmetrical dissipative terms. The particle is a dimer consisting of two ping-pong balls connected by a rigid rod, and its two balls are filled with granular particles of the same total mass but of different grain size. This dimer placed on a vibrating plate exhibits 3 types of motion – by tuning the frequency and the amplitude of the vibration, the dimer undergoes either a directed motion toward the small (or large) grain-filled side or an unbiased random motion. We investigate the various modes of motion both experimentally and numerically and show that the directed motion is a result of the asymmetric damping due to the size difference in the filling grains. Furthermore, the numerical simulation reveals that the dimer’s dynamics in either directed motion mode resembles a limit cycle attractor that is independent of its initial condition.

Spontaneous population oscillation of confined active granular particles

“…Due to symmetry breaking, the granular dumbbell converts the energy from the vertical vibration of the shaker into a horizontal self-propulsion along its long axis, whose self-driving mechanism is similar to those of previously designed active granular particles. 34,35 Fig. 1(c) plots representative trajectories of the active dumbbell, showing the directed motion accompanied by stochastic turns due to rotational noise (mean square displacement of the active granular dumbbell is provided in the ESI †).…”