Net motion induced by nonantiperiodic vibratory or electrophoretic excitations with zero time average

TL;DR

This paper demonstrates how nonantiperiodic, asymmetric oscillatory forces can induce net motion in macroscopic objects and colloids, with experimental and numerical evidence showing controllable direction reversal.

Contribution

It introduces two new experimental systems showing net motion from asymmetric oscillations, extending the concept beyond previously studied microscopic and quantum systems.

Findings

Net motion observed in macroscopic objects and colloids due to asymmetric forcing

Direction of motion can be controlled and reversed by waveform sign change

Experimental results align with numerical simulations

Abstract

It is well established that application of an oscillatory excitation with zero time-average but temporal asymmetry can yield net drift. To date this temporal symmetry breaking and net drift has been explored primarily in the context of point particles, nonlinear optics, and quantum systems. Here, we present two new experimental systems where the impact of temporally asymmetric force excitations can be readily observed with mechanical motion of macroscopic objects: (1) solid centimeter-scale objects placed on a uniform flat surface made to vibrate laterally, and (2) charged colloidal particles in water placed between parallel electrodes with an applied oscillatory electric potential. In both cases, net motion is observed both experimentally and numerically with nonantiperiodic, two-mode, sinusoids where the frequency modes are the ratio of odd and even numbers (e.g., 2 Hz and 3 Hz). The observed direction of motion is always the same for the same applied waveform, and is readily reversed by changing the sign of the applied waveform, for example, by swapping which electrode is powered and grounded. We extend these results to other nonlinear mechanical systems, and we discuss the implications for facile control of object motion using tunable periodic driving forces.