Twisting and buckling: a new undulation mechanism for artificial swimmers

TL;DR

This paper introduces a novel artificial swimmer made of a polarized ferrogel cylinder that undulates and swims on water when subjected to a transverse oscillating magnetic field, utilizing a buckling instability mechanism.

Contribution

It presents a new undulation mechanism for artificial swimmers based on torsional buckling induced by magnetic fields, supported by elasticity modeling.

Findings

Undulation modes match elastic rod bending modes.

Critical magnetic field for buckling can be predicted.

Multiple undulation modes observed depending on length.

Abstract

We present an artificial swimmer consisting in a long cylinder of ferrogel which is polarized transversely and in opposite directions at each extremity. When it is placed on a water film and submitted to a transverse oscillating magnetic field, this artificial worm undulates and swims. Whereas symmetry breaking is due to the field gradient, the undulations of the worm result from a torsional buckling instability as the polarized ends tend to align with the applied magnetic field. The critical magnetic field above which buckling and subsequent swimming is observed may be predicted using elasticity equations including the effect of a magnetic torque. As the length of the worm is varied, several undulation modes are observed which are in good agreement with the bending modes of an elastic rod with free ends.