# Nonlinear parametric excitation effect induces stability transitions in swimming direction of flexible superparamagnetic microswimmers

## TL;DR

This paper investigates how nonlinear parametric excitation causes stability transitions in the swimming direction of flexible superparamagnetic microswimmers, combining theoretical analysis, numerical simulations, and experimental validation to reveal a critical magnetic field amplitude effect.

## Contribution

It introduces a novel flexible microswimmer with a superparamagnetic head and demonstrates the experimentally observed 90-degree swimming direction transition predicted by theory.

## Key findings

- Confirmed the 90-degree transition in swimming direction experimentally.
- Showed the transition depends on magnetic field frequency and amplitude.
- Identified an optimal amplitude for maximum swimming speed.

## Abstract

Microscopic artificial swimmers have recently become highly attractive due to their promising potential for biomedical applications. The pioneering work of Dreyfus et al (2005) has demonstrated the motion of a microswimmer with an undulating chain of superparamagnetic beads, which is actuated by an oscillating external magnetic field. Interestingly, it has also been theoretically predicted that the swimming direction of this swimmer will undergo a $90^\circ$-transition when the magnetic field's oscillations amplitude is increased above a critical value of $\sqrt{2}$. In this work, we further investigate this transition both theoretically and experimentally by using numerical simulations and presenting a novel flexible microswimmer with a superparamagnetic head. We realize the $90^\circ$-transition in swimming direction, prove that this effect depends on both frequency and amplitude of the oscillating magnetic field, and demonstrate the existence of an optimal amplitude, under which, maximal swimming speed can be achieved. By asymptotically analyzing the dynamic motion of microswimmer with a minimal two-link model, we reveal that the stability transitions representing the changes in the swimming direction are induced by the effect of nonlinear parametric excitation.

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Source: https://tomesphere.com/paper/1705.03486