Direct Measurement of Lighthill's Energetic Efficiency of a Minimal Magnetic Microswimmer

TL;DR

This study directly measures the energetic efficiency of a magnetic microswimmer using experimental and numerical methods, providing insights into optimizing its propulsion performance in viscous fluids.

Contribution

It introduces a method to directly determine Lighthill's efficiency of a microswimmer through combined experimental measurements and simulations.

Findings

Successfully measured the microswimmer's efficiency experimentally.

Identified key degrees of freedom for propulsion.

Discussed potential improvements for efficiency tuning.

Abstract

The realization of artificial microscopic swimmers able to propel in viscous fluids is an emergent research field of fundamental interest and vast technological applications. For certain functionalities, the efficiency of the microswimmer in converting the input power provided through an external actuation into propulsive power output can be critical. Here we use a microswimmer composed by a self-assembled ferromagnetic rod and a paramagnetic sphere and directly determine its swimming efficiency when it is actuated by a swinging magnetic field. Using fast video recording and numerical simulations we fully characterize the dynamics of the propeller and identify the two independent degrees of freedom which allow its propulsion. We then obtain experimentally the Lighthill's energetic efficiency of the swimmer by measuring the power consumed during propulsion and the energy required to translate the propeller at the same speed. Finally, we discuss how the efficiency of our microswimmer could be increased upon suitable tuning of the different experimental parameters.