Control and controllability of microswimmers by a shearing flow

TL;DR

This paper investigates how background fluid flow can be used to guide and control microswimmers, analyzing effectiveness, robustness, and practical considerations for flow-mediated control strategies.

Contribution

It introduces a general flow-based control method for microswimmers, analyzing its efficacy and robustness, and discusses practical implications for real-world applications.

Findings

Flow-mediated control can effectively guide microswimmers in simple geometries.

Control robustness decreases with measurement inaccuracies and rotational noise.

Careful assessment of policy and behavioral robustness is essential for practical control schemes.

Abstract

With the continuing rapid development of artificial microrobots and active particles, questions of microswimmer guidance and control are becoming ever more relevant and prevalent. In both the applications and theoretical study of such microscale swimmers, control is often mediated by an engineered property of the swimmer, such as in the case of magnetically propelled microrobots. In this work, we will consider a modality of control that is applicable in more generality, effecting guidance via modulation of a background fluid flow. Here, considering a model swimmer in a commonplace flow and simple geometry, we analyse and subsequently establish the efficacy of flow-mediated microswimmer positional control, later touching upon a question of optimal control. Moving beyond idealised notions of controllability and towards considerations of practical utility, we then evaluate the robustness of this control modality to sources of variation that may be present in applications, examining in particular the effects of measurement inaccuracy and rotational noise. This exploration gives rise to a number of cautionary observations, which, overall, demonstrate the need for the careful assessment of both policy and behavioural robustness when designing control schemes for use in practice.