# Taxis of Artificial Swimmers in a Spatio-Temporally Modulated Activation Medium

## TL;DR

This paper investigates how artificial microswimmers respond to a spatio-temporally modulated activation medium, revealing that their drift direction depends on their dynamics and the properties of the activation pulses.

## Contribution

It provides analytical and numerical analysis of artificial swimmer taxis in a modulated medium, highlighting the roles of persistence length and ballistic-diffusive dynamics.

## Key findings

- Swimmers drift parallel or anti-parallel to activation pulses depending on pulse speed and width.
- Finite persistence length determines drift in the same direction as pulses.
- Ballistic and diffusive properties influence drift in the opposite direction.

## Abstract

Contrary to microbial taxis, where a tactic response to external stimuli is controlled by complex chemical pathways acting like sensor-actuator loops, taxis of artificial microswimmers is a purely stochastic effect associated with a non-uniform activation of the particles' self-propulsion. We study the tactic response of such swimmers in a spatio-temporally modulated activating medium by means of both numerical and analytical techniques. In the opposite limits of very fast and very slow rotational particle dynamics, we obtain analytic approximations that closely reproduce the numerical description. A swimmer drifts on average either parallel or anti-parallel to the propagation direction of the activating pulses, depending on their speed and width. The drift in line with the pulses is solely determined by the finite persistence length of the active Brownian motion performed by the swimmer, whereas the drift in the opposite direction results from the combination of ballistic and diffusive properties of the swimmer's dynamics.