Self-propulsion of a spherical electric or magnetic microbot in a polar viscous fluid

TL;DR

This paper investigates how a spherical microbot can self-propel in polar viscous fluids using electric or magnetic fields, analyzing the fluid dynamics and propulsion velocity through ferrohydrodynamics and perturbation theory.

Contribution

It introduces a theoretical model for microbot propulsion in polar fluids driven by oscillating charge densities and polarization lag, expanding understanding of ferrohydrodynamic propulsion mechanisms.

Findings

Propulsion velocity derived to second order in charge density

Electrical torque density causes fluid movement

Model applicable to electric and magnetic microbots

Abstract

The self-propulsion of a sphere immersed in a polar liquid or ferrofluid is studied on the basis of ferrohydrodynamics. In the electrical case an oscillating charge density located inside the sphere generates an electrical field which polarizes the fluid. The lag of polarization with respect to the electrical field due to relaxation generates a time-independent electrical torque density acting on the fluid causing it to move. The resulting propulsion velocity of the sphere is calculated in perturbation theory to second order in powers of the charge density.