Helical Propulsion in a Viscous Heterogeneous Medium

Abstract

We characterize the propulsion of externally-actuated helical robots inside a viscous heterogenous medium. The method of regularized Stokeslets is implemented in three-dimensional space for computing the Stokes flow around a helical robot and immersed obstacles (spherical microparticles) in the medium. The helical robot is actuated using a permanent magnet-based robotic system with two synchronized rotating dipole fields. Our simulations and experimental results demonstrate propulsion enhancement with the concentration of the immersed obstacles in the viscous medium regardless of the actuation frequency. Numerical results show that the swimming speed is increased approximately by a factor of 2 for a 5% increase in the concentration of immersed obstacles with diameter of 30 $\mu m$, at actuation frequency of 1 Hz. At this actuation frequency, our experimental results show that the swimming speed is increased by a factor of 1.4. At relatively high actuation frequency (8 Hz), simulation and experimental results also show increase in the swimming speed by factors of 1.4 and 1.3, respectively.