Performance enhancement of uni-flagellated magnetic microswimmer via asymmetry

Abstract In this paper, we investigate the dynamics and performance of a uni-flagellated magnetic microswimmer in the presence of structure asymmetry with respect to the horizontal body axis. The swimmer consists of a spherical magnetic head connected to a slender tail via a torsional spring and is driven by a planar oscillatory magnetic field. The asymmetry is introduced in the design by attaching the tail at a specific angle to the local tangential vector of the head. The equation of motion is formulated under low Reynolds number ( Re ) condition by using resistive force theory and solved numerically. The swimming modes reveal that asymmetry in the design generates a non-zero y -direction propulsion which was absent for symmetric swimmer. The performance of the swimmer is characterized by the net propulsion velocity and energy efficiency. The relative performance of the asymmetric microswimmer is found to be dependent on the actuation frequency, aspect ratio (tail length to head radius), stiffness of the spring, and asymmetry angle. The results show that it is possible to obtain enhanced performance of asymmetric swimmer compared to symmetric case. Analytical analysis is done under small actuation amplitude approximation to optimize the parameters for maximizing the velocity, and the values obtained are found to be similar to those obtained from numerical analysis. An experiment is performed using a scaled-up swimmer in Re ≈ 10 −2 , and the results correlate well with some of the theoretical results.