Research on the motion performance of a magnetic field controlled rice grain microswimmer

Four kinds of ellipsoidal microswimmer are proposed to precisely control the motion direction and velocity at a rotating magnetic field. Five motion behaviors including rolling, swinging, transitional, rotational, and move back and forth modes are found. The microswimmer keeps the swinging mode can change the motion direction, and the implementation of M-trajectory is present as an example to demonstrate the purpose of controlling motion velocity and direction. By adjusting the number or reversing the direction of magnetic rods in the microswimmer, the way to increase the motion velocity is found. When the magnetic field frequency is less than the out-of-step frequency (the maximum frequency at which the model follows the magnetic field changes without hysteresis), increasing the frequency boosts the motion velocity. The out-of-step frequency is increased by adding the number of magnetic rods, whereas it is decreased by reversing the polarity of magnetic rods. This interesting observation provides parameter basis for efficiently implementing direction or velocity control in two-dimensional (2D) magnetic field.