Characterizing Swimming Locomotions of an Asymmetrical Soft Millirobot in a Rotating Magnetic Field

Millimeter-scale robots have many applications in bioengineering fields due to their ability to be actuated remotely. Certain forms of locomotion allow them to achieve high swim speeds while maintaining controllability. The corkscrew locomotions have been achieved in previous soft robot studies, but their swim speeds were much lower than those exhibited by soft robots of different locomotions. In this paper, a corkscrew swimming motion with a high swim speed was achieved with a 3D rotating magnetic field by designing an asymmetrical soft robot made of flexible polymer embedded with magnetic particles and magnetized at a specific orientation. While this robot exhibited a rolling and transient locomotion at magnetic field frequencies lower than 40 Hz, at frequencies above 40 Hz, the robot exhibited corkscrew swimming locomotion. The swimming speed peaked at a velocity of about 30 mm/s at a magnetic field frequency of 49 Hz. Beyond this frequency, the swim speed of the soft robot decreased because the rotational frequency of the robot could not match the frequency of the actuating magnetic field.