Magnetically actuated soft small-scale robot for undulating swimming

Small-scale soft robots, capable of undulatory swimming propelled by distributed magnetic body torques, are numerically investigated under underwater conditions. These robots are composed of a stiff frame and a magnetic soft sheet. The stiff frame secures the ends of the magnetic soft sheet, preventing curling or rolling during swimming. To evaluate the impact on swimming dynamics, we systematically modulate the frequency of the driving magnetic field, the magnetization profiles of the robot, the material mechanical properties of the robot, fluid environment properties, and wall proximity. Results indicate that all these factors significantly affect the robot's velocity and directional stability. Higher driving frequencies reduce swimming velocity, while decreasing directional stability. Regarding magnetization profiles, increasing the number of periods reduces swimming velocity while segmented profiles reduce directional stability while maintaining high velocity. Robots designed with stiffer materials concentrated near the two ends exhibit faster swimming velocity. The robot maintains relatively stable motion and achieves high velocity in very close proximity to the wall, but it struggles to maintain directional stability at even slightly greater distances. In shear-thinning fluids, the robot achieves higher velocity due to low-viscosity corridors surrounding its body but experiences reduced directional stability. These findings provide significant insights for the design and optimization of soft small-scale robots capable of controlled swimming, with potential applications in fields such as targeted drug delivery and minimally invasive surgery.