Abstract: In order to achieve targeted therapy and minimally invasive surgery by active navigation in viscous fluids such as blood vessels and tissue fluids, magnetic microrobots with different structures have been developed. In the present study, a helical propulsion micro-robotic structure is designed based on a streamlined head with an inner helical groove and conical tail, aiming to enhance micro-robot motion velocity and stability enhancement through geometric optimization. The dynamics model of the microrobot is established based on the resistance theory to solve motion velocity. Based on multiphysics coupling theory, a simulation model of coil magnetic drive dynamics and microrobot fluid dynamics is established, revealing the nonlinear modulation mechanisms of magnetic field parameters, fluid viscosity, and structural parameters on moving performance. Simulation analysis shows that the shape drag coefficient of the inner helical groove is reduced by secondary flow vorticity. The flow separation was effectively suppressed by conical tail design with progressive curvature, achieving a 32.5% improvement in propulsion efficiency. The velocity of the micro-robot exhibits a nonlinear response to the rotational frequency of the magnetic field, with the critical step-out frequency governed by the synergistic modulation of the magnetic flux intensity, the fluid viscosity, and the average magnetization. The helical propulsion micro-robot of a streamlined head and a conical tail is developed, conducting experiments on micro-robot motion characteristics based on an established experimental platform. The validity of the theoretical model was verified using an established experimental system. The maximum swimming velocity of 1.3 mm/s was obtained with a conical tail of 5 mm, a pitch of 2 mm, a spiral turn of 2, a cone angle of 15°, and a line radius of 0.3 mm.

Key words: magnetic micro-robot, helical propulsion, conical tail, inner helical groove head, motion characterization