Propulsion and steering of helical magnetic microrobots using two synchronized rotating dipole fields in three-dimensional space

We control the motion of helical microrobots with average diameter of 500 μm in two-dimensional (2D) and three-dimensional (3D) spaces using two synchronized rotating dipole fields. The utilization of the two synchronized dipole fields not only increases the magnetic torque exerted on the magnetic dipole of the helical microrobot but also eliminates the magnetic field gradients along its lateral directions. Our finite element simulations and experimental results show that the utilization of two rotating dipole fields increases the magnetic field by 100%, as opposed to single rotating magnetic field. In addition, we show that the magnetic field gradient within the workspace of the microrobot is eliminated. Therefore, the lateral oscillations of the helical microrobot are mitigated within the center of two rotating dipole fields, and hence the motion of the microrobot is stabilized inside tubes with relatively large inner diameters, as opposed to the diameter of the helical microrobot. This strategy allows the microrobot to compensate for gravity and swim in 3D space inside water reservoirs at an average speed of 0.25 body lengths per second. In addition, closed-loop motion control of the helical microrobot is achieved in 2D space at an average speed of 2 mm/s and maximum steady-state error of 100 μm.