Two-Dimensional Contact and Noncontact Micromanipulation in Liquid Using an Untethered Mobile Magnetic Microrobot

This paper presents the manipulation of microspheres under water by use of an untethered electromagnetically actuated magnetic microrobot (Mag-$mu$Bot), with dimensions $hbox{250} times hbox{130} times hbox{100} mu$ m$^3$. Manipulation is achieved by two means: contact and noncontact pushing modes. In contact manipulation, the Mag-$mu$Bot is used to physically push the microspheres. In noncontact manipulation, the fluid flow generated by the translation of the Mag-$mu$Bot is used to push the microspheres. Modeling of the system is performed, taking into account micrometer-scale surface forces and fluid drag effects to determine the motion of a sphere within a robot-generated fluid flow. Fluid drag models for free-stream flow and formulations for near-wall flow are both analyzed and compared with the experiments, in which pushing of two sphere sizes, i.e., $hbox{50}$ and $hbox{230}, mu$m diameters, is characterized in a controlled, robot-generated flow. Dynamic simulations are provided using the developed physical models to capture this behavior. We find that the near-wall physical models are, in general, in agreement with the experiment, and free-stream models overestimate microsphere motion.