Characterization and control of biological microrobots

This work addresses the characterization and control of Magnetotactic Bacterium (MTB) which can be considered as a biological microrobot. Magnetic dipole moment of the MTB and response to a field-with-alternating-direction are characterized. First, the magnetic dipole moment is characterized using four techniques, i.e., Transmission Electron Microscopy images, flip-time, rotating-field and u-turn techniques. This characterization results in an average magnetic dipole moment of 3.32×10−16 A.m2 and 3.72×10−16 A.m2 for non-motile and motile MTB, respectively. Second, the frequency response analysis of MTB shows that its velocity decreases by 38% for a field-with-alternating-direction of 30 rad/s. Based on the characterized magnetic dipole moment, the magnetic force produced by our magnetic system is five orders-of-magnitude less than the propulsion force generated by the flagellum of the MTB. Therefore, point-to-point positioning of MTB cannot be achieved by exerting a magnetic force. A closed-loop control strategy is devised based on calculating the position tracking error, and capitalizes on the frequency response analysis of the MTB. Point-to-point closed-loop control of MTB is achieved for a reference set-point of 60 μm with average velocity of 20 μm/s. The closed-loop control system positions the MTB within a region-of-convergence of 10 μm diameter.