Efficient propulsion force and torque generation for implantable microrobot based on lorentz force using wireless power transfer system

Abstract

This research introduces a microrobot structure that generates propulsion force without additional actuator but using a wireless power transfer coils. As a method for increasing the efficiency of a microrobot, a method of propulsion a microrobot using a pair of power source and load coils and a coil generating a pair of magnetic forces is proposed. This has the advantage of maximizing the efficiency of the microrobot and enables rotation and movement in the desired direction. In addition, as the size of the microrobot becomes smaller, a method is proposed in which the vector in the vertical direction is dominant in the coil of the microrobot, and a propulsion method using the Lorentz force in the horizontal direction is proposed. In order to break the balance of the lateral force generated in the coil, the magnetic field is biased by using the magnetic body, thereby breaking the balance of the force and suggesting a method of propulsion it in one direction. As the microrobot becomes smaller, the propulsion force of microrobot becomes small, for the Lorentz force is proportional to the length of coil wire segment. Moreover, the power transfer efficiency also decreases as the mutual inductance decrease. To compensate the power transfer efficiency reduction problem, the Q-factor and coupling coefficient were considered. A magnetic material is inserted to increase the Q-factor and coupling coefficient between transmitting coil and receiving coil. By inserting the magnetic material inside of microrobot, the power transfer efficiency increases up to 14.6-times higher than without ferrite microrobot model. In this paper, the magnetic force on magnetic material under the time-varying magnetic field also introduced and analyzed. The magnetic force generated in magnetic material when the incident magnetic field affected is also contribute the propulsion for a microrobot. Combination of these two kinds of force generates more than three times higher force compare to the method that the Lorentz force based propulsion only. By using this magnetic material, the proposed microrobot achieved 3-times higher than without magnetic material inserted one. In addition, by controlling the incident magnetic field vector, it is able to generates torque, which is source of rotation. Electromagnetic field exposure problem for the human body is considered based on IEC 62905 standard. An electromagnetic simulation including human body model is conducted to verify the EMF exposure issue on human and confirmed that the proposed model compliant the standard of IEC62905. In this research, the operation of each propulsion method is explained and verified by simulation and experiment. The proposed method can be used not only for miniaturization of microrobot but also for medical use, and it can be used for internal monitoring, drug delivery and information acquisition of human body.