Magnetic Resonant Wireless Power Transfer for Propulsion of Implantable Micro-Robot.

Abstract

Small implantable micro-robots have variety of medical applications for minimally invasive surgery. Recent researches focus on the propulsion of the robot [1][2], by inserting permanent magnet and control its movement using magnetic field from Helmholtz coils. However, this type of propulsion has limitation that the magnetic field does not deliver the electric power to operate the active circuit of the robot. Therefore, the robot can perform the limited range of missions by its movement. To overcome the limitations, the active robot with both propulsion and power, wirelessly supplied from the outside is required.[3] However, when microwave electromagnetic field is used to transfer power, the efficiency is low as the receiving coil is very small, which means strong magnetic field is inevitable. In this paper, we propose a magnetic resonant wireless power transfer system [4] which can both generate the propulsion of the robot and deliver electric power using with the same coil. Fig. 1 shows the wireless power transfer system and the equivalent circuit consisting of transmitting and receiving coils. As the incident magnetic field and current are perpendicular, the Lorentz force is generated on the receiving coil. However, as the currents of the transmitting coil and the receiving coil have 90 degree difference in phase, so the time-average of force becomes zero in general wireless power transfer system. To solve this problem, the phase control of the receiving coil by changing the tuning capacitance (C2) at the receiving coil and change the phase difference to be close to 180 degree maintaining the current as high as possible. To generate the forward force on the loop, magnetic shielding is applied [5]. With 3-D magnetic field simulation using ANSYS Maxwell, a 1-mm square receiving coil can generate Lorentz force for the micro-robot to have the velocity of 2.6 mm/sec using the magnetic field of 5 􀀫T at 10 MHz as shown in Fig 2. As a result, strong propulsion force is generated from minimal magnetic field by applying magnetic resonant wireless power transfer.