Research On Coil Design For Magnetic Resonant Wireless Power Transfer System In Implanted Medical Device

The magnetic resonant wireless power transfer technology has become a research hotspot due to its simple structure,long transfer distance and high transfer efficiency.The application of magnetic resonant wireless power transfer technology in implanted medical system provides highly efficient and reliable power for implanted devices,and solves the urgent needs of patient for high quality,comfortable,safe and reliable medical care,and possesses a broad development prospect.However,the magnetic coupling coil as the core part of wireless power transfer system,its characteristics affect the transfer efficiency and the stability of output power of the system.For the implanted medical system,there is a large difference in the size of the transmitting coil and the receiving coil,so that the system has a short transfer distance and low transfer efficiency;in addition,the receiving coil easily moves in the human body,resulting in the output power cannot be kept constant.Therefore,this paper studies the optimal design of coil for magnetic resonant wireless power transfer system in implanted medical device to realize a high transfer efficiency and stable output power.The main research work of this paper includes:Firstly,the equivalent circuit model of magnetic resonant wireless power transfer system is built,and the expression of the power transfer efficiency and the optimized load are deduced,and the range of the system resonant frequency is given.The transfer and output characteristics of the system are analyzed when the coils detune,and the optimized design goal of coils is to increase the quality factor and coupling coefficient.Secondly,the relationship between the parameter design and its performance of magnetic coupling coil is analyzed,including the effects of coil type,structure and size on the quality factor,coupling coefficient and the uniformity of magnetic field;in addition,the calculation methods of coil inductance,resistance and mutual inductance are given,and the applicable range of inductance calculation formula is compared based on finite element analysis.The effects of skin effect,proximity effect on the coil resistance are also studied,and the optimization direction of turn space,wire diameter and the material of the wire are given.Then,the coil structure and parameters for wireless power transfer system in implanted spinal cord stimulator are optimized.The transmitting coil is segmented,and the electric field strength is compared with the unsegmented transmitting coil,and the excitation voltage on the transmitting coil is reduced by segmenting,which ensures the safety of wearing for patients.Finally,an experimental prototype for wireless transfer system in implanted medical device is built based on the optimized coil structure and parameters.The experimental results show that the efficiency of this system is greater than 40% at a coil separation of 5 cm,and a stable output power can be achieved in a larger range(18 cm × 10 cm),which improves the transfer efficiency and the stability of output power for wireless transfer system in implanted medical device.