Analysis And Design Of Magnetically Coupled Resonancebased Wireless Power Transfer System With Multiple Transmitters

Implantable devices provide a new option for monitoring and regulating physiological processes.With the development of Micro-Electro-Mechanical Systems,one of the major challenges is the power supply in miniaturizing the implantable devices.The traditional built-in battery cannot balance the small size of the battery and the demand for long-term supply.Wireless power transfer based on strongly coupled magnetic resonances(MCR-WPT)is able to deliver energy over a mid-range distance,which is an effective method to solve the long-term stable power supply for implantable devices.In order to provide long-term and stable power for biomedical implants in moving targets,this thesis adopts the genetic algorithm to optimize the trace width and the trace spacing of the planner spiral coil aiming at the the uniformity of the axial magnetic field distribution in the rechargeable area above it.HFSS simulation and the experimental result show that the coefficient of variation(COV)of optimized magnetic field is decreased obviously compared to the uniformly spaced regular coil.As the S parameter,passband ripple,transmission poles and coupling matrix in filter design correspond to the transfer efficiency,frequency division,maximum transmission efficiency,and the coupling coefficient among the coils in the MCR-WPT system respectively,the band-pass filter theory(BPF)model are established for the MCR-WPT system and the the MCR-WPT system with a single relay.Aiming at the maximum transmission efficiency of system,the genetic algorithm is used to get the optimal coupling matrix,and apply it in the design of the actual MCR-WPT system.To solve the problem of unbonded wireless power supply for the implanted device,the transmitter is required to cover the whole activity area of the organism,which inevitably result in a large transmitter and make the matching resonances between the transmitter and the receiver difficult.Therefore,a power transmission pad composed of seven planar spiral coilsc is used to cover the living area as the external transmitting end.This thesis analyzes the characteristics of the MCR-WPT system based on the power transmision pad.Taking use of the coupled-mode theory(CMT),the energy exchange among the coils is obtained,and two main result emerges:as the position of the receiver changes,the point of maximal transmission efficiency is where the axis of the receiver passes through the base plate’s vertex of the center coil of the power transmission pad,and when the position of the receiver is fixed,the coupling between the transmitting coil closest to the receiver and the receiver is the key factor in the system performance.For the matching resonances between the transmitter and the receiver,the equivalent circuit model is used to analyze the frequency splitting characteristics of the power transmision pad and the MCR-WPT system based on the power transmision pad.The result shows that the power transmission pad has two resonant frequencies,that is,there is frequency splitting.When the cross coupling between the receiver and the transmitters increases,another frequency division occurs,that is,the MCR-WPT system based on power transmission pad has three resonant frequencies.If the cross coupling decrease,the resonant frequencies of the system gradually change to two.Finally,an experimental platform is built to verify the correctness of theoretical analysis.