Wireless Power Transfer System Suitable For Implantable Brain-computer Interface

With the development of micro-electromechanical systems and implantable medicine,its application has sprung up.The advantages of portability,miniaturization,and biocompatibility have brought significant changes to these implantable equipment energy supply.However,the problem of energy supply has limited the further development of these new medical technologies.In particular,implantable BMI?Brain-Machine Interface?devices such as neuroelectric stimulators have higher requirements for miniaturization and integration.Nevertheless the traditional battery power supply has many drawbacks:taking up a bulky volume,needing to be replaced regularly,and possessing poor safety performance,ect.Wireless power transfer can solve the above problems effectively.Aiming at the wireless energy supply of implantable brain-computer interface,this thesis focuses on the magnetic resonance wireless power transmission system based on MEMS?Micro-Electro-Mechanical System?.Based on the circuit theory and coupled mode theory,the dual-coil wireless power transfer system is modeled and analyzed.It is concluded that the transmission performance is mainly affected by the coil impedance,coupling coefficient,resonance frequency and load resistance,and then these elements were analyzed through formula and simulation.In order to design a harmonic oscillator with excellent transmission performance,the relationship between parameters among the inductance value and quality factor of the resonance coil are simulated and optimized through HFSS?High Frequency Structure Simulator?modeling,mainly including turns,turn spacing,wire width and coil inner diameter.Combined with the design requirements,the structural parameters and winding mode of the asymmetric transceiver coil are determined,and then measured at 13.56MHz with a vector network analyzer and test fixture to acquire the resonator inductance and impedance.A series-series impedance matching circuit is designed in order to ensure the maximum power transmission,based on the theory of scattering matrix,a two-port network,and smith chart theory.After the simulation model is built in HFSS,S₁₁can reach-24.56d B at the resonance frequency point,and the matching effect basically reaches the design requirement.In order to provide a reliable and stable output voltage,the two-stage voltage double rectifier circuit is employed based on the full-wave rectifier circuit and the capacitor filter circuit to decrease the volume of the signal processing module,which convert the alternating current signal into a stable and pulsating direct current signal in the high frequency band.All the above circuit modules have been simulated and experimentally verified.Finally,multi-stranded copper Litz wire wound resonators are employed to build the wireless power transfer system.The RF characteristics of the transceiver coil,the function of the electrical signal processing circuit and the performance of the entire system are tested.Measurement results show that S₁₁ and S₂₁can reach-22.67d B and-11.23d B respectively,and the system transfer efficiency is 24.59%when the resonator is placed coaxially and the system operating frequency is 13.56MHz.The system can make light source equipment work successfully and the realization of wireless power transfer with small volume and good performance is of great significance to the development of electronic devices suitable for implantable BMI.