Research On Wireless Power Supply System For Implantable Medical Devices Without SAR Evaluation

At present,the safety problem of implantable medical wireless charging system based on magnetic coupling resonance type is specific absorption rate(SAR).In order to avoid SAR damage to the maximum extent,a resonant wireless power supply system based on LCC/C compensation was designed in the frequency range of 10 k Hz～100k Hz in this paper.SAR evaluation is not required in this frequency range.At the same time,the mechanism of eddy current generation in titanium alloy shell was analyzed,and a magnetic coupling mechanism was designed to reduce eddy current effect in titanium alloy shell,besides considering the frequency decrease,the coil offset and compensate the influence of parameters on the system transmission performance,a kind of compensation parameters optimization method was put forward,the best working frequency and the compensation parameters were determine based on the system and the corresponding safety assessment.Firstly,a loss circuit model considering equivalent series resistance(ESR)was established.By analyzing the output power and transmission efficiency of the system under different frequencies,compensation parameters,coupling coefficients,the optimal frequency(f =80k Hz)and compensation parameters(P=0.3)were determined comprehensively.According to the simulation results,the corresponding experimental system was built,and the energy supply efficiency and anti-offset ability of the system were tested.The experimental and simulation results show that the transmission efficiency of the system can reach 43.3%～73.2% when the working frequency is f =80k Hz and the lateral offset of the center distance between the two coils is 0～2/3.Effectively make up for the negative effect of the reduced working frequency on the transmission performance of the system.Finally,to evaluate the safety of the charging system,the finite element simulation software COMSOL was used to build a two-dimensional axisymmetric geometric model of human tissue,and the corresponding electromagnetic safety analysis and thermal analysis were carried out on the system through experiment and numerical simulations.In the process of charging for 30 min,the maximum internal electric field intensity was only 4.58V/m.In addition,the simulation results show that the maximum temperature rise of the tissue is only 0.9°C,and the error between experiment and simulation is 0.3°C,which meet the international safety standards and effectively improve the system safety.The paper has 52 figures,16 tables and 76 references.