| Nowadays the magnetic coupling resonant wireless power transmission technology hasreceived wide attention as a new theory by the scholars at home and abroad. But manyproblems have not been solved, especially in the aspect of the in vivo implantable devices.In this paper the small size magnetic coupling resonant wireless power transmissionused in implantable devices has been analysed. At first the magnetic coupling transmissionrule of wireless energy transmission system and the best working conditions are studied bycoupled-mode theory. Then the system numerical model is established and the small sizeresonator is designed on the basis of simulation analysis. Finally, the small size resonantsystem is placed in different experiment environments and the finite difference time domainmethod is used to calculate the SAR of human body to judge the safety of the power supplydevice.Main points of this paper are as follows:1. The coil energy transfer efficiency in the condition of strong coupling and weakcoupling using coupled-mode theory, the effects of the change of coil natural frequency onthe energy transfer state and the quality factor is calculated, and the effect of disturbance onthe work efficiency and the loss efficiency is studied.2. The cube spiral resonator and planar spiral resonator simulation model is established.The parameters influence on the resonance frequency of resonators by changing theresonator parameters is determined.The simulation results show that the coil wire diameterand the medium thickness of coil has the greatest effect on the resonant frequency. Thesmall size resonator with the volume of1.35cm3is designed based on the simulation.3. The human head and chest numerical simulation model is established and the SARof head and chest is calculated by FDTD when the implanted device is powered byWitricity system. As the results of the model calculation, the SAR values are lower than theinternational standard limit.4. Experiments are carried out to the cube spiral resonator, planar spiral resonator andsmall size plane spiral resonator respectively. The system transmission power andefficiency is calculated by changing the vertical distance between two resonators,horizontal displacement and rotation Angle. In addition, the system is placed in the air,simulated human body tissue fluid and fresh pork to transfer energy and the transmissionpower and efficiency under the different environment is studied. Experimental results showthat the simulated human body tissue fluid and the fresh pork have little effect on systemII transmission efficiency. Finally the voltage needed for the charging module is got byrectifier filter circuit.In this paper the transmission mechanism and transmission conditions of magneticcoupling resonant wireless power transmission system has been studied, and a small sizemagnetic coupling resonant wireless power transmission system suitable for implantabledevices has been designed based on the simulation.The biological safety to human bodywhen the system is working has been calculated for the first time in our country, and it haslaid a foundation for the wireless energy transmission technology developing in the medicalfield. |
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