Research On Metamaterials And Magnetic Resonance Wireless Power Transfer

With the increasing demand and the development of technology,wireless power transfer,as a flexible,safe and reliable energy transfer mode,becomes a hot research spot in recent years.Magnetic coupling wireless power transfer system has been most wildly and deeply studied among all wireless power transfer methods.However,the system efficiency decreases exponentially with the increasing transmission distance because of the divergence of magnetic field.In the past decades,researchers found the influence of coil’s resonance frequency on system efficiency and proposed four-coil magnetic resonance wireless power transfer system,which significantly increases power transfer efficiency.After that,most researches focused on the optimization of coil structure and the power electronic converters to further increase the system efficiency.Based on transformation optics theory,some other researchers manipulated electromagnetic fields in wireless power transfer systems by means of metamaterial,which showed a novel method to increase system efficiency.In this paper,I research the multi-coil magnetic resonance wireless power system as well as the application of metamaterial devices in wireless power system,and experimentally validates the theoretical analysis.(1)The existing modeling methods of magnetic resonance wireless power system are studied and compared.Based on the lumped element circuit model,the three-coil and four-coil wireless power transfer systems are respectively analyzed and compared with the traditional two-coil wireless power transfer system.The system efficiencies with changing parameters are analyzed according to the simulation results.The 100 k Hz and 6.8MHz wireless power transfer platforms are established to validate the theoretical analyses and realize the high efficiency wireless power transfer at mid-range distance.(2)The media electromagnetic tensor formulas are derived based on the transformation optics.The existing metamaterial devices designed for wireless power transfer system are summarized according to their functions and material characteristics.The simulation results validate the effects of two kinds of shifting medium devices.Based on the shifting medium devices,an improved metamaterial shifting shell is designed.With this improved shifting shell,the magnetic field can be shifting a distance,which can not only enhance the mutual inductance of the sending and receiving coils without changing the transmission distance but also limit the strong magnetic field distribution to keep the users away from electromagnetic radiation in a wireless power transfer system.Moreover,based on the effective medium theory,the simplification of the shifting shell is analyzed and discussed,which provides a feasible simplification method for the improved shifting shell.(3)The existing modeling methods of metamaterial unit cell are studied and compared.Based on the lumped element circuit model,the metamaterial unit cell array is modeled and analyzed.The analysis on the unit cell array circuit model has the same conclusions as those of the existing modeling methods.Experiments with the metamaterial slab on the6.8MHz wireless power transfer platform are analyzed and explained by the circuit model to give suggestions for further design.