| The magnetic resonance wireless power transfer is a new technology,by means of which the power is transimitted through the coupling of magnetic fields via resonant coils,and has attracted many researchers and engineers all over the world because of its larger transfer distance,high efficiency,high power and a lot of potential applications.Up to now,to carry out it,lots of research work have been done and many results are obtained,however,there is still a big problem,that the transfer efficiency decreases sharply with the increase of the transfer distance,which is difficult to satisfy the practical applications.To further improve the transmission efficiency problems,according to the low loss characteristics of superconducting materials and the ability of artificial metamaterials to regulate electromagnetic waves,this paper carried out the theoretical and experimental studies of new magnetic resonance wireless power transfer technology for the superconducting materials,metamaterials,superconducting metamaterials and superconducting-ferromagnetic metamaterials.The main contents of this thesis are as follows:(1)The relevant theories of superconducting materials,metamaterials and electromagnetic field regulation technology are derived and analyzed.Based on the magnetic dipole model of magnetic resonance wireless power transfer system,the distribution and evolution characteristics of electromagnetic field are analyzed and discussed.In addition,present research status on this subject around the word is summed up and the challenges of the researches are analysed.(2)The resistance of the resonant coil is an important factor to influence the transmission efficiency.Therefore,the transmission efficiency can be effectively improved by the low loss characteristics of the superconductor.The current density of superconducting materials is much larger than that of conventional conductive materials,which means that the magnetic flux is also enchanced.Therefore,a superconducting relay magnetic resonance wireless power transfer system with three coil structure is proposed for reducing resistance and increasing current.The influence of the loss of the relay resonant coil on the transmission efficiency of the magnetic resonance wireless power transfer system is analyzed through the coupling mode theory and the equivalent circuit theory.The results show that the ohmic resistance of the relay coil can be really reduced.And the transmission efficiency of magnetic resonance wireless power transfer system can be improved effectively.The magnetic field distribution of two coil,three coil structure,copper relay and superconducting relay wireless power transfer system is simulated respectively by finite element method.The results show that the superconducting relay magnetic resonance wireless power transfer system can enhance the magnetic field intensity of the receiving coil compared with the copper relay magnetic resonance wireless power transfer system.The experiment of relay magnetic resonance wireless power transfer system is designed and carried out.The parameters of inductance,resistance,quality factor and overall efficiency of resonance coil are tested,and the superiority of superconducting relay magnetic resonance wireless power transfer is verified.(3)Inserting the metamaterials into the transmitting and receiving coils of wireless power transfer system can improve the transfer efficiency of it.However,with the increase of transmission distance,the distance between resonance coils will cause the resonance frequency of the system changing,and the maximum transmission efficiency of the system can not be improved by a single frequency metamaterial,and in order to solve this problem,a frequency adjustable negative magnetic metamaterial structure with an open resonant ring is proposed and applied to the system achieving frequency adjustable.Based on the finite element method,this paper simulates the relationship between the frequency point of the unit structure and the external capacitance,and optimizes the performance of the unit structure.The relationship between surface current of the tunable supermaterial at the resonance frequency and the phase of external field is analyzed.The magnetic resonance wireless power transfer system with tunable metamaterial as relay coil is established.The influence of external capacitance,different period units and the location of metamaterial on the transfer efficiency of the system is analyzed.Simulation results show that in a certain frequency band,the metamaterials can realize the tunability of frequency and has negative equivalent permeability.According to this,6×6 negative magnetic permeability adjustable metamaterial board was fabricated,and a four coil magnetic resonance wireless power system experiment was built.The main factors affecting the transmission performance of the system,such as external capacitance,the location of metamaterials,etc.,are experimentally studied.The results showed transmission efficiency of our system is improved,which verifies the effectiveness of the design.(4)The singular electromagnetic properties of superconductors have great potential value in solving the inherent problems of metamaterials,especially in terms of loss.Based on the YBCO HTS film,a helical superconducting metamaterial structure unit is constructed,and the influence of dielectric type,film size,superconducting coil geometry on the electromagnetic performance of the system is simulated.The results show that the helical superconducting metamaterial structure is more suitable for miniaturization and low loss magnetic resonance wireless power transfer system.(5)Based on the theory of transform optics,superconducting-ferromagnetic metamaterials which can regulate electromagnetic fields are designed.As we have known,the superconducting-ferromagnetic metamaterial with anisotropy electromagnetic can regulate the distribution of electromagnetic field,thus,change the direction of electromagnetic wave propagation and realize the convergence of electromagnetic field.Therefore,this metamaterial is applied to the magnetic resonance wireless power transfer system in order to enhance the magnetic field intensity around the receiving coil and then improve the transmission efficiency of the magnetic resonance wireless power transfer system.In this paper,we have applied superconducting-ferromagnetic metamaterials to the magnetic resonance wireless power transfer system with two coils structure for improving the transmission efficiency of the system.The magnetic field distributions of magnetic resonance wireless power transfer system with and without superconducting-ferromagnetic metamaterial are given.The influence of resonant coil shape(distribution of source magnetic field),the size of superconducting-ferromagnetic metamaterial and the relative position of superconducting-ferromagnetic metamaterial and resonant coil are studied.Simulation and experimental results prove the feasibility of superconducting-ferromagnetic metamaterials in improving the transmission efficiency of the system.In summary,from the results of our research works have narrated in this thesis,it can be concluded that by using superconducting materials,metamaterials,superconducting metamaterials and superconductor-ferromagnetic metamaterial in the system,the loss of the resonant coil can be reduced,the attenuation of the magnetic field is suppressed,the volume of the system can be reduced and the magnetic field is focused,the magnetic field intensity around the receiving coil of the system is enhanced,and the transfer efficiency of the magnetic resonance wireless power transfer system is enhanced.This thesis provides a theoretical basis,technical means and experimental basis for exploring the electromagnetic field control of magnetic resonance wireless power transfer system and improving the transmission efficiency of the system. |
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