Research On Electromagnetic Wave Spatial Energy Focusing And High Performance Rectennas In Microwave Power Transmission System

Microwave Power Transmission?MPT?is an energy transmission method,in which electricity is converted into microwave and transmitted through space in a radiation manner.Compared with the other wireless power transmission?WPT?methods?electromagnetic coupling,electromagnetic resonance and laser?,MPT is suitable for power transmission from low power to high power,and from short distance to long distance,and has great flexibility and development prospects.In order to improve the performance of MPT systems,in this dissertation,we start the research from two aspects.On the one hand,by studying the generation of non-diffractive beam or focusing beam,the electromagnetic wave can reach the target through space to achieve energy non-diffusion,thereby improving the electromagnetic wave space transmission efficiency;On the other hand,by improving the performance of the rectenna,more DC energy is output,the performance of the MPT system can be improved.The main innovations of the dissertation are as follows:In the aspect of improving the spatial energy transmission performance of electromagnetic waves,in order to prevent the interaction between the dielectric objects and the electric field existing around the transmitting and the receiving antennas from affecting the spatial transmission efficiency of electromagnetic energy,firstly,we study the Transverse Electric-polarized magnetic Bessel antenna.According to the duality theorem,based on the Transverse Magnetic-polarized electric Bessel antenna,we propose a magnetic Bessel antenna in microwave band for the first time.Next,based on the deduction of the impedance value of an inductive impedance surface,and the establishment of the dispersion equation,we design a grid-type inductive impedance surface structure,and apply it to this Bessel antenna to generate a Bessel wave with specific wave number.In order to excite the low-sidelobe homogeneous magnetic field Bessel beam distribution in the antenna,we design two kinds of central-feeding structures,which are a spiral coil that mimics a flat wound coil,and a half-ring coil with metamaterial structure that mimics an ideal loop coil.These efforts provide the foundation for the electromagnetic power transmission by using non-diffractive beams.Next,we theoretically study the physical mechanism of the generation of focusing beams.By analyzing the focusing property of the inward-propagating zeroth-order Hankel wave function(H₀^?1?),we propose a leaky-wave antenna--the Inward-propagating Zeroth-order Hankel Leaky Wave?IZHLW?antenna to generate the focusing beam.In order to remove the inherent singularity of the H₀^?1?wave,an absorber consisting of a lossy material and a high-impedance surface structure are successively used to eliminate the tailing,and a good focusing beam is achieved.Through this work,we propose a truly original focusing beam generation method and its antenna structure design method,which has great innovation value in theory and application.In the aspect of improving the performance of rectennas,we study the dual-frequency rectenna that can receive multiple-frequency electromagnetic waves simultaneously,and the reconfigurable rectennas that can change the operation modes and be applied to different scenarios.Firstly,a dual-frequency doubler rectenna is proposed.By applying L-shaped stubs to the rectifying circuit,the rectenna can achieve high rectification conversion efficiency at both frequencies.Next,we propose some reconfigurable rectennas,such as a frequency reconfigurable rectenna and a polarization reconfigurable rectenna.With the implementation of the reconfigurable technology in both the receiving antenna and the rectifying circuit,the problem of achieving good matching between the antenna and the rectifying circuit when receiving electromagnetic waves with different frequency/polarization is solved,thereby the rectenna can achieve high rectification conversion efficiency in multiple modes.In order to further broaden the application of the rectenna,we propose a multi-functional frequency reconfigurable dual-port rectenna,with the two ports being used for the communication and rectification,respectively.Besides,the two ports can operate simultaneously or separately,and work in the same band or in their respective bands.At last,we study the transmission efficiency of the MPT system.Based on the conjugation impedance matching and the pattern matching theories,we analyze the transmission performance of the non-diffractive near-field MPT system.We analyze the coupling between the non-diffractive transmitting antennas and receiving antennas in the near-field range,and then build the equivalent circuit of the near-field MPT system,and also study the transmission efficiency of the near-field MPT system.In summary,in this dissertation,we have studied the energy radiation,transmission,receiving and conversion parts of MPT systems,and analyzed the near field properties of the non-diffractive beams and focusing beams,and also the radiation and rectification characteristics of the rectennas.We have investigated the design of several non-diffractive antennas,focusing antennas,and high-performance reconfigurable rectennas,and proposed the basic analytic model of a near-field MPT system.It is hoped that this dissertation can provide valuable theoretical support for the research of high-performance MPT systems,thus advancing the further development of them.