Research On Plane Wave-Flying Electromagnetic Toroid Pulses Converter Base On Metasurfaces

The flying electromagnetic toroids(FETs)are a kind of finite energy non-diffracting beams,which have important application prospects on railless acceleration,novel multipole excitation,localized energy transmission,high-sensitivity detection,and so on.However,the current research on FETs mainly focuses on the theoretical solution of its equations,topological structure,and potential applications,which are still at the theoretical level.This is because FETs have not been produced so far.To lead the research on FETs from theories to experiments and applications,the propagation property and generation method of FETs are studied in this thesis.The main content of this thesis is as follows:In the first part,the propagation properties of FETs are studied.Firstly,the propagation properties of the ideal FETs are researched and analyzed.Based on the FETs field equation,the topological structure and the spatial distribution of its field components are calculated and analyzed.The time-domain and frequency-domain characteristics of the real part and imaginary part pulses in free space are studied.The slowly spreading propagation characteristics and reflection characteristics of FET are analyzed.Then the finite difference time domain(FDTD)method is used to simulate and analyze the self-healing characteristics of FETs,including aperture truncation excitation and discrete excitation,which provides the basis for the subsequent generation of the FETs.In the second part,the generation scheme of FETs are studied,including array arrangement method and unit design.First,the theoretical scheme of the electromagnetic flying ring generator based on the metasurface is explained.To convert a plane wave into FET,it is necessary to realize a metasurface array that can generate a specific spatial frequency spectrum distribution and a specific spatial polarization distribution.Then,according to the spatial frequency spectrum distribution and self-healing characteristics of the FETs,we proposed the array arrangement method of the metasurface and the design index of each position unit of the array.Finally,based on the design index,some frequency selective surface units and polarization conversion surface units are designed by topology optimization.In the third part,the performance of the plane wave-FET conversion array is analyzed.Firstly,the polarization conversion array and frequency selection array designed are simulated separately to analyze the polarization performance and frequency selection performance of both.Then,the polarization conversion array and frequency selection array are combined for full-wave simulation,and the effect of the FET generated is analyzed by quantitative comparison with the ideal FET.Finally,the polarization performance and frequency selection performance of the array are verified by experiments.