Research On Broadband Electromagnetic Waves Collimation Based On Metalens

This Thesis focuses on the issues of broadband electromagnetic wave focusing of anisotropic metamaterial lenses.Aiming at the solving of problems of the bandwidth and design efficiency of metamaterial lenses,which are used in optical sensing systems and highgain antenna systems.1.A model of multiple beams collimation at mid-infrared band is proposed based on hyperbolic metamaterial.Firstly,the theory of hyperbolic metamaterial and its realizing approaching have been studied.Then,one-dimension photonic crystal is constructed by graphene-silicon dioxide multilayered structure,which realizes specific hyperbolic dispersion for the controlling of electromagnetic waves.This model could transform the isotropic wave front into uni-directional wave.The simulation results indicate that single beam and multiple beams collimations can be achieved by the designed hyperbolic metamaterial at mid-infrared band(31 THz-37 THz).Besides,parameters studies,including chemical potential of graphene,stacking layers and filling ratio which have impacted on electromagnetic waves collimation,are quantitatively studied.These results illustrate that optimized performances of collimation can be obtained with appropriate filling ration and stacking layers.In addition,the gain could be dynamically controlled by adjusting the voltage gain by tuning the chemical potential of the graphene.The fabrication and processing techniques are also discussed.2.All-dielectric ultra-broadband transmitarray antenna at the microwave band is proposed based on genetic algorithm optimization and 3D print technology.Firstly,the numerical computations and theory analyses of broadband transmitarray have been studied.Then,the all-dielectric element with high permittivity substrate is designed,and its characteristics are investigated.The results show that the element can achieve wide range of phase compensation and high transmission ratio.Based on the above results and the specific phase arrangement requirements of the broadband transmitarray,with genetic algorithm as optimization method and broadband phase characteristics conditions,the broadband elements that meets the requirements of the transmission array are calculated,which can be used to form the high gain broadband transmitarray(fed by horn antenna).Finally,the transmitarray was processed using 3D printed jet fusion technology and the polyamide 12 as the material,which was tested in an anechoic chamber.The results show that,in the 9-20 GHz bandwidth,the gains are larger than 16 d Bi with the maximum gain of 23 d Bi.The gain are increased by 8-12 d B in the band while compared to the feeding antenna,and the 1 d B gain bandwidth reaches 29%.3.Aiming at the existing problems of complicated designing approach and low degree of automation designing,electromagnetic inverse algorithm for broadband metalen is proposed based on the ideas of electromagnetic inverse scattering.The inverse algorithm based on the method of moments discussed for the metal-dielectric broadband metalens,and the inverse algorithm based on the finite time-domain difference method is analyzed for the all-dielectric metalens.Then,a 2D-FDTD inverse algorithm is implemented to realize the all-dielectric metalens element,and by defining the evaluation function F,the effect function M and the antenna evaluation function Q to quantify evaluation standards,the foundation for integrated design is discussed for the first step.It provides a novel solution and research path for solving the broadband electromagnetic wave focusing and efficient designing of metamaterial lenses.