Manipulations Of Electromagnetic Waves By Coding Metamaterials And Their Applications

Metamaterials are artificial periodic or aperiodic structures composed by subwavelength artificial composite materials.Due to its unique electromagnetic properties,which can realize a series of outstanding functions,such as anomalous reflection,anomalous refraction,electromagnetic cloak,polarization convertor and so on,the metamaterials have broad application prospects in aviation,aerospace and information.And artificial metamaterials have drawn serious attention in past decades.Metasurfaces are the two-dimensional form of artificial metamaterials,which have the advantages of low-profile,low-loss,low-cost and easy to fabricate.Recently,a new concept of digital coding metamaterials has been raised by Prof.Tiejun Cui from Southeast University to manipulate reflected or transmitted EM waves flexibly,which extremely extends the application of metamaterials.This thesis focuses on the design and applications of coding metamaterials,including coding metamaterials based on swarm intelligence algorithm,new type of amplitude-modulated metamaterials,and phase-amplitude modulation hybrid coding metasurfaces.The main contents of this thesis are listed as follows.1)The synthesis of meta-array far-field patterns based on particle swarm optimization algorithm.After setting the predesigned objective function of far-field patterns,the coding patterns of metasurfaces can be optimized by particle swarm optimization algorithm using MATLAB software,and the results can be effectively obtained combining with fast Fourier transform(FFT).Taking a full consideration of different kind of situations,choosing the suitable parameters can accelerate the convergence of the particles and not trap into local optimal solution,which is easier converge to the global optimal solution in a limited number of iterations and obtain the far-field patterns eventually.2)The theory and experiment of optical transparent amplitude modulation coding metasurfaces.The optical transparent coding metasurfaces are constructed by optical transparent materials,which elements can cover from total reflection to total absorption.Based on different predesigned coding sequences in metasurfaces,the incident waves can obtain different amplitude response,which can achieve beam modulation,target stealth,information transfer and so on.That is,the transparent coding metasurfaces have bright application prospects in microwave and light frequency.3)The theory and experiment of transmission type phase-amplitude hybrid coding metasurfaces.Hybrid coding metasurfaces containing eight 3-bits hybrid coding elements can generate amplitude-modulated orbital angular momentum(OAM).Meanwhile,combining with convolution operation smoothly,the radiation can continuously scan using this kind of hybrid coding metasurfaces and a new dimension will be added.4)The design of transmission type asymmetric transmission amplitude-modulated coding metasurfaces.The asymmetric transmission amplitude-modulated coding metasurfaces are constructed by digital coding particles with high transmissivity.Each particle covers from the total reflection to total transmission.After discretizing the transmission amplitude,2-bits or even higher-bit amplitude modulation metasurfaces can be achieved.Arraying different coding sequences,transmission beam can be manipulated freely and asymmetric transmission coefficient can be controlled indirectly.