The Research Of Terahertz Electromagnetic Metamaterial Broadband Absorber

With the rapid development of terahertz technology in the applications of biomedical,homeland security,communications and imaging,terahertz absorber,as one of the important terahertz devices,has potential applications in those technologies.However,due to the lack of natural materials in the terahertz range,the development of terahertz technology lagged behind,and the emergence of metamaterial has become one of the methods to solve the problem.In this thesis,the metamaterial based absorber is thoroughly studied and four broadband terahertz metamaterial absorbers are presented.Firstly,the basic structure of metamaterials is briefly introduced,the principle of absorption of metamaterial absorbers is described by the effective medium theory and equivalent circuit theory,then typical structure and properties of metamaterial absorbers are analyzed.Secondly,four broadband terahertz metamaterial absorbers based on circle rings are presented using the Finite-Difference Time-Domain methods by CST MWS 2012,and the influences of various geometrical and material parameters on the absorption performance are discussed.The first absorber is a structure of planar arrangement of three different sizes of circle rings,it can achieve a broadband absorption of 0.338 THz with the absorptivity beyond 90%,and the FWHM(Full Width at Half Maximum)is 21.94% with respect to the central frequency.The second absorber is a vertical stacked structure of three different sized circle rings and three different thickness dielectric layers,of which the bandwidth with the absorptivity beyond 90% is 0.492 THz,the FWHM is 41.44%.The bandwidth can be expanded by stacking more circle rings and dielectric layers.The third absorber is an improved structure based on the second absorber,it replaces the top-level ring structure of the second absorber with two nested circle rings.The absorber can achieve a broadband absorption of 0.896 THz with the absorptivity beyond 90%,the FWHM is 61.20%.The structure of the absorber is simpler,and the absorption performance is more superior.The fourth absorber is based on two split circular rings,of which the bandwidth with the absorptivity beyond 90% is 0.848 THz,the FWHM is 83.29%.Compared to the previous three absorbers,it has a simpler structure and is easy to be fabricated.In terms of absorption performance,all the four absorbers are insensitive to the TE and TM polarizations,and have good absorptivity with large incident angles.Finally,the fourth sample is fabricated and it is tested by using the terahertz time-domain spectrometer,and the experimental results and simulation results are analyzed.In conclusion,the broadband terahertz metamaterial absorbers presented in this thesis have good absorption performance,and can play an important role in the terahertz technology.