Research On Graphene-based Tunable Broadband Metamaterial Absorber

Metamaterial(MM)is a kind of man-made materials that do not exist in nature,and have many unique properties that natural materials do not possess.As an important branch of MM research,MM absorber is a hot spot in current research.The traditional MM absorber consists of a metal resonator,a dielectric spacer,a metal plate,similar to a "sandwich" structure,which can achieve perfect absorption of electromagnetic wave(EM)in a specific frequency band.In recent years,tunable MM absorbers have broad application prospects in sensing,detection,energy collection,etc.because their absorption frequency bands can be changed without changing their structural parameters.Usually in the design of the absorber,tunable frequency characteristics can be achieved by introducing switchable diodes,phase change materials,photosensitive materials or graphene.In this paper,based on graphene materials,two tunable terahertz MM absorbers are designed in this paper.The CST commercial software is used for simulation analysis to study the absorption characteristics and absorption mechanism of the designed absorber.The main contents are as follows:The first chapter mainly introduces the research background of MM absorbers and the research progress of tunable absorbers at home and abroad.Chapter 2 designs a tunable terahertz MM absorber based on an unpatterned graphene.Its unit structure consists of four layers a metal resonator with " " gap,an unpatterned graphene layer,a dielectric layer,and a metal ground plate.By adjusting the Fermi energy of the graphene,the structure can achieve dynamically tunable broadband absorption characteristics Simulation results show that when the graphene Fermi energy is adjusted to 0.1e V,the bandwidth of over 90% absorptivity reaches 1.25 THz,and the relative bandwidth is about 49%.The broadband absorption mechanism is explained by analyzing the electricfield and current distribution.In Chapter 3,a tunable terahertz absorber/reflector based on the patterned graphene.Its unit structure consists of a patterned graphene on the top layer,an intermediate dielectric layer,and a gold plate on the bottom layer.The patterned graphene layer includes two square graphene rings and a square graphene sheet.By independently adjusting the Fermi energy of the graphene sheet and square graphene rings on the patterned graphene layer,the structure can work in a reflection state or a tunable broadband absorption state.Specifically,when no bias voltage is applied to the patterned graphene,the structure can nearly totally reflect the incident EM waves;when the Fermi energy of the square graphene sheet and the two square graphene rings is adjusted to 1e V,the structure works in a broadband absorption state,where the absorption bandwidth of the over 90% absorptivity is 2.0THz-3.75 THz,and the relative absorption bandwidth reaches 61%.The mechanism of broadband absorption is demonstrated by the impedance characteristics,electric field and current distribution.In addition,by analyzing the absorption characteristics of two kinds of the proposed above absorbers for the EM waves with different polarization angles and incident angles,it is found that they possess broadband absorption characteristics that are insensitive to polarization angle and incident angle.Chapter 4 summarizes the research results of the full text and looks forward to the next work.