Study Of Flexble Terahertz Metamaterial Absorbers

With the development of the terahertz science,the terahertz devices like terahertz filters and absorbers,which can improve the transmission performance,have also become a central issue.However,due to the lack of natural materials for terahertz wave response and detection,the development of terahertz is seriously restricted.The appearance of metamaterials(MMs)has provided great convenience for the research and design of terahertz devices.By changing the geometric parameters of the unit-cell structure of MMs,one or both of its electric permittivity and magnetic permeability can be negative in a specific frequency range which changes its resonant electromagnetic response.So MMs has a very significant application prospect in the electromagnetic invisibility,photoelectric detection and so on.Compared with the conventional absorber,the MMs absorbers at microwave,light wave,especially terahertz bands have attracted much attention due to the advantages such as high absorptivity,thin thickness,light weight,frequency selectivity,and design flexibility.The absorption characteristics of different types of MMs absorbers were studied in this thesis.The main works and novel results of this thesis are listed as follows:First,an optically switchable MMs absorber is designed and investigated theoretically in the terahertz regime.By embedding Si in the opening resonance ring,adjusting the pump intensity to change the conductivity,we demonstrate a blue-shift of the resonance frequency varying from 0.684 THz to1.414 THz.We further analyze the mechanism of the two resonance absorption frequencies,and the effect of geometrical parameters on the absorption properties of the tunable MMs absorber.The parameters include thicknesses and dielectric constants ? of polyimide,cell sizes b,widths ? and opening length c of SRRs,and length and conductivities ? of the photosensitive silicon.Second,based on the cross structure,the single-band,double-band and multi-band MMs absorbers are constructed.Firstly,a perfect MMs absorber is designed and a strong resonance frequency is found at 1.74 THz.Based on the theory of resonance circuit,we further studied the dependence of resonance absorption frequency on the geometric parameters of the cross structure.Secondly,on the basis of the cross structure,a dual band MMs absorber was constructed by adding metal lines to the up,down,left and right sides of cross structure,and two resonance frequencies were observed at 0.89 THz and 2.18 THz,respectively.Finally,a multi-band MMs absorber was designed,and had five resonance frequencies at 0.996 THz,1.194 THz,1.870 THz,1.990 THz and 2.298 THz,respectively.These MMs absorbers have many advantages such as simple structure and excellent performance and so on,which has certain referential significance and research value.