Study On Design And Performance Control Of Terahertz Metamaterials

Terahertz(THz)wave is widely applied in safety inspection,material investigation,secret communication and etc.,owing to its unique properties.With the limitations of THz emission and detection technologies,THz becomes the last gap of the electromagnetic spectrum.Owing to their outstanding electromagnetic properties,metamaterials have become an important branch of electromagnetics.Through reasonably desigining the structural and material parameters of metamaterials,the electromagnetic wave can be arbitrarily tailored.Accordingly,THz MMs that were invented recently provide an opportunity for the development and applications of THz technology.In this thesis,THz metamaterial absorbers(MAs)were designed,fabricated,and systematically investigated.The main results of this work are shown as follows:(1)A novel spiral-shaped metamaterial absorber was designed.Particularly,the THz responses of the as-designed MA can be effectively adjusted just by altering the spiral number and its location.Simulation results revealed that compared with the traditional MAs,such spiral-shaped metamaterial absorbers exhibit stronger coupling,largely due to the continuous alteration in the spiral radius.Moreover,the response frequencies obtained by CST simulations agree well with those theoretically estimated by standing wave formula,suggesting high predictability of the response frequency for such MAs.(2)Masks and photolithography of the micro-electromechanical system(MEMS)technology were ultilized in successfully fabricated flexible MAs,respectively.Characterizations of the surface topography revealed that the metal cubes fabricated on the flexible MAs by mask technology are more regular.Moreover,the SiNx mask can be reused for the next fabrication.(3)The response frequencies of the flexible metamaterial absorbers can be adjusted by bending them with external force,from 4.45 THz to 5.26 THz,tuning ranges reaching 0.81 THz.This result was theoretically elucidated by equivalent circuit approach.(4)(3-Mercaptopropyl)trimethoxysilane(MPTS)was coated on the fabricated flexible MAs by self-assembling.The self-assembled MPTS was verified by Fourier transform mid-infrared spectroscopy.THz spectra measurements indicated that after self-assembling,the response frequencies of the MAs at 4.80 THz and 8.10 THz shift to 4.72 THz and 8.04 THz,respectively,and the absorptions turn higher.