Research On Dynamical Tunable Terahertz Absorber Based On Metamaterials

The frequency range of terahertz wave is defined between 0.1 THz and 10 THz.With the rapid growth of ultra-fast laser technology,many scholars at home and abroad are interested in the research of terahertz functional deceives.Terahertz metamaterial absorbers become a research topic due to their wide range of applications.Once the absorber of traditional"sandwich"structure(metal-medium-metal)is processed,its absorption performance is often fixed.If there is a need for abosrption of other functions,it must be redesigned and reprocessed,which is greatly limited the practical application of the absorber.Therefore,tunable metamaterial absorbers came into being.This kind of absorber can change the tunable properties of added active metamaterials to adjust the absorption performance of the whole structure without changing its structure.This thesis focuses on the tunable metamaterial absorber in terahertz wave,and designs three kinds of tunable terahertz metamaterial absorber,then analyzes their absorption performance obtained from simulation in detail respectively.The main research contents are as follows:(1)A broadband tunable terahertz absorber is proposed,which is composed of vanadium dioxide composite pattern,a dielectric layer and a metal layer.It can successfully extends the absorption bandwidth with an absorptance of greater than 90%to 4.10 THz,covering from 3.25 THz to 7.35 THz.When the conductivity of vanadium dioxide changed from 200 S/m to 2×10~5S/m,the absorption rate of the absorber is dynamically adjusted from 3.6%to 100%.In TE and TM polarization modes,when the incident angle increases to 60°and 40°,the absorption rate of absorber is still greater than 90%.(2)A dual-band tunable terahertz metamaterial absorber with five layers is proposed.It can realize a special requirement of one unchanged absorption peak and other moving absorption frequencies.When the Fermi energy level of the upper graphene is fixed at 0.7 e V,and the Fermi energy level of the lower graphene increases from 0 e V to 0.9 e V,the absorber has a perfect absorption peak fixed at 6.32 THz and a blue-shift frequency band,moving from 4.02 THz to 4.81 THz.When the incident angle increases from 0°to 50°,the absorber still has the same absorption characteristic.(3)A switchable bifunctional terahertz metamaterial absorber based on vanadium dioxide and graphene mixture material is proposed.When vanadium dioxide transfers from a metallic state to an insulating state,this structure achieves the functional switching from dual-band to single-band absorbers,and also achieves the characteristic switching of complete reflection and absorption at the local frequency points of 4.24THz and 5.22 THz.The conductivity of vanadium dioxide is 2×10~5S/m,the absorption rate of absorber can be dynamically modulated from 24.29%to 99.93%by controlling the Fermi energy level of graphene from 0 e V to 0.9 e V.In TE and TM polarization modes,until the incident angle reaches 35°and 25°,respectively,the absorber can still achieve the switching function of having opposite absorption characteristics at local frequency points.The three different types of absorbers designed in this thesis achieve dynamic adjustment of the absorption bandwidth,absorption frequency and absorption rate of absorbers.Due to the flexible tunability of the absorbers,they have a great potential application value in photoelectric switches and optical modulation.