The Research Of Tunable Terahertz Absorber Based On Graphene

Terahertz has the advantages of strong controllability,strong penetration,and non-ionizing radiation.It has a wide range of applications in medical imaging,security detection,and wireless communications.However,in the terahertz band,the absorber is one of the functional devices for regulating the terahertz wave.Its development is slow,and there are many problems such as low absorption efficiency,single function,non-dynamic regulation,and thick device,which can not meet the current application scenarios.As a material with excellent photoelectric properties and absorption properties,has been considered as a promising candidate material for regulating terahertz waves in the field of terahertz absorption devices.This dissertation aims to design two different types of tunable terahertz absorbers based on graphene materials for the above problems.The specific research contents are as follows :(1)A broadband polarization insensitive terahertz absorber based on patterned graphene is proposed,which adopts a metal-dielectric-graphene sandwich structure.The pattern of graphene is a circular aperture array etched on a square block of graphene.The results of simulations and theoretical analysis show that the absorption exceeds 99% in0.93-1.65 THz while 90% in 0.80-1.87 THz.The absorption performance of the device can be enhanced not only by altering physical dimensions of graphene pattern,but also by changing the chemical potential of the graphene.When the chemical potential increases from 0.1 e V to0.7e V,the corresponding terahertz absorption will increase from 59.1% to 99%,achieving dynamic regulation.The correctness of the absorber results is verified by the impedance matching theory,and the mechanism of absorption is disclosed by distribution of electric-field intensity.In addition,the device is insensitive to polarization under different polarization modes and incident angles.This tunable broadband absorber is promising in terahertz technology fields such as imaging,detection and stealth.(2)A tunable dual-band terahertz(THz)absorber using U-shaped graphene metamaterials is designed and simulated.The structure of the device consists of three layers :the top layer is a periodic array of two opposite U-shaped single-layer graphene patterns,the middle layer is a polyimide dielectric spacer layer,and the underlying substrate is a thin gold plane.The simulation results show that the device forms two absorption bands : the first band is almost perfect absorption,the frequency range is 2.29-3.11 THz,the 3d B bandwidth is 0.82 THz,and the maximum absorption of the second band is 86.04% at 7.94 THz.By adjusting the Fermi energy of graphene from 0.1e V to 0.6e V,the absorption performance of the absorber can be tuned,and the maximum absorption of the first band can increase from44.29% to nearly 100% and the second band increase from 5.71% to 86.04%.In addition,the sensing performance of the device is also studied.A layer of the object to be measured is placed above the absorption device.The results show that the device is sensitive to the refractive index of the surrounding medium,indicating that it has good sensing characteristics.