Research Of Terahertz Absorbers Based On Novel Artificial Metamaterials

With the rapid development of the metamaterial(MM),its absorption characteristics also have been received more and more attentions.Compared with the conventional absorber,the MM absorber has several unparalleled advantages,such as high absorptivity,thin thickness,light weight,tunable frequency,desired electromagnetic parameters and many potential applications in undamaged detections,THz imaging and stealth technology.Through optimization of structural parameters,we study a multiband and broadband MM absorber.On this basis,we introduce the semiconductor material into the key parts of the MM absorber and discuss the method of enhanced magnetic resonance in detail.The main contents of this dissertation are as follows:Firstly,we study a multiband MM absorber operating at terahertz frequencies.The design,characterization,and theoretical calculation of the high performance MM absorber is reported.By virtue of combining dual and single band MM absorber,a multiband MM absorber is presented.Theoretical and simulated results show that the MM absorber has four distinct absorption points at frequencies 0.57 THz,1.03 THz,1.44 THz and 1.89 THz,with the absorption rates of 99.9%,90.3%,83.0%,96.1%,respectively.The simulation is made on a frequency band between 0.1THz and 2.2 THz.Multiband MM absorber extend the absorption band and the thickness of the absorber is 3% of the center wavelength.The structure of the multiband MM absorber is easy and can be extended into other frequency ranges by changing its size.Secondly,we study a design of a broad-band planar MM absorber at terahertz frequencies.Simulation results show that the MM absorption at normal incidence is above 90% in the frequency of 6.56-8.10 THz,with absorptive bandwidth of 1.54 THz.This design provides an effective way to construct broad band absorber.The coupling of adjacent four dual-band sub-cells can introduce additional capacitance to affect the performance of absorber.The broad-band planar MM absorber is polarization insensitive.For many potential applications,it would be desirable to create MMs that exhibit a controlled active,dynamical,and/or tunable response.Tunable MMs are designed to work at a variable frequency controlled by some external stimulus within a frequency band instead of operating at a fixed frequency only determined by their geometry.Finally,We propose a design and numerical study of three optically switchable MM absorbers in the terahertz regime.The blue shift of tunable MM absorber absorption peak frequency can be dynamically shifted from 0.68 THz to 1.61 THz,with a broadband tuning range of 57.8%.Through the simulation and the calculated surface current densities,the electrical resonance gradually weakens and the magnetic resonance strengthens with light energy enhancement;The resonance peak of the absorption spectra of redshift tunable MM absorber shows a shift from 1.17 to 0.68 THz,with granting a resonance tuning range on the order of 42%.As the conductivity increases to 300000 S/m,the photoconductive silicon can be changed from semiconductor to conductor.The gaps of the SRRs resonator are bridged by conductor silicon.It will affect the resonant absorption characteristics of the MM absorber;The blueshift and redshift tunable absorber in a MM absorber structure is proposed.By the optimal design,we found the design of geometrical parameters.The absorption is due to electrical and magnetic resonance for low frequency and determined by the interaction of dipole resonance and magnetic resonance for high frequency.With the light energy increases,the current distribution changes from the two outside split-ring resonators to internal split-ring resonator.