Study On The Design And Theory Of Multi-functional Metamaterials Absorber

In recent 20 years,metamaterial absorber has potential applications in many fields,such as biosensing,electromagnetic stealth,solar cell,infrared imaging and so on,owing to its simple structure and high absorption.From the view of number and bandwidth,metamaterial absorber can be classified as three types,named single-band,multi-band and wide-band absorber.To date,theoretically and experimentally,metamaterial absorber has made great progress.However,most traditional absorbers have some disadvantages,such as depending on polarization and incident angle of light,lacking of dynamic adjustment of resonance frequency,as well as single-functional feature,leading to the constrained development in basic performance and high integration.Considering these questions,designing a metamaterial absorber with high efficiency and multi-function is the current popular research topic.In this thesis,through the numerical methods,finite-difference time-domain（FDTD）and the analysis of coupled-mode theory,optoelectronic devices based on graphene,topological dirac semimetals and phase-change materials are designed,optimized and applied.The main results are as follows:（1）An ultra-thin and multi-band coherent perfect absorber is proposed.The graphene surface plasmons are excited by putting graphene onto high-contrast gratings（HCGs）.Coherent perfect absorption is obtained by employing two counter-propagating plane waves to illuminate the system from forward and backward,respectively.The good agreement between theoretical analysis and numerical simulated results demonstrates that our proposed structure based on HCGs-graphene is feasible to realize coherent perfect absorber.The present coherent perfect absorber can still achieve multi-and narrow-band absorption with high intensity under a relatively large incident angle±55.Besides,by dynamically adjusting the Fermi energy of graphene and the phase difference of the two conter-propagating waves,we realize the active tunability of resonance frequency and absorption intensity simultaneously,which is the unique feature of graphene-based coherent perfect absorber.Especially,the proposed device possesses an extremely thin feature even up to 7 nm,demonstrating great promising for integrated microelectronics devices.（2）A convertible metamaterial device based on topological dirac semimetals（TDSM）and vanadium dioxide（VO₂）is proposed,which presents the switching characteristic from triple-band to broad-band.The simulated results demonstate that when VO₂ is in the fully insulating state,the proposed convertible device presents three distinctive absorption peaks.While,when VO₂ is in the fully metallic state,the convertible device expresses a broad-band absorption feature.By changing the conductivity of VO₂,the absorption intensity of this broad-band can be dynamically adjusted.Importantly,without making any change to the structure parameters,the system can present a unique triple-band to broad-band conversion by simply choosing different polarization directions of light.At the same time,benefitting from the variable Fermi energy of TDSM,resonance frequency can be dynamically tuned.This designed concept breaks the limitation of most absorber,that is,only with single-functional characteristic,such as multi-band or broad-band,and provides a new idea for frequency selective energy storage and convertible devices.（3）A bidirectional-and dynamical-tunable terahertz absorber is proposed through designing structure formed by two layers of TDSM plate with rectangular apertures and a dielectric spacer.By adjusting transverse distance between the top and bottom rectangular apertures,perfect absorption can be realized.Owing to the 180 rotation along z direction,perfect absorption still can be obtained whether light irradiates from the front or back of the system,indicating a performance of bidirectional absorption.In contrast to most absorbers,such a bidirectional design possesses double efficiency,which can improve the utilization of resource.（4）A novel mechanism to continuously reconfigure a terahertz resonator between one-port and two-port configurations via phase-change material for efficient electromagnetic modulation is proposed.We computationally show that the system behaves as a one-port device with near-perfect absorption and two-port device with high transmission up to 92%when VO₂ is in the metallic rutile phase and insulating monoclinic phase,respectively.Moreover,due to the reversible phase-change property of VO₂,the energy can be continuously and reversibly modulated between various intermediate states.More importantly,the proposed device is compatible with wide-angle operation and robust against structural distortion.In the end,we explain the method of coupled-mode theory in details,comparing the theory and simulated results to demonstrate the feasibility of our reconfigurable resonator.