| Terahertz(THz)wave is located between infrared and microwave bands,and has been rapidly developed and widely used in wireless communication,security systems,biological imaging,future sixth generation wireless networks and other fields.Metamaterials are periodic subwavelength structures that recombine natural materials,and have many electromagnetic properties that natural materials do not have.The effectiveness of manipulating terahertz radiation using their electromagnetic properties has been thoroughly investigated.Metamaterials enable many terahertz devices,including absorbers,sensors,detectors and optical switches.Among them,terahertz metamaterial absorbents have attracted much attention for their wide applications in non-destructive testing,sensing and imaging.In this paper,metamaterial absorbers working in the terahertz band are studied and discussed.The research work is as follows:(1)We designed and manufactured a triple-band narrowband terahertz metamaterial absorber with three concentric square ring metallic resonators,a polyethylene terephthalate(PET)layer,and a metallic substrate.The simulation results demonstrate that the absorptivity of 99.5%,86.4%,and 98.4%can be achieved at resonant frequency of 0.337,0.496,and 0.718 THz,respectively.The experimental results show three distinct absorption peaks at 0.366,0.512,and 0.751 THz,which is mostly agreement with the simulation.The three narrowband absorption peaks are derived from the strong electric and magnetic resonance of the three rings,respectively.The three peaks of the absorber are sensitive to the surrounding environment,and can realize refractive index sensing.In addition,the absorber has the characteristics of independent polarization,and large angle incidence.The narrow-band flexible metamaterial absorber has broad application prospects in sensing and filtering fields.(2)We designed and numerically investigated an all-silicon broadband terahertz metamaterial absorber.This type of absorber exhibited a very wide absorption bandwidth of～1.3 THz for absorption efficiency of>90%.We also simulated the absorption spectra of the absorber under different structural parameters,and analyzed the absorption mechanism from the distribution of the electromagnetic fields.Herein,electric and magnetic resonances are proposed that result in perfect broadband absorption.In the case of transverse electric field(TE)polarization and transverse magnetic field(TM)polarization,the all-silicon terahertz absorber is angle insensitive at an incidence angle of 0-70°.In addition,owing to the highly structural symmetry,the absorber has a polarization-independent characteristic.Compared with previous metal-dielectric-metal sandwiched structure,the all-silicon metamaterial absorbers avoid the disadvantages of high ohmic losses,low melting points,and high thermal conductivity of the metal,which provides a new scheme for the research of all dielectric wideband absorber.(3)We designed and numerically investigated a tunable terahertz metamaterial absorber that is electrically and optical dynamically tunable based on graphene and doped silicon,respectively.The THz absorber exhibits an absorbance of 97.5%at a resonant frequency of 0.245 THz.When the Fermi energy of graphene increases from0 to 1 e V,the peak absorbance decreases from 97.5%to 56.2%;as the pump fluence of doped silicon layer increases from 0 to 100μJ/cm~2,the peak absorbance decreases from 97.5%to 42.8%.The amplitude modulation depth T of our designed absorber is approximately 0.55.Electric and magnetic resonances are proposed,which allows for nearly perfect absorption.Finally,the absorption characteristics were investigated under incident angles from 0°to 75°for both transverse electric and transverse magnetic modes.The tunable terahertz absorber can realize electrical and optical modulation,which provides certain theoretical value for the subsequent research of dynamic tunable absorber. |
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