The Study Of Metal/dielectric Metamaterials Absorber Based On Graphene

Metamaterials are artificially structured materials that can be realized by impinging metal-dielectric stacks and can have a negative dielectric constant or/and magnetic permeability.The interaction between the surface metal and the free electrons of the incident electromagnetic waves will cause the excitation of surface plasmon polaritons（SPPs）,which leads to the localization of electric and magnetic fields,resulting in light-material interactions suitable for absorption.However,the strong interaction between different resonators in this type of absorber greatly limits the number of ideal absorption bands.It is found through research that the absorptance and resonance frequency of this type of the metamaterials absorber both depend on the size of the patterned metal shape.Although the resonance frequency and absorptance can be changed by changing the structural parameters,once the absorber parameters are determined,these properties cannot be changed,which greatly limits the practical applications of the metamaterial absorber.Therefore,it is of great significance to study absorbers with multi-band absorption,tunable resonance frequency and absorptance.As a new type of two-dimensional metamaterial,graphene has optical properties similar to the metal.Compared to the strong interaction between metal resonators,graphene can achieve the better effect of multi-band absorption.Changing the Fermi level of graphene can also change the resonance frequency and absorptance of the absorber.Based on the above analysis,this paper designs some graphene-based metamaterial absorber structures and leads to detailed research and analysis of the absorption characteristics and resonance principles.The main research contents are as follows:1.A tunable,multi-band,selective absorber composed of multiple layers.Each layer consisted of Si O₂/graphene/Si C,and a layer of silver was used as the ground plane of the entire structure.Simulation results show that we can passively and actively coordinate the resonant frequency of the perfect absorption peak by changing the geometric parameters of the array and the Fermi level of the graphene.The absorber is not sensitive to the angle of incidence and the direction of polarization.We propose a theoretical basis for the formation of multiple absorption peaks.The theoretical calculations are in good agreement with the simulation results.In addition,we simulated the three-and four-layer structures.The results show that in the terahertz（THz）band,composite structures of three and four layers can obtain three and four perfect absorption peaks,respectively.2.A tunable coordinated multi-spectral absorber is proposed that combines graphene with metal-dielectric-metal structures to obtain three nearly perfect absorption peaks in the wavelength range of 8-14μm.The parameter inversion method is used to extract the equivalent impedance and explain the phenomenon of multi-band absorption.When the Fermi level of graphene changes,its resonance frequency can be well tuned.By changing the structural parameters of the gold ring,we can get a narrowband absorption peak and a broadband absorption peak.The bandwidth of the broadband absorption peak where the absorptance exceeds 80%is 0.8μm.3.A coordinated multi-band absorber based on the combination of patterned graphene and single-layer graphene is proposed.On the one hand,the multi-layer film structure is proposed.Equivalent circuit model（ECM）and parameter inversion are used to explain the physical mechanism of absorption.The results show that four gradually decreasing ultra-high absorption peaks are formed in the range of 0-1.1THz.Numerical simulation and theoretical calculation are in good agreement.The proposed structure is insensitive to the incident angle and polarization state of incident light.When the Fermi level of graphene changes,its resonance frequency and absorption peak can be well tuned.By changing the height of the multi-layer film,a high-absorption three-band refractive index sensor can be formed in the range of 0-1.9THz.The sensitivity of the obtained sensor is 50GHz/RIU and the coefficient of determination value（R²）obtained by linear fitting is 0.9989.On the other hand,on the basis of the original structure,the multi-layer film dielectric is replaced with a dielectric Si.The absorber can also obtain four gradually decreasing absorption peaks within 0-1.9THZ.At this time,the absorber is not sensitive to the polarization state of the incident light.In addition,the fourth absorption peak is selected as the working frequency of the refractive index sensor,and its maximum sensitivity is 48GHz/RIU.