Broadband Perfect Absorber In Mid-infrared Region

Metamaterial is a new kind of artificial material, which can realize different electromagnetic properties through designing various sub-wavelength structural units. In order to realize the wanted electromagnetic properties, we can design the geometric parameters of the metamaterials’ subwavelength structurale units. As the resonance of metamaterials may induce strong surface currents and form huge local field effect under electromagnetic field with certain frequency, the local electric field intensity will be increased dramatically, leading to huge dielectric loss and metal ohmic loss around the resonance frequency in metamaterials. Previous researchers generally focus on trying to reduce the above losses to realize better negative refraction and negative permeability properties. In this paper, we mainly show that the perfect absorption for certain frequency can be realized by designing metamaterials’ geometry for the sake of the impedance match between surface of metamaterial and free space. Using the methods of simulation and theory analysis, this article mainly conducts the systematic research on cross-structure metamaterial perfect absorber, especially its absorption properties in the mid-infrared(MIR) region. Besides, we experimentally fabricated the optimized monolayer cross-structure metamaterial perfect absorber arrays.Based on the basic principle, we respectively simulated the monolayer and bilayer cross-structure absorbers’ MIR spectrum properties under normal incidence using commercial finite element method software(COMSOL Multiphysics). We studied the different influence of incident angle on the structure’s absorb effect. Furthermore, using the equivalent LC circuit model we analyzed the dependance of resonance frequency on cross-structure’s geometric parameters and middle dielectric layer’s permittivity.Using the S-parameter inversion method, we calculated the effective electromagnetic parameters of the cross-structure metamaterial and obtained the impedance and energy loss at resonance frequency. The result shows that the impedance of the structure matches the free space very well. We analysis the electromagnetic loss mechanism at resonance according to the cross-structure metamaterial perfect absorber’s electromagnetic loss factor. We realize the aim of modulate this metamaterial perfect absorber’s resonance absorption position by changing the structure’s geometric parameters and middle dielectric layer’s permittivity value. Based on the cross-structure metamaterial perfect absorber, we optimize the structure to design a bowtie absorber and realize broadband absorption.