Polarization-independent L-shaped Perfect Metamaterials Absorber In Mid-infrared Region

Metamaterials are artificial materials engineered to exhibit extraordinaryelectromagnetic properties that are not available in nature. Potential applications ofmetamaterials are diverse and include sub-wavelength imaging and invisible cloaks.When the impedance of the metamaterials matches to that of free space, it ispossible to realize perfect absorption of specific frequency in the incidenceelectromagnetic waves through carefully designing of the size and the geometricshape of the unit cell. This metamaterial perfect absorber has potential applicationsin, e.g. THz imaging, material detecting and solar cell. In this paper, we study theabsorption mechanism of L-shaped metamaterial absorber in mid-infraredwavelength regime with the combining of numerical simulation method andtheoretical analysis.First of all, based on the absorption theory of electromagnetic in frequencyselective surface, we calculate the spectrum characteristics of the single L-shapedmetamaterial absorber using the finite element method in mid-infrared wavelengthregime. The variation of absorption spectrum with the incident angle in thismetamaterials absorber is performed under different electromagnetic polarization.Based on the electric field distribution, we can know that the dual-band absorber isformed by the magnetic polarization resonance. We also study the variationtendency of the intrinsic frequency with structure parameter through the LC circuitmodel in the single L-shaped metamaterial absorber. The simulation result is fitedwell with that of the finite element method.Then, we proposed a wide-angle, polarization-independent and dual-bandperfect metamaterial absorber with a structure formed by dual L-shaped goldresonators in mid-infrared wavelength regime. The variation tendency of the theabsorption spectrum with the incident angle and the azimuthal angle in differentpolarization is also studied. We also explain the physical mechanism of dual-bandabsorption through the excitation of surface plasmon polariton in themetal-dielectric-metal film.Finally, the equivalent electromagnetic parameters of the dual L-shapedmetamaterial perfect absorber is calculated by the S parameter inversion method.We analysis the impedance matching condition between the free space and theabsorber for the resonance wavelength. According to the electrical and magneticloss tangent, we could achieve the loss mechanism of incident electromagnetic wavein the absorber. Through changing the structural parameters of the dual L-shaped metamaterial absorber, the resonance absorption wavelength could be controlled. Amulti-band perfect absorption is achieved with two pairs of L-shaped structures withdifferent size.