Study On Nearly Perfect Absorption Of Infrared Periodic Microstructure

Electromagnetic wave absorbers can receive the electromagnetic wave. In order to effectively use the electromagnetic wave, the devices with important application background are needed. Nowadays, the traditional intrinsic absorption is poor in wavelength selection with low absorptivity, and strongly dependent on the material. The multiple beam interference absorption is very sensitive to the incident angle and the polarization with narrow bandwidth. The thickness of absorption structure is an integral multiple of the quarterwave length, which is usually very large. Recently, a new type of electromagnetic resonant absorbers based on artificial metamaterial overcomes those drawback and is more suitable for the practical application. The near-perfect absorbers have very high absorptivity, and can work over a wide range of incident angle. The broadband absorption, dual-band absorption and multi-band absorption can also be realized by constructing the composite structure. In addition, the thickness of the near-perfect absorbers is much smaller than the incident electromagnetic wavelength, which can bend or cover on the surface of the object, and the structures are very simple and easy to make. More importantly, through the optimizations of the size and shape as well as the selection of the materials, the near-perfect absorbers can work in a wide wavelength range extended from the microwave band, terahertz band to infrared band, and even visible band. In this paper, we mainly design and numerical investigate the infrared near-perfect absorbers based on periodic microstructure. We also analyze the modulation of various structural parameters on the absorption spectra, as well as the influence of the incident angle, the polarization angle and the azimuthal angle on the absorp tion spectra.The single-band absorbers are limited in some applications, we present two benchmarks of dualband absorption based on magnetic polaritons(MPs). One is the multi-sized structure with identical dielectric spacing layer and the other is the multilayer structure of the same strip width. According to the independent properties of the MPs which is elucidated by the electromagnetic field distributions at resonances, we propose a parallel LC circuit model to explain and predict the multiband resonant absorption. We present the application of the parallel LC circuit model to preliminarily design a broadband absorber to realize the broadband absorption covering the wavelength range of 8-12 μm. All the corresponding structural and optical parameters are derived directly using the parallel LC circuit model with the proper initial parameters and approximations. This broadband absorber can also be omnidirectional and polarization insensitive with the absorptivity above 90% covering the wavelength range of 8-12 μm by constructing a two- dimensional(2D) periodic structure in the same design principle. Based on the 2D periodic structure, we design a mid-infrared ultra-broadband absorber with the absorptivity above 90% covering the wavelength range of 9-19 μm.The multiple-band absorbers are usually designed as composite structures, we design and investigate a dual-band infrared near-perfect absorber based on the asymmetric T-shaped structure. We find that the sidebands of dual-band absorption peaks are very low, and the period of the absorber is very small that can overcome the influence of the surface plasmon polaritons. Both the two absorption peaks can be finely tuned independently by varying the geometry of the asymmetric T-shaped structure. The designed dual-band absorber can operate well over a wide range of incident angles for both absorption peaks. Subsequently, the asymmetric T-shaped structure is simplied to the asymmetric L-shaped structure and we investigate the influences of the surface plasmon polaritons. In the asymmetric L-shaped structure of long cavity, the incident angle has little influences on the absorption spectra of the asymmetric L-shaped structure. In the asymmetric L-shaped structure of short cavity, the strong coupling between magnetic polaritons and surface plasmon polaritons will suppress the magnetic polaritons in the short cavity.Most polarization insensitive absorbers are realized by relatively complex two dimensional periodic structures, we design and investigate the near-perfect absorber based on a simple and flexible one-dimensional(1D) structure. One is based on a 1D metallic grating with a pair of metal–dielectric bilayer on the grating ridge and high refractive index medium filling into the grating grooves. The other is based on a 1D stacked array consisted of vertically cascaded two pairs of metal-dielectric bilayer. Due to the special absorption mechanism and carefully designed geometries, the complexity of the metamaterials absorbers are amazingly reduced from two dimensions to one dimension without any losses in performance. According to the analysis of the electromagnetic field distributions at resonances, we present the physical mechanisms of the near-perfect absorption for the TM and TE polarization, respectively, which are further expound and estimated. In addition, the high absorptivity is very robust to the incident angle, polarization angle and azimuthal angle around the designed wavelength.