Designing Broadband Metamaterial Perfect Absorbers Based On Surface Plasmon Metamaterial

The band of light from visible to infrared has important applications in photovoltaic,solar cells,filtering,photothermal conversion.Therefore,the research of the broadband metamaterial perfect absorber（BMPA）in this band is of great significance.The research of the absorber has shown that the surface plasmons resonance（SPR）excited in the metamaterial absorber（MMA）can effectively absorb electromagnetic waves,thus,the absorber can achieve perfect absorption by optimizing the structure.However,there are still some challenges in the design of BMPA,such as:the absorption performance of the absorber is greatly affected by the polarization angles and the incidence angle of the light source,and the narrowbandwidth and complex structure is not conducive to manufacture etc.In this paper,MMA structuresare designed by two methods of horizontal and vertical arrangement.In addition,the numerical calculation by finite-difference time-domain（FDTD）method is carried out.The main contents of this thesis are as follows:（1）A broadband metamaterial perfect absorber with four-layer simple cuboid structure is designed.By placing the anti-reflection dielectric layer Silicon nitride（Si₃N₄）on the pattern layer metal,a broadband metamaterial perfect absorber of electric-metal-dielectric-metal（DMDM）four-layer simple cuboid stacked are formed.The anti-reflection layer effectively improves the short-wave absorption performance of the absorber.The average absorption rate reaches 98.1%at the wavelength500～2400 nm（bandwidth:1900 nm）.The physical mechanism of high absorption and ultra-broadband can be explained by the common contribution of SPR,magnetic polaritons resonance（MPR）,Titanium（Ti）high loss and Si₃N₄strong ability of capturing electromagnetic waves.In addition,the average absorption can reach above94%at an incidence angle of 50°in TM/TE modes,and when the various structural parameters of the absorber are within the range of±25%,an excellent absorption performance can be still maintained.The loss of solar energy was only 3.9%at the wavelength of 280～2500 nm.The photothermal conversion efficiency is 98.0%and96.8%in the 500 K and 1000 K operating temperatures.（2）Based on the proposed DMDM four-layer simple cuboid broadband absorber,an X-cavity is etched into the patterned metal to excite strong local surface plasmons resonance（LSPR）.The calculation results show that the X-cavity does excite a strong LSPR and effectively enhances the absorption in the 900～1800 nm band.The absorber average absorption can reach to 97.6%at the wavelength 400～2500 nm（bandwidth of 2100 nm）.Furthermore,in TM/TE mode,the average absorptionis maintained above 94%at an incidence angle of 50.The excellent absorption performance is maintained over a wide range of structural parameter variations.The difference of physical mechanism of the absorption between X-cavity absorber and the absorber proposed in Chapter 3 is that the cavity resonance is excited at short wave（417 nm）,which reaches 100%absorption at this resonance peak,resulting in the absorption spectrum of the X-cavity absorber perfectly match with the absorption spectrum of the standard solar radiation in the 280～2500 nm band,with a total absorption of 99.2%of the solar radiation energy.The photothermal conversion efficiencies are 99.1%and 97.9%at operating temperatures of 500 K and 1000 K respectively.The two absorbers based on our proposed DMDM structure have advantages of wide bandwidth,high average absorption rate,simple structure,polarization-independent,large-angle incidence insensitivity and high tolerance of manufacturing errors.They have important applications in the fields of solar energy capture,photothermal conversion,etc.（3）An ultra-broadband metamaterial perfect solar absorber（UBMPA）based on Si₃N₄-Ti（ST）group four-layer cuboid stacked pyramidal is designed and simulated,the average absorption achieved 99.6%in the operating wavelength range of400～4000 nm.In addition,the absorber also achieves an average absorption of 94.5%in the operating band when the edge’s length in the fourth ST group varies with a range greater than±58%,the average absorption is maintained above 91.8%at an incidence angle of 60°in both polarization modes.The proposed stacked absorber has the advantages of ultra-broadband,excellent absorption performance,polarization-independent,large-angle incidence insensitivity,fewer stacking layers,high manufacturing error tolerance and low fabrication cost,and has important potential applications in solar cells,detectors,thermal emitters and other fields.