Design And Optimization Of Wide-band Metamaterial Absorber With Atmospheric Transparent Window

Metamaterial absorbers are subwavelength periodic structures that can achieve complex spectral responses through the design of their micro/nano structures.They are widely used in narrowband and broadband spectral absorption fields.Among them,the absorbers working in the 8-13μm band have attracted widespread attention from researchers due to their application in radiative cooling.The basic principle of passive radiative cooling is that the atmosphere has a higher transmittance for electromagnetic waves in this band,allowing the heat from the surface to be radiated into space for cooling.In this study,the dielectric structure of metamaterial absorbers working in the 8-13 μm band was designed and optimized.The main work carried out is as follows:(1)A method for optimizing multi-layer dielectric film absorbers was proposed,which improves the absorptive performance of the structure by adding a specific patterned surface to the surface of the multi-layer dielectric film.The pattern arrangement was designed using genetic algorithms and reached convergence after an average of 30 iterations.Numerical simulation results show that the optimized structure has an average absorption rate of 81.63%in the 8-13 μm band,which is an improvement of 9.6%compared to the pre-optimization structure.It was also found that the absorption performance of the structure is significantly improved when the height of the metal pattern reaches 1.9 μm(aspect ratio of 14.6),with an average absorption rate of 95.83%,where the absorption rate in the 8-11.77μm band is above 90%.The effect of structural parameter changes on absorption performance was also investigated.(2)A radiator for radiative cooling was designed,which uses a patterned SiO2 grid array on a certain thickness of SiO2 to achieve high absorption in the 8-13 μm band and a cooling power of 154W/m2.Genetic algorithms were used to optimize the arrangement of the grid pattern,which converged after an average of 20 iterations.Numerical simulation results show that the structure has an average absorption rate of 98.81%in the 8-13 μm band,an improvement of 22.92%compared to the structure without a grid pattern array,with an average reflectance of 91.51%in the solar spectrum band.The effect of the structural size parameters on absorption performance was investigated,and the absorption mechanism was analyzed based on the field distribution.The angle sensitivity of the structure was also studied,and the calculation results showed that the average absorption rate of the structure is above 85%when the incident angle is less than 70 degrees,and the structure is insensitive to polarization.This structure provides reference value for the design of radiative cooling absorbers.