Radiation Regulation Based On Organic Hybrid Metamaterials Films

With the rapid development of the society,our demand for energy and energy conservation becomes more and more urgent.Solar energy is one of the main directions on energy utilization in the future.The sunlight is a kind of energy a kind of electromagnetic wave,which is also called solar radiation.Its main energy is distributed in the ultraviolet light,visible light and near-infrared region.At present,the utilization of solar energy mainly includes photovoltaic power generation,solar heating and photosynthesis.In this paper,the properties of sunlight in different media and structures are discussed and the regulation on thermal radiation is studied theoretically and experimentally.Firstly,we propose a random metamaterial,which can enhance the transmission of sunlight,and resuce mid-infrared radiation energy emitted indoors to enhance the greenhouse effect.Then,the reflectance and transmittance in the ultraviolet-infrared(UV-IR)range under different structures,concentrations and thicknesses were calculated by Matlab which is based on the Mie scattering and the surface plasmonic effects,and the optimized design was carried out.In this work,the metamaterial film was prepared by sol-gel methods according to the design optimization scheme.The properties of samples were characterized and and the process was summarized.Then,such random metamaterial film was prepared on a large scale.Two same size house models with film and without film were prepared to test the heating performance of the film.The indoor temperature of the model with the film was about 8℃ higher than that of the model without film.Further,a subwavelength grating structure encapsulated in PMMA with excellent property of the wavelength selectivity is theoretically proposed and experimentally carried out.Due to the lower-index contrast in our design compared to the common high index contrast grating(HCG),this technology has a low refractive contrast.Therefore,this design is called as low index contrast grating(LCG).Contrary to the assumption that high contrast is necessary for good optical selectivity,the gratings in this work is made of polymethyl methacrylate and titanium dioxide,which possesses an index contrast of n～1.2 in the visible light region.Generally,high contrast gratings are suspended in vacuum or made of metal materials with high energy consumption,it is difficult to realize large-scale applications with low cost.The low contrast grating proposed in this work is expected to achieve low cost and large scale production.Meanwhile,methods such as modal analysis and effective medium theory(EMT)are used to predict optical properties of LCGs.We found that LCGs are well-described by both methods,providing good optical selectivity,and less sensitive to the changes of structural parameters such as grating height compared to HCGs.In this work,a low contrast subwavelength grating is designed which can reflect the specific wavelength and possess the high transmittance at other angles and other wavelengths.This structure is expected to be applied to the light capture of the direct incident light,such as augmented photosynthesis,monochromatic light-emitting diodes that produce white light,and spectral conversion of single-band solar cells.In the design,we also used commercial finite-difference time-domain software(FDTD module in lumerical)for simulation calculation and particle swarm optimization to optimize the optical structure to minimize its transmittance at zero degrees around 530 nm.At last,this kind of subwavelength grating is prepared experimentally by means of nano-micromachining.The results are in good agreement with the theoretical calculation results.