The Control Of Nanostructures' Radiative Properties Based On Infrared Atmospheric Window

As a section of the electromagnetic wave spectrum,the infrared atmospheric window has a wide range of important applications in military and civilian fields such as infrared temperature measurement,imaging,thermal camouflage,night vision,and radiation refrigeration.In recent years,the development of nanomaterials,quantum physics and micro-nano processing and manufacturing technology has given new vitality to related technologies.As an important branch of infrared detectors,uncooled bolometers put forward demands for ultra-thin absorbers with broadband and high absorption.As an important feasible solution to energy problems,radiant refrigeration has problems in how to carry out effective dynamic control.The rise of metamaterials and their combination with phase change materials provide solutions to above problems.The report on the application of phase change materials to multi-stage dynamic radiant regulation also pointed out the direction for the active regulation of radiant cooling.Based on the infrared atmospheric window band,this thesis uses surface plasmon theory and phase change materials to optimize the design and analysis of the metamaterial absorber(radiator).This dissertation first studied the absorber of the uncooled bolometer,and designed two metamaterial absorbers with four-layer structure of Ti/Ge/Doped-Si/Ti with periodic elliptical surfaces.Among them,the single elliptical absorber can achieve a high absorptivity of over 90% in the range of 8.8?12.5 ?m.The average absorptivity can reach 96.5%.There are two absorption peaks at 9.43 ?m and 11.65 ?m,and their absorptivities are 98.8% and98.9%,respectively.The four-elliptical absorber can achieve an absorptivity of more than 80%in the wide spectrum band of 8-15 ?m in the infrared detection working band,and the average absorptivity of this band can reach 89.5%.Further analysis of the spatial distribution of electromagnetic fields and light-to-heat conversion reveals that surface plasmon theory is the cause of its wide spectrum and high absorption.In addition,the sensitivity analysis of the structural parameters of the metamaterial absorber and the polarization and incident angle provides a theoretical basis for the design and preparation.Finally,the influence of the spacing on thermal noise is analyzed based on the mechanism of near-field radiative heat transfer.Then,in this thesis,three metamaterial emitters are designed based on the dynamic regulation of radiant cooling in combination with phase change materials.The metamaterial transmitter before the phase change has the characteristics of wide spectrum and high emissivity in the long-wave infrared band.Through the phase change conversion of the phase change material,the emissivity of the transmitter can be greatly adjusted.The average emissivity difference between the two phases in the 8?13 ?m radiant cooling band can be up to 51%,which can be used to actively control of the radiant cooling,thermal infrared camouflage,etc.Analysis of the absorptivity under different polarizations and different incident angles revealed that there is basically no change in the emission when the incident angle is below 20°.