Study On Spectral Radiative Properties Of The Typical Solid Microstructure Surfaces And Their Application

Owing to their advantages of rich radiative properties and strong tuning capabilities,the microstructure surfaces are widely used in the fields of target detection,spacecraft thermal control,and solar energy utilization.At the same time,the microstructural surface based on reversible thermochromic materials has a wide application prospect in the above fields because of its radiative properties which can change with temperature reversibly.Although many studies on the radiative properties of microstructure surfaces have been carried out.However,only a few pieces of research have been focused on radiative properties of grating-like microstructure surfaces generated by machining,especially considering the fact that the influence of the substrate morphology on the surface radiative properties is still unclear.At the same time,anodizing treatment is often carried out on aluminum alloy surface to improve the surface corrosion resistance and wear resistance in which process a layer of porous anodic aluminum oxide(AAO)photonic crystal microstructure coating is formed on the surface,which changes the surface radiative properties significantly.Whereas such a topic is still lacking systematic research.In addition,compared to the AAO coating with stable radiative properties,the thermochromic smart coating based on vanadium dioxide(VO₂)can automatically tailor its radiative properties according to the temperatures.It thus has great potential usage in the field of spacecraft thermal control and energy-saving smart windows.Although many studies have been carried out on VO₂ thermochromic smart coatings,the regulating characteristics of radiation characteristics and application performance of smart coatings remain to be further studied.Based on the above-mentioned background,this paper firstly takes the grating-like microstructure surfaces produced by machining and the AAO photonic crystal microstructure coating produced by aluminum alloy anodizing as the research objects.A new style of scatterometer is designed and built for studying the scattering characteristics of the actual processed surface and the surface of the AAO coating,which provides reference and data support for the scattering problem of the related surface.On the other hand,the finite difference time domain(FDTD)method is employed to study the influence of structural parameters on the surface infrared radiative properties.Moreover,VO₂ multilayer smart coating in thermal management area and VO₂ core-shell nanoparticle-based coating used in smart window are studied respectively from the aspect of influence mechanism,i.e.,how the structural parameters and materials will affect their spectral radiative properties and tuning capabilities.The main work of this paper includes:A new style of automatic scatterometer is designed and built.The performance of the instrument was verified by a silicon wafer and a standard diffuse reflector plate.The bidirectional reflectance distribution function(BRDF)of grating-like microstructure surface produced by plain milling,planer processing,and flat grinding were measured using the developed scatterometer.The results show that when the incident plane is parallel and perpendicular to the fringes of the milling surface,the surface BRDF exhibits diffuse and specular reflection distribution characteristics,respectively.However,the BRDF variation of planer processing and flat grinding surface with the incident azimuth angle is completely opposite to that of the plain milling surface.The Monte Carlo ray tracing(MCRT)method was used to study the scattering distribution of grating-like surfaces in hemispheric space under different polarized light and incident angles.The results show that the scattering range of the grating-like machined surface in hemispheric space is elliptical.In order to investigate the influence of substrate morphology on the spectral radiative properties of grating-like microstructure surface,well-defined grating surface models,such as rectangular,sine,arc tip,and sawtooth,were established in this paper.In addition,considering that the morphology of the processed surface has certain randomness,the Gaussian grating-like surface model was also established.By using FDTD method,the influence of surface roughness,period length,surface morphology,incident light polarization state on its surface spectral emissivity were studied.The results show that the spectral absorptivity of the sinusoid,circular cusp,and triangle grating surface are close to each other.The spectral absorptivity of Gaussian random grating-like surface is the highest under the same roughness.To study the radiative properties of the AAO coating produced by anodic oxidation of aluminum alloy,the surface scattering characteristics of AAO coating were experimentally studied by using the scatterometer developed in this paper,and the infrared spectral emissivity of the AAO coating was theoretically studied by FDTD method.Based on the experimental and calculation results,the influence rules and mechanism of structure parameters of AAO coating on the surface BRDF and infrared spectral emissivity were analyzed.It turns out that the BRDF of AAO coating surface is mainly affected by the porosity.This can be explained by the change of the equivalent refractive index of the AAO coating as the porosity changes.The infrared spectral emissivity of AAO coating is determined by the porosity and thickness concurrently.The emissivity of AAO coating decreases with the increase of porosity and increases with the increase of film thickness in the wavelength range of 3?10?m.In the wavelength range of 10?15?m,the emissivity of AAO coating increases with the increase of porosity but does not change with film thickness.Compared with the AAO coating,the VO₂ thermochromic microstructure coating has the unique advantage of its radiative properties reversibly changing with temperature,which makes it very promising in the fields of smart thermal control coatings and energy-saving smart window coatings.The VO₂ multilayer film which can be applied to spacecraft thermal control was investigated based on the transfer matrix method.More specifically,this topic includes the study of the influence of structural parameters and the refractive index of the spacer layer on the radiative properties and emissivity control ability of VO₂/Spacer/Al sandwich structure smart coating.Secondly,for the VO₂ core-shell nanoparticle-based thermochromic smart window coating,the equivalent medium theory combined with the transfer matrix method was employed to figuring out the influence law and mechanism of the optical constants of the shell material,shell thickness,particle volume fraction,and coating thickness on the radiative properties and regulation performance of smart window coatings.The results show that the refractive index of the Spacer material mainly affects the emissivity of the metallic state of the smart coating with VO₂/Spacer/Al structure,and the optimal refractive index ranges from 3.2 to 4.2.For the VO₂ core-shell nanoparticle-based smart window coating,it is found that when the refractive index of the shell material is between 1.6 and 2.3,it can play a role in improving the solar energy modulation of the smart window coating,and there exists an optimal relative shell thickness.