Design,Fabrication And Characterization Of The Multilayer Film Based Spectrally Selective Emission Material For Infrared Stealth

The development of infrared detection technology and the precision-guided weapons poses a serious threat to the survival and safety of the military targets,infrared stealth technology has become an important factor to promote the battle effectiveness of the targets and win modern war.As a new infrared stealth material,the spectrally selective emission materials can suppress the infrared radiative characteristics of an object and achieve infrared stealth by the reductions of emissivity and real temperature.Generally,this type of materials has low emissivities in the two atmospheric windows（3-5μm and8-14μm）,and high emissivity outside the atmospheric windows for radiative cooling.Spectrally selective emission material can effectively solve the compatibility problem of emissivity and real temperature existing in the traditional infrared stealth materials,and is of great significance to infrared stealth and has a promising application prospect.Nowadays,the nanostructures are most extensively utilized to design and fabricate the selective emissive materials.However,the nanostructure based selective emissive material suffers from the poor spectral selectivity,complex structure and fabrication process,and the poor thermal stability.In addition,the radiative cooling performance by enhancing the thermal radiation in the non-atmospheric window and the infrared stealth performance of the spectral selective emission materials have not yet been systematically studied.In this thesis,by utilizing the intrinsic infrared optical characteristics of the ultrathin metallic film and dielectric material,the multilayer film based infrared selective emitter,with remarkable spectral selectivity,simple structure and good thermal stability is proposed for infrared stealth.By theoretical analysis and experimental characterizations,the tuning of the infrared spectral characteristics,variable temperature infrared emissivity,radiative cooling performance and infrared stealth performance of the multilayered selective emitter are fully studied.Our work is of great significance to promote the application of selective emission materials in infrared stealth technology.The thesis is divided into the following three parts:1.Ultrathin metallic film based multilayered selective emitter for infrared stealthA selective emitter for infrared stealth based on the intrinsic spectral characteristics of the ultrathin Ag film and the impedance matching principle was proposed.The high infrared extinction coefficients and the tunneling effect of the ultrathin Ag film make it a potential candidate to enhance the infrared radiative characteristics.An infrared transparent germanium（Ge）film was utilized and combined with the ultrathin Ag film to design a Ag/Ge multilayered selective emitter,which has low-emissivity(ε_3-5μm=0.18;ε_8-14μm=0.31)in the atmospheric windows and high-emissivity(ε_5-8μm=0.82)outside the atmospheric window.According to the variable temperature infrared emissivity measurements,the proposed emitter can retain its spectral selectivity from ambient temperature to 200℃effectively.Moreover,compared with the low-emissivity material,the Ag/Ge multilayered selective emitter exhibits lower real temperatures and higher radiative cooling efficiency owing to the strong thermal radiation in the 5-8μm range in both vacuum and indoor environments,and the maximum real temperature gaps between these two materials are 120℃and 15℃,respectively.Finally,the advantages of the Ag/Ge multilayered selective emitter over the low-emissivity material in infrared stealth were analyzed by theoretical simulations and experiments.The maximum radiation temperature gaps between the Ag/Ge multilayered selective emitter and the low-emissivity material in the 3-5μm and 8-14μm ranges are 19℃and 11℃,respectively.Overall,the Ag/Ge multilayered selective emitter can suppress the infrared characteristics and the radiation temperature of an object by reducing its emissivities in the atmospheric windows and real temperature,and exhibits better infrared stealth performance.2.A multilayered selective emitter for high-temperature infrared stealthHerein,by the optimization of the material system,a multilayered based infrared selective emission material with good thermal stability was proposed for high-temperature infrared stealth.With an ultrathin refractory molybdenum（Mo）film and transition metal oxide,hafnium oxide（Hf O₂）film,a Hf O₂/Mo multilayered emitter with remarkable spectral selectivity and good thermal stability is proposed.The emitter has low-emissivity in the 3-5μm atmospheric window(ε_3-5μm<0.3),and high-emissivity in the 5-8μm(ε_5-8μm>0.75).According to the infrared emissivity measurements,the multilayered emitter can retain its spectral characteristics from ambient temperature to700℃effectively in both vacuum and nitrogen conditions,while the spectral selectivity degrades owing to the oxidation of the ultrathin Mo film and the formation of the molybdenum-hafnium oxide（Hf Mo₂O₈）in the high-temperature air condition.The spectral selectivity and thermal stability of the Hf O₂/Mo multilayered emitter facilitate it to be applied in the infrared stealth of the high-temperature component of a spacecraft.3.A fully dielectric multilayered selective emitter for infrared stealthA multilayered selective emitter with a fully dielectric structure was proposed for infrared stealth based on the intrinsic high-reflectance band of aluminum nitride（AlN）.The infrared spectral characteristics and infrared optical constants of the AlN were first characterized to verify the existence of the high-reflectance band in the 11-15.5μm,and to analyze the feasibility of the application of AlN in selective emission infrared stealth material.Furthermore,the high-reflectance band of AlN was combined with a Ge/Mg F₂band-pass filter film to design a fully dielectric spectrally selective emissive infrared stealth material.According to the infrared emissivity measurements,the proposed material that functions from ambient temperature to 400℃is engineered to be low-emissive in the atmospheric windows(ε_3-5μm=0.26;ε_8-14μm=0.29)and high-emissive in the 5-8μm non-atmospheric window(ε_5-8μm=0.79).Owing to the low-emissivity in the atmospheric windows and radiative cooling performance,the AlN based selective emissive material exhibits better performance in infrared stealth compared with the AlN based low-emissivity material,and the maximum radiation temperature gap between the two materials in the 8-14μm range is 8.5℃.Finally,we achieve infrared-radar compatible stealth by integrating the fully dielectric AlN based selective emission material with a microwave absorber.The multispectral stealth material can retain the infrared spectral selectivity and exhibit an absorptivity higher than 0.9 at 8-11 GHz,simultaneously.