Study On Multilayer Infrared Absorber With Tunable Structural Colors

Nowadays,electromagnetic waves are used more and more widely in human society.At the same time,the development of social life and science and technology is also inseparable from the development of electromagnetic wave control technology.Therefore,the research on the manipulation of electromagnetic waves has always been important research field.However,most of the traditional devices that can manipulate electromagnetic waves have used the intrinsic properties of materials.Such devices usually have large volume,and it is difficult to control electromagnetic waves flexibly,which limits the practical application of traditional electromagnetic devices.In recent years,a new artificial material,metamaterial,which has developed rapidly with the development of micro-nano processing technology,has brought a broad prospect and hope for the electromagnetic control materials.Among them,the metamaterial absorbers(MA)attract the attention of considerable researchers owing to their enhanced performance and reduced thickness.The application of MA in ultraviolet,visi-ble,infrared and microwave bands has been extensively studied.And,infrared MA have ex-cellent application prospects in electromagnetic stealth,infrared imaging,passive cooling and sensing,etc.Therefore,the research on infrared MA has been a research hotspot in the field of metamaterials.However,most of these MA can only manipulate electromagnetic waves in one band,and few researchers have paid attention to multi-spectral manipulation.At present,most of the existing researches on multi-spectral manipulation focus on the realization of daytime passive cooling.In addition to infrared metamaterial absorbers used in daytime radiant cooling,the traditional infrared MA can only realize high-efficiency absorption in the infrared band,and cannot manipulate the electromagnetic wave in the visible region to change their surface color,which limits their application in practice.The surface color of object is an important factor affecting people's perception of object.Therefore,the research on the surface color of met-amaterial absorbers has practical significance.Thus the research of this thesis is mainly fo-cused on the metamaterial absorber with structural color.The main research contents are as follows:1.Infrared broadband multilayer film absorber with tunable structural colors.A multi-layer film structure consisting of alternately sub/[Nichrome/Ge/Nichrome/Zn S/Ge/Zn S]/Air from bottom to top was designed.The optimal geometric parameters of the structure are ob-tained by using genetic algorithm and transfer matrix method.Utilizing the high inherent loss characteristics of nichrome,the structure has excellent broadband absorption performance in the atmospheric transparent window.Its average absorptivity in the 8-13?m band is higher than 95%,and the maximum absorptivity can reach 99.27%.Moreover,when the thickness of the top layer film changes,the visible reflective spectrum of the structure will also change,which means that the surface color of the structure can be adjusted by changing the thickness of the top layer film within a certain range.At the same time,by calculating the infrared ab-sorption spectrum when the thickness of the top layer changes between 130nm-260nm,it is determined that the absorption performance of the structure is insensitive to the change of the thickness of the top layer.This shows that the structure can adjust the surface color by chang-ing the thickness of the top layer film while maintaining its infrared absorption performance.In addition,the infrared absorption performance of the structure is insensitive to the incident angle.The proposed MA still maintains relatively high absorptivity at large incident angles regardless of the incident polarizations.However,the incident angle has an effect on visible reflection spectrum.When the incident angle increases,the reflection peak is slightly blue-shifted,so the surface color of the structure changes slightly.2.Infrared multilayer absorber with tunable structural colors and tunable absorptivity based on Ge₂Sb₂Te₅(GST).A multilayer film structure consisting of alternately sub/[Au/GST/Ge/Zn S]/Air from bottom to top was designed.Among them,GST is a kind of phase change material which can convert between crystalline state,amorphous state and intermedi-ate state.When GST is crystalline state,due to the inherent loss of crystalline GST,the de-signed structure has a wide bandwidth absorption peak with a maximum absorptivity of 92.06%at about 10.9?m,and the average absorption rate is 65.71%in the 8-13?m.When the GST is amorphous state,the maximum absorptivity of the structure is only 9.17%,because the amorphous GST is transparent in this band.The dielectric constant of intermediate GST was obtained by Lorentz-Lorenz relation,and the absorption spectrum of the structures with dif-ferent crystallization fraction of GST are simulated calculation.When the crystallization frac-tion of GST increases gradually,the maximum absorptivity and average absorptivity of the structure will gradually increase,which means that the infrared absorptivity of the structure can be adjusted by controlling the phase transition of GST.At the same time,this structure can also adjust its surface color by changing the thickness of the top layer film.Finally,the influence of the thickness of the top layer film and the incident angle on the infrared absorp-tion performance of the structure was studied by simulation.In this thesis,the lithography-free multilayer infrared absorbers with tunable structural colors are designed,and these are studied and analyzed in detail through numerical simulation.The absorber with tunable structural color can meet people's needs for the surface color of the object,so our research has great practical value.