Thermal Tuning Intelligent Infrared Absorber

In recent years,infrared absorber has become an important research hotspot in the field of electromagnetic metamaterials(MA)due to its unique characteristics of electromagnetic resonance.With the rapid development of new phase change materials,infrared absorber not only has all the characteristics of metamaterials,but also becomes more and more intelligent with improved research and application value.In this paper,based on the classic metal/dielectric/metal sandwich structure and thermally induced phase transition properties of vanadium dioxide(VO2)films,thermal tuning infrared absorbers were designed and fabricated by using VO2 films as the bottom metallic layer or the dielectric layer of the infrared absorbers.We also have studied the dispersion characteristics of the relative dielectric constant of VO2 films in different states and the working mechanism of our infrared absorbers.The innovations of this paper can be summarized as follows:(1)We have studied the dispersion properties of the relative dielectric constants of VO2 thin films in its metallic state,insulating state,phase transition state and composite state with effective media theory(EMT)and nonlinear curve fitting method.According to the simulation and experiment,this method is simple and accurate,and it is also applicable to the complex substance.(2)Using the VO2 film as the bottom metallic layer or the dielectric layer,sandwich infrared absorbers with metal/dielectric/metal structure were designed and fabricated.When VO2 film was used as the bottom metallic layer,the design of our infrared absorber had no absorption peak and its reflectance was above 40% below the phase transition temperature Tc;when its temperature rose above Tc,there existed standing wave and magnetic resonance at the wavelength of 3.2 ?m and 7.5 ?m.When VO2 film was used as the dielectric layer,our infrared absorber had a strong broadband absorption peak at ? = 9.9 ?m below Tc,while its reflectance rose above 90% in the whole mid-infrared atmospheric window with its temperature rising above Tc.(3)Based on the sandwich infrared absorber with double dielectric layers,we proposed a method to realize broadband absorption which was based on the coupling between standing wave and magnetic resonance.According to our experimental result,there existed a strong absorption peak(absorptance is more than 80%)with 2.9 ?m bandwith in the center wavelength of 8.32 ?m for our broadband infrared absorber.This kind of broadband infrared absorber is easy-fabricated,and its absorption properties can be easily tuned by temperature.(4)Based on the thermal tuning intelligent infrared absorber,an easily identifiable and stable infrared watermark was designed and fabricated.During the phase transition region of VO2 film(61 ~71?C),the radiation temperature of the graphic area composed of infrared absorbers varied only 1.4?C(44.1 ~ 45.5?C),and its average emissivity in the heating process ranged from 0.45 ~ 0.56.Meanwhile,the radiation temperature varied only 0.4?C(42.6 ~ 43?C),and its average emissivity ranged from 0.45 ~ 0.51 in the cooling process.However,the radiation temperature of the area with continuous Al film on its surface varied from 21.3 ~ 21.9?C,and its average emissivity was around 0.04 both in the heating cycle and cooling cycle.