Study Of Metamaterial Electromagnetic Absorber From Visible To Mid-infrared Spectrum

Metamaterial electromagnetic absorber is a new type of artificial electromagnetic material that have emerged in recent years,and their unique electromagnetic properties have rapidly become a research hotspot in the field of electromagnetic absorbers.Since the first successful realization of metamaterial electromagnetic absorber in 2008,metamaterial electromagnetic absorbers have developed into a new discipline integrating physics,engineering,materials science,and optoinformatics under the wide attention of domestic and international academia and industry.This dissertation focuses on the metamaterial electromagnetic absorber devices in the visible to mid-infrared wavelengths,using theoretical simulations to guide the experimental preparation.A more systematic study has been carried out to analyze the mode of interaction between electromagnetism and matter in the visible to mid-infrared wavelengths.The detailed research work and innovations in this thesis are as follows:First,a new ultra-broadband metamaterial electromagnetic absorber is designed and simulated in the visible to near-infrared band.The structure of the proposed absorber is silicon dioxide（Si O₂）,titanium（Ti）,magnesium fluoride（Mg F₂）and aluminum（Al）in order from top to bottom,with the upper Si O₂ and Ti layers as rectangular cubes.Simulation results show that the absorber has an average absorption of 95.14%in the visible to near-infrared（405-1505 nm）band.This ultra-broadband perfect absorption is attributed to the combined excitation of propagating surface plasmon resonance（PSPR）,local surface plasmon resonance（LSPR）,and Fabry-Perot cavities.In addition,the absorber is insensitive to the incident angle of the electromagnetic wave and is not affected by the polarization of the electromagnetic wave.The absorber has promising applications in the fields of thermoelectric devices and solar photothermal conversion.Second,a metamaterial dynamic thermal radiation modulator is simulated and designed in the near-to mid-infrared band,which can be used as an internal and external radiation switch in the mid-infrared atmospheric window（3.5-5 and 8-14μm）.The radiator employs a vanadium dioxide（VO₂）material with phase change properties and a multilayer metal-dielectric-metal structure（MIM）.Its broadband radiation and dynamic thermally tunable properties are determined by a combination of separated magnetic resonance,surface equipolar excitations,and the thermal phase change properties of VO₂.When the ambient temperature is lower than the VO₂ phase transition temperature,the regulator can absorb heat from the outside to achieve temperature increase;when the ambient temperature is higher than the VO₂ phase transition temperature,the regulator can radiate heat to the outside to achieve temperature reduction.These phenomena show that the regulator has potential applications in intelligent temperature control systems.Third,a superhydrophobic subambient radiation cooler for humid environments was designed and fabricated in the mid-infrared band,which consists of 200 nm-thick silver（Ag）,100μm-thick polyvinyl fluoride（PVF）film,and 20 nm-diameter modified Si O₂ nanospheres.The Si O₂nanospheres modified by low surface energy polymer materials not only enhance the infrared radiation of the cooler,but also increase the roughness of the cooler surface,making it superhydrophobic.The average absorption of the radiative cooler is less than 4%in the solar radiation spectrum and more than 90%in the atmospheric window band.Experimental results show that the cooler can reduce surface dew retention in high humidity environments thereby achieving radiative cooling below ambient temperature,which is important for changing energy consumption patterns in humid and hot regions.