Design And Simulation Of Broadband Infrared Absorber With Adjustable Absorption Characteristics

Electromagnetic wave absorbers working in microwave,terahertz,infrared,visible and ultraviolet bands are research hotspots in the field of electromagnetics,and such electromagnetic absorbers have broad application prospects in optical sensors,photothermal energy converters,imaging and stealth cloaks.The electromagnetic absorber uses the most appropriate combination of materials and absorption mechanisms to make it show perfect absorption effect.The electromagnetic absorber uses the most appropriate combination of materials and absorption mechanisms to make it show perfect absorption effect.For most electromagnetic absorbers that currently exist,once manufactured,their structure is fixed,and they can only achieve specific absorption in a specific wavelength range.To solve this problem,researchers often integrate active materials with adjustable properties into electromagnetic absorbers to achieve adjustable absorption characteristics.Vanadium dioxide（VO₂）is an excellent active material,which can adjust its conductivity by thermal control,applied field and other methods,and has the characteristics of fast response and high control strength.In this paper,two infrared absorbers with adjustable bandwidth based on active material VO₂ are designed,and their absorption characteristics are studied by finite element method,and the specific work is as follows:（1）Based on VO₂,titanium dioxide（TiO₂）and sodium fluoride（Na F）materials,a multilayer truncated infrared absorber with adjustable absorption characteristics was designed.The absorption characteristics were analyzed by finite element method,including the relationship between absorber absorption rate and structural parameters,incidence angle,polarization angle and working wavelength,and these phenomena were analyzed in detail based on field distribution.The results show that the absorption mechanism of the absorber is mainly the surface plasma resonance effect.Under the condition of optimal structural parameters,the adjustability of the absorption characteristics can be achieved by adjusting the conductivity of VO₂.When VO₂ is in the metallic state,the absorption rate of the absorber exceeds 90%in the wavelength range of 12～51μm.Among them,in the wavelength range of 21～25um and 35～43um,the absorption rate can reach 99.8%,the average absorption rate can reach 96.4%,and the relative bandwidth can reach 124%.In the range of incidence angle of 0～55°,TM waves in the wavelength range of 12～52μm,TE waves in the wavelength range of 20～45μm,the absorption rate can reach more than 80%.When the incident wave is incident perpendicularly,the absorption rate is not sensitive to the angle of polarization.By changing the conductivity of VO₂ when other parameters remain unchanged,the absorption rate of the absorber can be adjusted to achieve the adjustability of the absorption rate.（2）Based on VO₂,TiO₂ and lithium fluoride（LiF）materials,a dynamically adjustable infrared ultra-broadband absorber with absorption characteristics was designed.The calculation of its absorption characteristics using the finite element method shows that:The absorption mechanism of this absorber is mainly the surface plasmon resonance effect.By adjusting the conductivity of VO₂,the absorption characteristics of the absorber can be adjusted.When VO₂ is in the metallic state,for TM waves,when the incidence angle is increased from 0°to 60°,the absorption rate of the absorber can be maintained at about 90%in the wavelength range of 17～55μm.For TE waves,when the angle of incidence is increased from 0°to 55°,efficient absorption of about 90%can still be achieved in the wavelength range of 10～55μm.When TM wave or TE wave is incident vertically,in the16～60μm band,the absorption rate is greater than 90%,and the absorption bandwidth can reach 54μm,of which in the wavelength range of 21～26μm,28～36μm and 42～53μm,the absorption rate can reach more than 98%,and it has polarization insensitive characteristics.When other parameters remain unchanged,As the conductivity of VO₂ changes from200000S/m to 20S/m,the absorption curve decreases significantly,and the corresponding three absorption peak-to-peak values are also decreasing,which can convert the ultra-wideband absorber into a multimodal absorber.The two different structures of infrared absorbers designed in this paper can realize the ultra-broadband perfect absorption and the wide angle of incidence absorption in the infrared band,and both can adjust the absorption characteristics of the absorber by adjusting the conductivity of VO₂.It provides a certain theoretical basis for the design,production and application of tunable infrared absorber,which is expected to be applied in polarization detectors,thermal emitters,infrared sensors and other fields.