Research On Visible-near-infrared-mid-Infrared Multi-band Stealth

The art of detection technology has been gradually developed for decades in the aspects of detection spectrum band(from single band to multiband),integration(from single units to arrays),and field of view(from a fixed one to a tunable one),with sensitivity,accuracy,detection range,anti-interference,and convenience improved continuously.Correspondingly the requirements for stealth have also been raised in terms of spectrum range(multiband and wide range)and scalability.The recently developed hyperspectral detection technology,being able to record spectral information for thousands of continuous bands,can be integrated with satellite remote sensing systems to achieve large-scale and high precision detection.Thus,higher requirements have been proposed for stealth technology.This paper adopts the methods of simulation and experiment.Two sorts of software(TFCalc and FDTD)are utilized to design structures and analyze spectra to meet stealth requirements of different levels and spectrum bands,including the requirements of second-level hyperspectral stealth,first-level hyperspectral stealth,simultaneous second-level hyperspectral stealth&mid-infrared stealth,and simultaneous first-level hyperspectral stealth&mid-infrared stealth requirements.Through optimization,different optical film structures are obtained to meet corresponding stealth requirements.The optical films can simultaneously realize stealth in the spectrum range of 400-2500nm(the special reflection spectrum range of green plants),and low radiation in the mid-infrared atmospheric window.100%of the spectrum in the 400nm-2500nm band meets the green plant reflection channel.The spectral distance between the spectrum of the optical film and the spectrum of standard green plant is 1.85,the spectral angle is less than 0.12rad.The average emissivity in the mid-infrared atmospheric window is less than 0.1.Besides,the radiative heat dissipation channel is realized in the non-atmospheric window(5-8μm),with transmittance greater than 0.5.The stealth performance is improved and the stealth spectrum range is expanded as well.As a further step,the designed structures are modified to meet the demands of existing fabrication methods.The samples are fabricated using the method of vacuum evaporation.The reflectance,transmittance,and absorptivity of the samples are measured and then compared with the reflection channels of green plants;the influence of incident angle on reflection spectrum is also studied in the experiment.Then scanning electron microscope is utilized to measure the thickness of different layers in the structure,and the influence of thickness change on reflectivity is examined.When the deviation of the film thickness is within ±3%,the characteristic of reflectivity can meet the requirement of the reflection channel of the green plant.Besides,the sample can maintain angular adaptability when the incident angle is within 30°;hence the sample can adapt to different incident angles of sunlight(due to the nearly constant reflectivity at different incident angles),and answer to stealth requirements in different practical scenarios.