To restrain the infrared radiation from high temperature objects to decrease the probability of being discovered by infrared detectors operating in the mid- and far-infrared atmospheric windows, we design a one-dimensional heterostructure photonic crystal (PC) using low-cost coating materials Te and ZnSe, and test its reflection spectra and radiant temperature. The tested results show that this PC has high average reflectance in 3- to 5-μm and 8- to 14-μm wavebands, which is 86.72% and 72.91%, respectively, and the corresponding emissivity is 0.072 and 0.194, respectively. The radiant temperatures of the PC are always lower than those of the background, with the maximal difference of the radiant temperature being 31.97°C corresponding to a background radiant temperature of 75.64°C. The study confirms that the deposited PC can effectively decrease the infrared radiation in mid- and far-infrared bands.
In the near and middle infrared atmospheric window, infrared stealth material require a low absorptivity (which means a low emissivity according to Kirchhoff’s law of black body), at the same time, it also requires high absorptivity so as to decrease the reflectance at military laser wavelength of 1.06μm. Under this circumstances, compatible stealth of infrared and laser is an urgent demand, but the demand is ambivalent for conventional materials. Photonic crystal (PC), as a new type of artificial periodic structure function material, can realize broadband thermal infrared stealth based on its high-reflection photon forbidden band(also called photonic band gap). The high-reflection photon forbidden band of PC can be adjusted to near and middle infrared wave band through some rational methods. When a defect was added into the periodic structure of PC, a “hole-digging” reflection spectrum, which is high absorption at military laser wavelength of 1.06μm, can be achieved, so compatible stealth of near and middle infrared and military laser wavelength of 1.06μm can be achieved too. <p> </p>In this paper, we selected near and middle infrared-transparent materials, Te and MgF<sub>2</sub> , as high refractive index and low refractive index material respectively, and designed a one-dimensional one-defect-mode PC whose photon forbidden band was broadened to 1-5μm by constructing two photonic crystals into one. The optical property of the PC was calculated by Transfer matrix method(TMM) of thin-film optical theory, and the results shows that the as-designed PC has a high spectral reflectance in the near and middle infrared band, among which the reflectivity in 1.68μm∼5.26μm band reached more than 90%, and the 2.48∼5.07μm band even reached 99.99%. The result also shows that between the band gap of 1-5μm, there are one defect mode locating in the wavelength of 1.06μm, whose reflectance is below 0.70%, which means its spectral absorptivity is greater than 99.30%. All the above we have discussed proved that this “hole-digging spectrum” PC can realize the compatible stealth of near and middle infrared and 1.06μm military laser.
By using the electromagnetic wave reflection characteristics of the plasma,
the plasma can be used to design the reflector antenna. the paper designs a metal
parabolic cylindrical antenna and a plasma luminescence parabolic cylindrical
antenna, and uses CST software calculating the radiative properties of them,
analysising the key parameters of plasma luminescence parabolic cylindrical antenna
radiation and scattered radiation resistance. Simulation results show that selecting
appropriate plasma column spacing, plasma frequency, collision frequency, the
plasma luminescence parabolic cylindrical antenna has the same radiation
performance with metal parabolic antenna, at the same time, the RCS of plasma
antenna in working and not working are smaller compared with the metal antenna,
especially in plasma does not work ,the bistatic RCS reduced to a greater extent than
the previous related literature design.
Graphite with good extinction performance can be used as electro-optical passive jamming material for infrared and laser detection. In order to acquire the extinction characteristic of graphite smoke for terahertz wave (THz wave), graphite powder was dispersed in a KBr matrix with concentrations of 0.6 wt% and 1.0 wt% respectively, and those composites were processed in the stoving system and were then pressed into pellets. Meanwhile, the pure KBr powder pellet was prepared with same method under same condition. By utilizing THz-TDS, the THz transmission spectrums of those samples were measured in the frequency range 0.2-1.1 THz. Then, the absorption coefficients of those samples were deduced based on the material parameter estimation method. The experimental results indicate that the absorption coefficients of those samples are enhanced with the increasing THz frequency and that of them are improved with the concentrations of graphite at the same frequency. The results obtained demonstrate that THz wave has strong penetration capacity through graphite smoke and THz radar will be promising for use to make up for the deficiency of the infrared and laser detection system and to detect the targets coated with graphite smoke.