Abstract
In modern thermal infrared applications, multi-spectral camouflage scenarios should be developed to mitigate the thermal signature of an object. In general, camouflage needs to be satisfied in two main optical ranges: visible, and infrared (IR). In the IR range, two main camera modes are deployed to detect the IR signature of an object: i) short-wave IR (SWIR) cameras that detect the solar photons reflected off a surface, ii) mid-wave IR (MWIR) and long-wave IR (LWIR) cameras that directly collect the blackbody photons emitted from a hot object. Therefore, in an ideal scheme to acquire a multi-spectral camouflage function with self-cooling capability, the object should have: i) perfect absorption in the SWIR range, ii) perfect reflection in the MWIR and LWIR ranges, iii) perfect absorption and one-way transmission in non-transmissive IR (NTIR) window (to radiatively cool itself), and iv) visible transparency (to keep background visual appearance intact and to minimize the heat build-up due to solar absorption). In this paper, an all-dielectric nanoantenna emitter design is developed to comply with all the above-mentioned requirements. The approach relies on the indium tin oxide (ITO) grating structures coated on a flexible and transparent substrate (polystyrene). The spectral behaviors of the proposed structure are obtained using both analytical and numerical approaches. The design has an absorption peak with 0.8 amplitude in the SWIR mode (for the backward and forward illuminations), while it shows average reflections ≅ 0.7 in the MWIR and LWIR ranges for the forward illumination. The peak values of transmission and absorption within the NTIR window for the forward illumination are around 0.6 and 0.9, respectively. Meanwhile, the use of lossless materials within the visible range provides visible light transmission and minimizes the heat build-up due to solar absorption. In addition, the radiated power calculation model is utilized to demonstrate the low power detection on the IR cameras.
Highlights
Camouflage technology is developed to conceal the signature of an object from potential threats
We propose an all-dielectric metamaterial design to simultaneously satisfy all the above requirements for multi-spectral camouflage which acts as a visibly transparent multifunctional window by hiding the indoor main targets from the thermal as well as reflected IR cameras in addition to cooling itself and the surrounding medium due to the realization of wavelength-selective emission and transmission spectra within the NTIR range
Emitter at room temperature in the MWIR and LWIR ranges are reduced by 83.19% and 72.32% compared to the blackbody radiation, respectively
Summary
Camouflage technology is developed to conceal the signature of an object from potential threats. The advancement in sensors pushed this field to multi-spectral camouflage requirements in order to cover the multiple detection scenarios [1]–[3]. Camouflage needs to be satisfied in two main wavelength ranges; i) visible, and ii) infrared (IR). The use of pigments with proper coloration can provide visual camouflage via imitating the surrounding background or by resembling something else. For the IR case, we need to cover multiple detection ranges to mitigate the IR signature of an object without disturbing the visible appearance. According to Planck’s radiation law [4], [5], a blackbody in thermal equilibrium with a temperature above the absolute zero spontaneously and continuously emits electromagnetic
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