A Transparent All-Dielectric Multifunctional Nanoantenna Emitter Compatible With Thermal Infrared and Cooling Scenarios

Abstract

In modern warfare, multi-spectral camouflage must be developed to conceal the thermal signature of an object. In general, camouflage needs to be satisfied in two main optical ranges: visible, and infrared (IR). In 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) windows (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 has been developed to comply with all the above 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 SWIR mode (for the backward and forward illuminations), while it shows > 0.7 average reflections in the MWIR and LWIR ranges for the backward illumination. The peak values of transmission and absorption within the NTIR window for the backward 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 infrared cameras.INDEX TERMS Binary grating, Metamaterial, Nanoantenna emitter, Plasmonic, Thermal camouflage I. INTRODUCTIONCamouflage technology is developed to conceal the signature of an object from potential threats. However, the advancement in sensors pushed this field to multi-spectral camouflage requirements in order to cover the multiple detection scenarios [1]-[3]. In general, camouflage needs to be satisfied in two main wavelength ranges; i) visible, and ii) infrared (IR). For the visible range, the use of pigments with proper coloration can provide visual camouflage via imitating the surrounding background or by resembling something else. However, 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

Microheater-Integrated Spectrally Selective Multiband Mid-Infrared Nanoemitter for On-Chip Optical Multigas Sensing

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Phase-change Fano resonator for active modulation of thermal emission

“…[6][7][8][9][10] Therefore, metasurface and plasmonic nanostructures with wavelength selectivity can be utilized to artificially engineer the emission response of a host platform by realizing perfect absorption, which enables thermal applications such as IR imaging, noncontact thermometry, radiative cooling, [11][12][13][14][15] and thermal camouflage. [16][17][18][19] For the radiative cooling purpose, the spectral position of the emissive power must be located within the atmospheric transmissive window (8-14 μm). At the same time, thermal camouflage requires spectral coverage placed within the non-transmissive window (5-8 μm).…”

Polarization Insensitive Phase Change Material-Based Nanoantenna Array for Thermally Tunable Infrared Applications

“…On the other hand, the emissivity of a structure at the thermodynamic equilibrium is connected to its absorptance as ε(T, λ) = α(T, λ), according to Kirchhoff's radiation law. Therefore, tailoring the optical absorption response of a design is effectively equivalent to controlling its radiation character [2]- [5]. A common approach to control the thermal radiation that originates from the very top surfaces of an object is to design a wavelength-selective IR absorber/emitter.…”