Browsing by Subject "Thermal camouflage"

Now showing 1 - 5 of 5

Open Access
Adaptive thermal camouflage using sub-wavelength phase-change metasurfaces
(Institute of Physics Publishing Ltd., 2022-12-09) Omam, Zahra Rahimian; Ghobadi, Amir; Özbay, Ekmel; Khalichi, Bahram
Sub-wavelength metasurface designs can be used to artificially engineer the spectral thermal signature of an object. The real-time control of this emission can provide the opportunity to switch between radiative cooling (RC) and thermal camouflage functionalities. This performance could be achieved by using phase-change materials (PCMs). This paper presents a sub-wavelength dynamic metasurface design with the adaptive property. The proposed metasurface is made of vanadium dioxide (VO2) nanogratings on a silver (Ag) substrate. The design geometries are optimized in a way that both narrowband and broadband mid-infrared (MIR) emitters can be realized. At low temperatures, insulating VO2 nanogratings trigger the excitation of Fabry–Perot mode inside the grating and surface plasmon polaritons at the metal–dielectric interface with an emission peak located in the MIR region to maximize the RC performance of the design. As temperature rises, the PCM transforms into a metallic phase material and supports excitation of Wood's anomaly and localized surface plasmon resonance modes. Accordingly, the thermal signature is adaptively suppressed.
Open Access
Exceptional adaptable MWIR thermal emission for ordinary objects covered with thin VO2 film
(Elsevier Ltd, 2021-01-25) Durna, Yılmaz; Kocer, Hasan; Aydın, Koray; Cakir, Mehmet Cihan; Soydan, Mahmut Can; Odabasi, Oguz; Işık, Halil; Ozbay, Ekmel
Monotonous thermal radiation emitted from an ordinary object can be brought into a dynamic and versatile form that can be shaped according to the application area with the ingenious design of the surface coatings. Building the coatings with phase change materials provides exceptional and surprising properties in terms of tunability, adaptability and multifunctionality. In this paper, we investigate the thermal radiation properties in the MWIR band through comprehensive thermographic measurements and theoretical methods while a thin (similar to 90 nm thick) vanadium dioxide (VO2) layer on the sapphire substrate (VO2 thin film) is placed on different ordinary objects under heating/cooling conditions. It is indicated that the emission of the metal object (low emittance) can be boosted and the emission of the blackbody-like object (high emittance) can be suppressed at the relevant temperatures. The thermal emission of the objects covered with thin VO2 film at high temperatures (>75 degrees C) is determined by only the VO2 thin film, since the VO2 layer is completely metallized and the MWIR radiation of the underlying object is masked. When the actual temperature of the object behaving like a blackbody rises up to 95 degrees C, the temperature detected in the MWIR thermal camera is reduced by more than 20% to approx. 75 degrees C due to the VO2 thin film on this object, providing thermal camouflage. It is experimentally and theoretically revealed that the underlying physical mechanism on these strange results is associated with the drastic change in the infrared optical parameters of the VO2 as a result of the applied temperature. (C) 2020 Elsevier Ltd. All rights reserved.
Open Access
Graphene-Based Adaptive Thermal Camouflage
(American Chemical Society, 2018) Salihoğlu, Ömer; Uzlu, H. B.; Yakar, Ozan; Aas, Shahnaz; Balci, Osman; Kakenov, Nurbek; Balci, S.; Olcum, S.; Süzer, Şefik; Kocabas, Coşkun
In nature, adaptive coloration has been effectively utilized for concealment and signaling. Various biological mechanisms have evolved to tune the reflectivity for visible and ultraviolet light. These examples inspire many artificial systems for mimicking adaptive coloration to match the visual appearance to their surroundings. Thermal camouflage, however, has been an outstanding challenge which requires an ability to control the emitted thermal radiation from the surface. Here we report a new class of active thermal surfaces capable of efficient real-time electrical-control of thermal emission over the full infrared (IR) spectrum without changing the temperature of the surface. Our approach relies on electro-modulation of IR absorptivity and emissivity of multilayer graphene via reversible intercalation of nonvolatile ionic liquids. The demonstrated devices are light (30 g/m2), thin (<50 μm), and ultraflexible, which can conformably coat their environment. In addition, by combining active thermal surfaces with a feedback mechanism, we demonstrate realization of an adaptive thermal camouflage system which can reconfigure its thermal appearance and blend itself with the varying thermal background in a few seconds. Furthermore, we show that these devices can disguise hot objects as cold and cold ones as hot in a thermal imaging system. We anticipate that, the electrical control of thermal radiation would impact on a variety of new technologies ranging from adaptive IR optics to heat management for outer space applications.
Open Access
Mid-infrared adaptive thermal camouflage using a phase-change material coupled dielectric nanoantenna
(Institute of Physics Publishing Ltd., 2021-04-23) Buhara, Ebru; Ghobadi, Amir; Khalichi, Bahram; Kocer, Hasan; Özbay, Ekmel
Recently, camouflage technology has attracted researchers' attention in a large variety of thermal applications. As a special phase change material (PCM), vanadium dioxide (VO2) is an excellent candidate for the studies conducted on thermal camouflage technology. VO2 has a transition from the insulator phase to the metal phase with the increase of the temperature. With regards to this unique feature, VO2 can contribute dynamic properties to the camouflage design. In this paper, a PCM–dielectric based metamaterial mid-infrared adaptive thermal camouflage nanoantenna is designed to perfectly mimic the atmospheric windows. The adaptive property of the proposed structure is obtained by using an ultrathin VO2 interlayer embedded within the grating. The spectral responses of the structure are computed using the finite difference time domain method, and the invisibility of the structure is proved using power calculations in the different mid-infrared regions.
Open Access
A Transparent all-dielectric multifunctional Nanoantenna emitter compatible with thermal infrared and cooling scenarios
(IEEE, 2021-06-30) Ghobadi, Amir; Osgouei, Ataollah Kalantari; Koçer, Hasan; Özbay, Ekmel
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.