Browsing by Author "Kocer, Hasan"

Now showing 1 - 4 of 4

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
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
Nano shell impact on Huygens’ metasurface dipolar resonances and optical response
(Optica, 2021-09) Kocer, Hasan; Işık, Halil; Durna, Yılmaz; Khalichi, Bahram; Kurta, Hamza; Özbay, Ekmel
Due to several advantages over conventional devices for the control of electromagnetic (EM) radiation, the demand for metasurface utilization based on artificially engineered micro and nanostructures is boosted, especially in new generation devices. Among the metasurfaces family, there has been a growing interest in Huygens’ metasur faces that are easy to fabricate due to their lower aspect ratio compared to their counterparts and also provide alternative electromagnetic radiation control by tuning the dipolar electric and magnetic resonances. In this study, an all-dielectric Huygens’ metasurface consisting of the high-refractive-index nano shells embedded in the low-refractive-index environment is designed and extensively investigated numerically and analytically in the near infrared spectrum. By simply tuning the nano shell inner radius, the effects on the dipolar resonances are unveiled specific to the proposed design. To assess the EM wave interactions in the designed Huygens’ metasurface, an ana lytical model based on the coupled discrete dipole approach is applied for selected distinct cases of the designed metasurface. It is shown that the spectral position of the dipolar resonances can be detuned or tuned simultaneously depending on the structural parameter of the meta-atoms arranged in a periodic array. This study sheds light on the physics and abilities of the nano shell structure as a Huygens’ metasurface for the potential applications of metasurface-based light–matter interaction including imaging and sensing.
Open Access
Phase-change Fano resonator for active modulation of thermal emission
(Royal Society of Chemistry, 2023-06-10) Khalichi, Bahram; Ghobadi, Amir; Kalantari Osgouei, Ataollah; Rahimian Omam, Zahra; Kocer, Hasan; Ozbay, Ekmel
Optical modulation of heat emission using spectrally selective infrared (IR) metasurface nanoantenna designs has found potential applications in various fields, including radiative cooling and thermal camouflage. While radiative cooling requires emitters to emit within atmospheric transmissive windows (mainly located at 8–14 μm), thermal camouflage structures have to operate within the non-transmissive window (5–8 μm) to hide an object from thermal imaging systems and cameras. Therefore, a passive nanoantenna structure cannot satisfy both conditions simultaneously. In this paper, we propose an adaptive nanoantenna emitter made of samarium nickelate (SmNiO3) phase change material to cover both functionalities with a single Fano resonator-based design. As the temperature rises, the thermal signature of the nanoantenna at the transmissive window is suppressed; therefore, a better camouflage performance is achieved. The dynamic tunability of switching from radiative cooling to thermal camouflage of the proposed Fano resonator-based design is quantitatively demonstrated using emissive power calculations under different conditions.