Browsing by Subject "Polarization insensitivity"

Now showing 1 - 4 of 4

Open Access
Optically transparent metamaterial RF absorbers
(2023-05) Şahin, Furkan
Recent advances in metamaterials have allowed to impart unique properties to flat RF absorbers including broadband absorption, low thickness (in terms of the longest operating wavelength) and polarization insensitiveness, all essential to high-performance absorbers. For these RF absorbers, introducing additional properties of high optical transparency (in the visible range) and mechanical ro-bustness opens up also stealth window applications. However, achieving all of these critical characteristics in a single design is a challenging task. In this thesis, to address this challenge, we propose and demonstrate an optically transpar-ent, broadband, and polarization-insensitive RF absorbing metamaterial that is extremely thin (thickness = 0.079λL; λL: longest operating wavelength). Our design consists of a single dielectric layer of polymethyl methacrylate (PMMA) sandwiched between the top and bottom indium tin oxide (ITO) films, altogether providing high optical transmission. The bottom ITO film acts as a ground plane, which reduces the RF transmission significantly. On the other hand, the top ITO film adorns a unique pattern that minimizes the RF reflection across a particular frequency range. Here we obtained these customized ITO patterns using a novel design methodology. We developed the fabrication process specific to the pro-posed RF structure and fabricated their prototypes. To validate numerical simu-lation results, we measured experimentally the RF absorption of these fabricated prototypes. The experimental results show that the proof-of-concept absorbers achieve over 90% absorption between 4.4-11.2 GHz and over 95% absorption between 4.8-10.6 GHz. Furthermore, we found the fabricated absorbers to be in-sensitive to polarization angles and preserve 90% absorption for oblique incidence angles of 60° for TM and 40° for TE polarizations in agreement with the numer-ical predictions. Also, besides RF characterizations, we optically recorded the transmittance in the visible range to be 65% on average for the tested absorbers. These findings indicate that the proposed single-dielectric-layered architecture of optically transparent, broadband, polarization-insensitive RF absorbers, featur-ing a record relative thickness of 0.079λL, holds great promise for use in stealth window applications.
Open Access
Polarization insensitive phase change material-based nanoantenna array for thermally tunable infrared applications
(Institute of Electrical and Electronics Engineers, 2022-09-21) Khalichi, Bahram; Omam, Zahra Rahimian; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, Ekmel
Thermal radiation management is an emerging application of metamaterials owing to their exotic electromagnetic radiative properties. Herein, a thermally tunable phase change material-based nanoantenna array is reported to manipulate electromagnetic waves for potential applications in radiative cooling and multispectral camouflage from thermal infrared detectors. The simulation results show that the proposed nanoantenna array possesses high reflectance exceeding at least 60% within the 3−5 µm and 8−12 µm wavelength ranges, indicating low thermal emissivity, while the reflectance value increases as the temperature rises. Additionally, the wavelength-selective nanoantenna emitter operates with high absorption and therefore emission within the non-atmospheric window (5−8 µm). The thermally tuning feature leads to further controlling the absorption and, therefore, the emission performance of the nanoantenna and corresponding infrared signatures detected by thermal cameras.
Open Access
A Transmissive all-dielectric metasurface-based nanoantenna array for selectively manipulation of thermal radiation
(Institute of Electrical and Electronics Engineers, 2022-09-21) Khalichi, Bahram; Omam, Zahra Rahimian; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, Ekmel
In this study, a wavelength-selective thermal nanoantenna emitter based on metamaterial design with heat radiation signature management and radiative cooling property is proposed. The design can be considered as a multifunctional window by reducing the heat signature and releasing the heat energy within the non-atmospheric window. The approach relies on the indium tin oxide cubic-shaped unit cell coated on a flexible and transparent substrate (polystyrene). The spectral behaviors of the proposed structure are obtained using the finite difference time domain method, where the power calculation model is utilized to demonstrate the radiative cooling efficiency and low power detection on infrared cameras.
Open Access
Visible light nearly perfect absorber: an optimum unit cell arrangement for near absolute polarization insensitivity
(OSA - The Optical Society, 2017) Ghobadi, Amir; Hajian, Hodjat; Gökbayrak, Murat; Dereshgi, Sina Abedini; Toprak, Ahmet; Butun, Bayram; Özbay, Ekmel
In this work, we propose an optimum unit cell arrangement to obtain near absolute polarization insensitivity in a metal-insulator-metal (MIM) based ultra-broadband perfect absorber. Our findings prove that upon utilizing this optimum arrangement, the response of the absorber is retained and unchanged over all arbitrary incidence light polarizations, regardless of the shape of the top metal patch. First, the impact of the geometry of the top nanopatch resonators on the absorption bandwidth of the overall structure is explored. Then, the response of the MIM design for different incidence polarizations and angles is scrutinized. Finally, the proposed design is fabricated and characterized. © 2017 Optical Society of America.