Browsing by Subject "absorption"

Now showing 1 - 4 of 4

Open Access
Graphene-enabled electrically switchable radar-absorbing surfaces
(Nature Publishing Group, 2015) Balci O.; Polat, E.O.; Kakenov, N.; Kocabas, C.
Radar-absorbing materials are used in stealth technologies for concealment of an object from radar detection. Resistive and/or magnetic composite materials are used to reduce the backscattered microwave signals. Inability to control electrical properties of these materials, however, hinders the realization of active camouflage systems. Here, using large-area graphene electrodes, we demonstrate active surfaces that enable electrical control of reflection, transmission and absorption of microwaves. Instead of tuning bulk material property, our strategy relies on electrostatic tuning of the charge density on an atomically thin electrode, which operates as a tunable metal in microwave frequencies. Notably, we report large-area adaptive radar-absorbing surfaces with tunable reflection suppression ratio up to 50 dB with operation voltages <5 V. Using the developed surfaces, we demonstrate various device architectures including pixelated and curved surfaces. Our results provide a significant step in realization of active camouflage systems in microwave frequencies. © 2015 Macmillan Publishers Limited. All rights reserved.
Open Access
Practical multi-featured perfect absorber utilizing high conductivity silicon
(Institute of Physics Publishing, 2016) Gok, A.; Yilmaz, M.; Bıyıklı, N.; Topallı, K.; Okyay, Ali Kemal
We designed all-silicon, multi-featured band-selective perfect absorbing surfaces based on CMOS compatible processes. The center wavelength of the band-selective absorber can be varied between 2 and 22 μm while a bandwidth as high as 2.5 μm is demonstrated. We used a silicon-on-insulator (SOI) wafer which consists of n-type silicon (Si) device layer, silicon dioxide (SiO2) as buried oxide layer, and n-type Si handle layer. The center wavelength and bandwidth can be tuned by adjusting the conductivity of the Si device and handle layers as well as the thicknesses of the device and buried oxide layers. We demonstrate proof-of-concept absorber surfaces experimentally. Such absorber surfaces are easy to microfabricate because the absorbers do not require elaborate microfabrication steps such as patterning. Due to the structural simplicity, low-cost fabrication, wide spectrum range of operation, and band properties of the perfect absorber, the proposed multi-featured perfect absorber surfaces are promising for many applications. These include sensing devices, surface enhanced infrared absorption applications, solar cells, meta-materials, frequency selective sensors and modulators. © 2016 IOP Publishing Ltd.
Open Access
Synthesis and dye sensitized solar cell applications of Bodipy derivatives with bis-dimethylfluorenyl amine donor groups
(Royal Society of Chemistry, 2015) Çakmak, Y.; Kolemen, S.; Buyuktemiz, M.; Dede, Y.; Erten-Ela, S.
Three Bodipy dyes with strong absorptivities in the visible and near infrared regions were designed, synthesized and their potential as photosensitizers for liquid electrolyte-based dye sensitized solar cells have been evaluated. For the first time Bodipy derivatives with bis-dimethylfluorenyl amine donor groups which were known for their bulky structures as donor groups have been used together. We altered our mostly used triphenylamine group with these and investigated the dye-sensitized solar cell efficiencies of this new class of Bodipy dyes. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015.
Open Access
Triangular metallic gratings for large absorption enhancement in thin film Si solar cells
(Optical Society of American (OSA), 2012) Battal, E.; Yogurt, T.A.; Aygun L.E.; Okyay, Ali Kemal
We estimate high optical absorption in silicon thin film photovoltaic devices using triangular corrugations on the back metallic contact. We computationally show 21.9% overall absorptivity in a 100-nmthick silicon layer, exceeding any reported absorptivity using single layer gratings placed on the top or the bottom, considering both transverse electric and transverse magnetic polarizations and a wide spectral range (280 - 1100 nm). We also show that the overall absorptivity of the proposed scheme is relatively insensitive to light polarization and the angle of incidence. We also discuss the implications of potential fabrication process variations on such a device. © 2012 Optical Society of America.