Browsing by Subject "Transmission"
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Item Open Access China in Denmark the transmission of Chinese art and architecture from the view of Jørn Utzon’s Danish socio-cultural background(SINTEF Academic Press, 2017) Chen-Yu, C.; Goad, P.; Myers, P.Danish architect Jørn Utzon’s lifetime obsession with Chinese art and architecture is well known. However, why Utzon was interested in China and how he perceived Chinese art and architecture were not clearly explained in the previous studies. To answer the above questions with a better understanding of Utzon and his Danish socio-cultural background, the authors examines the experiences of the young Utzon and his connection with varied ideas and artefacts associated with China. The authors argue that the path leading to Utzon’s reception of Chinese art and architecture can be traced back to the intermittent three-hundred-year connection between China and Denmark generally, and the legacy of the Royal Danish Academy of Fine Arts in particular. Together, these represent an amalgamation that assimilated diverse aspects of China taken by different people before and during Utzon’s early career. This further provided Utzon with the impetus to construct his own understanding of Chinese art and architecture with his pivotal study trip to China in 1958. Thus, China could serve as both Utzon’s aesthetic inspiration and confirmation for his architectural works.Item Open Access Experimental study of broadband unidirectional splitting in photonic crystal gratings with broken structural symmetry(American Institute of Physics, 2013-04-15) Colak, E.; Serebryannikov, A. E.; Cakmak, A. O.; Özbay, EkmelIt is experimentally demonstrated that the combination of diode and splitter functions can be realized in one broadband reciprocal device. The suggested performance is based on the dielectric photonic crystal grating whose structural symmetry is broken owing to non-deep corrugations placed at one of the two interfaces. The study has been performed at a normally incident beam-type illumination obtained from a microwave horn antenna. The two unidirectionally transmitted, deflected beams can show large magnitude and high contrast, while the angular distance between their maxima is 90° and larger. The dual-band unidirectional splitting is possible when using TM and TE polarizations. © 2013 American Institute of PhysicsItem Open Access Fano resonances in THz metamaterials composed of continuous metallic wires and split ring resonators(Optical Society of America, 2014) Li, Z.; Cakmakyapan, S.; Butun, B.; Daskalaki, C.; Tzortzakis, S.; Yang, X.; Özbay, EkmelWe demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices. (C) 2014 Optical Society of AmericaItem Open Access Focusing of electromagnetic waves by a left-handed metamaterial flat lens(Optical Society of America, 2005-10-31) Aydin, K.; Bulu, I.; Özbay, EkmelWe present here the experimental results from research conducted on negative refraction and focusing by a two-dimensional (2D) left-handed metamaterial (LHM) slab. By measuring the refracted electromagnetic (EM) waves from a LHM slab, we find an effective refractive index of -1.86. A 2D scanning transmission measurement technique is used to measure the intensity distribution of the EM waves that radiate from the point source. The flat lens behavior of a 2D LHM slab is demonstrated for two different point source distances of ds = 0.5λ and λ. The full widths at half maximum of the focused beams are 0.36λ and 0.4λ, respectively, which are both below the diffraction limit. © 2005 Optical Society of AmericaItem Open Access Frequency dependent steering with backward leaky waves via photonic crystal interface layer(Optical Society of America, 2009) Colak, E.; Caglayan, H.; Cakmak, A. O.; Villa, A. D.; Capolino, F.; Özbay, EkmelA Photonic Crystal (PC) with a surface defect layer (made of dimers) is studied in the microwave regime. The dispersion diagram is obtained with the Plane Wave Expansion Method. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Two facts are noted: First, a guided (bounded) wave is present, propagating along the surface of the dimer-layer. Second, above the light line, the fast traveling mode couple to the propagating spectra and as a result a directive (narrow beam) radiation with backward characteristics is observed and measured. In this leaky mode regime, symmetrical radiation patterns with respect to the normal to the PC surface are attained. Beam steering is observed and measured in a 70 degrees angular range when frequency ranges in the 11.88-13.69GHz interval. Thus, a PC based surface wave structure that acts as a frequency dependent leaky wave antenna is presented. Angular radiation pattern measurements are in agreement with those obtained via numerical simulations that employ the Finite Difference Time Domain Method (FDTD). Finally, the backward radiation characteristics that in turn suggest the existence of a backward leaky mode in the dimer-layer are experimentally verified using a halved dimer-layer structure. (C) 2009 Optical Society of AmericaItem Restricted İnönü’nün gururu: Ford Otosan İnönü Fabrikası(Bilkent University, 2024) Saydan, Erberk; Şenkaya, Hasan Utku; Yavuz, Oğulcan; Tan, Yunus; Hazar, Melis Öykü; Çengil, YiğitFord Otosan İnönü Fabrikası Eskişehir’in İnönü ilçesinde kurulmuştur. Ford Otosan’ın en önemli fabrikalarından biri olan bu fabrika özellikle ağır ticari araçların üretimi konusunda uzmanlaşmıştır. Ford Otosan fabrikası ülkemizdeki sanayinin gelişmesine büyük katkı sağlamasıyla birlikte açıldığı İnönü ilçesinde de istihdamın artmasına ve buna bağlı olarak nüfus artışına da sebep olmuştur. İnönü Fabrikası, motor üretimi, araç montajı ve Ar-Ge faaliyetleri gibi birçok alanda hizmet vermektedir. Fabrikada üretilen F-Max serisi kamyonlar ve yerli üretim şanzıman hem yerel pazarda hem de uluslarası pazarlarda fabrikanın öne çıkmasını sağlamıştır. Fabrika, Türk mühendislerin tasarladığı ve geliştirdiği ağır ticari araçlarla birlikte dünya çapında tescillenmiş başarılara imza atmıştır.Item Open Access Isolation and one-way effects in diffraction on dielectric gratings with plasmonic inserts(Optical Society of America, 2009-01-02) Serebryannikov, A. E.; Özbay, EkmelDiffraction of plane waves on dielectric gratings with planar plasmonic inserts is studied with the emphasis put on the anomalous selectivity of diffraction orders. It is shown that some formally propagating orders can be suppressed within a wide frequency range. The effect of suppression is more general than the isolation effect observed earlier in zero-permittivity and (near-)zero-index slabs and sensitive to the frequency dependent peculiarities of the field distribution within the plasmonic layer. It is required that the real part of the permittivity of this layer is positive less than unity. The wideband features of the suppression effect, i.e., one-way transmission and diffraction-free reflection are demonstrated. Narrowband selectivity effects are also studied. The structures suggested can be used for extending the potential of technologies that are based on multibeam operation and field transformation. (C) 2008 Optical Society of AmericaItem Open Access Modeling of spirals with equal dielectric, magnetic, and chiral susceptibilities(Taylor & Francis Inc., 2008) Saenz, E.; Semchenko I.; Khakhomov, S.; Guven, K.; Gonzalo, R.; Özbay, Ekmel; Tretyakov, S.In this article, we study spiral particles with optimized design parameters, which can make possible the realization of media with equal dielectric, magnetic, and chiral susceptibilities. Two different spiral structures are investigated: the canonical spiral (which consists of a split loop with two straight-wire sections, orthogonal to the loop plane and connected to the edges of the gap) and the true helix (which is obtained by bending a wire with a constant pitch angle). The transmission and reflection coefficients of arrays of spiral particles are obtained under plane wave excitation by numerical simulation. The properties of slabs formed by periodic chiral and racemic arrays of spirals are investigated. Good agreement is found between the presented results and the previously reported theoretical and experimental studies.Item Open Access Multifrequency spatial filtering: a general property of two-dimensional photonic crystals(Elsevier, 2016) Serebryannikov, A. E.; Colak, E.; Petrov, A.; Usik, P. V.; Özbay, EkmelSpatial filtering, an analog of frequency-domain filtering that can be obtained in the incidence angle domain at a fixed frequency is studied in the transmission mode for slabs of two-dimensional rod-type photonic crystals. In the present paper, the emphasis is put on the demonstration of the possibility to obtain various regimes of spatial filtering, i.e., band-stop, band-pass, and low-pass filtering in different frequency ranges in one simple configuration. The operation is based on the use of several Floquet-Bloch modes with appropriate dispersion properties, so that such one or two co-existing mode(s) contribute to the forming of a proper filter characteristic within each specific frequency range. It is shown that high-efficiency transmission and steep switching between pass and stop bands can be obtained in the angle domain for wide ranges of variation of the problem parameters. In particular, by varying the rod-diameter-to-lattice-constant ratio, one attains lots of freedom in the engineering of spatial filters with desired transmission characteristics.Item Open Access One-way Rayleigh-Wood anomalies and tunable narrowband transmission in photonic crystal gratings with broken structural symmetry(American Physical Society, 2013-05-03) Serebryannikov, A. E.; Özbay, EkmelIn photonic crystal (PC) gratings whose structural symmetry is broken owing to one-side corrugations, the Rayleigh-Wood anomalies can appear in a one-way manner. In the combination with the vanishing coupling to the lowest Floquet-Bloch mode at the upper band edge, these anomalies lead to the appearance of the defect-mode-like, i.e., very narrow one-way transmission, peak, which cannot appear in the corresponding slab of PC without corrugations. Such a sole peak can be transformed into a one-way transmission band with a desired width by varying angle of incidence. The nonoverlapping and thus switchable one-way (higher-order) and two-way (zero-order) transmission bands can be obtained in both the frequency and incidence-angle domains. Adjustment of PC lattice and corrugation parameters allows one to obtain two subsequent one-way bands, every being connected with a certain higher diffraction order. Conditions required for the appearance of a narrow one-way transmission band in the vicinity of a Rayleigh-Wood anomaly are well consistent with typical dispersion features of a very large class of PCs and do not need unusual performances.Item Open Access Photonic bandgap narrowing in conical hollow core Bragg fibers(AIP Publishing, 2014) Ozturk, F. E.; Yildirim, A.; Kanik, M.; Bayındır, MehmetWe report the photonic bandgap engineering of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightly smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap. A narrow transmission bandwidth is particularly desirable in hollow waveguide mid-infrared sensing schemes, where broadband light is coupled to the fiber and the analyte vapor is introduced into the hollow core to measure infrared absorption. We carried out sensing simulations using the absorption spectrum of isopropyl alcohol vapor to demonstrate the importance of narrow bandgap fibers in chemical sensing applications.Item Open Access A transparent 90 degree polarization rotator by combining chirality and electromagnetic wave tunneling(AIP Publishing, 2012-02-03) Mutlu, M.; Özbay, EkmelA three-layer chiral metamaterial is constructed by using two layers of four mutually rotated resonators and a subwavelength mesh sandwiched symmetrically between these layers. The resulting structure is an ultrathin, transparent, and polarization angle independent 90 degrees polarization rotator. Due to the electromagnetic tunneling effect exerted by the negative permittivity mesh, a cross-polarization conversion efficiency of 99% and 93% is achieved numerically and experimentally. The structure is modeled using the effective medium theory and then the transfer matrix method is applied to demonstrate the existence of the tunneling resonance theoretically.Item Open Access A two dimensional nanopatterned thin metallic transparent conductor with high transparency from the ultraviolet to the infrared(American Institute of Physics, 2012-11-01) Du, Q. G.; Sathiyamoorthy, K.; Zhang, L. P.; Demir, Hilmi Volkan; Kam, C. H.; Sun, X. W.The optical properties of a two-dimensional nanohole patterned aluminum thin film in hexagonal lattice are studied. The transmission dip can be moved out from the visible range by manipulating the lattice constant. The resulting nanopatterned thin film is demonstrated to exhibit a high transparency in a wide wavelength range. The origins of the transmission dip and the transmission drop are explained. For constant resistance, thicker films with a larger filling ratio lead to better transmittance in the visible range. Angular response of the nanopatterned metallic film is also analyzed, and transmittances using several other metals are compared.Item Open Access Wave propagation in metamaterial structures and retrieval of homogenization parameters(2007) Ircı, ErdinçElectromagnetic wave propagation in metamaterial structures (metamaterial slabs, metamaterial cylinders, metamaterial coated conducting cylinders etc.) are investigated. Scattered and transmitted electromagnetic fields by these structures due to electric line sources or plane wave illuminations are found. A generic formulation of these wave propagation problems is done, enabling any kind of metamaterial or conventional material to be used, having any sign combination of constitutive parameters and having any electric and/or magnetic losses. For one of these propagation problems i.e., metamaterial coated conducting cylinders illuminated normally with plane waves, achieving transparency and maximizing scattering are investigated thoroughly. It is found out that, rigorous derivation of transparency and resonance (scattering maximization) conditions for PEC core cylinder case under the sub-wavelength limitations yields the same conditions of two electrically small concentric layers of conjugately paired cylinders, given in the literature (when the inner core layer is also taken to the PEC limit). These transparency and resonance conditions are found to be heavily dependent on the permittivity of the metamaterial coating (for TE polarization) and the ratio of core-shell radii. The relations between the permittivity of the coating and the ratio of core-shell radii are investigated for achieving transparency and scattering maximization. Numerical results show that these analytical relations are quite successful and work better when the cylindrical scatter is electrically very small. A novel homogenization method for the retrieval of effective constitutive parameters of metamaterials is proposed and implemented. The method is based on the simple idea that the total reflection coefficient from a finite metamaterial structure has to resemble the reflection from an homogeneous equivalent. While implementing the method, 1, 2, . . ., 20 unit cells of the same metamaterial structure are stacked and their reflection coefficients are collected. The homogenization quality of the metamaterial is evaluated in terms of various factors, which showed that the method is very successful to retrieve the effective constitutive parameters of the metamaterial. Finally, another method has been proposed for the retrieval of surface wave propagation constants on any periodic or non-periodic grounded slab medium. As a preliminary, the method is applied to grounded dielectric slabs. The numerical results generally show good agreement with their theoretical counterparts.