Browsing by Subject "Materials"

Now showing 1 - 8 of 8

Open Access
Bi-angular lens for material characterization
(IEEE, 1994) Yaralıoğlu, Göksen Göksenin; Atalar, Abdullah; Köymen, Hayrettin
In this paper a new lens design is proposed for characterization of layered materials. Lamb wave lens employs Lamb waves for this purpose since these waves propagate along interfaces. However, below cut-off angle, the critical angles of Lamb wave modes are low and the generated V(z) curves have small number of oscillations, which in turn causes measurement difficulties and accuracy degradation. Bi-angular lens described in this paper, generates an extra obliquely incident wave, instead of normally incident beam, in order to provide the reference specular reflection. Simulation results as well as experimental results are presented and it is shown that a high sensitivity can be obtained by using this new lens.
Open Access
Experimental verification of metamaterial loaded small patch antennas
(Emerald Group Publishing Limited, 2013) Alici, K. B.; Caliskan, M. D.; Özbay, Ekmel; Bilotti, F.; Toscano, A.; Vegni, L.
Purpose - Metamaterial unit cells composed of deep subwavelength resonators brought up new aspects to the antenna miniaturization problem. The paper experimentally demonstrates a metamaterial-inspired miniaturization method for circular patch antennas. In the proposed layouts, the space between the patch and the ground plane is filled with a proper metamaterial composed of either multiple split-ring or spiral resonators (SRs). The authors have manufactured two different patch antennas, achieving an electrical size of ?/3.69 and ?/8.26, respectively. The paper aims to discuss these issues. Design/methodology/ approach - The operation of such a radiative component has been predicted by using a simple theoretical formulation based on the cavity model. The experimental characterization of the antenna has been performed by using a HP8510C vector network analyzer, standard horn antennas, automated rotary stages, coaxial cables with 50 O characteristic impedance and absorbers. Before the characterization measurements we performed a full two-port calibration. Findings - Electrically small circular patch antennas loaded with single layer metamaterials experimentally demonstrated to acceptable figures of merit for applications. The proposed miniaturization technique is potentially promising for antenna applications and the results presented in the paper constitute a relevant proof for the usefulness of the metamaterial concepts in antenna miniaturization problems. Originality/value - Rigorous experimental characterization of several meta material loaded antennas and proof of principle results were provided. Copyright © 2013 Emerald Group Publishing Limited. All rights reserved.
Open Access
Fine-tuning the dispersion and the mobility of BaO domains on NO x storage materials via TiO2 anchoring sites
(American Chemical Society, 2010) Andonova, S. M.; Şentürk, G. S.; Ozensoy, E.
In an attempt to control the surface dispersion and the mobility of BaO domains on NOx storage materials, TiO2/TiOx anchoring sites were introduced on/inside the conventional γ-Al 2O3 support matrix. BaO/TiO2/Al 2O3 ternary oxide materials were synthesized via two different sol-gel preparation techniques, with varying surface compositions and morphologies. The synthesized NOx storage materials were studied via XRD, Raman spectroscopy, BET surface area analysis, TPD, XPS, SEM, EDX-mapping, and in situ FTIR spectroscopy of adsorbed NO2. NOx uptake properties of the BaO/TiO2/Al2O3 materials were found to be strongly influenced by the morphology and the surface structure of the TiO2/TiOx domains. An improved Ba surface dispersion was observed for the BaO/TiO2/Al2O3 materials synthesized via the coprecipitation of alkoxide precursors, which was found to originate mostly from the increased fraction of accessible TiO 2/TiOx sites on the surface. These TiO2/ TiOx sites function as strong anchoring sites for surface BaO domains and can be tailored to enhance surface dispersion of BaO. TPD experiments suggested the presence of at least two different types of NOx species adsorbed on the TiO2/TiOx sites, with distinctively different thermal stabilities. The relative stability of the NOx species adsorbed on the BaO/TiO2/Al2O3 system was found to increase in the following order: NO+/N2O 3 on alumina ≪ nitrates on alumina < surface nitrates on BaO < bridged/bidentate nitrates on large/isolated TiO2 clusters < bulk nitrates on BaO on alumina surface and bridged/bidentate nitrates on TiO2 crystallites homogenously distributed on the surface < bulk nitrates on the BaO sites located on the TiO2 domains. © 2010 American Chemical Society.
Open Access
k · p Parametrization and linear and circular dichroism in strained monolayer (janus) transition metal dichalcogenides from first-principles
(American Chemical Society, 2021-04-08) Aksu Korkmaz, Yağmur; Bulutay, Ceyhun; Sevik, C.
Semiconductor monolayer transition metal dichalcogenides (TMDs) have brought a new paradigm by introducing optically addressable valley degree of freedom. Concomitantly, their high flexibility constitutes a unique platform that links optics to mechanics via valleytronics. With the intention to expedite the research in this direction, we investigated ten TMDs, namely MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2, MoSSe, MoSeTe, WSSe, and WSeTe, which particularly includes their so-called janus types (JTMDs). First, we obtained their electronic band structures using regular and hybrid density functional theory (DFT) calculations in the presence of the spin–orbit coupling and biaxial or uniaxial strain. Our DFT results indicated that against the expectations based on their reported piezoelectric behavior, JTMDs typically interpolated between the standard band properties of the constituent TMDs without producing a novel feature. Next, by fitting to our DFT data we generated both spinless and spinful k · p parameter sets which are quite accurate over the K valley where the optical activity occurs. As an important application of this parametrization, we considered the circular and linear dichroism under strain. Among the studied (J)TMDs, WTe2 stood out with its largest linear dichroism under uniaxial strain because of its narrower band gap and large K valley uniaxial deformation potential. This led us to suggest WTe2 monolayer membranes for optical polarization-based strain measurements, or conversely, as strain tunable optical polarizers.
Open Access
Metamaterial based telemetric strain sensing in different materials
(Optical Society of American (OSA), 2010) Melik, R.; Unal, E.; Perkgoz, N.K.; Puttlitz, C.; Demir, Hilmi Volkan
We present telemetric sensing of surface strains on different industrial materials using split-ring-resonator based metamaterials. For wireless strain sensing, we utilize metamaterial array architectures for high sensitivity and low nonlinearity-errors in strain sensing. In this work, telemetric strain measurements in three test materials of cast polyamide, derlin and polyamide are performed by observing operating frequency shift under mechanical deformation and these data are compared with commercially-available wired strain gauges. We demonstrate that hard material (cast polyamide) showed low slope in frequency shift vs. applied load (corresponding to high Young's modulus), while soft material (polyamide) exhibited high slope (low Young's modulus).
Open Access
Observation of negative refraction and negative phase velocity in true left-handed metamaterials
(SPIE, 2005) Özbay, Ekmel
We report a true left-handed (LH) behavior in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures. The magnetic resonance of the SRR structure is demonstrated by comparing the transmission spectra of SRRs with that of closed SRRs. We confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined left-handed transmission band with a peak value of -1.2 dB (-0.3 dB/cm) is obtained. We also report the transmission characteristics of a 2D composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement. The experimental results agree extremely well with the theoretical calculations.
Open Access
Sterilization of PMMA microfluidic chips by various techniques and investigation of material characteristics
(Elsevier, 2016) Yavuz, C.; Oliaei, S. N. B.; Cetin, B.; Yesil-Celiktas, O.
The sterilization of microfluidic chips is a vital step of the fabrication process prior to the customer use in biomedical applications. The aim of this study was to analyze the influence of different sterilization techniques and to compare the characteristics of the material before and after sterilization of polymethylmethacrylate (PMMA) microchips. For this, supercritical carbon dioxide (SC-CO2) along with standard sterilization methods such as ultraviolet (UV), heat (autoclaving), ethylene oxide (EtO) and hydrogen peroxide (H2O2) were applied. The treated microchips were analyzed by Scanning Electron Microscopy, Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy and Laser Scanning Microscopy in order to ascertain any changes in the chemical structure and surface morphology. The optimum sterilization parameters for SC-CO2 were elicited as 120 bar, 40°C and 60 min which provided complete sterility and did not alter the main properties of the polymer along with EtO and H2O2 sterilizations unlike heat and UV treatments. However, surface roughness and microchannel profiles were negatively affected. Although complete sterility was achieved, each protocol has its own strengths and weaknesses. © 2015 Elsevier B.V. All rights reserved.
Open Access
Understanding responses to materials and colors in interiors
(Wiley, 2017) Ulusoy, B.; Olguntürk, N.
This article investigates the free associations of materials and colors in the context of interior architecture. Materials and colors rarely appear alone in interiors; therefore, in the scope of this study, the researchers explored material pairs and color pairs in addition to single materials and single colors. To elicit free associations from these interior design elements, 192 randomly selected volunteers participated in an experiment using a group of material (fabric, timber, plasterboard) and color (red, green, white) models under controlled conditions. The results contribute to an increased understanding of the associations between the concepts of materials and colors in interiors. While, each model was associated with sensory descriptors, only some models were associated with symbolic or affective descriptors. Single materials were related to different descriptors in interiors on their own, but when they were paired they were associated with fewer affective descriptors. The results showed that color pairs were always associated with all types of descriptors with an exception of red and green color pair, which was not mentioned with affective descriptors. The study findings are expected to be beneficial for interior architects, architects, product designers and researchers who want to shape and investigate a user's experience of interiors. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 261–272, 2017. © 2016 Wiley Periodicals, Inc.