Yazar "Salman, Aysevil" seçeneğine göre listele

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    Acoustic Mach-Zehnder interferometer utilizing self-collimated beams in a two-dimensional phononic crystal
    (Elsevier Science Sa, 2014) Kaya, Olgun Adem; Cicek, Ahmet; Salman, Aysevil; Ulug, Bulent
    Numerical investigation of a Mach-Zehnder interferometer implemented by steering self-collimated acoustic beams in a two-dimensional phononic crystal is presented. Mirrors of the interferometer are optimized by modifying the radii of the steel cylinders in water so that the working frequencies lie in a band gap. The beam splitters optimized in a similar manner ensure equal splitting of the beams. In the all water case of host liquid, the interferometer operates unidirectionally such that transmission throughonly one of the two output terminals is achieved. Corresponding transmittances are 85.9% and 6.0% for the transmitting and blocked terminals, respectively. The device can be utilized in sensing variations in the weight fraction of ethanol in water in a cell on the path of one of the two split beams. Phase difference accumulated in the sample cell varies linearly with ethanol weight fraction up to 15%. Contrast ratio of the calculated transmittances can be used as a measure of ethanol content in water, as it varies as a cosine function of ethanol weight fraction. (C) 2014 Elsevier B. V. All rights reserved.
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    Determination of concentration of ethanol in water by a linear waveguide in a 2-dimensional phononic crystal slab
    (Elsevier Science Sa, 2014) Salman, Aysevil; Kaya, Olgun Adem; Cicek, Ahmet
    Numerical investigation of a linear defect waveguide in a two-dimensional phononic crystal slab of water cylinders in mercury host to sense the variation of ethanol concentration in a mixture with water is carried out. Waveguide geometry is optimized by varying the waveguide core width and introducing scatterers into the core to obtain an isolated defect band within the bandgap, as close to the gap center and as narrow as possible, in order to increase sensing ability. Transmission results calculated through three-dimensional steady-state finite-element method simulations are consistent with the position and the width of the defect band obtained by band structure computations, as a function of ethanol concentration. The band center varies linearly with ethanol concentration up to 15%, where it blue-shifts with increasing concentration at a rate of approximately 480 Hz per percent variation. The bandwidth also exhibits linear variation up to significantly smaller concentrations, whereas the values calculated through the transmission spectra are considerably smaller than those obtained by band structure computations. (C) 2014 Elsevier B.V. All rights reserved.
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    Evanescent coupling between surface and linear-defect guided modes in phononic crystals
    (Iop Publishing Ltd, 2016) Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, Bulent
    Evanescent coupling between surface and linear-defect waveguide modes in a two-dimensional phononic crystal of steel cylinders in air is numerically demonstrated. When the ratio of scatterer radii to the lattice constant is set to 0.47 in the square phononic crystal, the two types of modes start interacting if there is one-row separation between the surface and waveguide. Supercell band structure computations through the Finite Element Method suggest that the waveguide band is displaced significantly, whereas the surface band remains almost intact when the waveguide and surface are in close proximity. The two resultant hybrid bands are such that the coupling length, which varies between 8 and 22 periods, initially changes linearly with frequency, while a much sharper variation is observed towards the top of the lower hybrid band. Such small values facilitate the design of compact devices based on heterogeneous coupling. Finite-element simulations demonstrate bilateral coupling behaviour, where waves incident from either the surface or waveguide can efficiently couple to the other side. The coupling lengths calculated from simulation results are in agreement with the values predicted from the supercell band structure. The possible utilisation of the coupling scheme in sensing applications, especially in acoustic Doppler velocimetry, is discussed.
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    Low-concentration liquid sensing by an acoustic Mach-Zehnder interferometer in a two-dimensional phononic crystal
    (Iop Publishing Ltd, 2015) Salman, Aysevil; Kaya, Olgun Adem; Cicek, Ahmet; Ulug, Bulent
    Mach-Zehnder interferometer formed by liquid-filled linear defect waveguides in a two-dimensional phononic crystal is numerically realized for sensing low concentrations of an analyte. The waveguides in the square phononic crystal of void cylinders in steel, as well as their T branches and sharp bends are utilized to construct interferometer arms. Sensing low concentrations of ethanol on the order of 0.1% in a binary mixture with water is achieved by replacing the contents of a number of waveguide core cells on one arm of the interferometer with the analyte. Computations are carried out through the finite-element method in an approach that takes the solid-liquid interaction at the waveguide core cells into account. Band analyses reveal linear variation of the central frequency of the transmission band within a band gap for ethanol concentrations up to 3.0%. Phase difference due to the imbalance of the sample and reference arms of the interferometer also varies linearly with ethanol concentration, leading in turn to a cosine variation of the Fourier component of the temporal interferometer response at the central input-pulse frequency. The induced phase difference in the investigated configuration becomes a -0.78 pi and -0.65 pi per percent increase of ethanol concentration as calculated from the band-structure and transient data, respectively. This is confirmed by transient finite-element simulations where totally destructive interference occurs for a concentration of approximately 1.5%. The proposed scheme, which can easily be adopted to other binary mixtures, offers a compact implementation requiring small amounts of analyte.
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    Phononic crystal surface mode coupling and its use in acoustic Doppler velocimetry
    (Elsevier Science Bv, 2016) Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, Bulent
    It is numerically shown that surface modes of two-dimensional phononic crystals, which are Bloch modes bound to the interface between the phononic crystal and the surrounding host, can couple back and forth between the surfaces in a length scale determined by the separation of two surfaces and frequency. Supercell band structure computations through the finite-element method reveal that the surface band of an isolated surface splits into two bands which support either symmetric or antisymmetric hybrid modes. When the surface separation is 3.5 times the lattice constant, a coupling length varying between 30 and 48 periods can be obtained which first increases linearly with frequency and, then, decreases rapidly. In the linear regime, variation of coupling length can be used as a means of measuring speeds of objects on the order of 0.1 m/s by incorporating the Doppler shift. Speed sensitivity can be improved by increasing surface separation at the cost of larger device sizes. (C) 2015 Elsevier B.V. All rights reserved.
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    Sharp bends of phononic crystal surface modes
    (Iop Publishing Ltd, 2015) Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, Bulent
    Sharp bending of surface waves at the interface of a two-dimensional phononic crystal (PnC) of steel cylinders in air and the method of using a diagonally offset cylindrical scatterer are numerically demonstrated by finite-element method simulations. The radii of the diagonally offset scatterer and the cylinder at the PnC corner, along with the distance between them, are treated as optimization parameters in the genetic algorithm optimization of sharp bends. Surface wave transmittance of at most 5% for the unmodified sharp bend is significantly enhanced to approximately 75% as a result of optimization. A series of transmittance peaks whose maxima increase exponentially, as their widths reduce, with increasing frequency is observed for the optimized sharp bend. The transmittance peaks appear at frequencies corresponding to integer plus half-beat periods, depending on the finite surface length. The optimal parameters are such that the cylinder radius at the PnC corner is not significantly modified, whereas a diagonally offset scatterer having a diameter of almost two periods and a shortest distance of about 0.7 periods between them is required for the strongest transmittance peak. Utilization of PnC surface sharp bends as acoustic ring resonators is demonstrated.