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Öğe Acoustic beam splitting in a sonic crystal around a directional band gap(Iop Publishing Ltd, 2013) Cicek, Ahmet; Kaya, Olgun Adem; Ulug, BulentBeam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size, which facilitates circumvention of a directional band gap. Experiments reveal that two distinct beams emerge at crystal output, in agreement with the numerical results obtained through the finite-element method. Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space. Split beams propagate in equal amplitude, whereas beam splitting is destructed for oblique incidence above a critical incidence angle.Öğe 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, BulentNumerical 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.Öğe Acoustic tamm states of three-dimensional solid-fluid phononic crystals(Acoustıcal soc amer amer ınst physıcs, ste 1 no 1, 2 huntıngton quadrangle, melvılle, ny 11747-4502 usa, 2018) Korozlu, Nurettin; Kaya, Olgun Adem; Cicek, Ahmet; Ulug, BulentIn this work, the existence and propagation of acoustic Tamm states at the interface of air and a face-centered cubic solid-fluid phononic crystal composed of spherical air voids interconnected by cylindrical air channels are demonstrated. Supercell band structure computations via the finite element method reveal surface bands for Tamm states on (100), (110), and (111) surfaces of the phononic crystal. The states decay sharply into the phononic crystal so that only a two-row slab is sufficient to guide them over the respective surfaces without leakage, as confirmed by finite element simulations. In addition, surface wave propagation along the [10] direction of the (100) surface is experimentally demonstrated. Ability to confine the Tamm states in all three dimensions is a key aspect in designing few-layer-thick acoustic circuits. Low material filling fraction of the phononic crystal could be leveraged to realize lightweight all-acoustic systems where either bulk or surface states can be incorporated. (C) 2018 Acoustical Society of America.Öğe Acoustic Tamm states of three-dimensional solid-fluid phononic crystals(Acoustical Soc Amer Amer Inst Physics, 2018) Korozlu, Nurettin; Kaya, Olgun Adem; Cicek, Ahmet; Ulug, BulentIn this work, the existence and propagation of acoustic Tamm states at the interface of air and a face-centered cubic solid-fluid phononic crystal composed of spherical air voids interconnected by cylindrical air channels are demonstrated. Supercell band structure computations via the finite element method reveal surface bands for Tamm states on (100), (110), and (111) surfaces of the phononic crystal. The states decay sharply into the phononic crystal so that only a two-row slab is sufficient to guide them over the respective surfaces without leakage, as confirmed by finite element simulations. In addition, surface wave propagation along the [10] direction of the (100) surface is experimentally demonstrated. Ability to confine the Tamm states in all three dimensions is a key aspect in designing few-layer-thick acoustic circuits. Low material filling fraction of the phononic crystal could be leveraged to realize lightweight all-acoustic systems where either bulk or surface states can be incorporated. (C) 2018 Acoustical Society of America.Öğe Acoustic waveguiding by pliable conduits with axial cross sections as linear waveguides in two-dimensional sonic crystals(Acoustical Soc Amer Amer Inst Physics, 2013) Cicek, Ahmet; Kaya, Olgun Adem; Ulug, BulentPliable conduits composed of periodically arranged concentric aluminum tori in air, with their axial cross sections acting as linear waveguides in two-dimensional sonic crystals, are numerically shown to guide acoustic waves in three dimensions in a flexible manner. Waveguide band structures are obtained by exploiting axial symmetry in a super-cell approach through two-dimensional finite-element simulations under the periodic boundary conditions. One isolated band having a bandwidth of 19.66% or 10.10% is observed for each guide, whose cross section is either in square or triangular geometry, respectively. Corresponding mode profiles indicate efficient guiding, as the acoustic energy is mainly concentrated in the hollow-core region of the guides. Transmittance spectra calculated through finite-element simulations are in agreement with the computed guiding bands. Transmittance along the waveguides with square and triangular axial cross sections around mid-band frequencies of their guiding bands varies slightly from -6.05 and -6.65 dB to -5.98 and -8.86 dB, respectively, as the guide length is increased from 10 to 200 periods. Efficient guiding across the smooth bends over circular arcs up to 90 deg is also demonstrated through three-dimensional finite-element method simulations. (C) 2013 Acoustical Society of America.Öğe Acoustophoretic separation of airborne millimeter-size particles by a Fresnel lens(Nature Portfolio, 2017) Cicek, Ahmet; Korozlu, Nurettin; Kaya, Olgun Adem; Ulug, BulentWe numerically demonstrate acoustophoretic separation of spherical solid particles in air by means of an acoustic Fresnel lens. Beside gravitational and drag forces, freely-falling millimeter-size particles experience large acoustic radiation forces around the focus of the lens, where interplay of forces lead to differentiation of particle trajectories with respect to either size or material properties. Due to the strong acoustic field at the focus, radiation force can divert particles with source intensities significantly smaller than those required for acoustic levitation in a standing field. When the lens is designed to have a focal length of 100 mm at 25 kHz, finite-element method simulations reveal a sharp focus with a full-width at half-maximum of 0.5 wavelenghts and a field enhancement of 18 dB. Through numerical calculation of forces and simulation of particle trajectories, we demonstrate size-based separation of acrylic particles at a source sound pressure level of 153 dB such that particles with diameters larger than 0.5 mm are admitted into the central hole, whereas smaller particles are rejected. Besides, efficient separation of particles with similar acoustic properties such as polyethylene, polystyrene and acrylic particles of the same size is also demonstrated.Öğe Evanescent coupling between surface and linear-defect guided modes in phononic crystals(Iop Publishing Ltd, 2016) Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, BulentEvanescent 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.Öğe Focusing with two-dimensional angular-symmetric circular acoustic lenses(Pleiades Publishing Inc, 2011) Kaya, Olgun Adem; Cicek, Ahmet; Ulug, BulentFocusing properties of an acoustic lens based on a modified triangular sonic crystal slab whose columns are aligned on concentric arcs of equal radial distance are investigated. Capability of focusing normally-incident plane waves is demonstrated by means of Finite Element Method. Focusing mechanisms are discussed on the basis of band structures and equifrequency contours considering a model where triangular lattice is elongated along IK direction. Focusing behavior of the proposed lens is argued to arise from negative refractions at the air-lens interfaces accompanied by index guiding in its interiors. Wavelength-order confinement in the transverse direction is observed. Double focusing is attributed to geometrical effects and contribution of self guiding is discussed. Possibility of occurrence of birefraction at the input face of the lens together with positive refraction at the output face is also discussed.Öğe Gas sensing through evanescent coupling of spoof surface acoustic waves(Elsevier Science Sa, 2019) Cicek, Ahmet; Arslan, Yasin; Trak, Digdem; Okay, Fatih Can; Kaya, Olgun Adem; Korozlu, Nurettin; Ulug, BulentAn ultrasonic gas sensor based on evanescent coupling of spoof surface acoustic waves between two surface phononic crystals containing trapezoidal grooves on rigid slabs is theoretically and experimentally demonstrated. Sensing properties for carbon dioxide in dry air at 25 degrees C and 760 Torr are investigated as an example. Band structure analyses reveal two spoof surface acoustic wave bands with opposite parities when the separation of surface phononic crystals is 1.5 times the periodicity of grooves. The beat length varies with frequency and carbon dioxide volume fraction, where the increase of the latter results in red shift of a sharp intense output peak at 59.69 kHz at a rate of 17.70 mHz/ppm and 16.20 mHz/ppm for carbon dioxide volume fractions up to 10,000 ppm, as measured through Finite-Element Method simulations and experiments, respectively. Gas sensing can also be achieved by measuring the output acoustic intensity at constant frequency, which exhibits a steep decrease with carbon dioxide volume fraction up to 2000 ppm.Öğe Guiding airborne sound through surface modes of a two-dimensional phononic crystal(Iop Publishing Ltd, 2015) Cicek, Ahmet; Gungor, Tayyar; Kaya, Olgun Adem; Ulug, BulentExistence and guiding properties of surface modes bound to the interface between a finite two-dimensional phononic crystal and the host medium are experimentally and numerically demonstrated. Surface modes can be observed on both (1 0) and (1 1) surfaces of a square phononic crystal of steel cylinders in air. Numerical investigations of band properties and simulations of mode excitation are carried out through the finite-element method. Excited by the far field of a speaker, existence of surface modes is investigated by recording the sound field in the vicinity of the respective crystal surfaces. Both surface bands of the square phononic crystal depart from bulk bands and extend into the band gap for sufficiently high filling fractions. While such a surface band can be obtained for considerably smaller scatterer radii for the (1 0) surface, significantly higher radii around 0.49 of the lattice constant are required to obtain propagating surface modes on the (1 1) surface. Persistence of the guided surface mode along the (1 0) surface, where it diminishes in a length scale of the lattice constant in the transverse direction is demonstrated. The modes of the (1 1) surface decay faster into the air in the transverse direction. Guided modes on both surfaces propagate in a beating manner where the beat length can be determined by the wave number of the mode.Öğe Impacts of uniaxial elongation on the bandstructures of two-dimensional sonic crystals and associated applications(Elsevier Sci Ltd, 2012) Cicek, Ahmet; Kaya, Olgun Adem; Ulug, BulentInfluences of uniaxial elongation along the [11] direction of triangular and [10] direction of square sonic crystals under the constraint of conserved unit cell area are investigated by examining band structures and equi-frequency contours. Lowest-lying band gap of the triangular lattice observed at high filling fractions diminishes for negative elongation (compression), whereas another band gap develops at lower frequencies whose width reaches appreciable values for moderate elongation. The band gap of the square lattice, which appears at high filling fractions, is modified slightly with elongation. Frequency ranges of the bands, and thus the group velocities along the high-symmetry directions, vary with elongation which may be useful in applications like slow sound propagation. Elongation is observed to modify the equi-frequency contours significantly through reducing the lattice symmetry. The most prominent impact is the transformation of closed contours into open ones, whereas the rest are stretched either along or normal to the elongation axis of the 1st Brillouin Zone. This observation is utilized to implement wide-band all-angle self-collimation and superprism effect, which are demonstrated through Finite-Element computations. (C) 2011 Elsevier Ltd, All rights reserved.Öğe 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, BulentMach-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.Öğe Phononic crystal surface mode coupling and its use in acoustic Doppler velocimetry(Elsevier Science Bv, 2016) Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, BulentIt 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.Öğe Refraction-based photonic crystal diode(Optical Soc Amer, 2012) Cicek, Ahmet; Yucel, Melike B.; Kaya, Olgun Adem; Ulug, BulentA system composed of air holes in a dielectric host to form two square photonic crystals, with the same orientation and lattice constant but different scatterer radii, making an interface along their body diagonals, is numerically demonstrated to facilitate unidirectional light transmission. Band structure computations are carried out via the plane wave expansion method, whereas finite-difference time-domain simulations are carried out to investigate the transient behavior. Unidirectional light transmission is achieved over two adjacent stop bands along the Gamma X direction, which are circumvented in the forward direction by scaling down the wave vector and rotating the surface normal. Contrast ratios as high as 0.9 are attained within the lower stop band. (C) 2012 Optical Society of AmericaÖğe Refraction-type sonic crystal junction diode(Amer Inst Physics, 2012) Cicek, Ahmet; Kaya, Olgun Adem; Ulug, BulentUnidirectional sound transmission across a junction of two square sonic crystals with different orientations and lattice constants is numerically investigated. Re-scaling and rotating the wave vectors through refractions across the air-first sonic crystal interface and the junction, respectively, facilitate coupling into the spatial modes of the second crystal. Unidirectional transmission, demonstrated through finite element method simulations, is accomplished between 10.4 kHz and 12.8 kHz. Transmission values to the right and left are greater than 60% and less than 1.0%, respectively, between 11.0 kHz and 12.4 kHz, resulting in a contrast ratio greater than 0.9. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694020]Öğe Role of irradiation in the green synthesis of silver nanoparticles mediated by fig (Ficus carica) leaf extract(Pergamon-Elsevier Science Ltd, 2015) Ulug, Bulent; Turkdemir, M. Haluk; Cicek, Ahmet; Mete, AhmetBiosynthesis of silver nanoparticles in an aqueous mixture of fig (Ficus carica) leaf extract and AgNO3 solution exposed to a set of irradiances at different wavelengths are studied. Nanoparticle formation for irradiances between 6.5 mW/cm(2) and 13.3 mW/cm(2) in the 330-550 nm wavelength range is investigated and the results are compared to those of the nanoparticles synthesized in the dark and under direct sunlight. Ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy, along with particle size analysis and transmission electron microscopy are employed for the characterization of samples and extracts. Irradiance is found to have profound influence on the reduction rates. However, size and spherical shape of the nanoparticles are persistent, irrespective of irradiance and wavelength. Irradiance is discussed to influence the particle formation and aggregation rates through the formation of free radicals in the fig extract. (C) 2014 Elsevier B.V. All rights reserved.Öğe Self-collimated slow sound in sonic crystals(Iop Publishing Ltd, 2012) Kaya, Olgun Adem; Cicek, Ahmet; Ulug, BulentSelf-collimated slow-sound propagation in a two-dimensional rectangular sonic crystal composed of elliptical scatterers in air is numerically demonstrated. The group velocity at the centre and the edges of the fourth acoustic band is reduced to 45 m s(-1) and 30 m s(-1), corresponding to 1/8 and 1/12 of the speed of sound in air, respectively. Elimination of omni-directional reflections encountered in linear waveguides and the reduction of group-velocity dispersion at the mid-band frequencies lead to preservation of pulse shape and amplitude upon traversal of the sonic crystal. Wave transmission is increased from approximately -20 to -2.5 dB, with almost an order of magnitude enhancement, via injector layers optimized through a pattern search algorithm. Self-collimating performance of the system is not degraded under oblique incidence, except for pulse broadening due to increased effective source width.Öğe Sharp bends of phononic crystal surface modes(Iop Publishing Ltd, 2015) Cicek, Ahmet; Salman, Aysevil; Kaya, Olgun Adem; Ulug, BulentSharp 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.Öğe Slow sound propagation in a sonic crystal linear waveguide(Amer Inst Physics, 2012) Cicek, Ahmet; Kaya, Olgun Adem; Yilmaz, Mukremin; Ulug, BulentA linear waveguide along the [11] direction of a triangular sonic crystal, composed of aluminum cylinders in air is shown both experimentally and numerically to facilitate slow sound propagation. Supercell-based calculations through the finite element method reveal a band centered at approximately 16.0 kHz with 255 Hz span, exhibiting linear variation away from band edges, for the lattice constant and cylinder radii of 21.7 mm and 10.0 mm, respectively. The experimental setup is based on monitoring the propagation of a Gaussian-enveloped sinusoidal pulse at 16.0 kHz inside the waveguide. Numerical behavior of the Gaussian pulse is investigated by time-dependent finite-element computations. The experimental and numerical group velocities are found to be 26.7 m/s and 22.6 m/s, respectively. Being congruous with the experimental findings, numerical transient study of the system reveals significant longitudinal compression commensurate with the calculated group index. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676581]Öğe Superprism effect in a deformed triangular sonic crystal(Iop Publishing Ltd, 2011) Kaya, Olgun Adem; Cicek, Ahmet; Yilmaz, Mukremin; Ulug, BulentThe superprism effect in a two-dimensional sonic crystal composed of lead cylinders in water aligned on a lattice obtained by varying the angle between the primitive vectors of triangular lattice is numerically investigated. Symmetry breaking influences the equi-frequency contours to reflect the lattice symmetry, so that compression along a direction leads to smaller critical angles of incidence. The whole 0 degrees-90 degrees range is spanned by the refracted waves at the water/sonic crystal interface for frequencies between 165 and 183 kHz, in the third band, and angles of incidence between 0 degrees and 15 degrees. The studied superprism behaviour can be used to achieve both spectral and angular resolution. The refraction angle varies linearly for small angles of incidence below 3 degrees at a constant frequency, while its frequency dependence at a given angle of incidence is quadratic for small frequencies. Finite-element computations reveal that waves are refracted into the angles calculated from the equi-frequency contours with small beam divergence at any frequencies and angles of incidence.
