Browsing by Subject "Acoustics"
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Item Open Access Analytical regularization based analysis of a spherical reflector symmetrically illuminated by an acoustic beam(IEEE, 2000) Vinogradov, S. S.; Vinogradova, E. D.; Nosich, A. I.; Altintaş, A.A mathematically accurate and numerically efficient method of analysis of a spherical reflector, fed by a scalar beam produced by a complex source- point feed, is presented. Two cases, soft and hard reflector surface, are considered. In each case the solution of the full-wave integral equation is reduced to dual series equations and then further to a regularized infinite- matrix equation. The latter procedure is based on the analytical inversion of the static part of the problem. Sample numerical results for 50-λ reflectors demonstrate features that escape a high-frequency asymptotic analysis. (C) 2000 Acoustical Society of America.Item Open Access Classification of agricultural kernels using impact acoustic signal processing(Bilkent University, 2006) Onaran, İbrahimThe quality is the main factor that directly affects the price for many agricultural produces. The quality depends on different properties of the produce. Most important property is associated with health of consumers. Other properties mostly depend on the type of concerned vegetable. For instance, emptiness is important for hazelnuts while openness is crucial for the pistachio nuts. Therefore, the agricultural produces should be separated according to their quality to maintain the consumers health and increase the price of the produce in international trades. Current approaches are mostly based on invasive chemical analysis of some selected food items or sorting food items according to their color. Although chemical analysis gives the most accurate results, it is impossible to analyze large quantities of food items. The impact sound signal processing can be used to classify these produces according to their quality. These methods are inexpensive, noninvasive and most of all they can be applied in real-time to process large amount of food. Several signal processing methods for extracting impact sound features are proposed to classify the produces according to their quality. These methods are including time and frequency domain methods. Several time and frequency domain methods including Weibull parameters, maximum points and variances in time windows, DFT (Discrete Fourier Transform) coefficients around the maximum spectral points etc. are used to extract the features from the impact sound. In this study, we used hazelnut and wheat kernel impact sounds. The success rate over 90% is achieved for all types produces.Item Open Access Classification of closed and open shell pistachio nuts using principal component analysis of impact acoustics(IEEE, 2004-05) Çetin, A. Enis; Pearson, T. C.; Tewfik, A. H.An algorithm was developed to separate pistachio nuts with closed-shells from those with open-shells. It was observed that upon impact on a steel plate, nuts with closed-shells emit different sounds than nuts with open-shells. Two feature vectors extracted from the sound signals were melcepstrum coefficients and eigenvalues obtained from the principle component analysis of the autocorrelation matrix of the signals. Classification of a sound signal was done by linearly combining feature vectors from both mel-cepstrum and PCA feature vectors. An important property of the algorithm is that it is easily trainable. During the training phase, sounds of the nuts with closed-shells and open-shells were used to obtain a representative vector of each class. The accuracy of closed-shell nuts was more than 99% on the test set.Item Open Access Detection of insect damaged wheat kernels by impact acoustics(IEEE, 2005-03) Pearson, T. C.; Çetin, A. Enis; Tewfik, A. H.Insect damaged wheat kernels (IDK) are characterized by a small hole bored into the kernel by insect larvae. This damage decreases flour quality as insect proteins interfere with the bread-making biochemistry and insect fragments are very unsightly. A prototype system was set up to detect IDK by dropping them onto a steel plate and processing the acoustic signal generated when kernels impact the plate. The acoustic signal was processed by three different methods: 1) modeling of the signal in the time domain, 2) computing time domain signal variances in short time windows, and 3), analysis of the frequency spectra magnitudes. Linear discriminant analysis was used to select a subset of features and perform classification. 98% of un-damaged kernels and 84.4% of IDK were correctly classified.Item Open Access Dynamic correlations in double-layer electron systems(The American Physical Society, 2001) Tanatar, Bilal; Davoudi, B.We study the effects of dynamic correlations on the ground-state properties of a double-layer two-dimensional electron gas within the quantum Singwi-Tosi-Land-Sjölander theory (STLS). The intralayer and interlayer static structure factors, the pair-correlation functions, and the wave vector and frequency-dependent local-field factors have been calculated for a range of electron densities and layer separations. We find that the local-field factors have an oscillatory frequency dependence and the magnitude of interlayer local-field factors is about an order of magnitude smaller than that of the intralayer. Our results are compared with the random-phase approximation and the static STLS approximation to assess the importance of dynamical correlations. We also calculate the dispersion relations for the optical and acoustic plasmons and the damping of these modes to compare them with other mean-field theories, and we comment on the relevance of our results to the recent experiments.Item Open Access Effect of magnetic field on the radial pulsations of a gas bubble in a non-Newtonian fluid(Elsevier Ltd, 2015) Behnia, S.; Mobadersani F.; Yahyavi, M.; Rezavand, A.; Hoesinpour, N.; Ezzat, A.Dynamics of acoustically driven bubbles' radial oscillations in viscoelastic fluids are known as complex and uncontrollable phenomenon indicative of highly active nonlinear as well as chaotic behavior. In the present paper, the effect of magnetic fields on the non-linear behavior of bubble growth under the excitation of an acoustic pressure pulse in non-Newtonian fluid domain has been investigated. The constitutive equation [Upper-Convective Maxwell (UCM)] was used for modeling the rheological behaviors of the fluid. Due to the importance of the bubble in the medical applications such as drug, protein or gene delivery, blood is assumed to be the reference fluid. It was found that the magnetic field parameter (B) can be used for controlling the nonlinear radial oscillations of a spherical, acoustically forced gas bubble in nonlinear viscoelastic media. The relevance and importance of this control method to biomedical ultrasound applications were highlighted. We have studied the dynamic behavior of the radial response of the bubble before and after applying the magnetic field using Lyapunov exponent spectra, bifurcation diagrams and time series. A period-doubling bifurcation structure was predicted to occur for certain values of the parameters effects. Results indicated its strong impact on reducing the chaotic radial oscillations to regular ones. © 2015 Elsevier Ltd. All rights reserved.Item Open Access The effect of moisture content on sound absorption of expanded perlite plates(Elsevier, 2005-03) Yilmazer, S.; Ozdeniz, M. B.Expanded perlite is a porous, lightweight, fire resistant and moisture retaining material with sound and thermal insulation properties. In this research, acoustical behaviour of plates made of expanded perlite was studied experimentally. Since these plates are used for sound absorption, the acoustical parameter selected for this study is "sound absorption coefficient". Preliminary experiments indicated that moisture reduced the sound absorption coefficient on plates and there is not much significant difference between the dry and 50% humid conditions. However, there is a significant difference in acoustical properties for the 50-95% humid conditions. Thus, this interval was studied in detail. A number of expanded perlite plates having different mixtures were prepared and tested. It was observed that, coating the expanded perlite particles with sodium silicate increased the moisture resistance. and the addition of mineral fibres into the mixtures increased the strength and sound absorption coefficient of the plates.Item Open Access Finite element modeling of micro-particle separation using ultrasonic standing waves(ASME, 2014) Büyükkoçak, S.; Çetin, Barbaros; Özer, M. B.Acoustophoresis which means separation of particles and cells using acoustic waves is becoming an intensive research subject. The method is based on inducing an ultrasonic compression standing wave inside a microchannel. A finite element approach is used to model the acoustic and electro-mechanical behavior of the piezoelectric material, the micro-channel geometry as well as the fluid inside the channel. The choices of silicon and PDMS materials are investigated as the chip materials for the resonator. A separation channel geometry which is commonly used in the literature is implemented in this study and the fluid flow inside the microchannel geometry is simulated using computational fluid dynamics. The acoustic field inside the fluid channel is also be simulated using the finite element method. For the separation process to be successful micro-particles of different diameter groups should end up in different channels of the micro-separator. In order to simulate real life scenarios, each particle size group have a size distribution within themselves. For realistic simulation results the particles will be released into the micro separator from a different starting locations (starting location distribution). The results of this Monte-Carlo based finite element simulation approach will be compared with the reported experimental results.Item Open Access Framework for online superimposed event detection by sequential Monte Carlo methods(IEEE, 2008-03-04) Urfalıoğlu, Onay; Kuruoğlu, E. E.; Çetin, A. EnisIn this paper, we consider online seperation and detection of superimposed events by applying particle filtering. We concentrate on a model where a background process, represented by a 1D-signal, is superimposed by an Auto-Regressive (AR) 'event signal', but the proposed approach is applicable in a more general setting. The activation and deactivation times of the event-signal are assumed to be unknown. We solve the online detection problem of this superpositional event by extending the state space dimension by one. The additional parameter of the state represents the AR-signal, which is zero when deactivated. Numerical experiments demonstrate the effectiveness of our approach. ©2008 IEEE.Item Open Access Lumped element modeling of CMUT arrays in collapsed mode(IEEE, 2014-09) Aydoğdu, Elif; Özgürlük, A.; Atalar, Abdullah; Köymen, HayrettinThis study focuses on modeling collapsed modeoperation of CMUT arrays, and obtaining a small signal lumped element model for collapsed mode operation. Having the large signal model for single CMUT from previous studies, the mutual radiation impedance is presented for the collapsed mode, and a large signal model for a CMUT array is obtained for simulating the operation in both uncollapsed and collapsed modes. For faster computation, a small signal model for a CMUT cell is derived by linearizing the collapsed mode operation at a given bias point, and the computation time is reduced significantly. Using this model we are able to simulate a large array of collapsed CMUT cells. © 2014 IEEE.Item Open Access Noise problem in primary schools in Ankara(Bilkent University, 1994) Özüpek, AyşegülIn this study, the problem of noise in primary schools is examined, by indicating the negative effects of this problem on the physiological, psychological, and social well-being of human beings, and on the effectiveness of teaching and learning process. By proving the excessive noise levels in primary schools in Ankara, it is aimed that, to take attentions of specialists to the subject of noise, and to make them consider this problem in the planning of new schools and in the renovation process of older school buildings.Item Open Access Parametric nonlinear lumped element model for circular CMUTs in collapsed mode(2014) Aydoǧdu, E.; Ozgurluk, A.; Atalar, Abdullah; Köymen, HayrettinWe present a parametric equivalent circuit model for a circular CMUT in collapsed mode. First, we calculate the collapsed membrane deflection, utilizing the exact electrical force distribution in the analytical formulation of membrane deflection. Then we develop a lumped element model of collapsed membrane operation. The radiation impedance for collapsed mode is also included in the model. The model is merged with the uncollapsed mode model to obtain a simulation tool that handles all CMUT behavior, in transmit or receive. Large- and small-signal operation of a single CMUT can be fully simulated for any excitation regime. The results are in good agreement with FEM simulations. © 2014 IEEE.Item Open Access Passive sound control in symphony concert hall design(Bilkent University, 1995) Şahin, EbruIn this study, passive sound control in symphony concert hall was studied. Necessary criteria for concert halls were described and design of the enclosure for music is examined. An experimental study was done so as to make an evaluation of the present situation in one of the concert halls in Ankara.Item Open Access Perceived auditory environment in historic spaces of anatolian culture : a case study on Hacı Bayram mosque(International Institute of Acoustics and Vibrations, 2016) Acun V.; Yilmazer, Semiha; Taherzadeh, P.This article reports the initial finds of a research that is concerned with the perceived auditory environment within an historical mosque and its surroundings. Haci Bayram Mosque and its surrounding area of Hamamönü has been selected as the research site due to being the historical center of Ankara. Although there are studies concerned with the acoustical characteristics of mosques, there isn't enough research focusing on users' expectation and interpretation of the perceived auditory environment within a mosque. This study adopts the user focused of Grounded Theory to capture individuals' auditory sensation and interpretation of the perceived auditory environment within a historical mosque and its surroundings. In depth interviews are held with the congregation of the mosque and with the individuals sitting around the surrounding area. Based on their subjective responses, a theoretical framework is generated to gain an insight on the factors that affect individuals understanding and expectation from mosques. Acoustical characteristics of the mosque are analyzed by computer simulation and in-situ measurements of sound pressure levels. Objective room-acoustic indicators consist of reverberation time (RT) and speech transmission index (STI). The conceptual framework generated through Grounded Theory shows how perceived auditory environment may influence individuals' response to the physical environment of the mosque by showing the associations between the soundscape elements, spatial function and sense of place.Item Open Access Phase imaging in reflection with the acoustic microscope(A I P Publishing, 1978-01) Atalar, Abdullah; Quate, C. F.; Wickramasinghe, H. K.When a polished surface of a single crystal is examined with a converging acoustic beam the reflected signal has a characteristic response that is dependent upon the elastic properties of the reflecting surface. This property can be used in the acoustic microscope to monitor the thickness of layers deposited on these surfaces and the small‐scale variations of the elastic parameters in these materials.Item Open Access Radius of curvature estimation and localization of targets using multiple sonar sensors(A I P Publishing LLC, 1999-04) Barshan, B.; Sekmen, A. S.Acoustic sensors have been widely used in time-of-flight ranging systems since they are inexpensive and convenient to use. One of the most important limitations of these sensors is their low angular resolution. To improve the angular resolution and the accuracy, a novel, flexible, and adaptive three- dimensional (3-D) multi-sensor sonar system is described for estimating the radius of curvature and location of cylindrical and spherical targets. Point, line, and planar targets are included as limiting cases which are important for the characterization of typical environments. Sensitivity analysis of the curvature estimate with respect to measurement errors and certain system parameters is provided. The analysis and the simulations are verified by experiments in 2-D with specularly reflecting cylindrical and planar targets, using a real sonar system. Typical accuracies in range and azimuth are 0.18 mm and 0.1°, respectively. Accuracy of the curvature estimation depends on the target type and system parameters such as transducer separation and operating range. The adaptive configuration brings an improvement varying between 35% and 45% in the accuracy of the curvature estimate. The presented results are useful for target differentiation and tracking applications.A flexible and adaptive three-dimensional multisensor sonar system capable of estimating the location and radius of curvature of spherical and cylindrical targets is presented. The performance radius of curvature estimation is analyzed to provide information for differentiating reflectors with different radii. Results showed that the adaptive configuration improved the accuracy of the curvature estimate between 35% and 45%.Item Open Access Reflections on environmental control: luminous and sonic environments inside the design studio(Bilkent University, 1995) Önen, ÖmerIn this thesis, two environmental control parameters -lighting and acoustics - are studied. Since one of architecture's primary concerns is to provide human beings with comfort, emphasis is put on the approach that design decisions pertaining to lighting and acoustics should be considered in the earlier phases of the designing process. The design studio has been chosen since it houses many different functions simultaneously, with its significance as the place where design education actually begins. Accordingly, norms, numeric standards and common designing principles are compiled for design studios. Then, the lighting (luminance, illuminance) and acoustics (sound pressure level) performances of the design studios of the Faculty of Art, Design and Architecture of Bilkent University are measured. The results are, finally, evaluated and concluded with general technical advice for the amelioration of the measured studios.Item Open Access Signal and image processing algorithms for agricultural applications(Bilkent University, 2006) Dülek, BerkanMedical studies indicate that acrylamide causes cancer in animals and certain doses of acrylamide are toxic to the nervous system of both animals and humans. Acrylamide is produced in carbohydrate foods prepared at high temperatures such as fried potatoes. For this reason, it is crucial for human health to quantitatively measure the amount of acrylamide formed as a result of prolonged cooking at high temperatures. In this thesis, a correlation is demonstrated between measured acrylamide concentrations and NABY (Normalized Area of Brownish Yellow regions) values estimated from surface color properties of fried potato images using a modified form of the k-means algorithm. Same method is used to estimate acrylamide levels of roasted coffee beans. The proposed method seems to be a promising approach for the estimation of acrylamide levels and can find applications in industrial systems. The quality and price of hazelnuts are mainly determined by the ratio of shell weight to kernel weight. Due to a number of physiological and physical disorders, hazelnuts may grow without fully developed kernels. We previously proposed a prototype system which detects empty hazelnuts by dropping them onto a steel plate and processing the acoustic signal generated when kernels hit the plate. In that study, feature vectors describing time and frequency nature of the impact sound were extracted from the acoustic signal and classified using Support Vector Machines. In the second part of this thesis, a feature domain post-processing method based on vector median/mean filtering is shown to further increase these classification results.Item Open Access Structured least squares with bounded data uncertainties(IEEE, 2009) Pilanci, Mert; Arıkan, Orhan; Oguz, B.; Pınar, Mustafa C.In many signal processing applications the core problem reduces to a linear system of equations. Coefficient matrix uncertainties create a significant challenge in obtaining reliable solutions. In this paper, we present a novel formulation for solving a system of noise contaminated linear equations while preserving the structure of the coefficient matrix. The proposed method has advantages over the known Structured Total Least Squares (STLS) techniques in utilizing additional information about the uncertainties and robustness in ill-posed problems. Numerical comparisons are given to illustrate these advantages in two applications: signal restoration problem with an uncertain model and frequency estimation of multiple sinusoids embedded in white noise.Item Open Access Texturing of titanium (Ti6Al4V) medical implant surfaces with MHz-repetition-rate femtosecond and picosecond Yb-doped fiber lasers(Optical Society of American (OSA), 2011) Erdoǧan, M.; Öktem, B.; Kalaycioǧlu H.; Yavaş, S.; Mukhopadhyay P.K.; Eken, K.; Özgören, K.; Aykaç, Y.; Tazebay, U.H.; Ilday F.O.We propose and demonstrate the use of short pulsed fiber lasers in surface texturing using MHz-repetition-rate, microjoule- and sub-microjoule-energy pulses. Texturing of titanium-based (Ti6Al4V) dental implant surfaces is achieved using femtosecond, picosecond and (for comparison) nanosecond pulses with the aim of controlling attachment of human cells onto the surface. Femtosecond and picosecond pulses yield similar results in the creation of micron-scale textures with greatly reduced or no thermal heat effects, whereas nanosecond pulses result in strong thermal effects. Various surface textures are created with excellent uniformity and repeatability on a desired portion of the surface. The effects of the surface texturing on the attachment and proliferation of cells are characterized under cell culture conditions. Our data indicate that picosecond-pulsed laser modification can be utilized effectively in low-cost laser surface engineering of medical implants, where different areas on the surface can be made cell-attachment friendly or hostile through the use of different patterns. © 2011 Optical Society of America.