Browsing by Subject "Frequency domain analysis"

Now showing 1 - 20 of 31

Open Access
Analysis of errors in zero-free-parameter modeling approach to predict the voltage of electrochemical energy storage systems under arbitrary load
(Electrochemical Society, 2017) Ulgut, Burak; Uzundal, Can Berk; Özdemir, Elif
In a recently published article (J. Electrochem. Soc. 164 (2017) A1274-A1280), we described a new method to predict the voltage response of electrochemical energy storage systems during arbitrary load profiles. Our work shows that the impedance spectrum can be employed in the frequency domain in order to ultimately calculate the time domain behavior of the electrochemical energy storage system. The big advantage of this method is the fact that there are no free parameters and fits throughout. The present work deals with the sources of error in the above-mentioned prediction approach and looks for the effects of the various sources of error. The current analysis concludes that two big contributors to the overall error are the inaccuracies in the DC part of the prediction and the non-linearities that are not modeled by a linear impedance spectrum. Discussions are also made regarding ways to improve the performance of the modeling approach the most and where future work is going to be looking to improve.
Open Access
Circuit theoretical method for efficient finite element analysis of acoustical problems
(IEEE, 1998) Ekinci, A. Suat; Atalar, Abdullah
In the last decade, there has been an outstanding improvement in the computer aided design tools for VLSI circuits regarding solution times and the circuit complexity. This study proposes formulating the acoustic field analysis problem using FEM, and employing the recent speed-up techniques used in the circuit simulators. In this work, total mass, stiffness and damping matrices are obtained using the FE approach, and piped into a computer program which generates an equivalent SPICE compatible circuit netlist. This approach makes it possible to use the most recent circuit simulation techniques to simulate the acoustical problems. The equivalent electrical circuit is a resistor-inductor-capacitor (RLC) circuit containing controlled sources to handle the couplings. The circuit matrices are 6 times larger but are sparser. We analyze these circuits with a general-purpose circuit simulation program, HSPICE, which provides high accuracy solutions in a short time. We also use an in-house developed circuit simulation program, MAWE, which makes use of asymptotic waveform evaluation (AWE) technique that has been successfully used in circuit simulation for solutions of large sets of equations. The results obtained on several problems, which are solved in time and frequency domains using circuit simulators and the FE analysis program ANSYS, match each other pretty well. Using circuit simulators instead of conventional method improves simulation speed without a significant loss of accuracy.
Open Access
Coupled deconvolution for frequency extrapolation of electromagnetic solutions with matrix pencil method
(IEEE, 2005) Gürel, Levent; Yıldırım, Ferhat
Matrix pencil method (MPM) has been widely used to estimate the parameters of complex-exponential based models. An important application is the extrapolation of the frequency-domain solutions of electromagnetic problems. In this paper, we present a mathematical tool, namely, coupled deconvolution, which improves the performance of the MPM-based extrapolation of electromagnetic solutions.
Open Access
Coupled matrix pencil method for frequency extrapolation of electromagnetic solutions
(IEEE, 2005) Yıldırım, Ferhat; Gürel, Levent
Matrix pencil method (MPM) is used to extrapolate the available electromagnetic solutions in frequency domain to estimate the high-frequency solutions. A new approach, namely, coupled MPM, is introduced to obtain the electromagnetic solutions at intermediate frequencies using the available low-frequency and high-frequency data.
Open Access
An efficient algorithm to extract components of a composite signal
(IEEE, 2000) Özdemir, A. Kemal; Arıkan, Orhan
An efficient algorithm is proposed to extract components of a composite signal. The proposed approach has two stages of processing in which the time-frequency supports of the individual signal components are identified and then the individual components are estimated by performing a simple time-frequency domain incision on the identified support of the component. The use of a recently proposed time-frequency representation [1] significantly improves the performance of the proposed approach by providing very accurate description on the auto-Wigner terms of the composite signal. Then, simple fractional Fourier domain incision provides reliable estimates for each of the signal components in O(N log N) complexity for a composite signal of duration N.
Open Access
Equiripple FIR filter design by the FFT algorithm
(Institute of Electrical and Electronics Engineers, 1997-03) Çetin, A. Enis; Gerek, Ö. N.; Yardımcı, Y.
The fast Fourier transform (FFT) algorithm has been used in a variety of applications in signal and image processing. In this article, a simple procedure for designing finite-extent impulse response (FIR) discrete-time filters using the FFT algorithm is described. The zero-phase (or linear phase) FIR filter design problem is formulated to alternately satisfy the frequency domain constraints on the magnitude response bounds and time domain constraints on the impulse response support. The design scheme is iterative in which each iteration requires two FFT computations. The resultant filter is an equiripple approximation to the desired frequency response. The main advantage of the FFT-based design method is its implementational simplicity and versatility. Furthermore, the way the algorithm works is intuitive and any additional constraint can be incorporated in the iterations, as long as the convexity property of the overall operations is preserved. In one-dimensional cases, the most widely used equiripple FIR filter design algorithm is the Parks-McClellan algorithm (1972). This algorithm is based on linear programming, and it is computationally efficient. However, it cannot be generalized to higher dimensions. Extension of our design method to higher dimensions is straightforward. In this case two multidimensional FFT computations are needed in each iteration.
Open Access
Extraction of primary and secondary frequency control from active power generation data of power plants
(Elsevier Ltd, 2015) Ozer, B.; Arıkan, Orhan; Moral, G.; Altintas, A.
Frequency control is a vital component of a secure and robust power grid and it ought to be closely monitored. Frequency control consists of two main components; primary and secondary control and their contributions are usually aggregated in the active power generation data of a plant, which is acquired via Supervisory Control And Data Acquisition. In many cases, such as in Turkey, they are demanded to be evaluated separately due to different impacts on power system or different financial policies. However, this is not usually a straightforward process since primary and secondary response cannot be obtained distinctly. In this work, Extraction of Primary and Secondary Control (EPSCon) algorithm is introduced to extract primary and secondary response over active power generation data. Based on time and frequency domain characteristics of primary and secondary response, EPSCon is developed on a Expectation-Maximization type recursive scheme employing Generalized Cross Correlation and ℓ1 Trend Filtering techniques. Favorably, EPSCon uses a simple plant model built upon basic governor and plant load controller technical characteristics as an initial estimate of primary and secondary response.
Open Access
Fast computation of the ambiguity function and the Wigner distribution on arbitrary line segments
(IEEE, 2001) Özdemir, A. K.; Arıkan, Orhan
By using the fractional Fourier transformation of the time-domain signals, closed-form expressions for the projections of their auto or cross ambiguity functions are derived. Based on a similar formulation for the projections of the auto and cross Wigner distributions and the well known two-dimensional (2-D) Fourier transformation relationship between the ambiguity and Wigner domains, closed-form expressions are obtained for the slices of both the Wigner distribution and the ambiguity function. By using discretization of the obtained analytical expressions, efficient algorithms are proposed to compute uniformly spaced samples of the Wigner distribution and the ambiguity function located on arbitrary line segments. With repeated use of the proposed algorithms, samples in the Wigner or ambiguity domains can be computed on non-Cartesian sampling grids, such as polar grids.
Open Access
FEM Based design and simulation tool for MRI birdcage coils Including eigenfrequency analysis
(2012) Gürler, Necip; İder, Yusuf Ziya
Radio Frequency (RF) birdcage coils are widely used in Magnetic Resonance Imaging (MRI). Before the actual construction of the coil, not only calculating the capacitance value, which is necessary for the coil to resonate at the desired frequency, but also modeling the birdcage coil in a 3D simulation environment and making electromagnetic analysis in the volume of interest have importance in terms of observing the resonance behavior of the coil, electromagnetic field distributions inside the coil, or specific absorption rate (SAR) distribution for any object. For this purpose, we have made two different electromagnetic analyses of low-pass and high-pass birdcage coils in COMSOL Multiphysics. These are frequency domain analysis and eigenfrequency analysis. We have also developed a software tool using MATLAB® to make these electromagnetic analyses easily and according to the userspecified parameters. Simulation results for these analyses are provided. For the experimental results, we have constructed a hand-made lowpass birdcage coil and measured the resonant modes of the coil for different capacitance values. Our eigenfrequency analysis tool calculates the resonant modes with high accuracy
Open Access
Filtering in fractional Fourier domains and their relation to chirp transforms
(IEEE, 1994-04) Özaktaş, Haldun M.; Barshan, Billur; Onural, Levent; Mendlovic, D.
Fractional Fourier transforms, which are related to chirp and wavelet transforms, lead to the notion of fractional Fourier domains. The concept of filtering of signals in fractional domains is developed, revealing that under certain conditions one can improve upon the special cases of these operations in the conventional space and frequency domains. Because of the ease of performing the fractional Fourier transform optically, these operations are relevant for optical information processing.
Open Access
The fractional fourier transform and its applications to image representation and beamforming
(ASME, 2003-09) Yetik, I. Ş; Kutay, M. A.; Özaktaş, Haldun. M.
The ath order fractional Fourier transform operator is the ath power of the ordinary Fourier transform operator. We provide a brief introduction to the fractional Fourier transform, discuss some of its more important properties, and concentrate on its applications to image representation and compression, and beamforming. We show that improved performance can be obtained by employing the fractional Fourier transform instead of the ordinary Fourier transform in these applications.
Open Access
Generalized time-bandwidth product optimal short-time fourier transformation
(IEEE, 2002-05) Durak, Lütfiye; Arıkan, Orhan
By extending the time-bandwidth product concept to fractional Fourier domains, a generalized time-bandwidth product (GTBP) is introduced. The GTBP provides a rotation independent measure for the support of the signals in time-frequency domain. A close form expression for the adaptive kernel of STFT that provides the minimum increase on the GTBP of a signal is derived. Also, a linear canonical decomposition of the obtained GTBP optimal STFT is presented to identify its relation to the rotationally invariant STFT analysis.
Open Access
Generating time-varying road network data using sparse trajectories
(IEEE, 2016-12) Eser, Elif; Kocayusufoğlu, F.; Eravci, Bahaedd; Ferhatosmanoglu, Hakan; Larriba-Pey, J. L.
While research on time-varying graphs has attracted recent attention, the research community has limited or no access to real datasets to develop effective algorithms and systems. Using noisy and sparse GPS traces from vehicles, we develop a time-varying road network data set where edge weights differ over time. We present our methodology and share this dataset, along with a graph manipulation tool. We estimate the traffic conditions using the sparse GPS data available by characterizing the sparsity issues and assessing the properties of travel sequence data frequency domain. We develop interpolation methods to complete the sparse data into a complete graph dataset with realistic time-varying edge values. We evaluate the performance of time-varying and static shortest path solutions over the generated dynamic road network. The shortest paths using the dynamic graph produce very different results than the static version. We provide an independent Java API and a graph database to analyze and manipulate the generated time-varying graph data easily, not requiring any knowledge about the inners of the graph database system. We expect our solution to support researchers to pursue problems of time-varying graphs in terms of theoretical, algorithmic, and systems aspects. The data and Java API are available at: http://elif.eser.bilkent.edu.tr/roadnetwork. © 2016 IEEE.
Open Access
High resolution time-frequency analysis by fractional domain warping
(IEEE, 2001-05) Özdemir, Ahmet Kemal; Durak, Lütfiye; Arıkan, Orhan
A new algorithm is proposed to obtain very high resolution time-frequency analysis of signal components with curved time-frequency supports. The proposed algorithm is based on fractional Fourier domain warping concept introduced in this work. By integrating this warping concept to the recently developed directionally smoothed Wigner distribution algorithm [1], the high performance of that algorithm on linear, chirp-like components is extended to signal components with curved time-frequency supports. The main advantage of the algorithm is its ability to suppress not only the cross-cross terms, but also the auto-cross terms in the Wigner distribution. For a signal with N samples duration, the computational complexity of the algorithm is O(N log N) flops for each computed slice of the new time-frequency distribution.
Open Access
Independent estimation of input and measurement delays for a hybrid vertical spring-mass-damper via harmonic transfer functions
(IFAC, 2015-06) Uyanık, İsmail; Ankaralı, M. M.; Cowan, N. J.; Saranlı, U.; Morgül, Ömer; Özbay, Hitay
System identification of rhythmic locomotor systems is challenging due to the time-varying nature of their dynamics. Even though important aspects of these systems can be captured via explicit mechanics-based models, it is unclear how accurate such models can be while still being analytically tractable. An alternative approach for rhythmic locomotor systems is the use of data-driven system identification in the frequency domain via harmonic transfer functions (HTFs). To this end, the input-output dynamics of a locomotor behavior can be linearized around a stable limit cycle, yielding a linear, time-periodic system. However, few if any model-based or data-driven identification methods for time-periodic systems address the problem of input and measurement delays in the system. In this paper, we focus on data-driven system identification for a simple mechanical system and analyze its dynamics in the presence of input and measurement delays using HTFs. By exploiting the way input delays are modulated by the periodic dynamics, our results enable the separate, independent estimation of input and measurement delays, which would be indistinguishable were the system linear and time invariant. © 2015, IFAG.
Open Access
Kesirli fourier dönüşümünün zaman bölgesinde sonlu farklar yöntemine uygulanması
(IEEE, 2010-04) Sayın, I.; Arıkan F.; Arıkan, Orhan
Bilgisayarların hız ve belleklerinin gelişmesi ile birlikte elektromanyetik problemlerin çözümünde saysal yöntemler sıkça kullanılmaya başlanmış ve bu konuda çok sayda araştırma yapılmıştır. Saysal Elektromanyetik yöntemleri genel olarak zaman ve frekans tabanlı yöntemler olarak sınıflandırılabilir. Zaman tabanlı yöntemler geçici tepkilerin ve geniş bantlı problemlerin incelenmesinde kullanışlı olurken, frekans tabanlı yöntemler durağan hal tepkilerin ve dar bantlı problemlerin incelenmesinde en iyi çözümü vermektedir. Her iki yaklaşımın da avantajlarını ön plana çıkarabilecek bir yöntem geliştirilebileceği düşünülmektedir. Uzayda ve/veya zamanda Kesirli Fourier Dönüşümü uygulanarak bazı durumlarda hesaplama karmaşıklığı azaltılabilir. Kesirli Fourier Dönüşümü, sürekli Fourier Dönüşümünün genelleştirilmiş halidir. Son yıllarda bu konu üzerinde çeşitli çalışmalar yapılmakta ve uygulama alanları genişlemektedir. Genel olarak, sinyal işleme ve gürültü süzme gibi alanlarda kullanılmaktadır. Bu çalmada Kesirli Fourier Dönüşümü, ilk kez Maxwell denklemlerine zaman bölgesinde uygulanmış ve elde edilen diferansiyel denklemler sonlu farklar yaklaşımı ile ayrık hale getirilmiştir. Elde edilen ayrık sonlu fark denklemlerinin çözümü için öneriler sunulmuştur.
Open Access
A multiresolution nonrectangular wavelet representation for two-dimensional signals
(Elsevier, 1993) Çetin, A. Enis
In this paper, a new multiresolution wavelet representation for two-dimensional signals is described. This wavelet representation is based on a nonrectangular decomposition of the frequency domain. The decomposition can be implemented by a digital filter bank. The application of the new representation to the coding of quincunx and rectangularly sampled images is considered and simulation examples are presented.
Open Access
A new approach to time-frequency localized signal design
(IEEE, 2002) Özdemir, Ahmet Kemal; Aydın, Zafer; Arıkan, Orhan
A novel approach is presented for the design of signals in Wigner Domain. In this method, the desired signal features in the time-frequency domain are specified in two stages. First the user specifies the spine curve around which the energy of the desired signal is distributed in the time-frequency plane. Then, the user specifies the spread of the desired signal energy around the spine. In addition to this fundamentally new way of defining the time-frequency features of the desired signal, the actual synthesis of the signal is performed in a warped fractional Fourier transform approach [1]. After obtaining the designed signal, it is transformed back to the original time domain providing the final result of the new signal synthesis technique. In contrast to the conventional algorithms, the proposed method provides very good results even if the inner cross-term structure of the desired signal is not specified.
Open Access
A new method for the steady-state analysis of periodically excited nonlinear circuits
(Institute of Electrical and Electronics Engineers, 1996-12) Celik, M.; Atalar, Abdullah; Tan, M. A.
We propose a new method for the steady state analysis of periodically excited nonlinear microwave circuits. It is a modified and more efficient form of Newton-Raphson iteration based harmonic balance (HB) technique. It solves the convergence problems of the HB technique at high drive levels. The proposed method makes use of the parametric dependence of the circuit responses on the excitation level. It first computes the derivatives of the complex amplitudes of the harmonics with respect to the excitation level efficiently and then finds the Pade approximants for the amplitudes of the harmonics using these derivatives.
Open Access
A novel STFT implementation for the analysis of non-stationary jammer interference
(IASTED, 2004) Durak, L.; Arıkan, Orhan; Song, I.
A novel adaptive short-time Fourier transform (STFT) implementation for the analysis of non-stationary multi-component jammer signals is introduced. The proposed time-frequency distribution is the fusion of optimum STFTs of individual signal components that are based on the recently introduced generalized time-bandwidth product (GTBP) definition. The GTBP optimal STFTs of the components are combined through thresholding and obtaining the individual component support images, which are related with the corresponding GTBP optimal STFTs.