Papers by Keyword: Short Time Fourier Transform (STFT)

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Authors: Ik Keun Park, Yong Kwon Kim, Youn Ho Cho, Won Joon Song, Yeon Shik Ahn, Yong Sang Cho, Gye Jo Jung
Abstract: A preliminary study of the behavior of ultrasonic guided wave mode in a pipe using a comb transducer for maintenance inspection of power plant facilities has been verified experimentally. Guided wave mode identification is carried out in a pipe using time-frequency analysis methods such as wavelet transform (WT) and short time Fourier transform (STFT), compared with theoretically calculated group velocity dispersion curves for longitudinal and flexural mode. The results are in good agreement with analytical predictions and show the effectiveness of using the time-frequency analysis method to identify the individual guided wave modes. And, It was found out that longitudinal mode (0, 1) is affected by mode conversion less than the other modes. Therefore, L (0, 1) is selected as a optimal mode for evaluating location of the surface defect in a pipe.
Authors: Jing Lei Zhou, Fan Wang
Abstract: Chirp signal is a typical non-stationary signal, and have been widely used in communication, sonar, radar and so on. So, this signal is worth to analysis. In order to show the characteristics, this paper first introduces the definition and formula of each algorithm, then with all kinds of time-frequency analysis method to the signals, and the signal to add two sine signal noise are analyzed, the comparison of the characteristics of the method in the paper, and the signal for the analysis, the selection of an appropriate analysis. Through analysis and comparison, when dealing with the signal, Hilbert-Huang transformation not only has a better gathered characteristic, but also has a better resolution to distinguish the sine signal noise. Finally, use the MATLAB software simulation to obtain the result.
Authors: Chan Yik Park
Abstract: Various damage index (DI) algorithms of detecting changes such as a loosen bolt and a delamination development in a composite structure were examined using ultrasonic Lamb waves generated by embedded piezoelectric active sensors. The DI is a single value that is a function of response signal’s attenuation due to any damage or changes in a structure. Various DI algorithms such as active damage interrogation (ADI), time domain root men square (RMS), short time Fourier Transform (STFT) and time reversal (TR) were discussed. For experimental validation, a composite stiffened panel was used, and loosen bolt damage and low-velocity- impact damage were tested. In order to pitch and catch Lamb waves, surface mounted PZTs (lead zirconate titanate) were used. According to the DI algorithms, appropriate ultrasonic guided Lamb waves were selected for actuators. Each set of DI algorithm and drive signal showed different characteristics to detect the damage.
Authors: Heung Seop Eom, Jae Hee Kim, Young H. Kim, Sung Jin Song
Authors: Wei Gao, Huai Shan Liu, Jian Ye Sun
Abstract: Independent components analysis (ICA) with constraint of seismic wavelet estimated from bispectrum of seismic traces is combined with short time Fourier transforms (STFT) to improve the traditional frequency domain seismic deconvolution. Neglecting noise, the seismic record is changed from time domain to frequency domain with STFT in order to transform the common seismic model to the basic ICA model. By applying FastICA algorithm with constraint of seismic wavelet estimated from bispectrum of seismic traces, reflectivity series and the seismic wavelet can be produced in frequency domain and changed back to the time domain subsequently. The model and real seismic data numerical examples all show the algorithm valid.
Authors: Yang Jin, Zhi Yong Hao
Abstract: In this paper, we report the condition to keep the optimal time-frequency resolution of the Gaussian window in the numerical implementation of the short-time Fourier transform. Because of truncation and discretization, the time-frequency resolution of the discrete Gaussian window is different from that of the proper Gaussian function. We compared the time-frequency resolution performance of the discrete Gaussian window and Hanning window based on that they have the same continuous-time domain standard deviation, and generalized the condition under which the time-frequency resolution of the Gaussian window will prevail over that of the Hanning window.
Authors: Hao Yu, Jin Song Li, Yan Zhang, Guang Cheng Xu
Abstract: Spectral decomposition is to convert seismic signals from the time domain to the frequency domain by mathematical transformation, and analyze amplitude and phase response characteristics of different scale geological bodies. Spectral decomposition could get higher resolution than conventional seismic data. In the identification of the fault system, it is fit for fault interpretation and plane combination of the sections. In the reservoir prediction, it can identify the shape and contour of the reservoir. This document analyzed algorithm and applicability of short time Fourier transform, continuous wavelet transform and S-transform. Using these three methods for carbonate reservoir identification in MaiJie let gas field, Amu Darya Basin, it proves that the frequency division section is more clearly than conventional seismic section in reservoir and fault description. And S-transform gets the best result.
Authors: Wen Bin Lu, Feng Jie Sun, Ying Li Luo, Ying Yan, Zhi Jun Liu, Xiao Wei Bi, Peng Fei Li, Yong Quan Chen
Abstract: A set of TWACS system is designed and implemented in this paper by analyzing the transmission characteristics of the TWACS signals in the industrial power. And its synchronization information is modulated by pseudo-noise code, and the synchronous detection is conducted by using signal synthesis and time-frequency analysis to determined the demodulation domain, then data demodulation is realized by using cross-correlation technique. This method is able to adapt to the bad channel environment in the industrial power.
Authors: Zhi Bin Gao
Abstract: In order to extract major components of signal, multi-component nonstationary acoustic signal was analyzed with time-frequency analysis technique. By transforming multi-component nonstationary acoustic signal from time domain to time-frequency domain with short time Fourier transform, major components were determined according to spectrogram. Results show that major components and its time-frequency characteristic parameters can be extracted exactly. Short time Fourier transform is an effective method for extracting major components of nonstationary acoustic signal.
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