• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.1
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• pp.29-37
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• 1992

In this paper, a new and easy analytical method to get the Fourier transforms of a popular type of truncated raised cosine function and its powers (n=1, 2, :1‥‥ : positive integers) Is proposed. This new. method is based on the concept of the ( 1+D)_type partial response system, and the procedure is more compact than the conventional method using differentiations. Especially, the results are obtained as a sum of three functions which are easily manageable for each power And they are recursively related to their powers. Therefore, they can be excellently applied to the computer-aided numerical solutions.

• Economic and Environmental Geology
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• v.25 no.1
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• pp.73-77
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• 1992

This paper compares numerical quadrature techniques for computing an inverse Fourier transform integral in two-dimensional resistivity modeling. The quadrature techniques using exponential and cubic spline interpolations are examined for the case of a homogeneous earth model. In both methods the integral over the interval from 0 to ${\lambda}_{min}$, where ${\lambda}_{min}$, is the minimum sampling spatial wavenumber, is calculated by approximating Fourier transformed potentials to a logarithmic function. This scheme greatly reduces the inverse Fourier transform error associated with the logarithmic discontinuity at ${\lambda}=0$. Numrical results show that, if the sampling intervals are adequate, the cubic spline interpolation method is more accurate than the exponential interpolation method.

• Journal of Biomedical Engineering Research
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• v.24 no.6 s.81
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• pp.487-494
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• 2003

The sleep stages provides the most basic evidence for diagnosing a variety of sleep diseases. for staging sleep by analysis of EEG(electroencephalogram), it is especially important to detect the characteristic waveforms from EEG. In this paper, sleep EEG signals were analyzed using Fourier transform and continuous wavelet transform as well as discrete wavelet transform. Proposeed system methods. Fourier and wavelet for detecting of important characteristic waves(hump, sleep spindles. K-complex, hill wave, ripple wave) in sleep EEG. Sleep EEG data were analysed using Daubechies wavelet transform method and FFT method. As a result of simulation, we suggest that our neural network system attain high performance in classification of characteristic waves.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.3
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• pp.60-67
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• 2009

The phase retrieval problem is a problem of reconstructing a signal or the phase of Fourier transform of the signal from the magnitude of its Fourier transform. In this paper we address the problem of reconstructing an unknown signal from the magnitude of its Fourier transform and the magnitude of Fourier transform of another signal that is given by the addition of the desired signal. After we briefly mention the uniqueness conditions under which a signal can be uniquely specified from the given information and key equations of the iterative algorithm, we present mathematical background that the iterative algorithm converges to the desired signal, present an example that illustrates the performance of the reconstruction algorithm, and show its convergence property.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.270-276
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• 1999

Fourier transform has been one of the most commonly used tools in study of frequency characteristics of signal. However, based on the Fourier transform. it is hard to tell whether a signal's frequency contents evolve in time or not. Recently, to overcome Fourier transform fault. not to represent non-stationary signal, time-frequency analysis methods are developed and those can represent informations of signal's time and frequency at the same time. In this study we analysed ultrasonic signal for degraded SUS 316 with time-frequency analysis method. In particular the methods such as short time Fourier(STFT) and Wigner-Ville distribution(WVD) were used to extract frequency contents and characteristics from ultrasonic signals.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2505-2511
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• 2013

Many studies in detection and classification of the targets in the underwater environments have been conducted for military purposes, as well as for non-military purpose. Due to the complicated characteristics of underwater acoustic signal reflecting multipath environments and spatio-temporal varying characteristics, active sonar target classification technique has been considered as a difficult technique. And it has difficulties in collecting actual underwater data. In this paper, we synthesized active target echoes based on ray tracing algorithm using target model having 3-dimensional highlight distribution. Then, Fractional Fourier transform was applied to synthesized target echoes to extract feature vector. Recognition experiment was performed using neural network classifier.

• The Journal of the Acoustical Society of Korea
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• v.35 no.1
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• pp.8-15
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• 2016

As a generalized form of the conventional Fourier transform, fractional Fourier transform (FrFT) can analyze a signal at intermediate domain between time and frequency domains with a transform order ${\alpha}$. Especially, FrFT has a number of advantages in the analysis of LFM (Linear Frequency Modulation) signals due to its robustness to noise. In this paper, we have proposed a new method to detect and estimate the distance of the target from the FrFT spectrum of the received echo signal. Experimental results have validated the proposed method, and shown that reliable target distance could be estimated in noise and reverberation environments.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2002.12a
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• pp.423-426
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• 2002

Fourier 변환은 연속이며, 무한 회 미분 가능한 함수인 반면, Wavelet 변환은 시간적으로도, 주파수적으로도 국재화 시키는 함수를 사용하는 점에서 차이가 있다. Fourier 변환에 비해 Wavelet 변환은 고주파 성분에 대해서는 시간 분해능이 높고, 저주파 성분에 대해서는 주파수 분해능이 높아지므로, 주어진 신호에 대한 지식이 없이도 시간-주파수 해석이 가능하고, 고주파 성분을 갖는 특이점의 검출에도 적합하다. 그러므로 Wavelet 변환의 이러한 성질을 이용하여 변압기의 출고전 권선의 완전한 절연을 검증하고자 한다. 이때 시행하는 뇌 임펄스 내전압 시험 시 나타난 푸리에 변환과 Wavelet 변환 곡선을 비교 분석 및 해석을 통하여 유의수준 및 신뢰 구간 둥의 통계학적 분석을 이용, 해석하여 보다 정확한 그래프를 산출하므로서 과도구간에 대한 정밀한 해석을 하고자 한다.

• Journal of Power System Engineering
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• v.4 no.4
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• pp.16-24
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• 2000

고체내의 열에너지의 전달을 분석하기 위하여 고전적인 Fourier 열전도 법칙과 에너지 보존식에서 유도되는 열전도 방정식을 사용해 왔다. 이러한 열전도 방정식은 열전도가 무한한 속도로 진행된다는 것을 의미하고 있다. 그러나 극저온상태에서나 매우 급속한 열전도과정 중 매우 짧은 시간의 상태에서 non-Fourier 모델에 기초를 둔 쌍곡선형 열전도 방정식이 도입되었다. 최근의 이에 관한 연구에서 열전도가 파장의 형태로 유한한 전파속도를 갖는다는 것이 실험적으로 증명되었고 이로부터 여러 가지 실험적인 해석과 이론 해석이 전개되었다. 본 논문에서는 열전파 속도의 유한한 성질을 나타내는 수정된 열전도 법칙을 이용하여 1차원 평판에 대하여 공간에 대한 finite Fourier 변환 방법과 Green 함수 방법으로 해석하여 열전도파의 파동 성질, 공진 현상 및 위상차를 고찰하고자 한다. 열전도파가 갖는 모달 주파수에 대해 임계값을 갖으며 이 임계값을 초과할 때 공진 현상과 위상차를 고찰할 수 있었다.

• Korean Journal of Optics and Photonics
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• v.21 no.3
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• pp.91-96
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• 2010

The size of a reconstructed image depends on the reconstruction distance and wavelength. The double fourier transform method is proposed to eliminate the dependence on the reconstruction distance and wavelength. We can get a fixed reconstructed image size by using the double fourier transform method. Two wavelength digital holography is proposed to measure the step height, which is larger than a single wavelength. The two image size of different wavelength holograms should be the same in order to apply two wavelength digital holography. We use two wavelength digital holography and double fourier transforms to measure the step height. The measured data were reasonable and we found that the double fourier transform is useful in two wavelength digital holography.