• Title/Summary/Keyword: Fourier transform

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Stamping Tool Wearing Analysis by Time-Frequency Analysis (시간-주파수 분석에 의한 금형 마모 분석)

  • Lee, Chang-Hee;Han, Ho-Young;Seo, Geun-Seok;Kim, Yong-Yun
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.19 no.3
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    • pp.407-413
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    • 2010
  • This paper reports on the research which analyzes acoustic signals acquired in progressive compressing, hole blanking, and burr compacting process. An acoustic sensor was set on the bed of hydraulic press. Acoustic signal is generated from progressive stamping process. First the signal acquired from the unit process; compressing, blanking or compacting, is studied by Fourier Transform and Short Time Fourier Transform. The blanking process emitted ultrasonic signal with more than 20kHz, but the compressing and compacting processes emitted acoustic signals with lower than 10kHz. The combined signals periodically acquired right after the tool grinding were then analyzed. 70-80kHz signals appeared in time-frequency domain, but not in the frequency domain, the magnitude of which was related to the tool wear. Short Time Fourier Transform made up for the Fourier Transform in analyzing the emitted signal for stamping process in the ultrasonic domain.

Design of diffractive pattern elements using two-stage iterative Fourier transform algorithm (2 단계 iterative Fourier transform 알고리즘을 이용한 회절 무늬 소자의 설계에 관한 연구)

  • 정필호;조두진
    • Proceedings of the Optical Society of Korea Conference
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    • pp.296-297
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    • 2000
  • 프라운호퍼 회절에 의하여 주어진 세기 무늬를 발생시키는 회절광학소자(Diffractive Optical Element, DOE)는 회절무늬소자, 키노폼(kinoform), 컴퓨터 푸리에 홀로그램 (computer-generated Fourier hologram) 등으로 불리우며, 광정보처리, 광연결, 레이저가공에서 중요한 역할을 한다. 이 소자를 설계하는 매우 다양한 방법들이 제안되었는데, iterative Fourier transform 알고리즘(IFTA)과 이를 변형한 알고리즘들이 가장 널리 사용된다. IFTA는 fast Fourier transform(FFT)를 활용하므로 계산시간이 절감되지만 국소 최소점에 고착되는 stagnation문제가 있어 이를 해결하기 위한 많은 변형된 알고리즘들이 제안되었다. 본 연구에서는 최근에 제안한 new Pnoise algorithm with hybrid input-output algorithm(NPA-HIOA)$^{(1)}$ 의 설계 성능을 IFTA, hybrid input-output 알고리즘(HIOA), new Pnoise 알고리즘(NPA)$^{(2)}$ , Nonlinear Least-Square (NLS)$^{(3)}$ 등의 기존의 알고리즘들과 비교하고자 한다. (중략)

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Efficient Spectrum Sensing Method using the Short Time Fourier Transform algorithm (Short Time Fourier Transform 알고리즘을 적용한 효율적인 스펙트럼 센싱 기법)

  • Kang, Min-Kyu;Lee, Hyun-So;Hwang, Sung-Ho;Kim, Kyung-Seok
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • pp.375-378
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    • 2009
  • The Spectrum Sensing Technology is the core technology of the Cognitive Radio (CR) System that is one of the future wireless communication technologies. This is the technology that temporarily allocates the frequency bandwidth by scanning surrounding wireless environments to keep licensed terminals and search the unused frequency bandwidth. In this paper, we proposed the efficient Spectrum Sensing Method using the Short Time Fourier Transform (STFT). The Cosine and DVB-H signal with the 6MHz bandwidth is used as the Input Signal. And we confirm the Spectrum Sensing result using Modified Periodogram Method, Welch's Method for compared with Short Time Fourier Transform Algorithm.

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Effect of Synchronization Errors on the Performance of Multicarrier CDMA Systems

  • Li Ying;Gui Xiang
    • Journal of Communications and Networks
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    • v.8 no.1
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    • pp.38-48
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    • 2006
  • A synchronous multicarrier (MC) code-division multiple access (CDMA) system using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) for the downlink mobile communication system operating in a frequency selective Rayleigh fading channel is analyzed. Both carrier frequency offset and timing offset are considered in the analysis. Bit error rate performance of the system with both equal gain combining and maximum ratio combining are obtained. The performance is compared to that of the conventional system using correlation receiver. It is shown that when subcarrier number is large, the system using IFFT/FFT has nearly the same performance as the conventional one, while when the sub carrier number is small, the system using IFFT/FFT will suffer slightly worse performance in the presence of carrier frequency offset.

A Generalized Fourier Transform Based on a Periodic Window

  • Yoo, Kyung-Yul
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.4E
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    • pp.53-57
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    • 1996
  • An extension of the well-known Fourier transform is developed in this paper. It is denoted as the generalized Fourier transform(GFT), since it encompasses the Fourier transform as its special case. The first idea of this extension can be found on [1]. In the definition of the N-point discrete GFT, it first construct a passband in time which functions as a window in the time domain. An appropriate interpretation of each variables are introduced during the definition of the GFT, followed by the formal derivation of the inverse GFT. This transform pair is similar to the windowing in the frequency domain such as the subband coding technique (or filter bank approach) and could be extended to the wavelet transform.

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Characterization of Trabecular Bone Structure using 2D Fourier Transform and Fractal Analysis (Fractal dimension과 2차원 푸리에변환을 이용한 수질골의 특성화에 관한 실험적 연구)

  • Lee Keon Il
    • Journal of Korean Academy of Oral and Maxillofacial Radiology
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    • v.28 no.2
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    • pp.339-353
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    • 1998
  • The purpose of this study was to investigate whether a radiographic estimate of osseous fractal dimension and power spectrum of 2D discrete Fourier transform is useful in the characterization of structural changes in bone. Ten specimens of bone were decalcified in fresh 50 ml solutions of 0.1 N hydrochloric acid solution at cummulative timed periods of 0 and 90 minutes. and radiographed from 0 degree projection angle controlled by intraoral parelleling device. I performed one-dimensional variance. fractal analysis of bony profiles and 2D discrete Fourier transform. The results of this study indicate that variance and fractal dimension of scan line pixel intensities decreased significantly in decalcified groups but Fourier spectral analysis didn't discriminate well between control and decalcified specimens.

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Measurement of Mode Shape By Using A Scanning Laser Doppler Vibrometer (스캐닝 레이저 도플러 진동계를 이용한 모드 해석)

  • Gang, Min-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.10
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    • pp.2560-2567
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    • 2000
  • When spatially dense velocity distribution is measured by a scanning laser Doppler vibrometer, the Fourier transform method provides the real and imaginary parts of the mode shapes in the form of a polynomial. However the Fourier transform method is often impractical because the independent decomposition property of cosine and sine components into real and imaginary parts, respectively, does not hold due to the leakage problem which commonly occurs in the Fourier transform of harmonic signals. To deal with this problem, a Hilbert transform method is newly proposed in this article. The proposed method is free from the leakage problem and relatively robust to the scanning error. A simulation example is provided to verify the effectiveness of this method.

Measurement of Mode Shape By Using A Scanning Laser Doppler Vibrometer (스캐닝 레이저 도플러 진동 측정기를 이용한 모드 측정)

  • Kang, Min-Sig
    • Proceedings of the KSME Conference
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    • pp.420-425
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    • 2000
  • When spatially dense velocity distribution is measured by a scanning laser Doppler vibrometer, the Fourier transform method provides the real and imaginary parts of the mode shapes in the form of a polynomial. However the Fourier transform method is often impractical because the independent decomposition property of cosine and sine components into real and imaginary parts, respectively, does not hold due to the leakage problem which commonly occurs in the Fourier transform of harmonic signals. To deal with this problem, a Hilbert transform method is newly proposed in this article. The proposed method is free from the leakage problem and relatively robust to tire scanning error. A simulation example is provided to verify the effectiveness of this method.

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Analysis of the Radiation Pattern of a Microstrip Array Antenna on a Non-Planar Surface by using FOURIER TRANSFORM (FOURIER TRANSFORM을 이용한 비평면형 마이크로스트립 어레이 안테나의 복사패턴 해석)

  • 고광태;구연건
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.15 no.9
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    • pp.785-795
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    • 1990
  • For the far field radiation pattern of a microstrip array antenna which is conformed to a cylindrical surface and forms an arc array, an approximate analysis method using FOURIER TRANSFORM is presented. In this method, the conformal array antenna is projected on the effective aperture plane and assumed to be an aperiodic array with nonlinear phase tilt. The effective aperture plane includes four end-points of each arc on the cylindrical surface. When the effective aperture ratio which is normalized to the planar type is from 1.0 to 0.9, it is confirmed that this approximate method is valid. To the array on the effective aperture plane, it is assumed that the phase tilt is due to the distance between aperture plne and curvature surface. Specially, when the radius of arc is more than 5 times to its length, the FOURIER TRANSFORM METHOD could be used with only varying scale factors. The results of calculating by approximate method are good agreement with the results of COORDINATE TRANSFORM METHOD and experimentally measured value in the range of -40dB. And, the difference of half power angle is less than 5 degrees when the effective aperture ratio moer than 0.9.

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Effects and Limitations of Separating Overlapped Fingerprints Using Fast Fourier Transform (고속 푸리에 변환(fast Fourier transform, FFT)을 이용한 겹친지문 분리의 효과와 한계)

  • Kim, Chaewon;Kim, Chaelin;Lee, Hanna;Yu, Jeseol;Jang, Yunsik
    • Korean Security Journal
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    • no.61
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    • pp.377-400
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    • 2019
  • Photography is the most commonly used method of documenting the crime and incident scene as it helps maintaining chain of custody (COC) and prove integrity of the physical evidence. It can also capture phenomena as they are. However, digital images can be manipulated and lose their authenticity as admissible evidence. Thus only limited techniques can be used to enhance images, and one of them is Fourier transform. Fourier transform refers to transformation of images into frequency signals. Fast Fourier transform (FFT) is used in this study. In this experiment, we overlapped fingerprints with graph paper or other fingerprints and separated the fingerprints. Then we evaluated and compared quality of the separated fingerprints to the original fingerprints, and examined whether the two fingerprints can be identified as same fingerprints. In the case of the fingerprints on graph paper and general pattern-overlapping fingerprints, fingerprint ridges are enhanced. On the other hand, in case of separating complicated fingerprints such as core-to-core overlapping and delta-to-delta overlapping fingerprints, quality of fingerprints can be deteriorated. Quality of fingerprints is known to possibly bring negative effects on the credibility of examiners. The result of this study may be applicable to other areas using digital imaging enhancement technology.