• Title/Summary/Keyword: Coherent Source

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Indentification of Coherent/Incoherent Noise Sources Using A Microphone Line Array (독립, 비독립 음원이 동시에 존재할 경우 선형 마이크로폰 어레이를 이용한 소음원 탐지 방법)

  • 김시문;김양한
    • Journal of KSNVE
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    • v.6 no.6
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    • pp.835-842
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    • 1996
  • To identify the locations and strengths of acoustic sources, one may use a microphone line array. Apparent advantage of the source identification method utilizing a line array is that it requires less measurement points than intensity method and holography. This method is based on the information of magnitude and phase difference between pressure signals at each microphone. Since those differences are dependent on the source model, we have to assume them such as plane, monopole, etc. In this paper the conventional source identification methods such as beamforming method and MUSIC method are briefly reviewed by modeling a source as plane and spherical wave, then a modified method is introduced. This can be applied to sound field which may by either coherent or incoherent. Typical simulations and experiment are performed to confirm this identification method.

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Acoustic Source Modeling by Using ISC(Inverse Source Calculation) (역 행렬 계산을 이용한 실 소음원의 모델링)

  • 최재웅;이희준;강종민;강신일
    • Journal of KSNVE
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    • v.8 no.3
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    • pp.542-552
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    • 1998
  • The noise sources, structure-borne and/or air-borne, in machinery can be defined by their locations and strengths. However the locations of that noise sources are well known in many cases. In those cases, the problem can be defined as an inverse problem to known the strengths of the noise sources in the frequency domain, the modeling scheme is classified by thecoherent or incoherent source. This paper expands the basic concept to the case of the complex noise sources, in which the set of coherent and incoherent noise sources are matched with the noise of a real vehicle. The error factors in the experiment and the optimal number of the monopole sources to match the real suond filed are also investigated. The results of the noise source modeling of heavy machinery show that the incoherent and coherent/incoherent source models are applicable to the high frequency and the low frequency region, respectively. The noise source model also enables the noise source analysis to rank the contribution of real source group such as engine, T/M, exhuast, etc.

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Enhancing Nearfield Acoustic Holography using Wavelet Transform

  • Ko, ByeongSik
    • Journal of Mechanical Science and Technology
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    • v.18 no.10
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    • pp.1738-1746
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    • 2004
  • When there are low signal to noise relationships or low coherences between measured pressure and a reference sensor, a pressure field measured and estimated by NAH (Nearfield Acoustic Holography) becomes noisy on the hologram and source planes. This paper proposes a method to obtain the high coherent de-noised pressure signals from low coherent noisy ones by combining a wavelet algorithm with NAH. The proposed method obtains the de-noised field from acoustic fields on a noise source plane reconstructed through backward propagation of NAH. Thus this method does not need high coherent pressure signals on the hologram surface while the conventional nearfield acoustic holography requires high-coherent signals. The proposed method was verified by numerical simulation using noisy signals, composed of original signals and imposed noises distributed on the hologram surface.

Visualization of Multiple Incoherent Sources Using Nearfield Acoustic Holography (음향 홀로그래피를 이용한 다수의 완전 비상관 소음원들의 가시화)

  • 남경욱;김양한
    • Journal of KSNVE
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    • v.9 no.5
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    • pp.922-927
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    • 1999
  • The objective of this paper is to obtain the contribution of each source to the spectrum of pressure, when there are multiple incoherent sources in near-field acoustic holography. For this objective, we have to obtain signals very coherent to the input signals of the sources. To obtain the very coherent signals, many people have measured pressure signals in the vincinity of the sources. However, it is sometimes difficult to locate microphones near to the sources so that the signals are very coherent to the input signals. This paper proposed a method to obtain the very coherent signals by near-field acoustic holography. Therefore, the proposed method does not require the measurement of pressure near to each source. Simulation results for two incoherent monopole sources showed the possibility of the proposed method.

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A Study on Application and Validation of the Coherent Flamelet Model in Counterflow Turbulent Premixed Combustion (대향류 예혼합 난류 연소 유동에서의 Coherent Flamelet Model 적용 및 검증에 관한 연구)

  • Choi, C.R.;Huh, K.Y.
    • Journal of the Korean Society of Combustion
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    • v.1 no.2
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    • pp.51-58
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    • 1996
  • The coherent flamelet model(CFM) is applied to symmetric counterflow turbulent premixed flames. The flame source term is set proportional to the turbulence intensity to reproduce the experimental correlation of Abdel-Gayed et al. for the turbulent burning velocity. Flame quenching by the turbulent rate of strain is modeled by an additional multiplication factor to the flame source term. A modified form of CFM is employed to consider coexistence of burned and unburned premixture with ambient air. The predicted flame position and turbulent flow field coincide well with the experimental data of Kostiuk et al., although there is some discrepancy in the radial rms velocity component and integral length scale near the symmetric plane.

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New High Stability Excimer Laser for LTPS Manufacturing

  • Herbst, Ludolf;Paetzel, Rainer;Simon, Frank;Fechner, Burkhard
    • 한국정보디스플레이학회:학술대회논문집
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    • 2006.08a
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    • pp.540-543
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    • 2006
  • LTPS TFT backplanes for AM OLED displays have advantages in regard to reliability and performance compared to TFT backplanes based on amorphous silicon. However, the requirements for homogeneous laser crystallization during LTPS process are much higher than for LCD backplanes. Most important is the energy stability of the laser source. In this paper we describe a new excimer laser which meets the requirements of LTPS manufacturing process with high homogeneity.

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Simultaneous Addition and Subtraction of Optical Images by Using the Extended Incoherent Source (인코히런트 광원을 이용한 영상의 동기 가감)

  • Park, Hyung Rae;Jeon, Seok Hee;Park, Han Kyu
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.23 no.6
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    • pp.961-967
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    • 1986
  • A technique of optical image synthesis with an extended incoherent source is presented and compared with the coherent method. A holographic diffraction grating is fabricated by using Michelson interferometer, and by equalizing the 8th-order to the 2nd-order diffraction efficiency, complex amplitude addition and subtracdtion of optical images are simultaneously realized. The experiment shows that the quality of synthesized optical images in the incoherent method is improved in comparison with that of the coherent method by suppressing the coherent artifact noise.

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Receiver Front-End of Radar for the Coherent Operation (코히어런트 동작을 위한 레이다 수신기 전단부)

  • Lee, Taek-Kyung
    • Journal of Advanced Navigation Technology
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    • v.4 no.1
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    • pp.1-10
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    • 2000
  • When the magnetron is employed as a radar transmitter source, the receiver needs to detect the frequency and the phase of the transmitting signal for the coherent operation. The local oscillator frequency is tuned for the stable intermediate frequency and the coherent oscillator generates the stable signal which is phase-locked to the transmitting signal. In this paper, we designed and implemented the receiver front-end including AFC(Automatic Frequency Control) circuit, STALO(Stable Local Oscillator) and COHO (Coherent Oscillator) unit.

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