• 한국음향학회지
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• 제26권8호
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• pp.381-389
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• 2007

본 논문에서는 천해역에서 PN 신호열의 자기상관특성을 이용하여 수중 초음파통신 채널 특성을 측정하는 방법과 수신 신호 샘플 데이터로부터 수중통신 채널 특성 분석 결과에 대하여 기술한다. 수중음향통신 채널의 특성을 측정하기 위하여 두개의 PN 신호를 I-채널 및 Q-채널 데이터로 사용하여 QPSK 심볼을 생성하고, 5 kHz 심볼율과 25 kHz 반송파를 갖는 신호로 변조하여 전송한다. 수신부는 송신기에서 675 m와 1492 m 떨어진 위치에서 수신 신호를 샘플링하여 저장한다. 저장된 샘플 데이터를 이용하여 산란 함수, 상관 시간, 지연전력 프로파일, spaced-tone 자기상관함수, 지연 확산 및 상관 대역폭을 각각의 음파 전파 거리에 대하여 분석한다. 또한, 분석한 채널 특성을 토대로 수중 전송 시스템 설계 및 구현을 위한 설계 지침을 제안한다.

• 디지털융복합연구
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• 제11권7호
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• pp.209-214
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• 2013

음성 인식 시스템에서는 인식 성능 향상을 위한 방법으로 인간의 청취 능력을 인식 시스템에 접목하였으며 잡음 환경에서 음성 신호와 잡음을 분리하여 원하는 음성 신호만을 선택할 수 있도록 구성되었다. 하지만 실용적 측면에서 음성 인식 시스템의 성능 저하 요인으로 인식 환경 변화에 따른 잡음으로 인한 음성 검출이 정확하지 못하여 일어나는 것과 학습 모델이 일치하지 않는 것을 들 수 있다. 따라서 본 논문에서는 음성 인식 향상을 위해 감마톤을 이용하여 특징을 추출하고 음향 모델을 이용한 학습 모델을 제안하였다. 제안한 방법은 청각 장면 분석을 이용한 특징을 추출을 통해 인간의 청각 인지 능력을 반영하였으며 인식을 위한 학습 모델 과정에서 음향 모델을 이용하여 인식 성능을 향상시켰다. 성능 평가를 위해 잡음 환경의 -10dB, -5dB 신호에서 잡음 제거를 수행하여 SNR을 측정한 결과 3.12dB, 2.04dB의 성능이 향상됨을 확인하였다.

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.36-48
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• 1999

Fatigue life and crack retardation behavior after penetration were experimentally examined using surface pre-cracked specimens of aluminium alloy 5083. The Wheeler model retardation parameter was used successfully to predict crack growth behavior after penetration. By using a crack propagation rule, the change in crack shape after penetration can be evaluated quantitatively. Advanced, waveform-based acoustic emission (AE) techniques have been successfully used to evaluate signal characteristics obtained form fatigue crack propagation and penetratin behavior in 6061 aluminum plate with surface crack under fatigue stress. Surface defects in the structural members are apt to be origins of fatigue crack growth, which may cause serious failure of the whole structure. The nondestructive analysis on the crack growth and penetration from these defects may, therefore, be one of the most important subjects on the reliability of the leak before break (LBB) design. The goal of the present study is to determine if different sources of the AE could be identified by characteristics of the waveforms produced from the crack growth and penetration. AE signals detected in four stages were found to have different signal per stage. With analysis of waveform and power spectrum in 6061 aluminum alloys with a surface crack, it is found to be capabilities on real-time monitoring for the crack propagation and penetration behavior of various damages and defects in structural members.

• 한국생산제조학회지
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• 제23권4호
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• pp.330-336
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• 2014

The continuous chip generated in cutting process deteriorates workpiece, tool, and machine tool system. It is necessary to treat this continuous chip in ductile material machining condition for stable cutting. This paper deals with the chip control method using acoustic emission(AE) signal in pure copper turning operation. AE raw signals, root mean square(RMS) signals and wavelet transformed signals measured in turning process are introduced to analysis for chip patterns. With analysis of AE signals, it is obtained that the produced chip patterns are correlated with the specified AE signals which are transformed by fuzzy pattern algorithm. By this experimental investigation, the chip patterns can be classified at significant level in pure copper machining process and controlled from continuous chips to reduced-length stable chips.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.230-235
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• 1997

During laser welding, a laser induced matal vapour and plasuma is formed. The plasma shows strong fluctuation combined with acoustic sound emission. On-line monitoring of the process is possible by measuring and analysing the plasma and acoustic sound emission. This paper introduce the method of on line process monitoring in the laser beam welding and analysis being monitoring signal. The results show the complementary information on the process.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.558-563
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• 1992

Bearing information of target is used critically for target tracking in underwater environment. In passive sonar, target bearing measurements are obtained by processing the acoustic signal emanating from the target. PDA tracking algorithm is usually applied in this case since bearing measurements have several peaks due to interference with other acoustic sources or reflections from underwater media. In this paper, we propose a modified PDA algorithm adopting new probabilistic distributions of the number, position, and amplitude of peaks based on the analysis of real data. This algorithm is tested on real and artificially generated data. The computer simulation result shows improvement of the tracking performance.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권3호
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• pp.169-176
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• 2000

The partial discharge(PD) signal, may seems to be stochastic and merely random, was investigated using the method to discern between chaos and random signal, e.g. correlation integral, Lyapunov characteristic exponents and etc. For the purpose of obtaining experimental data, partial discharge detecting system via computer aided acoustic sensor, detect PD signal from the insulating system, was used. While this method is very different from typical statistical analysis from the point of view of a nonlinear analysis, it can provide better interpretable criterion according to the time evolution with a degradation process in the same type insulating system.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.169-172
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• 1999

Recently, the wavelet transform has been a new and powerful tool for signal processing. It is more suitable specially for the feature extraction and detection of non-stationary signals than traditional methods such as, the Fourier Transform(FT), the Fast Fourier Transform(FFT) and the Least Square Method etc. because of the characteristic of the multi-scale analysis and time-frequency domain localization. The wavelet transform has been developed for the analysis of PD pulse signal to raise in the progress of insulation degradation. In this paper, the wavelet transform was applied to one foundational method for feature extraction. For the obtain experimental data, a computer-aided partial discharge measurement system with a single acoustic sensor was used. If we are applying to the neural network method the accumulated data through the extracted feature, it is expected that we can detect the PD pulse signal in the insulation materials on the on-line.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1984년도 추계학술발표회 논문집
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• pp.27-32
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• 1984

When chopped light inpinges on some condenced matters such as HgS, HgI2 and GaSe semiconductors, in an enclosed cell, the acoustic signals are produced within the cell. These acoustic signals were detected by using a gas-phase microphone in order to investigate the physical properties of the samples. In order to carry out investigation, PA-cell was first designed and made so as to produce higher sensitivity to acoustic signals. Second, an analysis of the photoacoustic spectrum of the various compounds was carried out to obtain the intensity of the PA-signal in terms of light wavelength and to calculate the energy band gaps occuring according to energy transitions. The agreement between the results obtained by this conventional PAS technique and the results obtained by the optical spectrum method was good. In additional analysis conducted on the basis of the R-G theory and the Sze theory are capable of determining the characteristics of energy transition of semiconductors.

• 대한전자공학회논문지
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• 제17권6호
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• pp.17-23
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• 1980

표면파 전자기구의 송수신지성을 단극, 이극, 삼극, 트랜스듀서의 예를 들므로써 이론적으로 분석하였다. 전자기 이론에 의한 출력신호를 유도하였으며 기본분석방법은 일반적으로 널리 모든 유형의 표면파기구에도 이용될 수 있음을 보이고 있다. 이론적으로 장단점을 이해하고 결론적으로 광범위한 응용을 전제하고 있다.