• Computers and Concrete
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• 제20권5호
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• pp.595-603
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• 2017

Piezoceramic transducers have been widely used in the health monitoring of civil structures. However, in most cases, they are used as sensors either to measure strain or receive stress waves. This paper proposes a method of using piezoelectric transducers as strain gauges and acoustic emission (AE) sensors simultaneously. The signals received by piezoceramic transducers are decomposed into different frequency components for various analysis purposes. The low-frequency signals are used to measure strain, whereas the high-frequency signals are used as acoustic emission signal associated with local damage. The b-value theory is used to process the AE signal in piezoceramic transducers. The proposed method was applied in the bending failure experiments of two reinforced concrete beams to verify its feasibility. The results showed that the extracted low-frequency signals from the piezoceramic transducers had good agreement with that from the strain gauge, and the processed high-frequency signal from piezoceramic transducers as AE could indicate the local damage to concrete. The experimental results verified the feasibly of structural health monitoring using piezoceramic transducers as strain gauges and AE sensors simultaneously, which can advance their application in civil engineering.

• 한국전기전자재료학회논문지
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• 제29권2호
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• pp.114-119
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• 2016

This paper dealt with the propagation characteristics of acoustic signal in insulation oil for the purpose of improving the reliability of AE (acoustic emission) method used for condition monitoring of oil-immersed transformers. A discharge source was placed in insulation oil and AE sensors ($f_c$ :140 kHz) were attached on the oil tank to study the changes of velocity and propagation path with the depth and distance. The average velocity was 1,436 m/s and the velocity decreased with the increase of depth from the oil surface to 430 mm. The propagation paths were classified into three sections by the shortest reflection path of the detected signal. The minimum distinguishable distance in each section was 70 mm. It was also verified that PD (partial discharge) with a magnitude over than 500 pC can be detected by the AE sensors.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.311-314
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• 2001

This paper describes the simulation study, conducted on the propagation characteristics of AE signal in the connection of GIS. In the high voltage and large power system, the equipment with SF$\sub$6/ gas insulation which consists of the component part enclosed in the compressed gas has less affected by the environment than with air insulation. When the breakdown in the electric installation occurs, it takes much time to repair them though. Therefore it is very important to diagnose the propagation characteristics of AE signal in the GIS. So, in this investigation, we make a plane model of 362 kV GIS and modal and harmonic analysis to observe the vibro-acoustic property. Through the result of the analysis, we can make a further understanding on the vibro-acoustic characteristics of AE singnal in the connection of GIS.

• Composites Research
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• 제35권2호
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• pp.61-68
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• 2022

복합재료는 비강도, 비강성 및 내부식성 등이 우수하여 항공우주산업뿐만 아니라 다양한 산업에서 사용되고 있다. 그러나 복합재료는 충격에 취약하고 이러한 충격은 복합 재료 내부의 균열 형성과 균열 성장으로 이어져 구조 파단의 원인이 된다. 본 논문에서는 음향 방출 신호 및 유한요소해석(Finite element analysis, FEA)을 이용하여 복합재 적층판의 Mode I 파괴 모드의 특성을 분석하였다. DCB 시험은 탄소/에폭시 적층판의 Mode I 파괴 특성을 분석하기 위하여 수행되었고 시편의 파괴에 의해서 발생되는 탄성파를 측정하기 위하여 시편에 음향 방출 센서를 부착하였다. 누적 음향 방출 에너지와 균열 선단 위치의 관계를 이용하여 시편의 파괴 인성(Fracture toughness, G_I)을 계산하였다. 계산된 파괴 인성 값을 유한요소모델에 적용하여 해석을 수행하였고 하중-변위 곡선 및 균열 길이-변위 곡선을 통하여 DCB 시험 결과와 비교/분석하였다. 유한요소해석 및 DCB 시험의 결과가 잘 일치함을 보였다.

• 대한기계학회논문집A
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• 제35권9호
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• pp.1131-1136
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• 2011

본 연구는 자동차용 CNG 연료탱크의 파열시험시 발생하는 음향방출변수의 분석에 관한 내용이다. 연료탱크의 복합재료 중앙부 표면에 150kHz 공진형 AE센서를 부착하여 파열시험시 발생하는 음향방출 신호를 획득하고, 가압유지시간 동안의 hit, amplitude, count, duration, risetime, signal strength 등과 같은 음향방출 변수들을 분석하였다. 음향방출 변수 중 total count, total signal strength가 연료탱크 손상정도를 평가하는데 유용한 변수임을 알 수 있었다.

• 수산해양기술연구
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• 제58권2호
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• pp.130-140
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• 2022

Recently, wideband acoustic technology has been introduced and started to be used in fisheries acoustic surveys in various waters worldwide. Wideband acoustic data provides high vertical resolution, high signal-to-noise ratio and continuous frequency characteristics over a wide frequency range for species identification. In this study, the main characteristics of wideband acoustic systems were elaborated, and a general methodology for wideband acoustic data analysis was presented using data collected in frequency modulation mode for the first time in Republic of Korea. In particular, this study described the data recording method using the mission planner of the wideband autonomous acoustic system, wideband acoustic data signal processing, calibration and the wideband frequency response graph. Since wideband acoustic systems are currently installed on many training and research vessels, it is expected that the results of this study can be used as basic knowledge for fisheries acoustic research using the state-of-the-art system.

• 한국생산제조학회지
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• 제20권3호
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• pp.304-309
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• 2011

A monitoring system for magnetic abrasive polishing process is necessary to ensure the polishing products the high quality and integrity. Acoustic emission (AE) signal is known to reflect the material removal phenomena in other machining processes. In a case of the magnetic abrasive polishing of non-magnetic materials, application of AE method is very difficult because of lower machining force on the surface of workpiece and the level of AE signal is extremely lower. In this study, AE sensor-based monitoring system is applied to the magnetic abrasive polishing. The relation between the level of the AE RMS and the surface roughness during the magnetic abrasive polishing of magnesium alloy steel is investigated.

• 한국수산과학회지
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• 제43권1호
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• pp.83-88
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• 2010

Acoustic telemetry is a useful method to investigate fish behavior and is widely used to obtain biological information. In this study, the detection ability of a mooring-type acoustic telemetry system and the seasonal changes were studied for survey design and data analysis. The system detection range was examined with an underwater noise model, and seasonal changes were estimated with a ray-tracing program and underwater temperature profile data. The field experiment was conducted with two sets of pingers and six receivers to estimate the difference in detection rate by installation depth and to compare the model estimate. Results indicated that the long-range detection ability of the acoustic telemetry system was significantly affected by underwater temperature. The detection rate rapidly decreased near the sea surface or bottom despite that the near-range Signal to noise ratio was sufficient.

• Journal of Biosystems Engineering
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• 제23권6호
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• pp.621-628
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• 1998

In order to develop an inspection algorithm for an automatic eggshell inspection system, acoustic impulse response with neural network method was studied. An improved error backpropagation algorithm was selected as a loaming rule of neural network, and three layer network was chosen for the neural network architecture. Acoustic signals in time domain and theirs power spectrum were studied as the input to the neural network. The classification feasibility and success rate were investigated in terms of statistical analysis and neural network approach. As a result, the success rate was 95% with the statistical model having five independent variables. Among the neural network models studied, the power spectrum of acoustic signal as the input with 64 input neurons and the two impact data showed the success rate of 95.5% which was slightly higher than of statistical analysis.

• 한국정보전자통신기술학회논문지
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• 제2권2호
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• pp.29-36
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• 2009

비선형적인 위상 변화를 지닌 비정상(non-stationary)신호는 레이더(Radar), 통신(telecommunication), 생체공학, 지질탐사, 음향 등 여러 분야에서 쉽게 접하는 신호이다. 비정상신호는 일반적으로 시간에 따라 신호의 물리적 특성이 변화하는 신호를 의미하며, 순간 주파수는 신호의 특정시간에 해당하는 신호의 주파수를 의미한다. 이 논문에서는 순간 주파수를 결정하기 위한 연속 웨이브렛 변환의 적용에 대하여 논하였다.