• Title/Summary/Keyword: Acoustic detection

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Characteristics of Point-Focus Type Ultrasonic Transducer using PVDF Element (고분자(高分子) PVDF 진동자(振動子)를 이용(利用)한 점집동초음파탐촉자(点集東超音波探觸子)의 특성)

  • Han, E.K.;Hwang, S.T.;Lee, B.S.;Park, J.S.;Ogura, Y.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.12 no.2
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    • pp.7-13
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    • 1992
  • In this study, we examine the characteristics of beam and the effect of these characteristics on the flaw detection by using different type of two transducers, which are PZT and PVDF film transducer. Consequently, the detection of infinitesimal flaw is more possible than PZT, since it has beam width at focus of $60%{\sim}65%$ in contrast with PZT's. Moreover we can know PVDF transducer has superiority in detecting ability for sub-surface flaw detection in view of its acoustic impedance is near to water's and its focusing range is narrower than PZT's as $65{\sim}85%$ because it has spherical surface.

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A real-time acoustic echo canceller implemented on the multimedia PC (멀티미디어 PC상에 구현된 실시간 음향 반향제거기)

  • Cha, Youn-Cheul;Yoo, Jae-Ha;Youn, Dae-Hee
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.35S no.11
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    • pp.184-193
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    • 1998
  • In this paper, a real-time acoustic echo canceller is implemented using only PC's CPU without extra help from a DSP chip. The adaptive digital filter is designed efficiently so that it can be implemented in real-time and has a proper cancellation performance. It is proposed that a new double talk detector consumes a small computational complexity and guarantees the fast detection and robust operation. The real-time acoustic echo canceller consists of the full-duplex sound card and 166 MHz Pentium PC, and requires less than 10% CPU time.

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Acoustical analysis and signal processing for leak location of buried pipes (지하매설 배관의 누수지점 탐지를 위한 음향학적 해석 및 신호처리)

  • Lee Young-Sup;Yoon Dong-Jin;Baek Kwang-Hyun;Kim Sang-Moo
    • Proceedings of the Acoustical Society of Korea Conference
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    • spring
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    • pp.225-230
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    • 2004
  • Leak noise is a good source to identify the exact location of a leak point of underground water pipelines. Water leak generates broadband noise from a leak location and can be propagated to both directions of water pipes. However, the necessity of long-range detect ion of this leak location makes to identify low-frequency acoustic waves rather than high frequency ones. Acoustic wave propagation coupled with surrounding boundaries including cast iron pipes is theoretical analyzed and the wave velocity was confirmed with experiment The leak locations were identified both by the acoustic emission (AE) method and the cross-correlation method. In a short-range distance, both the AE method and cross-correlation method are effective to detect leak position. However, the detect ion for a long-range distance required a lower frequency range accelerometers only because higher frequency waves were attenuated very quickly with the increase of propagation paths. Two algorithms for the cross-correlation function were suggested and a long-range detection has been achieved at real underground water pipelines longer than 300m.

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Development of Acoustic Resonance Evaluation System to Detect the Welding Defects (용접 불량 검사를 위한 음향공진 검사 장치 개발)

  • Yeom, Woo Jung;Kim, Jin Young;Hong, Yeon Chan;Kang, Joonhee
    • Journal of Sensor Science and Technology
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    • v.28 no.6
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    • pp.371-376
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    • 2019
  • We have developed an acoustic resonance inspection system to inspect the welding defects in the mechanical parts fabricated using friction stir welding method. The inspection system was consisted of a DAQ board, a microphone sensor, an impact hammer, and controlled by a PC software. The system was developed to collect and analyze the sound signal generated by hitting the sample with an impact hammer to determine whether it is defective. In this study, 100% welded good samples were compared with 95%, 90%, and 85% welded samples, respectively. The variation of the completeness in welding did not affect the visual appearance in the samples. As a result of analyzing the natural frequencies of the good samples, the five natural frequency peaks were identified. In the case of the defective samples, the frequency change was observed. The welding failure detection time was fast enough to be only 0.7 seconds. Employing our welding defect inspection system to the actual industrial field will maximize the efficiency of quality inspection and thus improve the productivity.

Wavelet-based Time Delay Estimation in Tomographic Signals (웨이브렛을 이용한 해양음향 토모그래피 음파 도달시간 분석)

  • 오선택;조환래;나정열;김대경
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.2
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    • pp.153-161
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    • 2003
  • In this paper, we propose a wavelet-based detection method to identify efficiently the time-delay or multipath channel of ocean acoustic signals due to complex ocean medium and boundary layers. Our proposed method employs wavelet packet transform to analyze the received broadband acoustic signals and applies the matched filter to determine the time region of interest. Also, we present numerical testing that results on both the simulated and real data revealed the efficiency of this method in time-delay estimation and moreover its capability in estimating the time-delay of individual path in multipath channel, in which the arrival patterns are too close to be separated by the matched filter method.

Joint Adaptive Combining and Variable Tap-Length Multiuser Detector for Underwater Acoustic Cooperative Communication

  • Liu, Zhiyong;Wang, Yinghua;Song, Lizhong;Wang, Yinyin;Dai, Fusheng
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.12 no.1
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    • pp.325-339
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    • 2018
  • In this paper, we propose a joint adaptive combining and variable tap-length multiuser detector (MUD) for amplify-and-forward (AF) underwater acoustic cooperative interleave-division multiple access (IDMA) communication system. The proposed MUD jointly realizes tap-length adjustment, adaptive combining, and multiuser detection. In contrast to the existing methods, the proposed detector can adaptively combine the received signals from different nodes at destination, and does not need the assumption that full and perfect channel state information (CSI) of all the links at the receiver is known. Moreover, the proposed detector can adaptively adjust the tap coefficient vector and tap-length of each branch according to the specific channel profile of each branch. Simulation results validate the feasibility and show the advantages of the proposed detector against existing counterparts.

An Experimental Study on the Prediction of Progressive Cracking around Tunnel Fallout (터널 변상부 주변 진행성 예측에 관한 실험적 연구)

  • Lee, Jun-S.;SaGong, Myung;Ahn, Sung-Kwon;Yoo, Sang-Geon;Song, Suk-Jun
    • Journal of the Korean Society for Railway
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    • v.12 no.5
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    • pp.811-818
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    • 2009
  • An estimation method of the fallout volume of a tunnel under construction is proposed based on an empirical method called bulking factor. For this, the main causes of the tunnel fallout are investigated and the scale of the fallout which is not accessible is considered. The calculated height of the fallout area is compared with borehole core data and the accuracy and efficiency of the proposed method is demonstrated. Another experimental approach on the detection of a progressive cracking around the tunnel fallout is provided based on an acoustic emission method. From the field tests near the tunnel fallout, it is shown that additional progressive cracking of the reinforced area is not foreseen and the effectiveness of the reinforcement is proven.

A Study on the Characteristics of Electronic Magnetic Interference(EMI) in Acoustic Emission Testing for Corrosion Detection of Ground Tank (지상탱크의 부식감지를 위한 음향방출시험에서 발생한 전자기간섭신호의 특성 연구)

  • Kim, Sung-Dai;Jung, Woo-Gwang
    • Korean Journal of Materials Research
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    • v.17 no.5
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    • pp.239-243
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    • 2007
  • The evaluation and comparison have been made for the EMI noise which was included in the signal from the sensors in the acoustic emission testing for the bottom plate of ground tank at full. The EMI signal has been classified into two types. One is the signal with very short AE count, and this signal possibly can be filtered by front end filter setting of the channel count with low level of 4 and high level of $10^8$. The other EMI signal occurred from CH 1, CH 3 and CH 10, and had high and constant duration with high energy and count (maximun duration > $10^5\;{\mu}s$), and has characteristic gradient of accumulation amplitude distribution. This signal should be removed in the AE signal evaluation by filtering, because this may affect to the total gradient.

A Hybrid Transceiver for Underwater Acoustic Communication (수중음향 통신을 위한 혼합형 송수신기에 관한 연구)

  • Choi, Young-Chol;Kim, Sea-Moon;Park, Jong-Won;Kim, Seung-Geun;Lim, Yong-Gon;Kim, Sang-Tab
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2003.05a
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    • pp.319-323
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    • 2003
  • In this paper, we propose a hybrid transceiver for underwater acoustic communication, which allows the system to reduce complexity and increase robustness in time variant underwater channel environments. It is designed in the digital domain except for amplifiers and implemented by using a multiple digital signal processors (DSPs) system. The digital modulation technique is quadrature phase shift keying (QPSK) and frame synchronization is an energy (non-coherent) detection scheme based on the quadrature receiver structure. DSP implementation is based on block data parallel architecture (BDPA). We shaw experimental results in th? underwater anechoic basin at KRISO. The results indicate that the frame synchronization is performed without PLL. Also, we shaw that the adaptive equalizer can compensate frame synchronization error and the correction capability is dependent on the length of equalizer.

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Performance Characteristics of a 50-kHz Split-beam Data Acquisition and Processing System (50 kHz Split Beam 데이터 수록 및 처리 시스템의 성능특성)

  • Lee, Dae-Jae
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.54 no.5
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    • pp.798-807
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    • 2021
  • The directivity characteristics of acoustic transducers for conventional single-beam echo sounders considerably limit the detection of fish-size information in acoustic field surveys. To overcome this limitation, using the split-aperture technique to estimate the direction of arrival of single-echo signals from individual fish distributed within the sound beam represents the most reliable method for fish-size classification. For this purpose, we design and develop a split-beam data acquisition and processing system to obtain fish-size information in conjunction with a 50-kHz single-beam echo sounder. This split-beam data acquisition and processing system consists of a notebook PC, a field-programmable gate array board, an external single-transmitter module with a matching network, and four-channel receiver modules operating at a frequency of 50-kHz. The functionality of the developed split-beam data processor is tested and evaluated. Acoustic measurements in an experimental water tank showed that the developed data acquisition and processing system can be used as a fish-sizing echo sounder to estimate the size distribution of individual fish, although an external single-transmitter module with a matching network is required.