• Title/Summary/Keyword: Pulse-echo

Search Result 312, Processing Time 0.032 seconds

Development of Underwater Acoustic Performance Measurement System Using Pulse Tubes (펄스 튜브를 이용한 수중 음향 성능 측정 시스템 개발)

  • Seo, Yun-Ho;Kim, SangRyul;Lee, Sung-Min;Byun, Yang-Heon;Seo, Youngsoo
    • Transactions of the Korean Society for Noise and Vibration Engineering
    • /
    • v.24 no.5
    • /
    • pp.399-406
    • /
    • 2014
  • Underwater acoustic materials are installed in order to reduce reflection, transmission and radiation of an underwater structure. The acoustic performance of the materials should be evaluated in accurately-controlled environment in terms of temperature and static pressure. In this paper, two pulse tubes, which are equipped with temperature and pressure controllers, are designed and developed to evaluate echo reduction(ER) and transmission loss(TL) of underwater acoustic materials. The procedures of the evaluation are suggested and the validation is carried out by comparing theoretical values to experimental results for a simple stainless steel specimen and free surface. In result, it is validated that developed pulse tubes are able to measure ER and TL with 2 dB tolerance.

Echo canceller compensating a nonlinear distortion of D/A converter (D/A 젼환기의 비선형왜곡을 보상하는 Echo Canceller)

  • Jeong, Gi-Seog
    • Journal of the Korean Institute of Telematics and Electronics A
    • /
    • v.32A no.3
    • /
    • pp.10-17
    • /
    • 1995
  • this thesis proposes a new echo canceller that can be used in a fulll-duplex digital subscriber loopmodem. The modem suffers from nonlinear distortion such as transmitted pulse asymmetry, saturation in transformers, and nonlinearity of data converters. The proposed nonlinear echo canceller can compensate the nolinear distortion by using a nonlinear digital filter based on canonical pieceewise-linear (CPWL) function. Numerical results based on computer simulation are given in this paper. It is shown that the convergence characteristics depend on the initial values of weights of linear filters with absoluters and that the nonlinearity in digital-to-analog(D/A) converter can be compensated by a relatively small number linear filters with absoluters. It is also shown that the proposed algorithm has a faster convergence rate in comparison with Voterra algorithm.

  • PDF

The Comparative Study on the Optimized Images between Spin Echo and Turbo Spin Echo Pulse Sequences in the 1.0 T ; Aspect of T1 Weighted Image in the Brain (SE와 TSE기법의 최적영상에 관한 고찰 (Brain T1WI 측면에서))

  • Cho M.J.;Jeong H.J.;Yoo B.K.;Kim W.S.;Min K.H.;Kim S.R.;Song I.C.
    • Journal of The Korean Radiological Technologist Association
    • /
    • v.27 no.2
    • /
    • pp.95-103
    • /
    • 2001
  • Ⅰ. Purpose : The purpose of this study was to evaluate optimized images of Turbo Spin Echo(TSE) imaging technique in Brain MRI compared with Spin Echo(SE) technique. Ⅱ. Materials and Methods : A retrospective comparison between SE and TSE sequences was pe

  • PDF

Stable Bottom Detection and Optimum Bottom Offset for Echo Integration of Demersal Fish (저서어자원량의 음향추정에 있어서 해저기준과 해저 오프셋의 최소화)

  • 황두진
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.36 no.3
    • /
    • pp.195-201
    • /
    • 2000
  • This paper discusses methods for the stable bottom detection and the optimum bottom offset which enable to separate the fish echoes from the bottom echoes with echo integration of demersal fish. In preprocessing of the echo signal, the bottom detection has to be done stably against the fluctuation of echo level and the bottom offset has to be set to a minimum height such that near bottom fish echoes are included Two methods of bottom detection, namely echo level threshold method and maximum echo slope method were compared and analyzed. The echo level method works well if the ideal threshold level was given but it sometimes misses the bottom because of the fluctuation of the echo. Another method to detect the bottom which uses maximum echo slope indicates the simple and stable bottom detection. In addition, the bottom offset has to be set near to the bottom but not to include the bottom echo. Optimum bottom offset should be set a few samples before the detected bottom echo which relates the beginning of pulse shape and acoustic beam pattern to the bottom feature.

  • PDF

A Clinical Study on the Ultrasonographic Diagnosis of Sinusitis (부비동염의 초음파 진단법에 관한 임상연구)

  • 조재훈;이승은;한은정;김찬중;김윤범
    • The Journal of Korean Medicine
    • /
    • v.23 no.2
    • /
    • pp.88-96
    • /
    • 2002
  • Objective : This study attempted to evaluate the ultrasonographic diagnosis of sinusitis compared to X-ray diagnosis and further to help the diagnosis and treatment of sinusitis through oriental medicine. Methods : Both A-mode ultrasonography and X-ray were taken of 30 symptom-positive patients and 10 symptom-negative controls. Nasal obstruction, rhinorrhea, postnasal drip, headache (facial pain), hyposmia (anosmia), throat discomfort and chronic cough were included in the symptoms of sinusitis. Both ultrasonographic and X-ray findings were divided into four groups (clear, mucosal thickening, air-fluid level and cystic shape) according to severity. Results : 1. The symptoms of patients (n=30) were as follows: nasal obstruction (83.3%), rhinorrhea (70.0%), postnasal drip (60.0%), chronic cough (53.3%), headache (40.0%), throat discomfort (40.0%), hyposmia (26.7%). 2. There was a significant correlation between symptoms and ultrasonographic findings (n=40, ${\gamma}=0.550$, P=0.001). 3. There was a significant correlation between symptoms and X-ray findings (n=40, ${\gamma}=0.555$, P=0.001). 4. There was a significant whole coincidence between ultrasonographic and X-ray findings (n=60, ${\gamma}=0.335, P=0.00l). Moreover, there was a significant coincidental trend between the two findings as they became severe (n=60, ${\gamma}=6.284$, P=0.012). 5. The distance of the ultrasonographic echoes was as follows: clear echo (n=9, from transducer pulse to air mucosa echo) $0.90{\pm}0.19cm$, mucosal thickening echo (n=23, from transducer pulse to air mucosa echo) 1.85{\pm}0.14cm, air-fluid level echo (n=26, from transducer pulse to back wall echo) $3.70{\pm}0.16cm$. 6. The highest diagnostic reliability of the ultrasonographic findings compared to X-ray findings was as follows: over-diagnosis in clear finding 77.3%, matched diagnosis in mucosal thickening finding 62.0%, matched diagnosis in air-fluid level finding 86.7%, matched diagnosis and under-diagnosis in cystic shape finding 50.0%. 7. In mucosal thickening, air-fluid level and cystic shape finding, there was a significant individual coincidence between the ultrasonographic and X-ray findings. In clear finding, there was no significant individual coincidence between the two findings. Conclusion : The ultrasonographic diagnosis significantly reflects the symptoms of sinusitis like X-ray diagnosis and is a valuable tool to screen prognostic factors such as mucosal thickening, air-fluid level and cyst. Therefore the ultrasonography will be useful for the diagnosis and treatment of sinusitis in oriental medicine.

  • PDF

Tensor Components in Three Pulse Vibrational Echoes of a Rigid Dipeptide

  • Dreyer, Jens;Moran, Andrew M.;Mukamel, Shaul
    • Bulletin of the Korean Chemical Society
    • /
    • v.24 no.8
    • /
    • pp.1091-1096
    • /
    • 2003
  • The effects of different polarization conditions on vibrational echo signals are systematically explored for the rigid cyclic dipeptide 2,5-diazabicyclo[2,2,2]octane-3,6-dione. An anharmonic vibrational Hamiltonian is constructed by computing energy derivatives to fourth order using density functional theory. Molecular frame transition dipole orientations are then used to calculate polarization dependent orientational factors corresponding to various Liouville space pathways. Enhancement and elimination of specific peaks in twodimensional correlation plots is accomplished by identifying appropriate pulse configurations.

Ultrasonic Measurement of Interfacial Layer Thickness of Sub-Quarter-Wavelength

  • Kim, No-Hyu;Lee, Sang-Soon
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.23 no.6
    • /
    • pp.577-582
    • /
    • 2003
  • This paper describes a new technique for thickness measurement of a very thin layer less than one-quarter of the wavelength of ultrasonic wave used in the ultrasonic pulse-echo measurements. The technique determines the thickness of a thin layer in a tapered medium from constructive interference of multiple reflection waves. The interference characteristics are derived and investigated in theoretical and experimental approaches. Modified total reflection wave g(t) defined as difference between total and first reflection waves increases in amplitude as the interfacial layer thickness decreases down to zero. A layer thickness less than one-tenth of the ultrasonic wavelength is measured using the maximum amplitude of g(t) with a good accuracy and sensitivity. The method also requires no inversion process to extract the thickness information from the waveforms of reflected waves, so that it makes possible to have the on-line thickness measurement of a thin layer such as a lubricating oil film in thrust bearings and journal bearings during manufacturing process.

Detection of Tool Wear by Using the Ultrasonic In-Process Sensor (초음파 인프로세스 센서를 이용한 공구마멸 검출)

  • Kang, H.S.;Hwang, J.;Ko, B.J.;Chung, E.S.
    • Transactions of the Korean Society of Machine Tool Engineers
    • /
    • v.10 no.3
    • /
    • pp.55-60
    • /
    • 2001
  • A technique on the detection of tool wear based on the ultrasonic pulse-echo method in turning process is presented. The change in amount of the reflected energy from nose and flank of the tool can be related to the level of tool wear and mechanical integrity of the tool, that is, there exists an excellent correlation between the ultrasonic measurement and tool wear. As a results, the method is very useful for the prediction of cutting tool life and the determination of tool exchange period.

  • PDF

A Study on Suppression of Ultrasonic Background Noise Signal using wavelet Transform (Wavelet변환을 이용한 초음파 잡음신호의 제거에 관한 연구)

  • 박익근
    • Journal of the Korean Society of Manufacturing Technology Engineers
    • /
    • v.8 no.1
    • /
    • pp.135-141
    • /
    • 1999
  • Recently, advance signal analysis which is called "Time-Frequency Analysis" has been developed. Wavelet and Wigner Distribution are used to the method. Wavelet transform(WT) is applied to time-frequency analysis of waveforms obtained by an ultrasonic pulse-echo technique. The Gabor function is adopted as the analyzing wavelet. Wavelet analysis method is an attractive technique for evolution of material characterization evoluation. In this paper, the feasibility of suppression of ultrasonic background noise signal using WT has been presented. These results suggest that ultrasonic background noise ginal can be suppressed and enhanced even for SNR of 20.8 dB. This property of the WT is extremely useful for the detecting flaw echos embedded in background noise.und noise.

  • PDF

Thickness Measurement of A Thin Layer Using Plane Ultrasonic waves (평면 초음파를 이용한 미소 간극 측정)

  • 김노유
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 1995.10a
    • /
    • pp.415-418
    • /
    • 1995
  • This paper describes a new technique for thickness measurement of a very thin layer less than one-quarter of the wavelength of ultrasonic wave using ultrasonic pulse-echo method. The technique determines the thickness of a thin layer in a layered medium form the amplitudes of the total reflected waves from the back side layer of interst. Thickness of a very thin layer few inch deep inside the media can be measured without using a very high frequency ultrasonic transducer over 100MHz which must be used in the conventional techniques for the precision measurement of a thin layer. The method also requires no inversion process to extract the thickness from the waveform of the reflected waves, so that it makes possible on-line measurement of the thickness of the layer.

  • PDF