• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.180-185
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• 2004

Conventional ultrasonic examination to detect micro and small surface cracks is based on the pulse-echo technique using a normal immersion focused transducer with high frequency, or an angle-beam transducer generating surface waves. It is difficult to make an automatic ultrasonic system that can detect micro and small surface cracks and position in a large structure like steel and ceramic rolls, because of the huge data of inspection and the ambiguous position data of the transducer. In this study, a high-precision scanning acoustic microscope with a 10MHz large-aperture transducer has been used to assess the existence, position and depth of a surface crack from the real-time A, B, C scans obtained by exploiting the ultrasonic diffraction. The ultrasonic method with large aperture transducer has improved the accuracy of the crack depth assessment and also the scanning speed by ten times, compared with the conventional ultrasonic methods.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.801-802
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.529-530
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• 2009

• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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• pp.17-22
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• 2005

An experimental study was carried out to investigate the effect of local ultrasonic forcing on a turbulent boundary layer. Stereoscopic particle image velocimetry (SPIV) was used to probe the characteristics of the flow. A ultrasonic forcing system was made by adhering six ultrasonic transducers to the local flat plate. Cavitation which generates uncountable minute air-bubbles having fast wall normal velocity occurs when ultrasonic was projected into water. The SPIV results showed that the wall normal mean velocity is increased in a boundary layer dramatically and the streamwise mean velocity is reduced. The skin friction coefficient ($C_{f}$) decreases $60\%$ and gradually recovers at the downstream. The ultrasonic forcing reduces wall-region streamwise turbulent intensity, however, streamwise turbulent intensity is increased away from the wall. Wall-normal turbulent intensity is almost the same near the wall but it increases away from the wall, In tile vicinity of the wall, Reynold shear stress, sweep strength and production of turbulent kinetic energy were decreased. This suggests that the streamwise vortical structures are lifted by ultrasonic forcing and then skin friction is reduced.

• International Journal of Control, Automation, and Systems
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• v.6 no.5
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• pp.767-775
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• 2008

Methods used for exploring marine resources and spaces include positioning a probe under water and then recalling it after a specified time. Hydro-acoustic Releasers are commonly used for positioning and retrieving of such exploration equipment. The most important factor in this kind of system is the reliability for recalling the instruments. The frequently used ultrasonic signal detection method can detect ultrasonic signals using a fixed comparator, but because of increased rates of errors due to outside interferences, information is repetitively acquired. This study presents an effective ultrasonic signal detection algorithm using the characteristics of a resonance and adaptive comparator Combined with the FSK+ASK modulator. As a result, approximately 8.8% of ultrasonic wave communication errors caused by background noise and transmission losses were reduced for effectively detecting ultrasonic waves. Furthermore, the resonance circuit's quality factor was enhanced (Q = 120 to 160). As such, the bias voltage of the transistor (Vb= 3.3 to 6.8V) was increased thereby enhancing the frequency's selectivity.

• Journal of the Korean Society for Nondestructive Testing
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• v.10 no.1
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• pp.65-72
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• 1990

Comparison of acoustic emission, ultrasonic testing and crack gauge in 3-point bending testing have been studied. As the results, COD is indirectly assumed by strain gauge rate and grid pitch width when crack gauge grid is out. Acoustic emission is qualitatively able to measure crack growth by total count but ultrasonic testing has a difficulty in measuring it because of echo height fluctuation according to the change and pressure of UT. probe.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.283-292
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• 2009

Laser-based ultrasonic sensing requires the probe with fixed fecal length, but this requirement is not essential in laser-based ultrasonic generation. Based on this fact, we designed a pulsed laser-based ultrasonic wave propagation imaging (UWPI) system with a tilting mirror system for rapid scanning of target, and an in-line band-pass filtering capable of ultrasoaic mode selection. 1D-temporal averaging, 2D-spatial averaging, and 3D-data structure building algorithms were developed far clearer results allowing fur higher damage detectability. The imaging results on a flat stainless steel plate were presented in movie and snapshot formats which showed the propagation of ultrasound visible as a concentric wavefield emerging from the location of an ultrasonic sensor. A hole in the plate with a diameter of 1 mm was indicated by the scattering wavefields. The results showed that this robust UWPI system is independent of focal length and reference data requirements.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.189-200
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• 2005

Ultrasonic inspection methods are widely used for detecting flaws in materials. One of the more popular methods involves the extraction of an appropriate set of features followed by the use of a neural network for the classification of the signals in the feature space. This paper describes an approach which uses LMS method to determine the coordinates of the ultrasonic probe followed by the use of SAFT to estimate the location of the ultrasonic reflector The method is employed for classifying NDE signals from the steam generator tubes in a nuclear power plant. The classification results using this scheme for the ultrasonic signals from cracks and deposits within steam generator tubes are presented.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.6
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• pp.95-101
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• 2001

This work is concerned with construction of the intelligence stress predictor far compression strength evaluation using neural network-ultrasonic waves. The contact pressure in jointed plates was measured by using ultrasonic technique. Neural network is used to evaluate and predict contact pressure from the results of the calibration curves. The organized neural system was leaned with the accuracy of 99%, as a result of learning the ultrasonic echo ratio to the contact pressure measurement between SM45C and STS410 materials. And it could be evaluated and predicted with the accuracy of 90% in the evaluation of ultrasonic echo ratio difference in the same surface roughness and contact pressure, and 85% in the prediction of virtual ultrasonic echo ratio. Thus the proposed stress predictor is very useful for the evaluation and prediction of the contact pressure between SM45C and STS410 materials.

• Journal of the Korean Society of Radiology
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• v.13 no.6
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• pp.895-900
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• 2019

Ultrasound is known to be harmless to the human body and is widely used in obstetrics and gynecology to confirm the diagnosis and development status of fetus. Diagnosis Although long - term use of ultrasound may cause changes in body temperature, studies on the uterine temperature changes due to ultrasound have been lacking. The purpose of this study was to investigate the change of temperature according to ultrasonic scanning time using a self - produced uterine model phantom. Ultrasound equipment and a 4MHz convex probe were used to construct the uterine model phantom similar to the human uterus using acrylic and pig uterus, which are tissue equivalents. Three probe type thermometers were installed to measure the inside of the acrylic water tank, the uterus, and the atmospheric temperature. The temperature of the uterine phantom was ascertained by measuring the temperature of the subject for 6 hours, 361 times. In this study, the possibility of human body temperature elevation due to ultrasound could be confirmed and this study will be used as the basic data of ultrasonic heat absorption study.