• Journal of the Korean Society for Nondestructive Testing
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• v.6 no.2
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• pp.7-16
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• 1987

Eddy Current Examination is expected as the effective technique for nondestructive inspection of steam generator and various kinds of heat exchanging tubes made of STS - 304. In Case of E. C. T, a study on the various factors which have an effect on coil impedance is very important to the sensitivity of defect detection and the ratio of signal to noise. Therefore, this study analyzed coil impedance by means of the variational principle, the minimized theory of energy functional and the application of Finite Element Method. Really by using E. C. T, the relationship between the size of defects and the intensity of Eddy Current Signals can be obtained. Signal intensity becomes maximum at certain frequency. This frequency is affected by the characteristics and the position of signal sources.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.2
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• pp.21-25
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• 2011

Although many defects in PZR heater sleeve have been reported continually from operating experiences in oversea nuclear power plant, utilities get into difficulties in finding appropriate methods for diagnostics of the components due to the limited access or high radiation problems. Recently, as an alternative, diagnostics using Guided Wave Testing(GWT) are proposed and the attention of the methods has been growing gradually because of their long range inspection capability. This study is to investigate the effectiveness of GWT to detect PWSCC in welding points of PZR heater sleeve. Moreover, mode sensitivity analysis of GWT and optimal frequency for the diagnostics of PWSCC are presented by testing the mock-ups specimens that contain artificial flaws.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.239-242
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• 2001

Electronic Speckle Pattern Interferometry(ESPI) was proposed in the 1970's as a method of producing the interferogram without using traditional holographic technique. ESPI is more faster than Holography method, because the interferometric image is recorded and updated by the video camera every 1/30 second and whold-field inspection possibly. In this study using a non-contact optical technique that is suited for in-plane and out-of-plane deformation measurement. Thin plate with crack was analyzed by ESPI to determine the characteristics of vibration mode shape and natural frequency. Also, results of the experiment were compared with Finite Element Method(FEM).

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.6
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• pp.297-303
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• 2002

We have developed an on-line ultrasonic detector to monitor partial discharge in an operating transformer. The ultrasonic sensor has 150[KHz] resonance frequency and contains a pre-amplifier with 60[㏈] gain. The on-line ultrasonic detector has 50~300[KHz] frequency band-pass filter to remove electrical and mechanical noises from the transformer. This detector has an ultrasonic signal discrimination algorithm which discriminates ultrasonic signals due to partial discharge in a transformer. A moving average method of ultrasonic signal number was employed to effectively monitor the increasing trend of the partial discharge. This paper describes an experience of partial discharge detection in a 154[㎸] operating transformer using an ultrasonic detector. With regards to gas analysis in oil, C2H2 gas was produced with a warning level in this transformer We detected ultrasonic signals on the transformer steel wall, and estimated the position of partial discharge. With further inspection, we found carbonized marks due to partial discharge on the supporting bolt which fastens the windings.

• Journal of Biosystems Engineering
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• v.23 no.6
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• pp.615-620
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• 1998

The nondestructive internal quality evaluation of agricultural products has been strongly required from the needs for individual inspection. In recent, ultrasonic wave has been considered as a solution for this problem. It transmit well through most materials and can handle safely and easily. However, specially in a watermelon, it is known that general frequency band (higher than 20kHz) ultrasonic waves do not transmitted well due to severe attenuation. The objectives of this study were to find out the proper waveform and frequency of the ultrasonic waves that transmit well inside the watermelon, and to analyze the transmitted waveform in order to make clear the structure of wave propagation in watermelon. The result of several experiments showed that 2kHz shear wave was the most suitable for the detection of internal cavity in the watermelon. Also, it was found that the surface wave did not influence the directly transmitted bulk wave. These results could be a basis of application of ultrasonic wave on the evaluation of internal quality of the watermelon.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.79-79
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• 2009

Ultrasonic fine welding, cutting, cleaning, inspection and measurement is widely used in various fields over 20kHz. However, for High Frequency of 60kHz or more study areas is still insufficient, and the result is lacking. Therefore, this study used ultrasonic horn to the Bonding of Dissimilar Materials for effective design. Finite element analysis (FEA) is using the equations of motion to establish the model. The optimal design for the basic interpretation of vibration characteristics of the ultrasonic measures horn will examine the design.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.76-83
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• 2000

A 2-pole tunable bandpass filter was design and fabricated using ceramic coaxial resonators and varactor diodes for UHF band. By inspection of frequency characteristics of the T-and $\pi$-type inverter equivalent circuits, we can design a two-pole tunable BPF with only two varactors. The measured data of the filter show 800 MHz-900 MHz tunable center frequency range, 4.5 dB insertion loss, 0.5 dB passband ripple and at least 15 dB return loss, which agree well with the simulated results.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.4
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• pp.424-430
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• 2008

A new active vibration measurement system in electric power transmission line is presented, using in the nondestructive test. With a permanent magnet and a couple of coils, the system exerts impact force to a test object and in turn picks up the vibration of the object. The natural frequency with the amplitude obtained from the system are used as a basis for the detection of defects in the object. The system is controlled by an electronic device designed to facilitate the fully automated testing process with consistent repeatability and reliability which are essential to the nondestructive test. The system is expected to be applied to the wide area of defect detection including the classification of mechanical parts in production and inspection processes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1376-1383
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• 2001

Modem technology depends on the reliability of extremely high technology equipments. In the production of semiconductor wafer, optical and electron microscopes, ion-beam, laser device must maintain their alignments within a sub-micrometer. This equipment requires a vibration free environment to provide its proper function. Especially, lithography and inspection devices, which have sub-nanometer class high accuracy and resolution, have come to necessity for producing more improved giga and tera class semiconductor wafers. This high technology equipments require very strict environmental vibration standard, vibration criteria, in proportion to the accuracy of the manufacturing, inspecting devices. The vibration criteria of high sensitive equipment should be represented in the form of 'exactness' and 'accuracy', because this is used as basic data for the design of building structure and structural dynamics of equipment. This paper deals with the properties of time and frequency domain in order to obtain more improved vibration criteria for high sensitive equipment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.222-226
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• 1997

The reproducibility of measured level is a prior condition for the reliable assessment of the sound insulation performance. To review the reproducibility of impact sound level, 20 floors were selected in highrise apartment house, and then impact sound levels of two kinds of typical floors were measured with 10 times in each receiving point. The impact sound insulation class values were derived with a standard tapping machine and bang machine. Inspection of the result showed that smaller scale of the room caused to lower the reproducibility and that the higher values of standard deviation in lower frequency caused to deteriorate the reliability of assesment. Thus to enhance the reproducibility of the impact sound insulation class, greater allowable deviation of measured level is required in lower frequency than in higher one.