• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.123-124
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• 2007

• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.178-179
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• 2001

• Proceedings of the Optical Society of Korea Conference
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• 1999.08a
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• pp.64-65
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• 1999

• Proceedings of the Optical Society of Korea Conference
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• 2005.07a
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• pp.198-199
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• 2005

• Proceedings of the Optical Society of Korea Conference
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• 2006.02a
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• pp.223-224
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• 2006

• Proceedings of the Optical Society of Korea Conference
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• 2008.07a
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• pp.301-302
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• 2008

• Proceedings of the Optical Society of Korea Conference
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• 2002.11a
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• pp.72-73
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• 2002

• Proceedings of the Optical Society of Korea Conference
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• 2002.11a
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• pp.82-85
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• 2002

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.211-219
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• 2014

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.

• Journal of the Korean Society for Railway
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• v.15 no.3
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• pp.244-250
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• 2012

In this paper, The next Generation High Speed Railway Inverter system using RCF-PWM(Random Carrier Frequency Pulse Width Modulation) was developed to reduce electromagnetic noise. RCF-PWM method is randomized the switching frequency in the range between Semiconductor switching devices' maximum switching frequency and minimum switching frequency, Simulation program has been built using MATLAB/Simulink to verify the validity of study. Finally, the simulation results of Next Generation High Speed Railway inverter system using the RCF method was compared with the conventional SVPWM method.