| Summary: | 碩士 === 國立屏東商業技術學院 === 資訊管理系 === 92 === Ultrasound has many important applications in nondestructive testing. Since ultrasonic signal can penetrate many materials, it is widely used for detection of flaws. The evaluations of welding are the main purpose of this paper. The use of ultrasound is limited by several interferences, such as geometric inter-face, coarse grain, mode conversion and ringing. It will be practically difficult to perform evaluation if the originally received ultrasonic signal is used directly as false judgment may be obtained. This paper will use the methods of signal processing and wavelet transform to reject noisy signal and detect the position and relative information of flaws. Owing to effect that the sound beam will diverge in far field, the flaw information will be distorted in 2-D or 3-D ultrasonic images. Synthetic aperture focusing technique (SAFT) uses the methods similar to sensor fusion to reduce the distortion and increase the accuracy for evaluation. The appraisal of the size of the flaw utilizes the distance between the flaw and transducer. The size of flaw can then be measured according to a proportionally transfer function. We also performed measurement on various types of side-drilled holes and cracks. Simulations show that our method provides very effective results.
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