Flaw detection and sizing of ultrasonic images using wavelet transform and SAFT

Ultrasound has many important applications in nondestructive evaluation. Since ultrasonic signals can penetrate many materials, they are widely used for detection of flaws. However, the use of ultrasound is limited by interference, such as geometric interface, coarse grain, mode conversion and ringing. Hence it is practically difficult to perform evaluation directly using the originally received ultrasonic signal as false judgment may be obtained. This paper uses the methods of wavelet transform to reject noisy signal and detect the position and relative information of flaws. Owing to the effect of sound beam divergence in far field, the flaw information is distorted in 2D or 3D ultrasonic images. The synthetic aperture focusing technique (SAFT) uses methods similar to sensor fusion to reduce the distortion and increase the accuracy for evaluation. In this paper, the flaw was produced using a side-drilled hole. Measuring the size of flaw can be achieved by evaluating the traveling distance of the reflected signal. A proportional transfer function and lookup table can then be constructed for verifying the size of flaw. Simulations show that our method provides very effective results.