Applications of approximate wave analysis to ultrasonic flaw imaging

Two applications of approximate wave analyses to ultrasonic flaw imaging are presented. One is to apply a high frequency approximation for transmitted waves through curved interfaces to improve SAFT images of flaws in a structure with complex geometry. As examples, the improved SAFT is applied to pitch-catch data for flaws in an immersed round bar, and flaw images are compared with conventional SAFT images. Another application is to use a low frequency approximation to reconstruct a flaw shape of 3-D plate thinning from reflection coefficients of ultrasonic guided waves. By introducing a far field expression of Green´s functions and Born approximation into the integral expression, a Fourier transform pair is obtained between the shape function of thinning flaw and reflection coefficients of backscattered guided waves. Some numerical examples are illustrated to show the validity and effectiveness of our inverse approach.