Publication Date




Published in: Tribikram Kundu (ed.), Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, Proceedings of the SPIE/International Society for Optical Engineering, Vol. 5394, San Diego, CA, March 14-18, 2004, pp. 385-398.


This paper portrays work for the development of a Lamb wave scanning method for the detection of defects in thin plates. The approach requires the generation of an ultrasonic A0 and S0-mode Lamb wave using an incident transmitter excited with a tone burst centered at a near non-dispersive frequency. With a fixed relative separation both transmitter and receiving transducer remotely scan a specific line section of the plate. The arrival time information coming from incident and reflected waves contain information associated with the location of reflection surfaces or potential flaws. The Hilbert-Huang transform is applied to the intrinsic mode functions which permit the computation of the signal energy as a function of time, proportional to the square of amplitude of the analytical signal. The arrival times and amplitudes of the notch-reflected energy are used to calculate, by means of two geometric methods, the coordinates of the source of the reflections. The resulting coordinates outline the extent and relative direction of notches in two different scenarios. One is having notches in a 0 to 22.5 degree orientation in respect to the far edge of the plate and two with notches of various sizes at a single rivet hole. Results of experiments conducted on 1.6 mm thick Aluminum square plates, with the arrangement of notches as described, compare favorably with the actual notches.