Author(s)

Quanwei Feng, Xiaoming Chen and Songsong Li

Corresponding Author

Quanwei Feng

ABSTRACT

This paper developed an inspection and imaging system based on the theory of synthetic aperture focusing technique. Ultrasonic Lamb waves are applied in this system to detect the damage in the plate-like structures. Single mode Lamb wave was generated by electromagnetic acoustic transducers to reduce the influence of the multi-mode properties. This paper takes the advantage of the synthetic aperture focusing technique algorithm by performing the algorithm in the Fast Fourier domain to improve defects imaging resolution. This algorithm has been applied in an aluminum plate by detecting defects using A0 Lamb wave. 1 mm deep by 3 mm wide slot was machined into the plate to simulate defects. EMATs are carried by one guide rail with 0.05mm scanning accuracy to scan damage area to improve the defects imaging resolution. The best matched excitation frequency of A0 mode is confirmed as 132KHz through Lamb waves dispersion curves. The synthetic aperture focusing technique algorithm is developed in the Fourier domain to make the algorithm efficient and computation intensive and to benefit from Fast Fourier domain algorithm to reduce the processing time. The results show that the defects on the aluminum plate can be clearly detected and the improvement of the image resolution using the improved SAFT is about 20% compared with traditional SAFT algorithm.

KEYWORDS

Synthetic aperture focusing technique; Lamb waves; Nondestructive testing; EMAT