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Advances in Acoustics and Vibration
Volume 2012, Article ID 874081, 12 pages
http://dx.doi.org/10.1155/2012/874081
Research Article

Ultrasonic Flaw Imaging via Multipath Exploitation

1Center for Advanced Communications, Villanova University, Villanova, PA 19085, USA
2Electrical and Automatic School, Shanghai Institute of Technology, Shanghai 201418, China

Received 15 December 2011; Accepted 28 April 2012

Academic Editor: Erdal Oruklu

Copyright © 2012 Yimin D. Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We consider ultrasonic imaging for the visualization of flaws in a material. Ultrasonic imaging is a powerful nondestructive testing (NDT) tool which assesses material conditions via the detection, localization, and classification of flaws inside a structure. We utilize reflections of ultrasonic signals which occur when encountering different media and interior boundaries. These reflections can be cast as direct paths to the target corresponding to the virtual sensors appearing on the top and bottom side of the target. Some of these virtual sensors constitute a virtual aperture, whereas in others, the aperture changes with the transmitter position. Exploitations of multipath extended virtual array apertures provide enhanced imaging capability beyond the limitation of traditional multisensor approaches. The waveforms observed at the physical as well as the virtual sensors yield additional measurements corresponding to different aspect angles, thus allowing proper multiview imaging of flaws. We derive the wideband point spread functions for dominant multipaths and show that fusion of physical and virtual sensor data improves the flaw perimeter detection and localization performance. The effectiveness of the proposed multipath exploitation approach is demonstrated using real data.