Ultrasonic Lamb wave diffraction tomography

• Published in: Ultrasonics Vol. 39; no. 4; pp. 269 - 281
• Main Authors: Malyarenko, Eugene V, Hinders, Mark K
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2001; Elsevier Science
• Subjects: Acoustic signal processing; Acoustical measurements and instrumentation; Acoustics; Aircraft; Algorithms; Cross-disciplinary physics: materials science; rheology; Cross-hole; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Image Processing, Computer-Assisted; Lamb waves; Materials science; Materials Testing; Nondestructive testing: ultrasonic testing, photoacoustic testing; Physics; Ray tracing; SIRT; Tomography; Ultrasonography - methods; 43.60.Pt; Lamb waves; 43.60.Rw; Cross-hole; Tomography; Ray tracing; 43.20.Fn; SIRT; Wave diffraction; Hole; Acoustic measurement; Transit time; Image processing; Ultrasound imaging; Geometrical acoustics; Guided wave; Surface wave; Image reconstruction; Lamb wave; Wave scattering; Simulated annealing; Acoustic image; Shooting method; Aircraft; Non destructive test
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/S0041-624X(01)00055-5

Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. Unlike conventional ultrasonic C-scan imaging that requires access to the whole inspected area, tomographic algorithms work with data collected over the perimeter. Because the velocity of Lamb waves depends on thickness the travel times of the fundamental modes can be converted into a thickness map of inspected region. Lamb waves cannot penetrate through holes and other strongly scattering defects and the assumption of straight wave paths, essential for many tomographic algorithms, fails. Diffraction tomography is a way to incorporate scattering effects into tomographic algorithms in order to improve image quality and resolution. This work describes the iterative reconstruction procedure developed for Lamb wave tomography and allowing for ray bending correction for imaging of moderately scattering objects.