The effect of dispersion on long-range inspection using ultrasonic guided waves

• Published in: NDT & E international : independent nondestructive testing and evaluation 2001, Vol.34 (1), p.1-9
• Main Authors: Wilcox, P, Lowe, M, Cawley, P
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Dispersion; Exact sciences and technology; Guided waves; Lamb waves; Long-range testing; Materials science; Materials testing; Nondestructive testing: ultrasonic testing, photoacoustic testing; Physics
• ISSN: 0963-8695; 1879-1174
• DOI: 10.1016/S0963-8695(00)00024-4

The dispersion of ultrasonic guided waves causes wave-packets to spread out in space and time as they propagate through a structure. This limits the resolution that can be obtained in a long-range guided wave inspection system. A technique is presented for quickly predicting the rate of spreading of a dispersive wave-packet as it propagates. It is shown that the duration of a wave-packet increases linearly with propagation distance. It is also shown that the duration of a wave-packet after a given propagation distance can be minimised by optimising the input signal. A dimensionless parameter called minimum resolvable distance (MRD) is defined that enables a direct comparison to be made between the resolution attainable at different operating points. Some conclusions are made concerning the resolution of various operating points for the case of Lamb waves in an aluminium plate.