Use of lamb waves for the long range inspection of large structures

Lamb waves are very attractive for the quick inspection of large structures because they can propagate long distances along plates and shells. The chief drawback of Lamb wave inspection is that at least two modes exist at all frequencies and the modes are generally dispersive, which means that the received signals can be very complicated. As a result, the potential advantages of Lamb wave inspection have seldom been realized in practice. The key to the successful application of Lamb waves is the excitation of a single mode in a non-dispersive region. This paper discusses the selection of an appropriate mode and its excitation and reception. Examples of the use of Lamb waves for the detection of delaminations in composite materials and corrosion in pipes are then given.