Mode and Transducer Selection for Long Range Lamb Wave Inspection

Abstract

Lamb waves can propagate many metres along plate and shell structures, and so have great potential in 'smart structure' applications where it is important for a transducer to interrogate a significant area of the surrounding structure. However, there are many different types of Lamb wave and in order to obtain simple signals that can be reliably interpreted, it is important to excite a single mode in a well controlled direction. The choice of which Lamb wave mode to use in a particular application depends on numerous factors, including the resolution required, the type of defects or damage to be detected, the attenuation and the available transduction options. This paper sets out a rational procedure for identifying suitable Lamb wave modes and operating frequencies for a particular inspection task. It is shown that the properties of the system to be inspected determine which mode and frequencies can be used, and that this then dictates the type of transducer required. A procedure for evaluating the performance of Lamb wave transducers is also demonstrated. As an illustrative example, it is shown that the well known angle incidence transduction technique is not generally suitable in applications where the structure to be inspected is liquid loaded. In such cases it is necessary to consider alternative transduction options such as electromagnetic acoustic transducers (EMATs) or shear piezoelectric devices.

Baseline-free delamination inspection in composite plates by synthesizing non-contact air-coupled Lamb wave scan method and virtual time reversal algorithm

“…Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. modes can interrogate the entire thickness of plates [6,7]. Guo and Cawley [4] investigated the interaction between symmetric S 0 mode Lamb waves and delaminations at different interfaces in a composite plate through finite element analysis and experiment.…”

Reference-free crack detection under varying temperature

“…However, the majority of the past work has focused on selective generation of S 0 and A 0 modes (Giurgiutiu, 2005;Su et al, 2004;Wilcox et al, 2001;Yamanaka et al, 1991). For instance, by exciting PZTs A and D shown in Fig.…”

Transducer Placement Option of Lamb Wave SHM System for Hotspot Damage Monitoring

“…Given the Gaussian function G of an input image f (x,y) and feature scaling σ as given in Equation (8). The Laplacian operator ∇ 2 is given in Equation (9).…”

“…are assessed to calculate the damage index (DI). The most commonly used sensors for generating and capturing Lamb waves are piezoelectric transducers (PZT) [9]. Since PZTs are permanently attached to the surface of the structure, sensor placement becomes tremendously important because the quantification of DI relies heavily on the sensor positions.…”