Ultrasonic Lamb wave tomography in structural health monitoring

Variations of Lamb wave propagation reflect some changes in effective thickness and material properties caused by such structural flaws as corrosion, fatigue cracks, disbonds and voids that can then be mapped via a reconstructed tomographic image. Ultrasonic Lamb wave tomography can be used to evaluate structural integrity based on the variations in features extracted from measurements made by a transducer array from a reference point in time. In this paper, several tomographic imaging techniques, such as the filtered backprojection algorithm, the algebraic reconstruction technique and the reconstruction algorithm for probabilistic inspection of damage are compared, and the advantages and drawbacks of these methods, as well as practical considerations such as reconstruction fidelity, quality, efficiency and the minimum number of sensors required for each array geometry, are discussed, and some application examples are given.