High-resolution guided wave tomography

• Combining travel time and diffraction tomography leads to accurate thickness mapping of plate like structures.
• The use of iteration increases reconstruction accuracy without compromising the method’s robustness.
• Experimental results show that guided wave tomography can reconstruct residual wall thickness within 10% accuracy.

Quantifying wall thickness in the presence of corrosion damage allows the residual life of plate-like structures to be determined. Guided wave tomography is a solution which allows an area to be imaged with data from an array of ultrasonic transducers around the defect, using tomographic methods to establish wall thickness. We exploit the dispersive nature of Lamb waves travelling through the wall to convert the thickness variation into wave velocity variations, providing a mechanism to determine thickness from a velocity reconstruction. HARBUT (the Hybrid Algorithm for Robust Breast Ultrasound Tomography) has been developed to give high-resolution, accurate and robust reconstructions of ultrasonic velocity through the breast; in this paper we extend the method to generate thickness maps for guided wave tomography. By iterating HARBUT we show that we can improve the accuracy of reconstructions of the small, high contrast defects expected from corrosion, allowing estimates of thicknesses within 1 mm for a 10 mm plate from both simulated and experimental data.