Multi-Helical Path Exploitation in Sparsity-Based Guided-Wave Imaging of Defects in Pipes

In this paper, a defect localization scheme for cylindrical pipes is presented which relies on guided-wave scattering by defects. The proposed scheme is predicated on the use of a sparse array of ultrasonic transducers and the sparse nature of defects on the pipe surface. Two circular rings of transducers, functioning as transmitters and receivers, are used to encompass the region to be inspected. Multiple helical paths exist for waves to travel from the transmitters to the receivers, after being scattered by the defects. Model based dictionary matrices are constructed for each path, relating the signals arriving at the receivers to the locations of potential defects. The resulting linear signal model is inverted by group sparse reconstruction to localize defects present in the pipe. Experimental validations of the proposed multi-helical path exploitation approach are provided for defects on an aluminum pipe.