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Smart Structures and Systems
  Volume 4, Number 4, July 2008 , pages 449-464

A migration based reconstruction algorithm for the imaging of defects in a plate using a compact array
Ajith Muralidharan, Krishnan Balasubramaniam and C.V. Krishnamurthy

    An array based, outward monitoring, ultrasonic guided wave based SHM technique using a single transmitter and multiple receivers (STMR), with a small footprint is discussed here. The previous implementation of such SHM arrays used a phase-reconstruction algorithm (that is similar to the beam-steering algorithm) for the imaging of reflectors. These algorithms were found to have a limitation during the imaging of defects/reflectors that are present in the near-field of the array. Here, the near-field is defined to be approximately 3-4 times the diameter of the compact array. This limitation is caused by approximations in the beam-steering reconstruction algorithm. In this paper, a migration-based reconstruction algorithm, with dispersion correction in the frequency domain, is discussed. Simulation and experimental studies are used to demonstrate that this algorithm improves the reconstruction in the near-field without decreasing the ability to reconstruct defects in the far-field in both isotropic and anisotropic plates.
Key Words
    migration; STMR array; ultrasonic guided waves; SHM.
Center for Nondestructive Evaluation, Department of Mechanical Engineering, Indian Institute of Technology, Madras, Chennai-600036, India

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