Full-Waveform Inversion Imaging of Defects Using Guided Waves from a Magnetostrictive Patch Transducer with a Perpendicular Static Magnetic Field

Abstract

Conventional magnetostrictive patch transducers can suffer from a non-uniform static magnetic field and limited transduction efficiency in ultrasonic guided-wave testing. This study presents a transducer with a perpendicular static magnetic field and combines it with full-waveform inversion for guided-wave imaging of defects in plates and pipes. An equivalent surface-stress model was established for the proposed structure and validated by finite-element simulation. Guided-wave experiments were then used to determine how the static magnetic field affected signal amplitude and to compare the proposed design with other magnetostrictive patch transducers. Finally, transducer arrays acquired defect signals for full-waveform inversion imaging. The transducer effectively generated shear-horizontal guided waves. Signal amplitude reached its maximum at a surface magnetic flux density of approximately 70 mT and was about twice that obtained with a horizontal-field transducer based on the inverse Wiedemann effect. The plate-defect contours were clearly reconstructed, with maximum depth errors below 5.0%. Pipe imaging recovered the principal defect locations and contours. The proposed transducer therefore provides signals suitable for guided-wave full-waveform inversion imaging.