Omnidirectional Symmetrical Wave EMAT Design for High-Thickness Reinforced Steel Plates

This work proposes the use of Electromagnetic Acoustic Transducers (EMATs) for emitting Guided Waves (GW) in the Structural Health Monitoring (SHM) of Floating Production Storage and Offloading (FPSO) vessels. The large size and structural complexity of the vessel plates, including their reinforcement elements, pose challenges for the selective excitation and reception of distinct GW modes. In response, this study presents the design of an omnidirectional EMAT aimed at transducing fundamental symmetrical Lamb waves within the ship’s structural plates. To achieve this, finite element models were developed to design the coil and casing geometry, predict wave excitation phenomena, and simulate interactions with the vessel’s hull structure. Tests conducted on aluminium and steel plates validated the simulation models and enabled the characterisation of the transduced wave modes. The results demonstrate that the EMAT design achieves selective emission and reception of Lamb waves, particularly the first symmetrical Lamb wave mode, while maintaining a high signal-to-noise ratio even on reinforced steel plates. Finally, a sparse sensor array was deployed on an FPSO bulkhead sample, generating a damage map that confirmed the system’s ability to detect and locate defects within the structure. These findings suggest that the proposed EMAT design is well-suited for use in large-scale SHM applications, effectively addressing the challenges posed by complex structural geometries.