[4C4] Understanding wave modes generated in thick plates and concrete using magnetostrictive patch transducers
Z West, D Billson and O Trushkevych
University of Warwick, UK
Magnetostrictive patch transducers (MPTs) are an attractive alternative to conventional ultrasonic non-destructive evaluation (NDE) devices, offering improved adaptability, bandwidth, sensitivity, cost-effectiveness and temperature tolerance. These advantages position MPTs as a promising choice in environments where traditional systems fall short. Comprehensive studies into the performance of MPTs, particularly in thicker samples and heterogeneous materials such as concrete, remains underexplored. This work explores the wave modes produced on multiple media by a bidirectional MPT consisting of a rectangular Fe50Co50 patch excited using a racetrack coil and dual biasing magnets. While such configurations are well studied in thin plates, due to the intricate deformation profiles occurring in MPTs from the interactions between transducer geometry and magnetic field configuration, their behaviour in thick samples including concrete is far less trivial. We investigate the ultrasonic waves in concrete by integrating COMSOL Multiphysics modelling, laser vibrometry and experimental validation with piezo, electromagnetic acoustic transducer (EMAT) and MPT receivers, linking the deformation profile of the patch to the forces transmitted between transducer and sensor and to the resulting wave modes. In concrete, a similar ultrasonic behaviour can be observed to that in glass plates. As the samples become thicker, Rayleigh waves are observed in place of Lamb waves, as expected. We apply this understanding to multi-modal testing with a single transducer: by tracking how each specific mode is altered, multiple layers of structural information can be extracted from one data acquisition. It was also found that by varying the excitation frequency to match intended mode wavelengths, a single MPT set-up can be tuned to favour specific wave modes, including P, SH and Rayleigh waves, enabling mode-selective inspection strategies tailored to application needs.
