Design of Electromagnetic Acoustic Transducer for Helical Lamb Wave With Concentrated Beam

Guided wave is advantageous to inspect pipe-like structures because of its long-distance propagation. Due to the curved structure of pipeline, guided wave can spread spirally with a helix angle. However, the current transducers focus more on the narrow or omni-directional beam than the helical form. This work presents the designed transducer to generate helical Lamb wave with concentrated beam. The transducer is developed using permanent magnets and arc-coil based on the principle of electromagnetic-acoustic conversion. The numerical analysis applying finite element method is conducted to verify the theoretical model of the transducer. The angular profiles are obtained to study the propagation of helical Lamb wave. Further, experiments are designed to demonstrate the performance of proposed transducer. The results from the experiments show good agreement with the numerical simulations. Besides, the parameter of central width is investigated and the half-angle of divergence is calculated. The results are compared with that from traditional transducers. The comparison indicates the superiority of the proposed transducer in generating helical Lamb wave. Therefore, the designed transducer could be a potential alternation for pipeline inspection based on guided wave.