Development of an omni-directional magnetic-concentrator-type electromagnetic acoustic transducer

Abstract As an important branch of non-destructive testing, electromagnetic ultrasonic testing is widely used in various industries because of its high detection efficiency and the lack of a need for the test sample to have a coupling agent or a surface pretreatment. As a core component of electromagnetic ultrasonic testing, electromagnetic acoustic transducers (EMATs) have received extensive attention in recent years. However, the mode selectivity of EMATs is reduced because of the non-uniformity of the magnetic field of traditional permanent magnets and the multimode phenomenon of guided waves. To solve this problem, an omni-directional magnetic-concentrator-type electromagnetic acoustic transducer (OD-MC-EMAT) is proposed herein. Which was added to the magnetic concentrator on a traditional EMAT to guide and concentrate the magnetic field of traditional permanent magnets, thereby improving the defect inspection ability of the EMAT. The proposed OD-MC-EMAT consisted of a cylindrical permanent magnet, an omni-directional magnetic concentrator, and a multi-cluster of circular meander coils, and it exhibited better mode selectivity than a traditional EMAT. A finite element simulation and an experiment proved that the mode selectivity of the transducer improved after adding the magnetic concentrator, and experiments to study the transducer characteristics and defect detection were also carried out. Finally, the configuration of the OD-MC-EMAT was optimized through an orthogonal experiment. The influence of each parameter on the transducing efficiency of the proposed OD-MC-EMAT was studied, and the optimal parameter combination was confirmed.

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