Optimization Design of Focusing Electromagnetic Acoustic Transducer for Crack Detection of Pressure Structure

Abstract

High-precision detection of crack is of great significance to ensure the safety of pressure equipment in service. Electromagnetic ultrasound has the advantages of no coupling agent, no surface pretreatment, and non-contact. However, several problems such as low energy conversion efficiency and poor sound field directivity limit the application in crack detection. This paper designs a multi-layer line-focusing electromagnetic acoustic bulk wave transducer (MLF-EMAT). A simulation model containing MLF-EMAT is established based on the Lorentz force and magnetostrictive force transduction mechanism. The influence of some transducer parameters (wire width, wire thickness, coil turns, lift-off distance) on the echo response of crack has been studied. The orthogonal experimental design method is used to optimize the controllable parameters of the transducer. When the width of the permanent magnet is equivalent to the width of the coil, the larger the number of coil layers, the larger the amplitude of the echo response of crack. An experimental platform for electromagnetic ultrasonic testing is established, and several line-focusing electromagnetic acoustic transducers with multiple parameters are prepared. The comparison results show that the optimized MLF-EMAT significantly improves the signal-to-noise ratio of echo response of crack. The amplitude of echo wave is increased by about 78% compared with that before optimization, and the detection accuracy of crack notch depth is up to 0.05 mm. The MLF-EMAT proposed in this study lays the foundation for the application of crack detection or monitoring of pressure vessels and pipes under complex working conditions.