A new pulse electromagnet structure to model a transverse magnetic field to pick up the out-of-plane for laser-EMAT integrated system

Abstract

In order for an electromagnetic acoustic transducer (EMAT) to be able to pick up the out-of-plane vibrations of ultrasonic waves generated by the laser and to facilitate the movement of the system, a new pulse electromagnet EMAT is proposed, which can be combined with a laser to form a new laser–pulse electromagnet EMAT integrated system. Because of the unique structure of the pulse electromagnet EMAT, it can not only generate a uniform transverse magnetic field in the shallow surface of the specimen just below the EMAT receiving coil but also leave enough space above the magnetic field to ensure the smooth radiation of the laser source on the specimen. The optimal parameters of the probe are determined by combining the finite element simulation model and the orthogonal analysis method. The simulation and experimental results show that the pulsed electromagnet can generate at least 0.22 T transverse magnetic field in the specimen when each coil of C-electromagnet, respectively, injects 20 A. The pulsed electromagnet combined with the EMAT coil is used to receive various modes of ultrasonic vibration velocity with the out-of-plane component. It lays a foundation for the research on the simultaneous detection of railhead surface and internal defects by using the new laser–pulse electromagnet EMAT integrated system through one scan.