A flexible and noncontact guided-wave transducer based on coils-only EMAT for pipe inspection

Ultrasonic guided wave testing technique, with its advantages of long propagation distance, low attenuation and high testing efficiency, has been widely used in nondestructive testing and structure health monitoring for pipes. In this paper, a flexible and noncontact guided-wave transducer based on a novel and coils-only electromagnetic acoustic transducer (EMAT) is proposed. In this new transducer, a planar magnetic coil of racetrack shape fed with rectangular-pulsed current is used to produce a quasi-static magnetic field, while a planar meander coil fed with RF-pulse current is used for pulsing and receiving guided-wave signals. Based on the magnetostrictive mechanism, the proposed transducer can generate and receive guided wave of L(0,2) mode in ferromagnetic metal pipes without coupling medium. Electromagnetic fields for the two coils and the induced ultrasonic waves are studied by simulation. Both the simulation and experimental results show that the proposed transducer is effective for generating and receiving ultrasonic guided wave of L(0,2) mode in ferromagnetic pipes, and can be applied on detection for corrosion. Due to the flexible, noncontact feature, and compact configuration of the proposed transducer, it can be conveniently applied for pipes in different diameter with rusty surface or coating in narrow space. (C) 2020 Elsevier B.V. All rights reserved.