Direction-Controllable Electromagnetic Acoustic Transducer for Sh Waves in Steel Plate Based on Magnetostriction

Abstract

Abstract-Shear-horizontal (SH) wave is commonly used in monitoring and detecting steel plate structures. Electromagnetic acoustic transducer (EMAT) based on magnetostriction owns higher transducing efficiency and can be applied in non-contact situations. In some practical applications, it is necessary to inspect the structure on a specific direction and the inspecting direction is required to be variable and accurately controllable. This work proposes a novel direction-controllable EMAT for SH0 mode waves based on magnetostriction. Theoretical foundation and analysis on the magnetostriction model of the new EMAT and working parameters determination are conducted. The detailed structure and design of the new EMAT are presented, with the pre-magnetized open annular nickel strap bonded to the steel plate providing the circumferential static bias magnetic field, and the cooperation of embedded conductors in the rotating slider and open metal rings providing the dynamic magnetic field. Besides, the experimental system for the performance verification of the new EMAT is setup. Three indexes, the dead zone angle, focus angle and consistency error are defined to evaluate the performance quantitatively. The dead zone angle of the new EMAT is 28.74 • ; the focus angle is 10.7 • ; the consistency error is only 1.4%. Experimental results show that the proposed direction-controllable EMAT is highly directional. The stimulating direction can be accurately controlled, and the circumferential consistency is fairly high. The direction-controllable EMAT can hopefully provide a practical solution for directional monitoring and inspecting for steel plate structures.

Profile imaging of actual defects in steel plate based on electromagnetic ultrasonic SH guided wave scattering

“…3 illustrates the schematic diagram of the experimental platform. Four directioncontrollable transmitters [29] and "twenty omni-directional receivers are uniformly distributed in a circular shape on the steel plate. And there are five receivers between any two adjacent transmitters.…”

Characteristics of T(0, 1) Guided-Wave Point-Focusing Electromagnetic Acoustic Transducer for Pipe Inspection

“…The primary means of NDT include: ultrasonic testing [6], magnetic flux leakage testing [7], eddy current testing [8], radiation testing in medical treatment [9], and optical fiber for long-term strain detection for buildings [10]. Among these methods, ultrasonic testing, particularly with guided-wave technology, is widely used in industrial testing to detect defects in thin-walled plates and pipes [11][12][13]. As a sound detection technology, ultrasonic guidedwaves can travel very far along a pipe with little attenuation, and offer a clear directionality in the propagation process, so that defects in the specimen at various positions along the guidedwave propagation path can be detected [14].…”

Improvement of unidirectional focusing periodic permanent magnet shear-horizontal wave electromagnetic acoustic transducer by oblique bias magnetic field

“…Shear-Horizontal (SH) ultrasonic guided wave testing is a common detecting technology for metal plates, where the fundamental SH0 mode guided wave has been widely used in industry [18][19][20][21][22]. The SH0 guided wave has great advantages in the detection process as the group velocity is constant and does not change with the frequency [23][24][25][26]. Besides, when the SH0 mode guided wave encounters a defect in the process of propagation in the metal plate, the SH waves with mode conversion are hardly recognized and received by the reception transducer.…”