Electromagnetic Acoustic Detection of Steel Plate Defects Based on High-Energy Pulse Excitation

Abstract

The conventional electromagnetic ultrasonic transducers (EMATs) rely on the static magnetic field created by magnets. The magnet increases the size of the EMATs, and the strong magnetic force of the magnet attracts the detected steel and even ferromagnetic particles. It can cause mechanical damage to the transducer and the detected objects. A new high-energy acoustic excitation system, without a static bias magnetic is designed, which does not include any magnets. As the core of the system, the high-energy pulse excitation power supplies a transient high voltage to the excitation coil by the LC oscillation circuit. The maximum amplitude of current can reach 1700 A, which is much larger than the current in the conventional EMATs. Compared with the conventional EMATs, the intensity of the ultrasonic signal is greatly strengthened and the size of the EMAT is effectively reduced. Therefore, it can detect high-temperature steel plates at a higher lift-off distance. In this paper, the transduction mechanism of high-energy pulse electromagnetic acoustic on ferromagnetic materials was studied, and the high-energy pulse excitation coil used for the A0 mode Lamb wave was designed. The interaction rule of the magnetic field, the force field, and the acoustic field, was obtained. Then, the EMAT lift-off characteristic experiment of the high-energy pulse excitation was carried out, and the defect detection experiment was conducted on a cracked steel plate. The results show that the A0 mode Lamb waves have caused a high signal-to-noise ratio and can accurately locate the crack, which has a great advantage in detecting the microcrack defects of ferromagnetic materials.