Defect Detection and Identification of Point-Focusing Shear-Horizontal EMAT for Plate Inspection

Abstract

As a kind of nondestructive testing (NDT) method, shear-horizontal (SH)-guided wave detection technology is widely used on an electromagnetic acoustic transducer (EMAT). Although ultrasonic-guided waves perform well in defect location, it is difficult to obtain detailed information about defects, and the low efficiency of EMAT energy conversion still reduces the EMAT's performance. Therefore, in this work, the defect detection method of different shapes and sizes by point-focusing shear-horizontal (PFSH)-guided wave EMAT with the use of periodic permanent magnet (PPM) is investigated through simulation and experiment. For the purpose of defect classification and quantification, the extraction principles of defect features are obtained through simulation based on the circumferential scatter diagrams, and the neural network (NN) is used to process the features extracted from the experimental data. The results show that by extracting effective defect features from the scatter diagram, high-accuracy classification and high-precision quantification of defects under the influence of the focusing transducer can be achieved.

Enhancing the Lift-Off Performance of EMATs by Applying an Fe3O4 Coating to a Test Specimen

“…The maximum effective lift-off distance of EMATs is normally defined with the requirement of a reasonable signal-tonoise ratio (SNR), with some standards-setting this to be around 12 dB. Common methods to improve the SNR of EMATs include: improving the output power of the hardware circuit [5][6] and optimizing the design of the coil and magnet in an EMAT [7][8]. Increasing the excitation current of the EMAT coil is normally a direct and widely used method to improve the SNR [6].…”

“…However, more complicated and expensive electronics is needed to generate a large current, and there may be some safety hazards, especially for applications in the oil and gas industry. Compared with improving the output power of the hardware circuit, there are more studies on the optimization design of EMATs, mainly focusing on improving the strength of the static bias magnetic field and the dynamic alternating magnetic field [7][8][9][10]. As an example, an optimized Rayleigh wave EMAT can detect defects in rail at the center frequency of 200 kHz with a lift-off distance of 5 mm [9].…”

PPM EMAT for Defect Detection in 90-Degree Pipe Bend

“…PPM (Periodic Permanent Magnet) EMAT (Electromagnetic Acoustic Transducer) is currently used mainly to excite T (0, 1) mode-guided waves. With this transducer, T (0, 1) mode-guided waves can be excited in non-ferromagnetic pipes [31][32][33][34][35][36][37][38].…”

Hybrid Entropy in the Time-Frequency Domain for Grading Electrode Sediment Identification

“…To achieve nondestructive detection of pipe defects, numerous studies have focused on the use of electromagnetic acoustic transducers (EMATs) [8], circumferential Lamb waves [9], and ultrasonic guided waves [10]. However, the above methods can only detect defects on or near the surface of the workpiece, and are no longer applicable to the inspection of grading electrodes located inside composite pipes.…”