Designs for improving electromagnetic acoustic transducers’ excitation performance

Abstract

The main drawback of electromagnetic acoustic transducers (EMATs) is their low energy transition efficiency. For the purpose of increasing the amplitude of the received signal, a ferrite core (FC) and a bias magnet (BM) are utilized respectively to improve the EMAT's excitation performance in this paper. It indicates that the new configurations can increase the peak-to-peak amplitude of the received signal by a factor of 2.7 and 2.9, respectively. The reasons for the signal enhancement are also investigated through simulation and experimental methods. For the FC EMAT, improvement is achieved due to the enhancement of the dynamic magnetic field and the increase of coil inductance. In comparison, the change of the magnetostrictive transduction mechanism leads to the signal enhancement for the BM EMAT. The bias magnet magnetized the surface of the steel plate, which changes the signal excitation mechanism from domain wall movement to reversible domain rotations.

Fast Measurement of Magnetostriction Coefficients for Silicon Steel Strips Using Magnetostriction-Based EMAT

“…The efficiency of an EMAT is much lower than that of a piezoelectric ultrasonic transducer due to its complicated mechanism [24,25]. In order to obtain a higher signal-to-noise ratio (SNR), it is usually required to optimize the transducer [26,27,28]. The magnetostriction-based EMAT has proved to be useful in measuring the magnetostriction coefficients of silicon steel strips.…”

An effective method for differentiating inside and outside defects of oil and gas pipelines based on additional eddy current in low-frequency electromagnetic detection technique

“…The low-frequency electromagnetic field is applied by exciting coil, and the yoke in this excitation structure is selected as C-type, which can generate a higher low-frequency leakage magnetic field density than the conventional U-shaped yoke. 5) The LFET coil is generally used as the signal receiving medium [6][7][8] instead of magneto sensor [9][10][11] due to the lowfrequency leakage magnetic field signal on the surface of the inspected specimen is weak. The LFET coil's voltage output amplitude is directly proportional to the change rate of the lowfrequency leakage magnetic field magnetic flux, thereby making the determination of the surface defects of the inspected material convenient.…”