Numerical evaluation of focal position selection by line-focusing electromagnetic acoustic transducer with experimental validation

Abstract

2019) 'Numerical evaluation of focal position selection by line-focusing electromagnetic acoustic transducer with experimental validation.', International journal of applied electromagnetics and mechanics., 61 (3). pp. 341-355.Abstract-As the focal position of a line-focusing electromagnetic acoustic transducer (LF-EMAT) affects the intensity of the focal signal, we measure the displacement signal and the slection method of the focal line position is then studied in this work to improve the signal intensity and detection precision for a shear-vertical (SV) wave LF-EMAT. We calculate the magnetostatics filed and bulk wave propagation utilizing the finite element method (FEM). We simulate the characteristics of the SV wave, and we find that the radiant distance and propagation direction has a great influence on the amplitude of the displacement of the specimen. The superposition area of SV waves from different sources possesses better focusing ability, and the triangular area (normalized amplitude of the SV waves lower than 10%) near the surface of a specimen should be avoided to be chosen when designing the meander line coils. As for the line-focusing EMAT described in this manuscript, the selection of focal positions for different thickness specimens or detection depth is completely different. Moreover, we perform an experiment to validate the simulation results and lead to a conclusion that the position of the focal point is required to be appropriately close to the excitation coils to enhance the intensity of the signal, while the best focal position should be calculated.

A New Design to Rayleigh Wave EMAT Based on Spatial Pulse Compression

“…The coils used in the previous studies are normally meander line coils with equal spacing (ES). Some studies have shown that the meander line coils with unequal spacing (UES) are capable of exciting the focusing waves [15][16][17]. However, the UES coil structure leads to a novel and interesting phenomenon known as spatial pulse compression (SPC).…”