用于测厚和裂纹检测的正交横波电磁超声换能器仿真分析及实验研究

Shear waves have high sensitivity when measuring thickness in vertical incident direction, but oblique incidence probes are required in crack detection. The two tasks can not be finished with a single transducer at the same time. In this paper, firstly, an electromagnetic acoustic transducer (EMAT) of orthogonal shear waves is designed. It permits the excitation of two orthogonal polarized shear waves in an aluminum plate using two butterfly coils. Then a methodology for simultaneously measuring thickness, detecting cracks and determining the direction of cracks using the time of flight and amplitude difference of the back-wall reflection recorded with the two coils in the pulse echo mode is proposed. A 3-D FE model of the orthogonal EMAT is established, and the wave field generated by the EMAT and its interaction with a crack in the plate are simulated. The effect of coil spacing on the symmetry of the wave field is studied and the influence of crack size on the amplitude difference of received signals is analyzed. Finally, the experimental results showed that good performance of thickness measurement, crack detection and determination of crack direction simultaneously using the orthogonal EMAT, which make the technique a potential new method for online inspection of corrosion thinning and crack defects.