Focusing Dimension Optimization of Shear Vertical Wave EMATs Using Orthogonal Test Method

As a sound detection technology, electromagnetic acoustic transducers (EMATs) have been widely used in the field of NDT due to their advantages of non-contact and applicable in a complex environment. However, its low energy conversion efficiency has always been its main drawback, thus making it difficult to be used in industrial testing. Therefore, many focusing technologies have been designed to improve the energy conversion efficiency of the transducer, including line-focusing, point-focusing and phased array focusing. To our knowledge, a larger focusing area not only leads to the dispersion of energy but also reduces the quantitative analysis accuracy of the defect characteristics. However, the effect of the focusing area dimension on the defect detection accuracy has seldom been reported so far. Therefore, in this work, we have studied five factors that affect the dimension of the point-focusing shear-vertical (PFSV) wave focusing area, including coil width w, lift-off distance h(l), excitation current amplitude I-c, band-width factor alpha, CLS number n. Test results are determined by measuring the length and width of the 80% peak displacement contour. Then, the influence degree of various factors on test results is analyzed through finite-element simulation, and an optimized combination of parameters that rationalizes the focusing area dimension and focusing intensity is determined. Finally, experiments are carried out to verify the validation of optimization results, which indicates that the optimized PFSV EMAT can improve the focusing behavior and effectively reduce the focusing area dimension compared with the non-optimized one.