Orthogonal Optimal Design Method for Point-Focusing EMAT Considering Focal Area Dimensions

Abstract

Although ultrasonic focusing methods have been widely used in electromagnetic acoustic transducers (EMATs) to solve the problem of their low energy conversion efficiency, the influence of focusing accuracy on defect identification also warrants consideration. The dimension of the focal area that acts as an important factor and affects the detection accuracy has not been fully investigated recently to our knowledge. In this work, we report a parameter optimization method using an orthogonal test when considering the focusing intensity and focal area together. The results of the range analysis show that the factor lift-off distance hl has the greatest impact on signal intensity M. Considering the dimensions of the focal area, bandwidth factor α has the largest effect on the effective focal length Lfd. For effective focal width Wfd, the concentric line source (CLS) number n has the largest effect. Therefore, a smaller lift-off distance, larger CLS number, and suitable bandwidth factor α are required in a point-focusing SV EMAT (PFSV-EMAT). The optimal combination of parameters can be obtained by considering the influence of different factors on the results. The experiment shows that the signal intensity of the optimized transducer is nearly 400% higher than non-optimized ones and the effective focal length and width are reduced by 15% and 57%, respectively.