Effective Focal Area Dimension Optimization of Shear Horizontal Point-Focusing EMAT Using Orthogonal Test Method

Abstract

To overcome the shortcomings of low energy conversion efficiency of electromagnetic acoustic transducers (EMATs), point-focusing shear horizontal (PFSH) wave EMAT is used to focus the wave energy into a specific area. Many factors will affect the capability of the focusing transducer, and in addition to considering the signal intensity, the detection accuracy is also required to be investigated. Specifically, to simplify the test process, we use the orthogonal test method to study the effect of different influence parameters on signal intensity and focal area dimensions. Seven factors are selected, and three results are determined in the test. Range analysis shows that for signal amplitude $M$ , the top three impact factors are the coil width $w$ , coil turns $n$ , and focal length lF (equal to bandwidth factor $\alpha $ ). Moreover, magnet number $m$ and frequency $f_{c}$ dominate the effective focal length $l_{\text {fd}}$ , and aperture angle $\theta $ determines the effective focal width $w_{\text {fd}}$ . To enable higher signal intensity and smaller focal area dimensions, it is necessary to consider various factors on the PFSH-EMAT focusing performance. The test’s signal intensity with optimized parameters’ combination at the focal point is nearly 144.42% higher than the average of all the tests, $l_{\text {fd}}$ decreased by 37.84%, and $w_{\text {fd}}$ decreased by 50.59%. The experiment also verified that focusing EMAT with optimized parameters has a better focusing performance.