Meanderline Coil Arrangement of Ultrasonic Wave Line-Focusing Electromagnetic Acoustic Transducers

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 coil arrangement on defect identification also warrants consideration. In this work, for enhancing the focusing capability of a transducer, the influence of meanderline coil design method on the focusing performance for a line-focusing EMAT is studied. Different from the case where the focal position and line source are fixed in the traditional SV wave focusing transducer, we analyze the normalized signal amplitude at the focal line when the first line source position changed, and aim to find the optimal coil arrangement. Analytical, simulated, and experimental results show that as the first line source coordinates increase, all line sources will be closer to the focal position. However, the amplitude of the displacement at the focal line does not increase linearly, but increases first and then decreases. Therefore, the focusing performance of the transducer can be greatly improved by a reasonable coil arrangement discussed in this study.