Design and Characterization of a Dense Linear Array EMAT Based on Spatial Vertical Winding Coils for High-Resolution Imaging

To address the limitations of electromagnetic acoustic transducers (EMATs) in high-resolution defect detection, this paper proposes a dense linear array EMAT based on spatial vertical winding coils (SVWCs) and an edge-constrained permanent-magnet array (EC-PMA). While ensuring high transduction efficiency for individual elements, this design constrains the element pitch to 1.5 mm, significantly increasing the number of elements within a finite aperture and enabling the development of a 32-element dense array EMAT. The array performance was systematically characterized in terms of frequency response, lift-off attenuation, channel consistency, and inter-element crosstalk. The results show that the elements exhibit broadband characteristics within the effective frequency range. Echo amplitudes decay exponentially with increasing lift-off, following a similar trend across different frequencies and materials. Channel consistency was evaluated using the relative pulse-echo sensitivity variation, and the results showed that 96.88% of the channels exhibited variations within ±3 dB, indicating good uniformity. In addition, inter-element crosstalk is closely related to both frequency and element spacing: it increases with frequency, reaches a maximum near 7 MHz, and decreases as the transmitter-receiver distance increases. By combining the developed array EMAT with a total focusing method incorporating angle weighting factors, clear imaging of multiple side-drilled holes with diameters of 2.0 mm, 1.0 mm, and 0.5 mm was achieved in an 80 mm-thick P91 steel block. These results verify the feasibility and effectiveness of the proposed array EMAT for high-resolution defect imaging and provide a useful sensor foundation for advanced phased-array EMAT imaging.