High-efficiency A ₀ Lamb wave excitation: a synergistic approach via magnetic flux alignment and phase-mismatch mitigation

Electromagnetic acoustic transducers (EMATs) are widely employed for non-contact non-destructive evaluation (NDE). However, their practical application is often limited by low transduction efficiency. To address this challenge, this paper proposes a novel EMAT configuration designed to significantly enhance Lamb wave excitation efficiency by integrating a periodic permanent magnet (PPM) array with a non-equidistant meander-line coil (MLC). Unlike conventional equidistant designs susceptible to gradient-induced phase mismatch, the proposed design achieves superior spatial coupling between the coil geometry and the magnetic flux topology. The enhancement mechanism is two-fold: (1) by precisely aligning conductor segments with high-intensity magnetic flux regions, the localised Lorentz force density of individual segments is maximised through the effective utilisation of resultant magnetic field vectors, and (2) the non-equidistant arrangement mitigates the internal phase cancellation arising from spatial mismatch among different conductor subsets. Numerical simulations demonstrate that this synergistic approach effectively reduces destructive interference within the coil footprint. Quantitatively, the proposed EMAT achieves a 3.14-fold enhancement in the peak-to-peak amplitude of the A0 mode signal compared to conventional bulk-magnet EMATs at a centre frequency of 0.46 MHz. Furthermore, the design maintains high modal purity, providing a robust and sensitive solution for high-performance structural health monitoring.