Fatigue Crack Detection Using Lamb Wave Mixing Technique Based on Comb Piezoelectric Transducer

In the Lamb waves mixing technique, piezoelectric wafers and wedge-shaped transducers are commonly used for signal reception. However, piezoelectric wafers lack mode selectivity for Lamb waves, which hinders the extraction of weak mixing signals. Wedge-shaped piezoelectric transducers, meanwhile, impose strict directional requirements for receiving signals along the same line. To overcome these limitations, this study employs a comb-shaped piezoelectric transducer, which offers selectively reception of specific Lamb wave modes without directional constraints. A comb piezoelectric transducer for the mixing A₀ mode was designed and fabricated. The experimental measurement system of the mixed-frequency Lamb wave was constructed, and the comb piezoelectric transducer, piezoelectric wafer, and oblique split transducer were used as the receiving end respectively, and the results of the mixed-frequency signal measurements were compared and analyzed. Results demonstrate that compared with the other two transducers, the comb piezoelectric transducer exhibits no directionality for fundamental wave reception and yields a more pronounced mixed-frequency signal amplitude. Furthermore, the amplitude of the mixed-frequency signal shows a more significant correlation with microcrack length. This frequency-mixing wave reception method provides an effective technical approach for the nonlinear frequency-mixing Lamb wave evaluation of fatigue cracks in thin plates.