Developing a face-shear lead-free piezoelectric transducer through anti-parallel co-poling and its application to an omnidirectional piezoelectric transducer

Face-shear deformation was observed in various square piezoelectric transducers prepared using the anti-parallel co-poling method, which led to uniform polarization and the generation and receipt of pure fundamental shear horizontal (SH₀) waves without any Lamb wave. The amplitude of the SH₀ wave was found to be proportional to the piezoelectric charge constant (d₃₃) of the piezoceramic, suggesting that the d₃₃ value can be used as a figure of merit for piezoelectric transducers with strong SH₀ waves. The amplitude of the SH₀ wave associated with the square piezoelectric transducer is large at 0° and 90° but almost zero at 45°; therefore, a piezoelectric transducer with good omnidirectional properties needs to be developed. A ring-type omnidirectional piezoelectric transducer was produced using eight trapezoidal piezoceramics. The minimum amplitude of the SH₀ wave generated and received by the ring type-transducer exceeded 70% of the maximum amplitude. Hence, this ring-type transducer is highly omnidirectional and can be used for nondestructive testing and structural health-monitoring applications.