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 degrees and 90 degrees but almost zero at 45 degrees; therefore, a piezoelectric transducer with good omnidirectional properties needs to be developed. A ring-type omnidirectional piezoelectric trans-ducer 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.