Excitation and Reception of Shear Horizontal Waves by Using Face-shear Mode Piezoelectric Ceramics

The fundamental shear horizontal (SH0) wave in plate-like structures is extremely useful for non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive. However, currently the SH0 wave is usually excited by electromagnetic acoustic transducers (EMAT) whose energy conversion efficiency is fairly low. The face-shear (d36) mode piezoelectrics is more promising for SH0 wave excitation but this mode can only exist in single crystals of specific point groups and cut directions. Theoretically the d36 coefficient vanishes in piezoelectric ceramics because of its transversally isotropic symmetry. In this work, we realize the face-shear (d36) mode in both PZT-4 and PZT-5H via ferroelastic domain engineering. The obtained d36 coefficients can be up to 274 pC/N in PZT-5H ceramics and 108 pC/N in PZT-4 ceramics. We then successfully excite SH0 wave in the aluminum plate using the fabricated face-shear d36 PZT-4 square patch and receive the wave using a face-shear d36 PMN-PT sensor. Although lamb waves are also excited simultaneously, the excited SH0 wave can be dominate over the Lamb waves (S0 and A0) from 160 kHz to 280 kHz. In order to excite pure SH0 wave, a newly defined face-shear d24 PZT wafer was then proposed. Experiments show that pure SH0 wave mode can be excited by the d24 mode PZT wafers. Moreover, the face-shear d24 PZT wafer can also receive the SH0 wave only and filter the Lamb waves over a wide frequency range (120 kHz to 230 kHz in this work). This work could greatly promote the applications of SH0 wave in NDT and SHM.