SH guided wave excitation by an apparent face-shear mode (d₃₆) piezocomposite transducer: experiments and theory

The fundamental shear horizontal (SH₀) wave in plate-like structures is of practical importance in structural health monitoring (SHM) due to its non-dispersive characteristics. However, compared with Lamb waves, SH₀ wave is less used in practice since it is difficult to be excited by using conventional piezoelectric transducers. In this work, an apparent face-shear mode (d ₃₆) piezocomposite transducer was proposed to excite and receive SH₀ wave. The piezocomposite transducer was made up of epoxies and several hollow PZT squares of different sizes. The face-shear d ₃₆ mode was synthetized by the thickness-shear deformation of each side of the hollow PZT squares. Both finite element simulations and experimental testings showed that the apparent d ₃₆ piezocomposite transducer was capable of exciting pure SH₀ wave along four main directions (0°, 90°, 180° and 270°) from 70 to 150 kHz. Moreover, the piezocomposite transducer can filter Lamb waves and receive SH₀ wave only over a wide frequency range from 70 to 370 kHz. Based on Huygens' principle and the method of solving inclusion problem, an eigenstrain-based theoretical model was then proposed to describe the SH₀ wave field generated by face-shear transducers. Explicit analytical expressions for the piezocomposite transducer were successfully obtained and their accuracies were verified by both experiments and finite element simulations. Furthermore, some general guidelines based on the analytical model were presented for optimization of the transducer's dimensions. The proposed apparent d ₃₆ piezocomposite transducer may be a good candidate for exciting and receiving low frequency SH₀ wave in SHM systems, since it is lightweight and shows better surface conformability than PZT wafers. (paper)