A variable-frequency bidirectional shear horizontal (SH) wave transducer based on dual face-shear (d) piezoelectric wafers.

Focusing the incident wave beam along a given direction is very useful in guided wave based structural health monitoring (SHM), as it will not only save input power but also simplify the interpretation of signals. Although the fundamental shear horizontal (SH) wave is of practical importance in SHM due to its non-dispersive characteristics so far there have been very limited transducers which can control the radiation patterns of SH wave. In this work, a variable-frequency bidirectional SH wave piezoelectric transducer (BSH-PT) is proposed, which consists of two rectangular face-shear (d) PZT wafers. The opposite face-shear deformation of the two PZT wafers under applied electric fields makes the BSH-PT capable of exciting SH wave along two opposite directions (0° and 180°). Both finite element simulations and experimental testings are conducted to examine the performance of the proposed BSH-PT. Results show that pure SH wave can be generated by this BSH-PT and its wave beam can be focused bi-directionally. Moreover, the bidirectional characteristics of the BSH-PT can be kept over a wide frequency range from 150 kHz to 250 kHz. As the circumferential SH (CSH) wave in a thin hollow cylindrical structure is essentially equivalent to the SH wave in a plate, the proposed BSH-PT may also be very useful to develop a CSH-wave-based SHM system for hollow cylindrical structures.