Constrained thickness-shear vibration-based piezoelectric transducers for generating unidirectional-propagation SH0 wave.

Excitation of a pure guided wave with a controllable wavefield is essential in structural health monitoring (SHM). For example, a unidirectional-propagation guided wave can significantly reduce the complexity of signal interpretations by avoiding unwanted reflections. However, few transducers are currently capable of exciting a pure unidirectional-propagation guided wave, which cannot satisfy the emerging demands from the field of SHM. In this work, the thickness-shear vibration characteristics of the piezoelectric PZT wafer bonded on a waveguide are investigated by theoretical modeling and numerical simulations. It is found that there is a phase difference between the electric-excitation signal applied on the PZT wafer and the mechanical response signal of the bottom surface of the viscoelastic adhesive layer that connects the PZT wafer and waveguide. Moreover, such a phase difference can be adjusted by changing the equivalent width of the PZT wafer. Based on this finding, two piezoelectric transducers with different shape configurations are proposed to excite the unidirectional-propagation SH0 wave (the fundamental shear horizontal wave). Finite element simulations and experiments are conducted to verify the performances of the two unidirectional transducers. Results show that the two transducers can excite a pure SH0 wave and enhance the wave energy along a single direction. No time delay is required to excite the proposed transducers. Due to their simple configurations, the developed unidirectional SH0 wave transducers will have great potential applications in SHM.

Excitation of unidirectional SH wave within a frequency range of 50 kHz by piezoelectric transducers without frequency-dependent time delay.

Unidirectional generation of a pure guided wave mode is of practical importance in structural health monitoring (SHM). Currently, unidirectional propagation guided waves can only be generated by using transducer array in a phased array form, which is limited within a very narrow frequency range. If a variable-wavelength unidirectional wave source is required, both the transducer spacing and time delay usually need to be changed with frequency, which is against the permanent arrangement demand of transducers in SHM. In this work, inspired by the unique features of bidirectional SH0 wave (the fundamental shear horizontal mode) piezoelectric face-shear and thickness-shear transducers, a new method was proposed for generating unidirectional SH0 wave. Two types of transducer configurations (double-side and single-side) were designed to unidirectionally generate SH0 wave without frequency-dependent time delay. Both finite element simulations and experiments were conducted to validate the unidirectional features of the proposed double-side and single-side transducer configurations. Results shows that the double-side transducer configuration is capable of generating unidirectional propagation SH0 wave at the frequency range from 100 kHz to 150 kHz, while the corresponding working frequency range for the single-side one is from 100 kHz to 140 kHz. The proposed method provides a cheap way for generation of the unidirectional SH0 wave within a certain frequency range without adjusting the relative transducer spacing and the time delay with frequency, so it will have great potential applications in SHM.