Structure-guided piezoelectric transducer for unidirectional excitation and reception of Rayleigh waves

Rayleigh waves are crucial for nondestructive testing (NDT) of thick-walled structures. Unidirectional propagation of Rayleigh waves simplifies signal interpretation by minimizing unwanted reflections. Unidirectional Rayleigh waves are commonly generated using wedge transducers based on Snell's law. However, due to the large wave impedance difference between the wedge and the waveguide, there is a transmission loss at the interface. This work proposed a structure-guided transducer (SGT) for unidirectional excitation and reception of Rayleigh waves. The SGT consists of a wedge-shaped substrate and thickness-shear piezoelectric wafer. The substrate is fabricated using ferromagnetic material, which is impedance-matched to the steel structure for Rayleigh waves. The substrate facilitates the automatic control of the guided waves, guaranteeing the unidirectional capabilities of the SGT. Subsequent to the theoretical design, the performance of the SGT was assessed via finite element simulations and experiments. Results confirmed the generation of pure Rayleigh waves with a unidirectionality of approximately 13 dB. Moreover, the SGT can also act as a sensor to selectively capture Rayleigh waves from a specific direction, efficiently filtering out waves from other directions. The design of the SGT is both straightforward and conducive to manufacturing. It can prevent energy loss resulting from impedance mismatches between the wedge and the test structure. Additionally, the magnetic substrate of the SGT facilitates effortless attachment to steel structures, thereby simplifying installation and relocation. With these advantages, the SGT is highly likely to have substantial potential for applications in NDT.