Pipeline unidirectional guided wave generation based on a hybrid piezoelectric transducer ring and wave-packet modification

For pipeline inspection, unidirectional guided waves are needed to concentrate energy in a single propagation direction while suppressing backward-traveling components. Conventional time-delay methods rely on multiple transducer rings with fixed spatial spacing, making their unidirectional performance highly frequency-dependent. This paper proposes a frequency-flexible method for generating unidirectional guided waves by combining a hybrid piezoelectric transducer ring with a wave-packet modification method (WPMM). The ring is composed of alternately arranged thickness-shear (d15) and face-shear (d24) lead zirconate titanate (PZT) transducers, and the WPMM adjusts the excitation phase and amplitude of the d 15 and d 24 PZTs separately to achieve optimal interference at arbitrary frequencies. A theoretical model is developed to describe the mechanism of unidirectional guided wave generation enabled by this approach. The method is validated through finite element simulations and experimental measurements, with results compared to those obtained using the conventional time-delay method.