Torsional deformation-transferring waveguide for generating perfectly omnidirectional shear-horizontal waves in plate structures

Omnidirectional SH waves offer distinct advantages for the structural health monitoring of large-scale infrastructures by enabling rapid and wide-area scanning without signal distortion. Despite their potential, conventional omnidirectional SH wave transducers inherently limit their directional uniformity, due to their reliance on complex and segmented excitation sources. As a result, no transducer to date has achieved truly ideal omnidirectional SH wave excitation. Here, we propose a novel waveguide-type omnidirectional SH wave transducer (WG-OSHT) that achieves perfect omnidirectionality by leveraging torsional deformation transfer through a cylindrical waveguide. By developing a theoretical model for the frequency response of the waveguide-installed plate system, three key design parameters are identified, enabling tunable design to maximize SH wave energy generation at the desired target frequency. Experiments and finite element analyses confirm the generation of high-purity SH0 mode with nearly perfect omnidirectionality with no unwanted mode interference, and showing good agreement with the proposed theoretical model. This waveguide-based approach not only achieves ideal omnidirectional SH wave source for the first time but also enhances its applicability by simplifying fabrication through a significant reduction in segmented components. Furthermore, it expands the inspection capabilities to curved surfaces and extreme environments, including high-temperature and chemically hazardous conditions.