Shear Horizontal Waves Converted from Piezoelectric-Transducer-Activated Lamb Waves Using Topologically Designed Meta-Converters

Shear horizontal (SH) waves exhibit appealing features like non-dispersion (SH0 waves) and immunity to material nonlinearity, which benefit a range of applications, such as structural health monitoring (SHM). However, their effective excitation is challenging in practice due to the weak intensity of generated waves or the installation inconvenience of transducers. In this study, we propose an SH wave generation scheme based on mode conversion from piezoelectric-transducer-activated Lamb waves, with the help of add-on metamaterials. To this end, meta-converters, in conjunction with topology optimization methods, are employed to achieve high-efficiency conversion from Lamb waves to SH waves. 3D finite element models are employed to enable the destruction of structural symmetry in the out-of-plane, which is necessary for Lamb-wave-to-SH-wave conversion. In a broad band around the operation frequency, typical scenarios involving incident Lamb waves of varying modes and frequencies are considered, leading to a series of meta-converter designs. Taking incident waves as a baseline, the efficiency of the conversion is quantified in terms of the magnitude of the transmitted SH waves. Time-domain responses are analyzed to verify the efficient generation of SH waves. Finally, representative meta-converters are 3D-printed using the selective laser melting technique, with their capability for SH wave enhancement further validated by experiments. The proposed method offers an alternative and more generic route for SH wave generation, and paves the way for further SH-wave-based SHM applications.