Excitation and manipulation of guided shear-horizontal plane wave using elastic metasurfaces

The lowest order shear horizontal wave (SH₀ wave) is of great importance in structural health monitoring (SHM) and nondestructive testing (NDT), since it is the only non-dispersive guided wave mode in elastic plates. However, SH₀ wave is less used than Lamb waves in the past decades, which is mainly attributed to the fact that controllable excitation of pure mode SH₀ wave and manipulation of its propagation are more difficult than Lamb waves. In this work, inspired by the unique feature of SH₀ wave that it can propagate around curved surfaces with negligible reflection, metasurfaces based on multiple arch-shaped strips are proposed for generating plane SH₀ wave from a cylindrical wave source and realizing anomalous refraction of SH₀ wave. Firstly, after analyzing the wave modes in finite-width arch-shaped strips, the strips' capability of covering full 2π phase shift with high transmittances is demonstrated. Then three types of metasurfaces, i.e. the device for converting cylindrical SH₀ wave to plane wave, the metasurface for directional refraction and the one for delivering the wave energy along a circular path are designed and validated by simulations. After that, experiments are conducted to investigate the designed metasurfaces' performances and the obtained results are in good agreement with the design expectations. The proposed metasurfaces provide a cheap way to generate plane SH₀ wave and manipulate its propagation, which will have great potential applications in NDT and SHM. (paper)