Pillared elastic metasurface with constructive interference for flexural wave manipulation

In engineering, plate structures are one type of the main load-bearing structures. However, most of the designed plate-like metamaterials/metasurfaces need to be heavily grooved or drilled on the original plate surface, which will inevitably cause some destruction to the strength and stiffness of the host plate structures. To overcome this weakness, we propose a new conceptual design of pillared elastic metasurface (~0.495λ) to manipulate flexural waves in plates by considering constructive interference. The interference, which manifests itself as the coupling through out-of-plane vibration of the plate for the two adjacent subunits, is analyzed to reveal the physical mechanisms. In addition, we reveal the mechanism of the phase shift of transmitted waves across the sub-wavelength subunits and establish an analytical model for the multi-resonator subunits to accurately predict the phase shift and amplitude of the transmitted wave. We theoretically design and experimentally demonstrate the deflecting and focusing functionalities of the proposed elastic metasurface. Our design can provide a new route to broad applications of the constructive interference in elastic metamaterials/metasurfaces, which can be used to efficiently engineer arbitrary wave profiles.