Efficient elastic wave absorption via lossy hybrid elastic metasurfaces

The absorption of elastic waves is fundamental to vibration attenuation in solid structures. An elastic metasurface with a more compact size has been proposed for the design of a high-efficiency absorber on the edge of a plate. However, efficient absorption of the elastic waves inside a certain region of a plate remains a challenge, as follows from the maximum absorption capped at 0.5 for the transmission problem. To realize highly efficient absorption of the transmitted elastic waves, we here propose a lossy hybrid elastic metasurface consisting of a connecting-beam cell (to perform the transmission problem) and a cantilever-zigzag cell (to mimic the reflection problem) in each supercell. The connecting-beam cell is designed to maintain a low transmission coefficient, and the cantilever-zigzag cell is utilized for high-efficiency absorption of the reflected waves. By arranging the period of the supercell, high-order diffractions of the elastic waves are suppressed, making it a one-way omnidirectional absorber. The absorption coefficients could exceed 0.5 for incidence angles between \ensuremath{-}80\ifmmode^\circ\else\textdegree\fi{} and 80\ifmmode^\circ\else\textdegree\fi{} within the frequency range of 3.1--5.9 kHz. In addition, an optimized symmetric supercell is designed to realize omnidirectional absorption of the elastic waves, with absorption coefficients up to 0.98. A series of experiments are also carried out to verify the high-efficiency absorption characteristics of the proposed lossy hybrid metasurface, which are in agreement with the simulation results. Our work provides a novel strategy for the efficient absorption of the transmitted elastic waves, holding great potential for mechanical vibration suppression.