Non-Hermitian planar elastic metasurface for unidirectional focusing of flexural waves

Metasurfaces exhibiting spatially asymmetric inner structures have been shown to host unidirectional scattering effects, benefiting areas where directional control of waves is desired. In this work, we propose a non-Hermitian planar elastic metasurface to achieve unidirectional focusing of flexural waves. The unit cells are constructed by piezoelectric disks and metallic blocks that are asymmetrically loaded. A tunable material loss is then introduced by negative capacitance shunting. By suitably engineering the induced loss profile, a series of unit cells are designed, which can individually access the exceptional points manifested by unidirectional zero reflection. We then construct a planar metasurface by tuning the reflected phase to ensure constructive interference at one side of the metasurface. Unidirectional focusing of the incident waves is demonstrated, where the reflected wave energy is focused from one direction, and zero reflection is observed in the other direction. The proposed metasurface enriches the flexibility in asymmetric elastic wave manipulation as the loss and the reflected phase can be tailored independently in each unit cell. Published under an exclusive license by AIP Publishing.

Automated summary

This work proposes a non-Hermitian planar elastic metasurface that achieves unidirectional focusing of flexural waves by introducing tunable material loss and adjusting the reflected phase. Experimental results demonstrate that the metasurface can focus the incident wave energy from one direction and achieve zero reflection in the other direction.