Asymmetric flexural wave transmission based on dual-layer elastic gradient metasurfaces

Traditional asymmetric transmission of elastic waves is mostly based on mode conversion, which presents a real challenge to get pure-mode elastic waves. In this letter, without the aid of mode conversion, we present an innovative concept of asymmetric flexural wave transmission within a wide frequency band, based on dual-layer elastic wave gradient metasurfaces. According to the generalized Snell's law, we theoretically and numerically design and experimentally demonstrate the asymmetric flexural wave transmission by tuning the supercell lengths of dual-layer metasurfaces. The experimental results confirm that the proposed design provides a wide effective frequency band feature, which agrees well with the theoretical analysis and predictions. Our concept offers the flexibility to control the wave energy flow, opening the route to pragmatic applications in many fields, such as ultrasonic detection, energy harvesting, and vibration control.