Continuous-phase-transformation elastic metasurface for flexural wave using notched structure

An elastic metasurface is an artificial structure composed of subwavelength structures that can manipulate elastic waves with an arbitrary phase gradient transformation. However, most traditional elastic metasurfaces are designed with discrete phase shift, due to the coupling effect and resonance mechanism. In this study, we present a pioneering approach to designing elastic metasurfaces with a continuous phase transformation by incorpo-rating notched structures in solids. To achieve the continuous phase transformation, we establish the relationship between the notch depth and the effective phase velocity of flexural waves in notched plate-like structures by equivalently represent the structure as a thin plate. Two classical periodic elastic metasurface design concepts for anomalous refraction and wave focusing are demonstrated. The numerical and experimental results show that the continuous-phase-transformation elastic metasurface performs well in broadband. The proposed approach opens up new possibilities for realizing periodic curved elastic metasurfaces with a continuous phase gradient change. This innovation holds promise for a variety of applications in the field of elastic wave manipulation.