Non-resonant elastic metamaterials for broadband perfect mode conversion and negative reflection

Reflection control of elastic wave is of great importance. Recently, reflective metasurfaces governed by the generalized Snell's law offer a new degree of freedom to control the direction as well as the polarization of the reflected elastic waves. However, the underlining mechanism of the reflective metasurfaces is frequency-dependent, which significantly limits their practical applications. Here, we propose frequency-independent metamaterials called singly polarized solids (SPSs) for broadband reflection control of elastic waves. With the engineered SPSs, perfect mode conversion (PMC) and switching between positive reflection (PR) and negative reflection (NR) are achieved. Our work opens an approach to control the reflected elastic waves in a broad frequency range, and could find potential applications in structural health monitoring, nondestructive detection, and elastic wave devices.