Zero-angle refraction of elastic waves in metamaterials has attracted attention for its extraordinary wave collimation properties. However, earlier implementations relied on the specific flat equifrequency curve of the phononic crystals suffer from a narrow range of incident angles or operating bandwidths, which severely hinders the exploration and design of functional devices. Here, we propose an elastic near-zero refractive index metamaterial of a triangular lattice to realize topological zero refraction with arbitrary angles of incidence and wide working frequency range. Topological robustness of the zero-angle refraction of pseudospin-Hall edge state against defects is experimentally demonstrated. Furthermore, tunable wave mode conversion associated with the zero-angle refraction is revealed and discussed. These results provide a paradigm for the simultaneous control of the refraction properties of longitudinal and transverse waves that can be employed for designing the topological elastic antennas and elastic wave collimator.

超材料中弹性波的零角度折射以其非凡的波准直特性而备受关注。但是，依赖于声子晶体的特定平坦等频率曲线的较早实现方式具有窄范围的入射角或工作带宽，这严重阻碍了功能器件的探索和设计。在此，我们提出了一种三角晶格的弹性近零折射率超材料，以实现具有任意入射角和宽工作频率范围的拓扑零折射率。实验证明伪自旋-霍尔边缘状态的零角度折射的拓扑鲁棒性。此外，揭示并讨论了与零角折射相关的可调波模式转换。