Conventional studies of higher-order topological states are based on discrete lattice models (e.g., tight-binding models), here we review how to reveal the higher-order topology in quasi-continuous media (such as metamaterials, photonic crystals, and phononic crystals). We connect this topic with the symmetry eigenstates at high symmetry points and the emergence of Dirac cones at these points as the topological transitions. This paper gives good examples and tools for those who are interested in topological physics in metamaterials.

https://iopscience.iop.org/article/10.1209/0295-5075/ac5844