Fig. 1: Metagrating-based ultrathin waveguide.

a Schematic of the proposed waveguide constructed by two layers of elastic metagratings to confine the waves along an arbitrary route. The supercell, consisting of only two unit-cells, is periodically distributed in each metagrating. b The metagrating can omnidirectionally block flexural waves in a thin plate in the form of specular reflection. The interval of periodically repeated supercells L is less than half of the wavelength. c A diagram for how the metagrating omnidirectionally reflect an incident wave. k_x denotes the wavenumber along the metagrating. ξ and n denote reciprocal lattice vector and diffraction order, respectively. The black arrows represent wave vector k_x of incident and scattering waves, while green arrows represent wave vector k_x from metagrating diffraction. Upward (downward) arrows represent the reflection (transmission) of waves. The green box is the regime of propagation modes. The solid arrow in the green box indicates that the 0th order waves can propagate into far field, while the dashed arrows beyond the green box indicate other-order diffraction waves will decay evanescently in the near field. The y-axis represents the direction of wave vector k_y.