Fig. 5
From: Topological sound
Valley topological phase in a bilayer sonic crystal (BSC), adapted from ref. 81. a A schematic of the unit cell, where both the side and top views are shown. b Reduced phase diagram in dependence on the angles (α, β). The numerical phase boundaries (solid lines) confirm the model predictions (dots), which exhibits the closure of the omnidirectional band gap. c, d Show the projected dispersion relation along an interface separating two topologically distinct acoustic valley Hall (AVH) BSCs and acoustic layer-valley Hall (ALH) BSCs. e Simulated field pattern of sound concentration varying from the upper layer to the lower layer
