Figure 3. Strong topological protection of acoustic chiral modes against defects.

(a) Immunity of the nonreciprocal edge mode to various defects and turns. The one-way edge states flows seamlessly, regardless of the edge geometry, shape of the turn or the presence of localized defects. (b) Example of uni-rotational acoustic mode localized to a crystal defect in an inner edge. The colour map represents the acoustic pressure.