Tunable Topological Phononic Crystals

Topological insulators are of practical interest for the one-way wave propagation afforded by their edge states, and are not limited to electronic systems. In many cases the topological transition occurs when time-reversal symmetry is broken and is not tunable, but here the authors design a phononic crystal with a transition that c00exa00exn be tuned by varying the structure's geometric size, or the external airflow (velocity field). Their results are universal and should expand our ability to tailor sound waves, as in acoustic diodes.