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 c0{0ex}a0{0ex}n 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.