Phononic Crystal Tunable via Ferroelectric Phase Transition

Conventional phononic crystals have already been used to control acoustic waves, but would be much more versatile if one could conveniently tune their response during operation, without having to stop and manually swap out or rearrange their building blocks. The authors present a tunable phononic crystal composed of the ferroelectric ceramic Ba0.7Sr0.3TiO₃, which near room temperature undergoes a phase transition that can induce a 20% shift in the frequency of transmitted waves. This system is promising for ``smart'' versions of acoustic cloaks, isolators, waveguides, sensors, and filters.