Thermally-switchable bragg gaps in additively manufactured phononic crystals

Abstract Recently, additive manufacturing fabrications are commonly applied to produce acoustic metamaterials or phononic crystals as tools for complex geometrical designs. However, the material properties of those additive manufactured materials are less involved in the core portion of those phononic crystal designs. Here we report a purely materials-driven, temperature switchable PnC in which Bragg gaps appear or vanish as the lattice medium toggles between liquid water and solid ice. Six widely used additive manufacturing polymers were acoustically characterized, where stereolithography resins showed an impedance mismatch of ≈50 % with water but <1 % with ice, whereas inkjet agar gel exhibited the opposite trend. A 10 × 10 stereolithography resin PnC therefore displayed >20 dB on/off contrast at 145 kHz and around 300 kHz when cycled across 0 °C, confirmed experimentally and with plane wave and simulation models. Unlike previous thermally tuned phononic crystals that depend on volumetric swelling or liquid metal infiltration, the present approach preserves geometry, requires no external actuators and operates with sub 1 °C stability. This simple, robust strategy lays the foundation for band pass filters, steerable lenses and non-reciprocal acoustic circuits that can be frozen or thawed on demand.