Utilizing reversible solid–liquid phase transition to tune phononic bandgaps

Phononic crystals (PCs) are periodic synthetic materials that can manipulate the propagation of elastic waves and acoustic waves. However, for traditional phononic crystals, once the structure is identified, only a certain bandgap frequency can exist. Here, a supersaturated sodium acetate solution (SSAS) is introduced to realize a reversible liquid–solid phase transition by heating/cooling, which is utilized to tune the low-frequency bandgaps of elastic waves. Based on local resonance, we designed a one-dimensional (1D) PC, which consists of a 1D assembly of a series of goblets filled with the SSAS and heater pasted on the wall of the goblet. Low-amplitude transmission testing was conducted in both the liquid and solid states of the SSAS. An analytical model was proposed to calculate the first bandgap of the PC and to verify the testing results. In addition, numerical simulations were conducted to explore more bandgap zones. The results indicate that the phase transition induces tunable bandgaps of elastic waves. The underlying mechanism is that the phase transition leads to a unit cell stiffness and local heterogeneity. The bandgap from the solid to the liquid state is broadened by 20%. The findings reported here provide a new routine for designing architected metamaterial systems with broad and wide bandgaps for a wide range of potential applications in seismic, vibration, and acoustic wave control and guiding.