Ultrabroad acoustical limiting in nonlinear metamaterials due to adaptive-broadening band-gap effect

Nonlinear wave limiters transmit low-amplitude waves while blocking high-intensity ones for efficient target protection. However, the acoustical limiting effect in nonlinear materials remains hitherto unaddressed. In addition, tunable bandgap fosters advanced functions for devices, but it is still mostly regarded as a spatial and temporal invariant feature. In recent years, nonlinear acoustic metamaterials (NAM) have shown extraordinary properties for manipulating elastic waves. Here we achieve an enhanced nonlinear interaction in a different NAM. We theoretically and experimentally demonstrate that the NAM features an efficient acoustical limiting, and the limiting bandwidth adaptively broadens as the propagation distance/time increases. Within a short propagation distance, an ultrabroad limiting band is formed that overcomes the limitation of linear resonant bandgaps. It is clarified that the space-amplitude-dependent bandgap dominates the amplitude reduction, and the transient chaotic responses initialize the adaptive-broadening process. Our study highlights wave physics that could not obviously be realized in nonlinear optics. The self-adaptive band structures open up opportunities to realize exotic adaptive elements.