Hybrid broadband conduction and amplitude-driven topological confinement of sound via synthetic acoustic crystals

Abstract: Precise wave manipulation has undoubtedly forged the technological landscape we thrive in today. Although our understanding of wave phenomena has come a long way since the earliest observations of desert dunes or ocean waves, the unimpeded development of mathematics has enabled ever more complex and exotic physical phenomena to be comprehensively described. Here, we take wave manipulation a step further by introducing an unprecedented synthetic acoustic crystal capable of realizing simultaneous linear broadband conduction and nonlinear topological insulation, depicting a robust amplitude-dependent mode localized deep within - i.e. an amplitude-driven topological confinement of sound. The latter is achieved by means of an open acoustic waveguide lined with a chain of nonlocally and nonlinearly coupled active electroacoustic resonators. Starting from a comprehensive topological model for classical waves, we demonstrate that different topological regimes can be accessed by increasing driving amplitude and that topological robustness against coupling disorder is a direct consequence of symmetric and simultaneous response between coupled resonators. Theoretical predictions are validated by a fully programmable experimental apparatus capable of realizing the real-time manipulation of metacrystal properties. In all, our results provide a solid foundation for future research in the design and manipulation of classical waves in artificial materials involving nonlinearity, nonlocality, and non-hermiticity.