Multi-band controllable acoustic topological insulator based on stacked composite resonant cavities

The development of multi-band, wide-frequency, spectrum-tunable topological acoustic transmission is essential for the practical application of topological acoustic insulators. However, conventional approaches rely on complex structural reconfiguration or parameter modulation, which severely limits their flexibility. This paper addresses this issue by proposing a universal method of optimising multi-band structures based on stacked composite resonators. The key advantage of this strategy is that it provides comprehensive and flexible control over the number, width and position of operational frequency bands, simply by stacking and arranging resonators vertically. This approach neither alters the original scatterer geometry nor introduces additional parameters. Furthermore, it simplifies multiband control, allowing the operating bandwidth and position to be adjusted by merely altering the number and order of resonator layers. Research indicates that this method enables the on-demand introduction of multiple Dirac cones, as well as the flexible adjustment of existing frequency band widths and Dirac cone spectral positions. Each cone can open a bandgap independently and generate topologically protected one-way edge states. Superlattice simulations, acoustic field simulations and experimental measurements collectively confirm that all frequency bands exhibit the low transmission loss and strong defect immunity characteristic of topologically protected edge states. The proposed layered paradigm in this work revolutionises conventional band control approaches, offering a new way to develop high-performance, customisable, multiband acoustic topological devices.