Magnetically tunable bandgaps and interface localization in acoustic black hole metabeams

Acoustic black hole (ABH) structures provide an effective platform for manipulating flexural wave propagation. In this work, we propose a magnetically tunable ABH metabeam that achieves controllable bandgaps and interface-localized vibration modes through the combined effects of local resonance and band folding. The metabeam incorporates two symmetrically arranged magnetic spring–mass resonators in each unit cell, whose effective stiffness can be adjusted by an external magnetic field. A theoretical model based on the Gaussian expansion method is developed to predict the band structures of both unit cells and supercells, and the results are validated using finite element simulations. It is shown that the applied magnetic field induces bandgap opening at the band-folding points and enables continuous tuning of multiple bandgaps. By assembling two metabeams with opposite resonator arrangements, interface-localized modes are generated within the tunable bandgaps, while the uniformly applied magnetic field enables active tuning of their frequencies. The robustness of these interface modes against stiffness and geometric imperfections is also demonstrated. The proposed magnetically tunable ABH metabeam provides a practical approach for acoustic wave manipulation and adaptive vibration control.