Switchable Bidirectional Sound Absorption Via Exceptional Point Modulation in Acoustic Metastructures with...

Physics-driven acoustic metamaterials offer unprecedented capabilities in manipulating sound wave propagation. Among these, sound-absorbing metamaterials emerge as powerful tools for achieving subwavelength control and high-efficiency absorption. However, most existing designs are typically constrained to unidirectional absorption, limiting their applicability in noise-sensitive scenarios requiring bidirectional control. Here, a switchable bidirectional acoustic metastructure is presented, integrating interleaved resonator coupling with exceptional point (EP) modulation. By coordinating vertical and horizontal resonant interactions through tailored impedance matching and controlled energy dissipation, the system achieves broadband and frequency-selective absorption in both directions-validated through theoretical, numerical, and experimental analyses. Specifically, broadband absorption from 478 to 670 Hz and discrete peaks at 260 and 542 Hz under opposite incidences are observed within the deep-subwavelength scale. Compared to state-of-the-art unidirectional absorbers, the proposed structure maintains geometric compactness while delivering robust bidirectional performance. Beyond device-level innovation, a generalized theoretical framework is developed to translate the effective acoustic parameters of resonance-based metastructures into specific impedance forms, enabling integration into EP-based switching strategies. This enables the functional extension from unidirectional to bidirectional absorption across a wide range of metastructures. Overall, this work offers a novel physics-driven pathway toward practical, high-performance, and bidirectional acoustic wave control.