Harnessing nonlocal coupling effect to enhance broadband sound insulation in gradient acoustic metamaterial

While local-resonance acoustic metamaterials with parallel arrangements provide a feasible means for subwavelength control of sound waves, their practical applications are severely limited by the presence of multiple insulation valleys between the resonance effects. A new design framework for gradient-channel acoustic metamaterials is introduced by harnessing the nonlocal coupling effect. This mechanism strengthens the interaction between adjacent unit cells, with nonlocal regions acting as secondary acoustic sources. Consequently, phase cancellation is extended throughout the metamaterial, eliminating significant sound insulation valleys. Our theoretical, numerical, and experimental investigations reveal that the proposed nonlocal metamaterial enhances sound insulation by 15.8 % over the 400–2500 Hz range compared to conventional parallel metamaterials at the deep-subwavelength scale. Furthermore, a bilayer metamaterial, combining local and nonlocal designs, achieves an average sound transmission loss of 32.8 dB. By exploiting the nonlocal effect, this work significantly expands the design space for multi-channel acoustic metamaterials, enabling efficient manipulation of low-frequency waves over a wide bandwidth. It provides a novel route for developing ultrathin, high-efficiency sound insulators.