Harnessing diffraction with metamaterial noise barriers for enhanced sound attenuation.

Wave diffraction is typically regarded as a limiting factor in the performance of acoustic noise barriers, enabling sound to bend over finite structures and reducing attenuation, particularly at low frequencies. In this work, we demonstrate that diffraction can instead be harnessed as a functional mechanism for sound suppression by designing metamaterial barriers that incorporate a vertical array of resonators along the barrier surface. The proposed structure changes the dispersion characteristics of edge-diffracted waves and acts as a boundary that transforms diffraction into surface-guided wave propagation. Our analysis reveals that the metabarrier achieves broadband sound attenuation through two distinct mechanisms: (i) the formation of strong standing wave modes due to surface-guided waves confined along the barrier face, and (ii) resonance-induced evanescence decay resulting in localized band gap formation. Together, these effects lead to a substantial enhancement in insertion loss over a broad frequency range. Furthermore, we show that performance can be tuned by implementing double-sided arrays. These findings introduce a new framework for acoustic wave control, in which diffraction is not merely mitigated but actively exploited as a design-enabling feature.