Review of metamaterials principles and methods in ventilation ducts: 1928-2024.

Acoustic metamaterials (AMMs) have emerged as a promising strategy for low-frequency noise control in ventilation ducts, offering subwavelength, tunable solutions that overcome key limitations of conventional silencers, such as high pressure drop and reduced long-term performance. This review presents a structured analysis of 54 studies on AMMs for duct acoustics, with civil, mechanical, aerospace, and biomedical engineering applications. AMM unit designs are categorized by physical mechanism, including resonant cavities, acoustic membranes, Herschel-Quincke tubes, Fano-like interference structures, duct shape modifications, micro-perforated panels, and porous materials. The associated acoustic and flow-related performance parameters, such as insertion loss, transmission loss, absorption coefficient, flow velocity, temperature, pressure drop, Reynolds number, and Mach number, are systematically examined. Analytical, numerical, and experimental approaches are reviewed with attention to their respective merits and limitations, particularly in capturing multi-physical interactions between acoustics, fluid flow, and structural dynamics. Of the studies surveyed, 35 employed monophysical models, 8 used loosely coupled (monophysical parallel) methods, and only 11 adopted fully coupled multi-physical frameworks. This review highlights the need for integrated design methodologies and standardized evaluation under realistic flow conditions to advance the effective implementation of AMMs in ducted acoustic systems.