A comprehensive review of acoustic metamaterials: Applications and challenges for lightweight noise control in large-scale transportation

• Noise characteristics and reduction challenges in large-scale transportation are summarised. • Five major types of acoustic metamaterials and their research progress are reviewed. • Existing applications of acoustic metamaterials in large-scale transportation are presented. • Key challenges and future directions for practical implementation are proposed. Aiming to address the vibration and noise reduction requirements of large-scale transportation, the latest research advancements in acoustic metamaterials are classified and reviewed based on practical engineering challenges in this paper. First, the noise characteristics of large-scale transportation, including aircraft, high-speed trains, and ships, are summarised, with the challenges posed by space and weight limitations in noise control being highlighted. The latest research developments in acoustic metamaterials are then reviewed, focusing on four major categories: solid locally resonant metamaterials, membrane-type acoustic metamaterials, Helmholtz resonance cavity structures, and space-coiling metamaterials. Considering the coupling mechanisms among different structures, composite structures are additionally included as a fifth category. Furthermore, adaptive and multifunctional acoustic metamaterials are introduced as emerging directions. Subsequently, the feasibility of these acoustic metamaterials for noise reduction in large-scale transportation is evaluated, and the practical applications of the five established categories are summarised. Finally, challenges and future research directions in the use of acoustic metamaterials for vibration and noise reduction in large-scale transportation are outlined.