Tunable acoustic labyrinthine acoustic metamaterials for broadband noise absorption

Abstract

This study introduces the Adjustable Acoustic Labyrinth Metamaterial (AALM) as a novel solution for noise pollution, particularly for managing the unpredictable and shifting frequencies produced by vehicles and mechanical equipment. The AALM is an adaptable metamaterial that integrates labyrinth structures with Helmholtz resonators (HR) to deliver highly tunable sound absorption. The system's adaptability stems from two adjustable parameters: the number of active labyrinthine canals and the cross-sectional area of the wave entrance. This dual-control mechanism provides remarkable flexibility. By altering the quantity of coiled spaces, users can achieve major frequency adjustments of approximately 120 Hz. For fine-tuning, modifying the wave entrance allows for minor adjustments of about 10 Hz at low frequencies and up to 50 Hz at higher frequencies. This tunability enables the AALM to operate effectively across a broad spectrum from approximately 220 Hz to 2000 Hz, which covers a significant portion of the primary target range for noise control (100-2000 Hz). In total, the system offers 24 distinct operational modes, capable of producing 36 different absorption peaks that are near-perfect, especially in the low-frequency range. This makes the AALM a highly promising technology for advanced acoustic management.