Multi-mechanism assisted ultrathin labyrinthine metastructure for ultrabroadband sound insulation

Acoustic metastructures, with designable operating frequency bands and sub-wavelength artificial units, have been extensively studied in recent years for noise attenuation. However, existing metastructures commonly sacrifice structural compactness to increase operating bandwidth, thereby limiting their applications in wearable scenarios. To overcome this challenge, we propose an ultrathin labyrinthine acoustic metastructure featuring submillimeter-scale channels (LAMSC) with overall dimensions of 9.5 mm × 2.3 mm (diameter × thickness). Acoustic tests demonstrate ultrabroadband sound insulation across 100–6000 Hz range, which includes three sub-frequency bands dominated by thermoviscous absorption, acoustic reflection, and resonant absorption mechanisms, respectively. The sound transmission loss (STL) reaches 23.32–41.44 dB over the tested frequency range, along with a flatness of 14.43 dB@100–2000 Hz representing an improvement of 3.57–55.57 dB over the previously reported sound insulation metastructures. Then, the LAMSC is integrated into earplugs for α band electroencephalogram test under traffic noise, demonstrating a noise reduction of at least 20 dB. This work offers combined advantages of structural compactness and broadband sound insulation, providing the potential to be used for noise isolation in earplugs and other space-constrained applications.