Metamaterial based on labyrinthine tubes loaded periodically and ultra-low phase velocity to the low-frequency energy control

Abstract

Sound energy control at low frequencies (≤1000 Hz) is necessary and very important in acoustics, especially when considering scientific and technological aspects. In this work, a modular acoustic metamaterial composed of a main waveguide loaded with small quarter-wavelength tubes is presented. Theoretical, numerical, and experimental methods are used to describe the accumulation of sound absorption peaks below the structure's bandgap with the number of peaks proportional to the structure's periodicity. The origin of the bandgap is due to the loaded tubes in the main waveguide. Ultra-low phase velocity (c̃p=16 m/s) and critical coupling were obtained in the model, which allowed perfect sound absorption at 292 Hz with a structure reaching a ratio of λ/90. The experimental results in the impedance tube support the theoretical and numerical discussions and demonstrate a sound energy control of 89% and 84% at 686 and 422 Hz, respectively. Finally, this work contributes to advances in the field of control and manipulation of low-frequency sound energy through periodic structures.