Acoustic Perfect Absorption in Coupled Resonators with Deep Subwavelength Thickness

Acoustic metasurface with perfect absorption, deep subwavelength thickness, as well as broadband working frequency range is fascinating in noise control engineering, especially at extremely low frequencies. Here, we present an acoustic absorber with coupled resonators. By coupling two designed resonators with deep subwavelength thickness (~lambda/70), a hybrid resonance mode providing perfect acoustic absorption can be generated at extremely low frequencies. Theoretical modeling is carried out to investigate the coupling effect. And both the simulations and experiments showed excellent agreement with the predictions. The relative absorption bandwidth with large tunability (from 18% to >100%) can be achieved by coupling resonators from two to more. The proposed absorbers are potential to be widely used in noise control engineering due to the quality of deep subwavelength, mechanically stable, and can be easily fabricated.