High-efficiency sound absorption by a nested and ventilated metasurface based on multi-slit synergetic resonance

A nested, sound-absorbing, ventilated metasurface was proposed based on multi-slit synergetic resonance, which could simultaneously achieve high-efficiency (>0.85), sound absorption, and effective (speed ratio >0.67) ventilation in a frequency range of 470–657 Hz. The unit of the sound-absorbing and ventilated metasurface (USAVM) consisted of a ventilation channel and a stepped micro-slit absorber, which could effectively trade-off ventilation and absorption performance. The sound absorption mechanism was revealed via the coupling of the ventilation channel and micro-slit absorber, relying on strong air friction and the slit walls near the resonance frequency. Furthermore, after a parametric study of the USAVM, a compact nested metasurface with a thickness of only 39.1 mm (1/17 wavelength) was constructed using eight parallel USAVMs, with a surface panel area of only 1/7 of the traditional parallel structure. Finally, the sound absorption and ventilation performance of the nested metasurface were verified experimentally. In addition, the absorption bandwidth could be further improved by using more USAVMs. This work provides a new possibility for achieving highly efficient sound absorption with a subwavelength ventilated structure in a low-frequency range that could be applied in buildings or industrial areas. (paper)