Ultrabroadband Acoustic Ventilation Barriers via Hybrid-Functional Metasurfaces

Ventilation barriers allowing simultaneous sound blocking and free airflow passage are a great challenge but are necessary for particular scenarios calling for soundproofing ventilation. Previous studies using local resonance or Fano-like interference consider a narrow working range around the resonant or destructive-interference frequency. Efforts made with regard to broadband designs show a limited bandwidth typically smaller than half an octave. Here we conceptually propose an ultrabroadband ventilation barrier via hybridization of dissipation and interference. Confirmed by experiments, our hybrid-functional metasurface, empowered by its synergistic effect, significantly expands the range of the operating frequencies, enabling an effective blocking of more than $90\mathrm{%}$ of incident energy in the range from $650$ to $2000\phantom{\rule{0.2em}{0ex}}\mathrm{Hz}$, while its structural thickness is only $53\phantom{\rule{0.2em}{0ex}}\mathrm{mm}$ (approximately $\ensuremath{\lambda}/10)$. Our design showcases the great flexibility of customizing the broadband and is capable of tackling sound coming from various directions, which has potential in air-permeable yet soundproofing applications.