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 $2000\mathrm{Hz}$, while its structural thickness is only $53\mathrm{mm}$ (approximately $\lambda /10)$. 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.

Figure 1

(a) Conceptual view of the broadband ventilation barrier consisting of periodically arranged metaunits. (b) The designed metaunit is composed of eight layers. Each layer is split into two resonant chambers by a deflected blade (the first layer is removed to show the inner details). Here the cylindrical metaunit is designed as prescribed by the standard impedance tube for experiments. With the presented design strategy being followed, it can be straightforwardly reshaped as a cube and then periodically arranged to form a barrier. (c) Experimental setup, where the specimen is clamped in the impedance tube. (d) Theoretical (red line), simulated (black dashed line), and measured (blue dots) acoustic power transmission of the designed metaunit with $D=100\mathrm{mm}$, $d=44\mathrm{mm}$, $h=5.5\mathrm{mm}$, $b=1\mathrm{mm}$, $H=53\mathrm{mm}$, $\psi ={142.5}^{\circ }$, $\theta =5^{\circ }$, and $S_n=63.4{\mathrm{mm}}^2$. The inset shows an enlarged view of a three-dimensionally-printed specimen of the designed metaunit (right) and its inner structure (left).

Figure 2

(a) Numerically calculated absorption (red line) and reflection (black line) and measured absorption (red circle) and reflection (black circle) of the metaunit. The dashed gray lines refer to three representative frequencies, where the performance of the metaunit is dominated by absorption ($628\mathrm{Hz}$), absorption and interference ($824\mathrm{Hz}$), and interference ($1100\mathrm{Hz}$). (b) Axial-plane view of the simulated sound-field distributions at the three marked frequencies. The colors illustrate the power-dissipation density, and the arrows represent the energy-flow distribution. (c) Radial-plane view of the specific layers where the “active” resonators are located. The color illustrates the acoustic pressure distributions, and the arrows represent the local-velocity streamlines.

Figure 3

Variation of power transmission with (a) the thickness of each layer $h$, (b) the inner diameter of the central orifice $d$, and (c) the angle shift of the partition blade from layer to layer $\theta$. The dark regions represent effectively silenced zones. The dashed white lines in the color maps show the selected system parameters.

Figure 4

(a) The modified metaunit featuring three additional circumferential partition blades in each layer. (b) A photograph of the three-dimensionally-printed specimen and its inner structure. (c) The numerically calculated absorption (red line) and reflection (black line) and the measured absorption (red circles) and reflection (black circles) of the metaunit. (d) Theoretical (red line), simulated (dashed black line), and measured (blue dots) power transmission of the metaunit ($D=100\mathrm{mm}$, $d=44\mathrm{mm}$, $h=5.5\mathrm{mm}$, $b=1\mathrm{mm}$, $H=53\mathrm{mm}$, $\psi ={120}^{\circ }$, $\theta =8^{\circ }$, $S_n=42.3{\mathrm{mm}}^2$, and $t=1\mathrm{mm}$).

Figure 5

Power transmission for illumination by a plane wave with incident angles of $0^{\circ }$ (blue line), ${30}^{\circ }$ (red line), and ${60}^{\circ }$ (black line).

Figure 6

The ventilation characterization system and the measured wind-velocity ratio.