A compact honeycomb-based ventilated sound barrier with broad bandwidth and a subwavelength thickness

In this research, we propose a ventilated acoustic meta-panel with a honeycomb appearance to overcome the challenges of attaining ventilation capability, broad bandwidth, and insulation performance simultaneously in a miniaturized size. A hexagonal unit cell comprises a pair of dual parallel hollow channels and is interconnected with a meandered air-flowing path to reduce the resonant-induced transmission leakages and achieve broadband sound insulation while maintaining air ventilation and compact sizes. Each unit cell has a subwavelength thickness of 0.06 λ and a compact volume of 6.24 × 10−5 λ3 where λ corresponds to the lowest frequency of the bandwidth. The device is theoretically analyzed with an equivalent acoustic impedance model, considering the curved channel effects and thermoviscous loss for sound wave propagation within narrow tubes. The circuit model provides a design guideline to optimize the geometric parameters for desired frequency responses. The circuit simulations are compared with 3D finite element simulations considering thermal conductivity effects and viscous loss. The unit-cell simulation results showed a broad soundproof bandwidth ranging from 427 Hz to 5979 Hz with 90 % sound energy insulations. For practical examinations, a 3D-printing prototype is fabricated and inserted in a commercial impedance tube system with a diameter of 10 cm. The experimental results demonstrated a wide sound filtering bandwidth ranging from 422 Hz to 1800 Hz and an air ventilation capability of 12 %. The proposed thin panel with broadband sound insulations and sufficient air ventilations has potential applications such as noise reduction in high-speed trains and factories and sound silencing in hospitals.