Ultrasparse and omnidirectional acoustic ventilated meta-barrier

Sound barriers, aiming to block the noise propagation, have attracted substantial interest in diverse scenarios such as architectural design, transportation development, and aircraft/automotive engineering. However, conventional sound-proofing barriers in the bulky configuration simultaneously impede the free airflow, which is highly required in the applications calling for ventilation. Although the advances in acoustic metamaterials have opened new routes for designing air-permeable barriers, a well-ventilated and omnidirectional sound barrier with deep-subwavelength thickness remains challenging. Here, we theoretically propose and experimentally demonstrate an ultrasparse, ultrathin, and ultralight acoustic ventilated meta-barrier that is highly prohibitive to omnidirectional sound. The acoustic meta-barrier is designed by sparsely arranging the units composed of two central-symmetric cavities with the thickness about 0.12λ (λ is the sound wavelength) and the sparsity achieving up to 80%. A sound wave from all directions impinging to the meta-barrier is efficiently blocked, and the airflow is allowed to freely transport, maintaining the wind velocity ratio measured higher than 90%. Moreover, geometric parameter analysis is investigated to optimize and customize the meta-barrier according to the target frequency spectrum. The ultrasparse and omnidirectional acoustic ventilated meta-barrier in such a compact and open configuration would hold out promising solutions to sound insulation and offer an additional scheme to design sound-proofing yet air-permeable devices in various applications.