A low-frequency ultra-broadband ventilated acoustic isolator based on resonant black-hole metamaterials

Abstract Noise has long been recognized as an important factor affecting human well-being. A major challenge in acoustic research is the development of ventilated acoustic insulation materials that meet the need to block sound while allowing free passage of airflow. However, it is still necessary in specific situations where ventilated sound insulation is required. With the continuous progress in acoustic metamaterial research, studies using resonant cavity resonance or similar Fano interference principles have shown promising results in a narrow frequency range around specific frequencies. However, since noise typically encompasses a wide frequency spectrum, limited band absorption is not sufficient for effective sound attenuation. In this study, we propose a resonance-based, low-frequency, ultra-wideband ventilated acoustic isolator. The sound insulator consists of a Helmholtz resonant cavity and a black hole structure, resulting in a large bandwidth for low-frequency sound isolation. The presence of a center hole ensures efficient air circulation. The adjustable cavity allows precise control of the acoustic isolation performance and bandwidth. When multiple HR units are used in series, the transmission loss and bandwidth of this acoustic structure are significant. Simulations show transmission losses above 10 dB over the frequency range of 550 Hz to 1600 Hz. The overall dimensions of the silencer are 61 millimeters long and 100 millimeters in diameter, which is much smaller than the operating wavelength. The high sound attenuation observed under ventilated conditions can be attributed to the resonant sound absorption of the HR structure. Finally, the effect of different HR on the sound absorption bandwidth is analyzed, showing how the cavity volume affects the macroscopic acoustic properties. This silencer has several potential applications in acoustic engineering where simultaneous noise reduction and ventilation are required.