Ultra-open ventilated metamaterial absorbers for sound-silencing applications in environment with free air flows

Abstract

For most acoustic metamaterials, once they have been fabricated, their operating frequencies and functions cannot be adjusted, which is an intrinsic barrier for development of realistic applications. The study to overcome this limit has become an urgent issue at the heart of acoustic metamaterial engineering. Although with the advance of metamaterials in the past two decades, a series of methods such as electric or magnetic control have been proposed, most of them can only work in the condition of no fluid passage. Some metamaterials with large transmission losses have been proposed, but the sounds are essentially reflected rather than absorbed. Here, to overcome this intrinsic difficulty, we propose a ventilated sound absorber that can be manually tuned in a large range after being manufactured. During the tuning which is 2 achieved through an intricately designed slider, high-performance absorption and ventilation are both ensured. The tunable ventilated sound absorber is demonstrated experimentally and the effective model of coupled lossy oscillators can be employed to understand its mechanism. The manually tunable ventilated metamaterial has the potential application values in various complicated pipe systems that require frequency adjustment and it also establishes the foundation for future development of active tunable ventilated acoustic metamaterials.

Bilayer ventilated labyrinthine metasurfaces with high sound absorption and tunable bandwidth

“…We note that the thickness of the bilayer metasurface is in a subwavelength scale (1/5th) compared to the lower limit (305 Hz) of the absorption band. In addition, the relative bandwidth of absorption here is much larger than (7 times of) recent results with using a pair of Helmholtz resonators in the unit cell [37]. If the same wide absorption band is desired, seven pairs of Helmholtz resonators need to be adopted in the unit cell [37].…”

“…If the same wide absorption band is desired, seven pairs of Helmholtz resonators need to be adopted in the unit cell [37]. Moreover, when more different resonators are adopted in the unit cell, their coupling effects become more complex, resulting in lower peak absorption (< 92%) observed in experiments [37]. waves.…”

“…However, due to the employment of back reflectors without holes, the perfect sound absorbers cannot be applied in some occasions which require sound elimination and ventilation simultaneously. To overcome this problem, various types of metasurfaces with ventilation openings have been investigated [25][26][27][28][29][30][31][32][33][34][35][36][37][38]. It is found that when ventilation ducts exist in the metasurfaces, sound barriers with high reflection and low transmission can be realized [25][26][27][28][29][30][31].…”

Recent Advances in Acoustic Metamaterials for Simultaneous Sound Attenuation and Air Ventilation Performances

“…The acoustic performance of the presented acoustic metastructures can be customized as per the requirements. More recently, Xiang et al [109] demonstrated an ultra-open ventilated metamaterial absorber (UVMA). The absorber was comprised of weakly coupled split-tube resonators, which resulted in a simultaneous high-efficiency absorption and ventilation.…”

Bilayer ventilated labyrinthine metasurfaces with high sound absorption and tunable bandwidth

“…Near-perfect sound absorption can be achieved in metasurfaces with a small open area ratio 32 – 36 . However, high absorption is still hard to achieve especially when the metasurfaces have a large open area ratio 37 , 38 . In addition, the bandwidths of absorption peaks are usually narrow and difficult to adjust.…”