Broadband sound absorption by a nested doll metasurface using multi-slit synergetic resonance

Abstract

A sound-absorbing metasurface with a multi-slit synergetic resonant effect was studied that can achieve broadband sound absorption in a range betwen 500 Hz and 1150 Hz by using a nested doll supercell with a thickness of only 44.1 mm (the thickness being one sixteenth of the wavelength). The basic unit of the improved micro-slit absorber (IMSA), made by designing the slit of the micro-slit absorber as a type of step and locating it at the edge of the surface panel, is proposed for sound absorption at lower frequencies. The improved step slit can not only change the structure’s impedance to match the medium of air at a lower frequency, but can also guide sound waves into the slit and increase the air velocity step by step, which results in a strong friction loss in the lower micro-slit. On this basis, a nested doll supercell with eight integrated parallel IMSAs was designed and tested, and was able to achieve sound absorption in a range between 500 Hz and 1150 Hz. In addition, the bandwidth was further broadened (to between 330 Hz and 1150 Hz) by adding four additional IMSAs to the previous supercell, while the surface area of the panel only increased by about 20%. This work highlighted the potentially extensive application of broadband noise reduction due to its depth, i.e. subwavelength thickness, and the relatively small surface area of the panel.

Ultrathin Space‐Shift Phase‐Coherent Cancellation Metasurface for Broadband Sound Absorption

“…The development of metamaterial provides solutions for designing low-frequency absorbers with a sub-wavelength thickness. [13,14] The basic absorption metamaterial forms include Helmholtz resonators, [15][16][17] resonant membrane/plate structures, [18][19][20] Fabry-Pérot cavities, [12] slit-type absorbers, [21][22][23] and the combined or derived structures by these basic forms, [24][25][26][27][28][29][30][31][32][33] such as the widely used spacecoiling absorbers those combining from Helmholtz resonator and Fabry-Pérot cavity. [24][25][26][27][28] For the metamaterial and metasurface, the design method plays a really important role in achieving the excellent physical performance, especially for widening bandwidth and enhancing amplitude.…”

“…[24][25][26][27][28] For the metamaterial and metasurface, the design method plays a really important role in achieving the excellent physical performance, especially for widening bandwidth and enhancing amplitude. Several structural design methods are available for enhancing sound absorption performance or extending working bandwidth, including parallel synergistic coupling between multi-cells with gradient parameter distribution and weak coupling interaction between units, [12,16,17,19,21,22,34,35] increasing the number of resonance modes in a certain frequency band via the strong coupling interaction among the units to produce more absorption peaks, [18,33] parallel synergistic coupling between different types of soundabsorbing materials / structures, [29][30][31][32] and introducing artificial acoustic soft boundaries for reducing the sound reflection on the interface between the structure and air. [36,37] The most common and effective way to enhance the absorption performance is to use parallel superposition among weak coupling units, which could effectively broaden the working bandwidth to achieve the linear superposition.…”

Enhancing of broadband sound absorption through soft matter

“…The development of metamaterials provides new possibilities for designing low-frequency sound-absorbing structures with sub-wavelength thicknesses, such as resonant membrane-type, [10][11][12] labyrinth, [13][14][15] Helmholtz resonant cavity, 16,17 Fabry-Pe ´rot cavity, 18 and slit structures, 19 as well as secondary structures based on these forms. [20][21][22][23][24][25][26] In summary, there are generally three ways to broaden the absorption bandwidth.…”

“…Each unit produces an absorption peak, which is then connected to maintain a high sound absorption coefficient in a wide frequency band. 12,[16][17][18][19][22][23][24][25] If each unit can produce multiple absorption peaks, that is, high-order peaks, the sound absorption bandwidth can be further increased via multi-order multicell synergistic coupling. The second method involves expanding the number of resonance modes of the integrated structure via the strong coupling interaction between the cells to increase the number of absorption peaks and broaden the working bandwidth.…”

High-efficiency sound absorption by a nested and ventilated metasurface based on multi-slit synergetic resonance

“…Of these, sound absorption with subwavelength size has received considerable attention, leading to the development of many types of sound absorption metamaterials. The Helmholtz resonance AMM [7][8][9] is a typical structure that can achieve lowfrequency sound absorption in a relatively narrow frequency band. Another typical structure is the membrane-type AMM [10,11] that can achieve perfect sound absorption by combining a thin elastic membrane film and a small mass with a rigidback cavity.…”