Ultra-Thin Metasurface-Based Absorber of Low-Frequency Sound With Bandwidth Optimization

Abstract

We report, both theoretically and experimentally, a type of ultra-thin metasurface-based low-frequency sound absorber with bandwidth optimization. Such a metasurface unit consists of an ultrathin resonator (thickness∼1/90 wavelength) with a circular hole on the upper panel and four narrow slits inside a multiple-cavity structure. Eigenmode simulations of the unit show rich artificial Mie resonances, in which a type of monopolar Mie resonance mode can be obtained at 238.4 Hz. Based on the excitation of the monopolar mode, we can realize the near-perfect low-frequency sound absorption with the maximum absorption coefficient and fractional bandwidth of 0.97 and 12.9%, respectively, which mainly arises from the high thermal-viscous loss around the circular hole and four narrow slits of the unit. More interestingly, by combining 4 units with different diameters of the circular hole, we further enhance the fractional bandwidth of the compound unit to 18.7%. Our work provides a route to design ultra-thin broadband sound absorbers by artificial Mie resonances, showing great potential in practical applications of low-frequency noise control and architectural acoustics.

Rectangular extended neck Helmholtz resonant acoustic structure for low frequency broadband sound absorption

“…However, lowfrequency noise has a long wavelength and strong penetration, which means that eliminating it requires a thick noise reduction structure, contradicting the structural design [3]. Therefore, finding ways to effectively eliminate low-frequency noise using a simple, thin structure has become a popular research [4][5][6].…”

Editorial: Acoustic and mechanical metamaterials for various applications - volume II

“…The team from Xi'an Jiaotong University have designed metamaterials with excellent sound absorption performance in the range of 600-900 Hz, and applied them to noise control in substations (Yang et al, 2022). The team from Jiangsu University have reduced the thickness of the sound absorbing metasurface to an extremely thin range of approximately 1/90 wavelength (Guan et al, 2021).…”

Sound-absorption performance of a coupled square-neck embedded Helmholtz resonator

“…Gao et al 22) used a hybrid design of an individual unit cell comprising multiple resonators to expand the working bandwidth and downscale the resulting device size. Ge et al 25,26) proposed two types of open window structures that exhibit an unusual omnidirectional acoustic insulation, and this effect can be switched by changing the configuration of the blade array. Shen et al 27) designed an acoustic metamuffler; the average sound insulation is 20 dB at 100-1600 Hz, and the thickness is only 6.2 cm.…”