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.
Highlights
Studies on low-frequency sound absorption have attracted great scientific and engineering fascination due to its extensive practical applications in noise control, architectural acoustics, and environmental protection
We find that there exists a sound absorption peak at 239 Hz for both results, and the absorption coefficient can reach about 0.97, showing a near-perfect low-frequency sound absorption
We have demonstrated a metasurface-based unit with near-perfect low-frequency sound absorption based on artificial Mie resonances
Summary
Studies on low-frequency sound absorption have attracted great scientific and engineering fascination due to its extensive practical applications in noise control, architectural acoustics, and environmental protection. In the past few years, rapid development of metamaterials (Liu et al, 2000; Fang et al, 2006; Li et al, 2009; Toyoda et al, 2011; Christensen and de Abajo, 2012; Liang and Li, 2012; Quan et al, 2014; Cummer et al, 2016; Cheng et al, 2019; Gao et al, 2021) and metasurfaces (Li et al, 2013; Tang et al, 2014; Xie et al, 2014; Xie et al, 2017; Assouar et al, 2018; Holloway et al, 2019; Quan et al, 2019; Zhu and Assouar, 2019; Gao et al, 2020; Nikkhah et al, 2020) provides an unprecedented way to overcome the limits of conventional absorption materials and realize high absorption performance These absorbing structures usually contain subwavelength resonant units to enhance energy density and dissipate sound energy. The measured sound absorption spectra agree well with the simulated ones
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