Dual-frequency sound-absorbing metasurface based on visco-thermal effects with frequency dependence

Abstract

We investigate theoretically an acoustic metasurface with a high absorption coefficient at two frequencies and design it from subwavelength structures. We propose the use of a two-dimensional periodic array of four Helmholtz resonators in two types to obtain a metasurface with nearly perfect sound absorption at given target frequencies via interactions between waves emanating from different resonators. By considering how fluid viscosity affects acoustic energy dissipation in the narrow necks of the Helmholtz resonators, we obtain effective complex-valued material properties that depend on frequency and on the geometrical parameters of the resonators. We furthermore derive the effective acoustic impedance of the metasurface from the effective material properties and calculate the absorption spectra from the theoretical model, which we compare with the spectra obtained from a finite-element simulation. As a practical application of the theoretical model, we derive empirical formulas for the geometrical parameters of a metasurface which would yield perfect absorption at a given frequency. While previous works on metasurfaces based on Helmholtz resonators aimed to absorb sound at single frequencies, we use optimization to design a metasurface composed of four different Helmholtz resonators to absorb sound at two distinct frequencies.

Shape optimization of micro-acoustic devices including viscous and thermal losses

“…used in recent publications on metamaterial absorbing surfaces, such as [36,37]. The resonators in the example form two de-tuned pairs, upper and lower, with the same properties.…”

On the assembly of Archimedean spiral cavities for sound absorption applications: Design, optimization and experimental validation

“…Between those frequencies, the absorption coefficient remains higher than 0.8. Multiple coiled spaces based on the theory of HRs also have been studied [14,15], with the system being optimized accounting for more than one HR at once. Combination of MPPs and HRs [16,17], arrays of HRs with different dimensions [18,19] and honeycomb cells that mimic the behaviour of HRs [20] have also been tested to target a broader frequency range.…”

A parameter design method for multifrequency perfect sound-absorbing metasurface with critical coupled Helmholtz resonator

“…Traditional materials for sound-absorbing, such as porous materials, 1 have tiny inherent dissipation, making it challenging to absorb low-frequency noise with a subwavelength structure. Nevertheless, the subwavelength acoustic metasurfaces, such as Helmholtz resonator (HR), [2][3][4][5][6][7][8][9][10][11][12][13][14][15] micro-perforated plates (MPPs), [16][17][18] coiling space, [19][20][21][22] and membrane, 9,[23][24][25][26] manifest a promising prospect in absorbing low-frequency noise in the past years. Besides, acoustic metasurfaces with extraordinary physical properties are widely adapted to energy harvest, 27 time reversal, 28 acoustic focusing, 29 and acoustic holography.…”