Low-frequency acoustic metasurface containing series-type resonators with curled necks

Abstract

This study presents a novel acoustic metasurface with a coplanar series-type Helmholtz resonator with curled necks. Using extended necks that are embedded in cavities enables one to significantly reduce the resonance frequency of the resonator. The sound absorption performance of this metasurface is investigated theoretically, numerically, and experimentally. The absorption band can be easily adjusted by altering the neck length and diameter. To achieve a wide frequency band with high absorption, two inhomogeneous units are arranged in parallel. Theoretical and finite-element predictions exhibit good agreement with the experimental measurements. The results demonstrate that the proposed acoustic metasurface with subwavelength thickness is capable of effectively absorbing low-frequency sound.

Study on the acoustic performance of bending metasurface with ultra-thin broadband quasi-perfect sound absorption

“…Limited by the law of mass action and causality constraint, low-frequency broadband noise reduction has always been a hot and difficult issue in the field of noise control [1][2][3]. Although traditional sound absorption/ insulation materials have been widely used in the engineering field, large and bulky acoustic structures are often required for low-frequency and broadband noise, which seriously limited their applications in noise control [4][5][6]. Therefore, the emergence of acoustic metamaterials with small size control large wavelengths brings new directions for low frequency broadband noise control [7][8][9][10].…”

Aerodynamic noise control with an acoustic metasurface comprising an array of low-flow-sensitivity Helmholtz resonators

“…Rapid development of acoustic metamaterials with sub-wavelength size and anomalous dynamic equivalent parameters provide a new approach for the control of vibration noise [2][3][4][5][6]. Wide applications of HRs for noise control has inspired a significant amount of researches on the effect of the geometry on their acoustic performance of low-frequency and broadband control under no-flow conditions [7][8][9][10][11][12][13]. However, the flow-excited excitation are becoming more and more important due to their occurrence in practical situations such as the mean flow, self-sustained oscillations and high-speed pressure fluctuations [14], and the incident acoustic waves form unsteady vortices at the edge of the neck interface and the magnitude of the convective vorticity is mainly affected by the characteristics of the fluid flow and resonator [15][16][17].…”