Low-frequency one-third octave band near-perfect acoustic metasurface absorber with imperfect component resonator design

Abstract

In this paper, we propose an easily designable low-frequency acoustic metasurface (AMS) absorber composed of multiple imperfect microslit resonators designed to achieve near-perfect sound absorption within a one-third-octave-band. Some specific designs of one-third-octave-band near-perfect absorbers at 125, 250, and 500 Hz are presented. We have developed a robust and efficient user-friendly absorber design method combining the transfer matrix method and a unique geometry design rule of component resonators. To develop this design method, we conducted extensive numerical and experiment-based examinations by thermoviscous acoustic simulation and impedance tube measurements, particularly addressing the number of component resonators and their peak sound absorption coefficient. The numerical and experimental results demonstrated the importance of creating a coupled resonator with the appropriate number of imperfect component resonators, each with a lower sound absorptivity peak. These features are crucially important for achieving thin sound absorbers without compromising the desired sound absorption properties. Numerical sound absorptivity evaluation revealed that using more component resonators to create a coupled resonator enables individual component resonators to operate as resonators with lower sound absorptivity peaks. This simple operation achieves robust sound absorption characteristics with less degradation.