Sound Absorption Beyond the Fluid Compressibility Limit

Traditional resonator arrays can cope with a finite band of incident noise spectrum, but they cannot tackle a problem with truly broad frequency band, for which the upper limit of total sound absorption is imposed by the relative cavity fluid incompressibility towards the DC frequency. To exceed this limit, a quasi-zero-stiffness resonator with negative magnetic stiffness is proposed using a mechanical structure of magnetic bearing. Theoretical and experimental results of the normal incidence test show that the new device can achieve broadband sound absorption and is effective in the low-frequency region. The total sound absorption is improved by 68% above the limit, paving the way for a new strategy for low frequency broadband noise control.