Tunable acoustic absorbers with periodical micro-perforations having varying pore shapes

¹ MOE Key Laboratory for Multifunctional Materials and Structures, Xi'an Jiaotong University - Xi'an 710049, PRC
² State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an Jiaotong University Xi'an 710049, PRC
³ Department of Mechanical Engineering, The University of Hong Kong - Pokfulam Road, Hong Kong

^(a) fengxian.xin@gmail.com

Received: 11 September 2017
Accepted: 10 January 2018

Abstract

Circular pores with sub-millimeter diameters have been widely used to construct micro-perforated panels (MPPs), the acoustical performance of which can be predicted well using the Maa theory (Maa D.-Y., J. Acoust. Soc. Am., 104 (1998) 2861). We present a tunable MPP absorber with periodically arranged cylindrical pores, with their cross-sectional shapes systematically altered around the circle while maintaining their cross-sectional areas unchanged. Numerical analyses based on the viscous-thermal coupled acoustical equations are utilized to investigate the tunable acoustic performance of the proposed absorbers and to reveal the underlying physical mechanisms. We demonstrate that pore morphology significantly affects the sound absorbption of MPPs by modifying the velocity field (and hence viscous dissipation) in the pores. Pore shapes featured as meso-scale circular pores accompanied with micro-scale bulges along the boundaries can lead to perfect sound absorption at relatively low frequencies. This work not only enriches the classical Maa theory on MPPs having circular perforations, but it also opens a new avenue for designing subwavelength acoustic metamaterials of superior sound absorption in target frequency ranges.