Near-field effects on the sound transmission and absorption of elastic micro-perforated plates in impedance tubes

https://doi.org/10.1016/j.jsv.2021.116001Get rights and content
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Abstract

In this study, the effects of near-field waves on the sound absorption and insulation performance of elastic micro-perforated plates (MPPs) installed in impedance tubes are studied. The sound absorption coefficient and the sound transmission loss (STL) of MPPs are computed by solving structure-acoustic coupled equations, and the results are compared to those by the finite element method (FEM) to confirm the accuracy of the proposed method. As additional near-field waves are included, the results show convergence. For the low-frequency sound absorption of a circular plate without micro-perforations, the first peak frequency is derived analytically as a function of the cavity depth, radius and surface mass density of the plate. It is shown that as more near-field waves are included, the peak frequency moves toward a lower frequency. It is observed that as the mass density decreases or the radius of the tube increases, the peak shift increases. However, the difference between the two solutions remains constant with an increase in the cavity depth. The effect of the near-field waves on the STL of two identical plates is such that the single peak obtained from the plane wave solution splits when the near-field waves are included. As the cavity depth increases, the near-field waves decrease rapidly except the vicinity of the plates, which in turn results in the narrower split, and eventually splitted peaks reduce to a single peak. When two plates have different thicknesses, no peak splitting occurs. Rather, the peak shifts as additional near-field waves are included, similar to the case of sound absorption.

Keywords

Near-field effect
Micro-perforated plate
Impedance tube

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