Effect of slit length on linear and non-linear acoustic transfer impedance of a micro-slit plate

Alessia Aulitto,Ines Lopez Arteaga,Avraham Hirschberg,Esmée L.R.H Buijssen

doi:10.1051/aacus/2021059

Abstract

The effect of the slit length on the acoustic transfer impedance of micro-slit plates (MSPs) is investigated in the linear and non-linear regime for a specific slit geometry. This geometry is inspired by slits obtained by cutting and bending the plate. MSPs are plates with arrays of slit-shaped perforations, with the width of the order of the acoustic viscous boundary layer thickness. Impedance tube measurements on two accurately manufactured plates are compared to numerical solution of the Linearized Navier-Stokes equations and to analytical limits. The impedance of the plate is obtained by the impedance of a single slit divided by the plate porosity. The resistance of a slit is independent on the slit length and on the plate porosity. In the linear regime the resistance is accurately predicted by a two-dimensional numerical model. In the non-linear regime, the resistance is strongly dependent on the amplitude of the acoustic waves. The inertance of the slit is weakly dependent on the slit length and on the plate porosity, for low and moderate amplitudes. For high amplitudes, a complicated amplitude dependency of the inertia of short slits is found. One expects that most of the conclusions obtained can be generalised to other slit geometries.

Highlights

Micro-slit absorbers and plates (MSAs, micro-slit plates (MSPs)) have been proposed as sound absorbers at low frequencies, providing lightweight and compact solutions to substitute conventional materials [1]
As for circular micro-perforations, the dissipation of sound occurs mainly at the edges of the micro-slits [20, 25]. Both in the linear and non-linear regime, the resistance of a single slit is independent of the porosity of the plate and on the slit length
Combining the results obtained in the present work for a specific geometry with the earlier studies on linear acoustical properties of micro-slits one can conclude that the independence of resistance on the slit length is due to the fact that the resistance is mainly determined by the local acoustic flow around the edges

Summary

Introduction

Micro-slit absorbers and plates (MSAs, MSPs) have been proposed as sound absorbers at low frequencies, providing lightweight and compact solutions to substitute conventional materials [1]. MSPs are plates with slit widths in the sub-millimeter range and low porosity (order of 1%). Micro-slit plates are backed by a cavity forming micro-slit absorbers (MSAs). One of the advantages of this geometry is that the edges in contact with the slits are protected from external agents in harsh environments. Another advantage is the possibility to reach sub-millimeter slit widths.

Methods

Results

Conclusion