Acoustic performance of micro-grooved elements

Abstract

The acoustic performance of a new type of fibre-less sound absorber, the Micro-Grooved Element (MGE), is studied in this paper. The transfer impedance and the absorption coefficient of micro-grooved and Micro-Perforated Elements (MPEs) are measured, modelled and compared.A MGE is a double layer element that involves inlet/outlet slots and facing micro-channels engraved onto the mating surface of the layers. The main advantage of these elements is that, by means of a simple technological process, thin micro-channels with depth of less then 100µm can be easily engraved. This allows the MGEs exhibiting higher absorption coefficients compared to traditional MPEs with 300−700µm diameter of perforations. Moreover, due to the presence of surfaces surrounding the micro-channels, the MGEs show reduced resistance when exposed to high level of sound excitation. In this perspective, the performance of a MGE is more stable than the one of a MPE provided with the same porosity.A number of different MGEs with varied internal geometries has been tested at different excitation levels. The acoustics of the micro-channels is treated in details, the impedance end corrections are determined and the non-linear effects are accounted for. The linear behaviour of MGEs is described by adapting the models for slit-shaped perforated elements (SSEs). The quasi-and non-linear behaviours are expressed as a function of the Shear number and Strouhal number by curve fitting the experimental results.

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

“…In the linear regime, experimental results are compared to numerical solutions of the Linearized incompressible Navier-Stokes equations. Microperforated plates (MPPs) and micro-slit plates can be designed to obtain excellent linear acoustic properties but, at high amplitudes, the non-linear effects deteriorate the performance of the absorbers [6][7][8]. In practical applications, the acoustic particle velocity in the slits can reach high amplitudes.…”

“…In classical applications, a slit can be created by removing material from the plate [2,3,9]. Slits can also be generated by mating two slotted layers [6,10]. Alternative designs of MSAs have been reported in the literature [2,3,6,11,12].…”

Numerical simulations and experiments on thermal viscous power dissipation of perforated plates

“…At a certain approximation, the Maa model [Eqs. (1) and 2] meets to acoustic impedance for all |Ka| values. While for the numerical simulation aspect, the motion equation of viscous compressible Newton fluid, including the energy equation, is governed by…”

“…Since the 40s of the 20th Century, research on theory and application of MPPs have attracted great interest of researchers. 1 The reason is that MPPs have the advantages of simple structure and obvious sound absorption effect. They are widely used in muffler systems, sound absorbing panels, liners, architectural acoustics, industrial noise, combustion oscillation suppression, and pipeline noise elimination, etc.…”

Experimental Evaluation and Numerical Modelling Residual Stresses in Glass Panel

“…Multifunctional LGCP with improved strength and acoustic performance can be obtained by using novel acoustic interlayers covering strengthening and sound attenuation properties simultaneously. Development of new sound absorptive element for wide class of structures and applications is emerging research area [6][7][8][9].…”