Determining acoustic properties of open-cell metal foams using the multi-microphone transfer matrix method

Urban Neunert, Robert Kathan, Thomas Sattelmayer

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

Due to their special combination of material and structure, novel porous materials like open- cell metal foams are increasingly often used in technical applications. In many cases, they are inserted in systems with mean air flow. For this reason, the influence of the flow on the damping characteristics of the metal foam is of particular interest. One method to describe the acoustic properties of an acoustic system is the network model, which combines the transfer matrices of acoustical elements. A transfer matrix relates the sound pressure and acoustic velocity on each side of each element. The transfer matrix of sound-Absorbing materials is usually expressed as a function of its bulk properties (complex characteristic impedance and complex wave number). In the literature, several analytical models exist to predict the bulk properties of common porous media, which mainly differ in the values of their model parameters. In this work the multi-microphone transfer matrix method is used to measure the bulk properties and the flow resistance of open-cell metal foams with varying pore structure and pore volume density for different element lengths. The experiments are carried out over a wide frequency range up to 1000 Hz at different mean flows with Mach numbers below 0.05. The effects of flow velocity on the damping characteristics and on the flow resistance are investigated. The frequency dependent complex characteristic impedances and complex wave numbers for the measured metal foams are compared to those calculated by analytical models of related porous materials. Specific model parameters are determined by using a regression analysis based on their measured bulk properties. A relation for the influence of the mean flow on the model parameters is provided. The results indicate that the multi-microphone transfer matrix method combined with a regression analysis is a simple and reliable way to describe the acoustic properties of open-cell metal foams.

Original languageEnglish
Title of host publication13th International Congress on Sound and Vibration 2006, ICSV 2006
Pages292-299
Number of pages8
StatePublished - 2006
Event13th International Congress on Sound and Vibration 2006, ICSV 2006 - Vienna, Austria
Duration: 2 Jul 20066 Jul 2006

Publication series

Name13th International Congress on Sound and Vibration 2006, ICSV 2006
Volume1

Conference

Conference13th International Congress on Sound and Vibration 2006, ICSV 2006
Country/TerritoryAustria
CityVienna
Period2/07/066/07/06

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