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Abstract
There is a general lack of publications on the acoustical and related non-acoustical properties of nanofibrous media. This work attempts to contribute to this gap and to highlight problems associated with acoustic and related non-acoustic characterisation of these materials. The work, presumably for the first time, applies Biot- and Darcy-type mathematical models to explain the observed acoustical and related non-acoustical behaviours of the nanofibres. It identifies theoretical gaps related to the physical phenomena which can be responsible for the observed acoustical behaviours of nanofibrous membranes and it presents recommendations to fill these gaps. The novelty of this work is in the use of a robust theoretical model to explain the measured acoustical behaviour of thin nanofibrous membranes placed on a foam substrate. With this model the actual flow resistivity of nanofibers is estimated from acoustical data. It is demonstrated that a classical model for the flow resistivity of fibrous media does not work when the Knudsen number becomes greater than 0.02, i.e. then the diameter of nanofibres becomes comparable with the mean free path.
Highlights
Acoustic absorbers are commonly used to control sound levels for user comfort, meet regulatory specification or to provide audio privacy between domestic or commercial spaces
It used a robust theoretical model to explain the observed acoustical behaviour of thin nanofibrous membranes placed on a foam substrate
It used the acoustical data to estimate the actual flow resistivity of nanofibres. It demonstrates that a classical model for the flow resistivity of fibrous media does not work when the Knudsen number becomes greater than 0.02, i.e. the diameter of nanofibres becomes comparable with the mean free path
Summary
Acoustic absorbers are commonly used to control sound levels for user comfort, meet regulatory specification or to provide audio privacy between domestic or commercial spaces. These absorbers come in the form of layers of foam or glasswool. There are numerous difficulties associated with the characterisation of key intrinsic material parameters of the membranes, such as membrane thickness, density, and pore size These membranes typically lack sufficient thickness and high enough levels of stiffness to be tested for their acoustical properties using a standard method. It uses, probably for the first time, Biot- and Darcy-type mathematical models to explain the observed acoustical and related non-acoustical behaviour of nanofibres. It identifies theoretical gaps related to the physical phenomena which can be responsible for the observed acoustical behaviour of nanofibrous membranes and it makes recommendations to fill these gaps
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