Fractal phenomenon in sound absorbing behavior of down fiber assembly

Abstract

X-ray computed tomography (CT) can quantify variations in microstructure of materials. In this paper, we first demonstrated that by using a micro-CT method, we can characterize the internal porous structures of different fiber assemblies. Furthermore, the fractal dimension of the porous areas can be calculated based on the acquired two-dimensional cross-sectional images of the assemblies. Then after measuring the sound absorption behaviors of the assemblies, correlations between the fractal dimension, the pore structural characteristics, and the acoustic absorption property are analyzed. Results show that for down fiber assemblies, the fractal dimension increases with fiber mass, and decreases with the porosity. Also the maximum absorption coefficient α_m reaches a maximum value at a critical fractal dimension, while critical frequency f_r continuously decreases with the fractal dimension all the time.