[show abstract][hide abstract] ABSTRACT: This work reports on an application of the state vector (Stroh) formalism and Peano series expansion to solve the problem of sound propagation in a material with continuous pore stratification. An alternative Biot formulation is used to link the equivalent velocity in the oscillatory flow in the material pores with the acoustic pressure gradient. In this formulation, the complex dynamic density and bulk modulus are predicted using the equivalent fluid flow model developed by Horoshenkov and Swift [J. Acoust. Soc. Am. 110(5), 2371-2378 (2001)] under the rigid frame approximation. This model is validated against experimental data obtained for a 140 mm thick material specimen with continuous pore size stratification and relatively constant porosity. This material has been produced from polyurethane binder solution placed in a container with a vented top and sealed bottom to achieve a gradient in the reaction time which caused a pore size stratification to develop as a function of depth [Mahasaranon et al., J. Appl. Phys. 111, 084901 (2012)]. It is shown that the acoustical properties of this class of materials can be accurately predicted with the adopted theoretical model.
The Journal of the Acoustical Society of America 07/2012; 132(1):208-15. · 1.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: This work reports new data on the acoustical properties of open cell foam with pore stratification. The pore size distribution as a function of the sample depth is determined in the laboratory using methods of optical image analysis. It is shown that the pore size distribution in this class of materials changes gradually with the depth. It is also shown that the observed pore size distribution gradient is responsible for the air flow resistivity stratification, which is measured acoustically and non-acoustically. The acoustical absorption coefficient of the developed porous sample is measured using a standard laboratory method. A suitable theoretical model for the acoustical properties of porous media with pore size distribution is adopted. The measured data for open porosity, tortuosity, and standard deviation data are used together with this model to predict the observed acoustic absorption behavior of the developed material sample. The transfer matrix approach is used in the modeling process to account for the pore size stratification. This work suggests that it is possible to design and manufacture porous media with continuous pore size stratification, which can provide an improvement to conventional porous media with uniform pore size distribution in terms of the attained acoustic absorption coefficient.
Journal of Applied Physics 04/2012; 111(8). · 2.21 Impact Factor