Kv. Horoshenkov et Mj. Swift, The acoustic properties of granular materials with pore size distribution close to log-normal, J ACOUST SO, 110(5), 2001, pp. 2371-2378
The majority of realistic porous materials are composed of pores of which t
he shape is variable and the size of the pores normally obeys a distinctive
statistical distribution. Although the variation of pore shape is less imp
ortant, the statistical parameters of pore size distribution can have a con
siderable effect on the acoustic properties of porous media. This paper dis
cusses the application of a simple model for the prediction of the acoustic
properties of porous granular media with some assumed pore geometry and po
re size distribution close to log-normal. The model is based on the rationa
l (Pade) approximation approach [K. V. Horoshenkov, K. Attenborough, and S.
N. Chandler-Wilde, J. Acoust. Soc. Am. 104, 1198-1209 (1998)] which has be
en developed for some simple pore geometries. It is shown that the experime
ntally determined pore size distribution for a representative range of gran
ular materials is often close to log-normal. This assumption enables accura
te predictions of the acoustic performance of these materials using the pre
sented model. The water suction method is proposed to determine the paramet
ers of the log-normal distribution, which are the mean pore size, [phi], an
d its standard deviation, sigma. This method is nonacoustic, modelless and
well-adapted to acoustic materials and, unlike the BET method [S. Brunauer,
P. H. Emmett, and E. Teller, J. Am. Chem. Soc. 60, 309-319 (1938)], is eas
y to reproduce in any basic acoustic laboratory requiring no expensive part
s or chemicals. The proposed Pade approximation is based entirely on four m
easurable nonacoustic parameters, the porosity, Ohm, flow resistivity, R-b,
tortuosity, q(2) and the standard deviation of the pore size, sigma. The m
ethod is successfully tested on a representative selection of consolidated
and nonconsolidated porous granular materials. (C) 2001 Acoustical Society
of America.