  Sound absorption is an important technological task in machine-building and
civil engineering. Porous materials are traditionally used for these purposes,
as they are neither ignitable nor hygroscopic and thus suitable for noise
oppression, first of all in means of transportation. Absorption of acoustic
oscillation energy in porous metals occurs mainly due to viscous friction. A
theoretical description of the process of energy viscous dissipation in a
porous media on basis of Rayleigh classical model is given in paper [1],
whereas the modern level of theory is set forth in Johnson-Champoux-Allard
model [2]. Attempts of utilizing aluminum foam as the cheapest porous metal for
sound absorption are related to forming of the open porous structure by rolling
[3] or by heat treatment [4]. However, the sound absorption ratio of metal foam
presented in these papers does not rise over 80%, whereas it reaches 99.9% in a
wide frequency range when we take conventional sound-absorption materials (i.e.
glass-wool). The problem of foamed metal consists of considerable reflection of
acoustic waves from the surface.
