高温の雰囲気における多孔質材の吸音特性 : 特に板状材料の垂直入射吸音率について

概要

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Normal incidence absorption coefficients α of samples of metal-fibrous porous absorbing materials, whose thickness (d) is comparatively thin and specific flow resistance (R) is different, are measured in the atmosphere of high temperature between room temperature and 400℃. The change of absorption characteristics with temperature is investigated also theoretically. Because all of the characteristics of such a sample with back-air space show peaked forms, in this paper, aiming at the maximum absorption coefficients α_<max>, the resonant frequencies f_0, and the bandwidth in the neighborhood of f_0, these changes with temperature are inquired into closely. The experimental results indicate that f_0 and bandwidth always considerably increase as the temperature rises for every sample, on the other hand, that the change of α_<max> differs with each sample and shows the behavior of decrease or increase according to the value of unit-area specific flow resistance R_f (=R×d) at room temperature. It is found that these characteristics changes are explained quantitatively by using the Beranek eqation of α calculated from specific flow resistance (R) and considering temperature changes of sound velocity in the air (c), density of air (ρ), and coefficient of viscosity of air (η) included in the equation.
社団法人日本音響学会の論文
1984-09-01