Measured Variation of High Frequency Sound Absorption in Porous Metals Subject to Changes in Temperature and Temperature Gradient

Abstract

Porous metal, as a new acoustic material, bears the general metal properties, such as good conductivity, ductibility, heat transfer and high specific stiffness and intensity, and meanwhile exhibits good performance in sound absorption. Thus, it enjoys a growing popularity in industrial and civilian sound-absorbing applications where non-metallic materials are impracticable. Therefore it is of great significance to explore the sound-absorption properties of porous metals. The existing studies mainly focus on the low frequency range and are under uniform temperature assumption. In this paper, an experimental setup was built up to investigate the sound absorption of porous metals subject to temperature gradients, and much concern was paid to that of high frequency range. The setup is composed of five modules: I. heating module; II. cooling module; III. temperature controlling & testing module; IV. spectrum analyzer and V. impedance tube testing module. Based on this setup, the sound absorption of a hard-backed porous metal in a high-frequency range (2000–4000Hz)and under different temperature gradients (+2°C/mm, +4°C/mm and +6°C/mm) are measured, and results show that: 1) The sound absorption of porous metal is significantly influenced by temperature gradients; 2) The peak of sound absorption curve moves to a higher frequency range as the temperature gradient increases in the frequency range 2000∼4000Hz but the peak value decreases slightly; 3) The peak value of sound absorption curve enlarges as the temperature gradient increases but the frequency of peak value is fixed.