Measurements and empirical model of the acoustic properties of reticulated vitreous carbon

Abstract

Reticulated vitreous carbon (RVC) is a highly porous, rigid, open cell carbon foam structure with a high melting point, good chemical inertness, and low bulk thermal conductivity. For the proper design of acoustic devices such as acoustic absorbers and thermoacoustic stacks and regenerators utilizing RVC, the acoustic properties of RVC must be known. From knowledge of the complex characteristic impedance and wave number most other acoustic properties can be computed. In this investigation, the four-microphone transfer matrix measurement method is used to measure the complex characteristic impedance and wave number for 60 to 300 pore-per-inch RVC foams with flow resistivities from 1759 to 10,782 Pa s m(-2) in the frequency range of 330 Hz-2 kHz. The data are found to be poorly predicted by the fibrous material empirical model developed by Delany and Bazley, the open cell plastic foam empirical model developed by Qunli, or the Johnson-Allard microstructural model. A new empirical power law model is developed and is shown to provide good predictions of the acoustic properties over the frequency range of measurement. Uncertainty estimates for the constants of the model are also computed.

Bottom-up approach for microstructure optimization of sound absorbing materials

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Improvement of liquid absorption properties of nonwoven polypropylene substrates by low pressure plasma treatment with CH4-O2 mixture gas

“…This Modelling and Improvement of Absorbent Materials applied on periodic fitting panels. 39 together with an increase of the rigidity can be causing the worsening of the performance at low frequencies. For high frequencies (f > 900Hz) shaping increases the absorption performance.…”

Processing and Characterization of Epoxy/Luffa Composites: Investigation on Chemical Treatment of Fibers on Mechanical and Acoustical Properties

“…An impedance tube is a rigid, straight and smooth cylindrical pipe composed of two sections or tubes, a transmitting, and a receiving tube to test a material's acoustic absorption coefficient (α) by producing a sound wave incident on the material being tested; the difference between the incident and reflected wave is then measured. Based on Muehleisen (2005), the two-microphone method measures the magnitude and phase difference of the pressure reflection coefficients that are used to measure the sound absorption coefficients of composites.…”