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Low frequency sound propagation in activated carbon
F Bechwati1, M R Avis, D J Bull
1Acoustics Research Centre, University of Salford, Salford M5 4WT, United Kingdom.
The Journal of the Acoustical Society of America
|July 12, 2012
Summary
Activated carbon
Area of Science:
- Acoustics and Materials Science
Background:
- Activated carbon's surface interactions are known to affect gas molecules.
- The impact of these sorption effects on low-frequency sound waves is not fully understood.
Purpose of the Study:
- To investigate how the adsorption and desorption of gas molecules by activated carbon influence low-frequency sound wave propagation.
- To quantify the acoustic properties of activated carbon under varying sound pressures and frequencies.
Main Methods:
- Impedance tube measurements were used to analyze Helmholtz resonators with activated carbon backing.
- An apparatus was developed to measure activated carbon's effective porosity and adsorption levels.
- Sorption isotherms were measured to understand energy loss mechanisms.
Main Results:
- Activated carbon increased the compliance of the backing volume, particularly at lower frequencies.
- Sound pressure levels between 104-118 dB and frequencies of 20-55 Hz were tested.
- Excess absorption of low-frequency sound waves was primarily attributed to reduced surface reactance.
Conclusions:
- The study provides evidence that activated carbon's sorption properties affect low-frequency sound wave propagation.
- While adsorption is a likely cause, other phenomena cannot be entirely excluded.
- Decreased surface reactance, rather than surface resistance changes, is the main driver for excess sound absorption.
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