Acoustic absorption behaviour of a tall carbon nanotube forest

Abstract

Previous investigations have shown that a 3-mm-high carbon nanotube (CNT) forest has an acoustic absorption coefficient of about 5-10% within the frequency range 125 Hz-4 kHz, which is above that of conventional acoustic materials on a per-mass basis. It was hypothesised that a CNT array of greater height, lower density, and with a non-uniform arrangement of the nanotubes could enhance the amount of acoustic absorption. In order to investigate this hypothesis, an impedance tube test was conducted to measure the acoustic absorption coefficient of a relatively tall 6-mm CNT forest. The results indicate that a greater length and lower density of CNTs may improve the absorption performance of CNT-based acoustic absorbers. Analyses of the results showed anomalies in the measured acoustic absorption coefficient compared with previous investigations. Theoretical analyses were performed based on classical models of acoustic absorption to explain the anomalies. This study describes the factors that may affect the acoustic absorption behaviour of nanomaterials.