ABSTRACT
The present study deals with the sound absorption performance of natural fibres from the oil palm frond (OPF), mainly considered agricultural waste. Therefore, this study aimed to investigate the sound absorption performance of OPF fibre-reinforced composite under normal incidence sound. The materials used were OPF particles and urea-formaldehyde was used as an adhesive. The particleboards were produced with three particle sizes and four target densities. The absorption coefficient of normal incidence sound (αn) was tested using an impedance tube. The effects of particle size and bulk density were also evaluated. The findings reveal thatαn exceeded 0.45 at 1000 Hz and could reach 0.95 above 3.3 kHz. This occurred when the bulk density of the OPF composite particleboards ranged between 0.3-0.4 g/cm3, and the particle size varied between medium to coarse. The results also indicated that the absorption frequency and the degree of αn significantly increased as the bulk density decreased. Therefore, OPF fibres can be used to create sound-absorbing composite particleboards.
ABSTRACT
Conventional polyurethane foam has non-tunable sound absorption properties. Here, a magneto-induced foam, called magnetorheological (MR) foam, was fabricated with the feature of being able to tune sound absorption properties, primarily from the middle- to higher-frequency ranges. Three different samples of MR foams were fabricated in situ by varying the concentration of Carbonyl Iron Particles (CIPs) (0, 35, and 75 wt.%). The magnetization properties and tunable sound absorption characteristics were evaluated. From the magnetic saturation properties, the results showed very narrow and small coercivity of hysteresis loops relative to the soft magnetic properties of the CIPs. MR foam with 75 wt.% CIPs showed a higher magnetic saturation at 91.350 emu/g compared to MR foam with 35 wt.% CIPs at 63.896 emu/g. For tunable sound absorption testing, the effect of 'shifting' to higher frequency was also observed when the magnetic field was applied, which was ~10 Hz for MR foam with 35 wt.% CIPs and ~130 Hz for MR foam with 75 wt.% CIPs. As the latest evolution of semi-active noise control materials, the results from this study are valuable guidance for the advancement of MR-based devices.
