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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.
Highlights
Sound-absorbing materials are defined as having the ability to absorb the energy of sound waves as much as possible while minimizing reflection and transmitting the energy of the sound waves at the same time [1,2]
Carbonyl iron particles (CIPs), which are derived from the decomposition of pentacarbonyl iron, were used as magnetic particles and were purchased from CK Materials Laboratory Co
MR foam was developed using a combination of rigid polyurethane (PU) foam containing a polyether polyol (RG135NFDH1) reactant purchased from PPT (M) Sdn
Summary
Sound-absorbing materials are defined as having the ability to absorb the energy of sound waves as much as possible while minimizing reflection and transmitting the energy of the sound waves at the same time [1,2]. A few requirements of suitable sound-absorbing materials may need to be considered in order to minimize the noise generated; examples include porosity, weight, absorption ability, and range of frequency absorption [3,4]. These sound-absorbing materials are classified into three main groups: passive, active, and semi-active noise control materials [5,6]. Passive noise control materials can be defined as passively minimizing radiated noises by energy absorption [6,9,10] This material involves a method that does not require an external supply of control energy by dissipating the propagation of the acoustic waves through various damping mechanisms [1]
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