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.

Magnetorheological (MR) foam, which is comprised of magnetic particles inside the matrix phase, is capable of changing its physical and rheological properties corresponding to the applied magnetic field. However, the performance of this material seems unsatisfactory due to the nonuniform distribution of magnetic particles throughout the composite area resulting in uneven magnetic properties. Since uniform magnetic properties are significant regarding MR foam, in situ fabrication using a polyvinyl chloride mould can be used to achieve the targetted improvement. MR foam was prepared with various amounts of carbonyl iron particles (CIPs), 0, 35, 45 and 55 wt%, and investigated at three different positions (top, middle and bottom parts) with a vibration sample magnetometer. The results showed that the hysteresis loop at all CIP concentrations of 35, 45 and 55 wt% exhibited superparamagnetic properties with magnetic saturation. The M _s of the top, middle and bottom positions were almost the same with a small standard deviation below 2 Am ² kg ^–1 . Moreover, it is observed that the effect of porosity results in the enhancement of the magnetic saturation and remanence values. These results reveal the promising uniform magnetic properties of MR foam, which can benefit the industry by helping produce a consistent MR foam.