Sound absorption performance of porous metal fiber materials with different structures

Porous metal fiber materials (PMFMs) with gradient structure for the thickness above 10 mm can be used widely in the field of noise controlling because of excellent sound absorption coefficient. But, how does the sound absorption coefficient of PMFMs with the thickness below 3 mm? In the paper, green felts of 316L stainless steel fibers with fibers diameters of 8–20 μm were used to manufacture the PMFMs (the thickness of 2–3 mm) with different structures by the sintering process at the vacuum condition. Sound absorption coefficients of the PMFMs were measured in the 4206 two-microphone impedance tube with the sound wave frequency ranging from 50 Hz to 6400 Hz. The results show that the sound absorption coefficient of the PMFMs with gradient structure is largely affected by the interface between different layers. Furthermore, although the thickness of PMFMs is only 2 mm or 3 mm, the average sound absorption coefficient of gradient structure is much higher than that of single-layer structure at the same thickness.