A novel sintering based method to produce thin ultrahigh molecular weight polyethylene, UHMWPE, absorption material layer to increase absorption at low frequencies is introduced. The experimental impedance tube measurement results show that a 4 mm thick sintered sample layer increases absorption at a low frequency range below 1000 Hz compared with commercial melamine and polyester absorption foam samples. To cover a wider frequency range, multilayer structures composed of a sintered micro-porous material layer and commercial melamine and polyester foam layers are created and examined. The sintered sample layer also increases absorption in multilayer structures at low frequencies. Absorption coefficient values above 0.5 are reached starting from 200 Hz with multilayer structures. Software exploiting Biot's theory of porous materials has been adopted to fit the experimental absorption data for sintered samples, commercial foams and multilayers. Software based on Biot's theory was found to deliver quite good correlation with measured absorption coefficient values, with disagreements below 10% between the measured and estimated values.
Karhu, M., Lindroos, T. J., & Uosukainen, S. (2014). Manufacturing and modelling of sintered micro-porous absorption material for low frequency applications. Applied Acoustics, 85, 150-160. https://doi.org/10.1016/j.apacoust.2014.04.008