An experimental study of ultrasonic attenuation in microporous polyethylene

Auxetic foams, i.e. those possessing a negative Poisson's ratio, nu, are known to possess improved sound absorption properties when compared with conventional foams. In this study, the ultrasonic attenuation of another class of auxetic materials, microporous polymers, and in particular ultra-high-molecular weight polyethylene (UHMWPE), was examined experimentally, in comparison with a microporous positive nu form of UHMWPE and conventionally processed UHMWPE. It was found that the microporous polymers, whether auxetic or nor, showed very large enhancements in attenuation coefficient, alpha(mn), over the conventionally processed UHMWPE, with the highest measurable value being alpha(mn) = 47 dB/cm for the auxetic material, which is 1.5 times the highest value for the microporous positive nu UHMWPE and more than three times that for the conventionally processed material. In addition, the samples with the largest negative Poisson's ratio absorbed the signal so completely that no value of a was obtainable. (C) 1997 Elsevier Science Ltd.