Examination of acoustic behavior of negative poisson's ratio materials

Abstract

Negative Poisson's ratio (NPR) foams have been predicted to have unusual acoustic properties. To measure these, polyurethane foam was chosen to serve as a model system. Negative Poisson ratios were produced in open cell, reticulated polyurethane foams by heat setting the foam which had been three-dimensionally compressed 3·7-fold. Acoustic reflection measurements were made on unconverted foam, NPR uncovered foam, and on NPR foam with an unattached and attached cover. Foams tested had pore densities ranging from 25·4 to 254 pores per linear cm. NPR foams absorbed better than unconverted foams at all frequencies. Smaller pore-size NPR foams absorbed sound more efficiently at frequencies above 630 Hz than did those with larger pores, and those with covers were better sound absorbers in the frequency range 250–1000 Hz than the uncovered NPR foams. Unidirectional compression to one quarter of the original thickness reduced the Poisson ratio to zero and caused the foam to absorb nearly as well as did creation of the negative Poisson's ratio.