Acoustic properties of auxetic foams

Abstract

Auxetic foams have raised some interest in noise and vibration control applications as they showed unusual acoustic properties compared to conventional ones, particularly at low frequencies. Auxetic foams are porous materials with a negative Poisson’s ratio. They expand in all directions when only pulled in one. In this paper, the acoustic properties of auxetic foams are described both from a numerical and experimental point of view. The acoustic absorption properties of both auxetic and conventional foam samples were measured using a two-microphone impedance tube to provide a comparison between the two types of cellular solids. The acoustical properties of auxetic foams are discussed in terms of the dynamic parameters. A numerical model based on Biot’s theory is derived in which the dynamic coefficients of foams are evaluated. Results are compared and commented to provide explanations on the unusual acoustical behaviour of auxetic foams.