Design of multi-auxetic microstructures for sound absorbing applications

Abstract

Auxetics are known to improve sound absorption performance due to their irregular porous structure. However, it is still difficult to control the porous microstructure to absorb a specific frequency range, although mechanical rigidity and improved sound absorption performance were achieved by manufacturing polyurethane foam for auxetics. Hence, we report, for a first time, a multi-auxetic porous microstructure fabricated via a triaxial thermal compression method applied simultaneously with two or more different compression ratios. The upper and lower parts of the multi-auxetic foam have two or more different positive or negative Poisson’s ratio, respectively. Consequently, the manufactured multi-auxetic foam has a single negative Poisson’s ratio property with enhanced sound absorption performance in the low-frequency range by twisting and forming a long sound wave path. Moreover, it was confirmed that the multi-auxetic sound absorber has an adjustable sound absorbing performance in a specific frequency range according to the difference in variety of pore sizes for each upper or lower part as well as the direction of incidence of the sound waves. This work suggests that the multi-auxetic porous microstructure can be mass-produced by a simple and fast manufacturing method, and it can be provided at a low price by manipulating the cellular structure of the conventional material.