A novel design of mechanical metamaterial incorporating multiple negative indexes

Abstract

Mechanical metamaterials that combine multiple negative properties are rare, but have great appeal for applications in multipurpose devices. Herein, a novel metamaterial incorporating negative Poisson’s ratio, negative compressibility, and negative thermal expansion or swelling was proposed. The unit cell was designed by simulating the bond structure of lead monoxide crystals using elastic beams. Analytical models for the mechanical responses of the unit cell were established, and expressions for Young’s modulus, thermal expansion, Poisson’s ratio, and compressibility were derived and confirmed by numerical simulations. The results showed that the metamaterial not only displayed a negative Poisson’s ratio but also had negative linear and area compressibilities as well as negative linear, area, and volume thermal expansions if the geometric parameters were properly adjusted. Furthermore, metamaterials with negative linearity and area swelling were obtained experimentally by replacing the thermal expansion of the material with the water absorption expansion of a hydrogel. Such metamaterials with multiple negative indexes are expected to contribute to the feasibility of advanced multifunctional devices with mechanical, pressure, temperature, and moisture sensitivities.