Auxetic elastomers: Mechanically programmable meta-elastomers with an unusual Poisson's ratio overcome the gauge limit of a capacitive type strain sensor

How can we modulate the inherent Poisson's ratio value of soft elastomeric materials? The theoretical limit value of the Poisson's ratio of isotropic materials can be defined from −1 to 0.5 but elastomers generally take the Poisson's ratio of 0.5. Herein, we introduce and establish the concept of a mechanical meta elastomer called “auxetic elastomer”. This is a continuum-solid elastomer having unique programmable elastic properties of Poisson's ratio that are beyond their conventional ranges, and include in-plane negative and out-of-plane high positive Poisson's ratios. Leveraging these unique deformation characteristics, we applied auxetic elastomers as a soft dielectric material for a highly stretchable capacitive-type strain sensor that overcomes the inherent performance limitations in terms of the low gauge factor.