Highly sensitive, piezoresistive, silicone/carbon fiber-based auxetic sensor for low strain values

An auxetic structure as a substrate material in sensor applications improves sensitivity performance due to lateral expansion under tensile loading. The presented stretchable, highly sensitive at-low-strain piezoresistive sensor was manufactured by mixing the silicone rubber and chopped carbon fibers in an auxetic re-entrant structure form. Auxetic re-entrant die was printed by using a 3D printing technique. The main feature of this sensor is the high sensitivity for strains lower than 6%, in which previous sensors could not recognize this range of strain well. In order to justify the excellent performance of the sensor, the deformation modes of the auxetic re-entrant structures were investigated and also connected to piezoresistive sensitivity. The shifting strain is defined as strain value, where the Poisson's ratio of structure shifts from negative to positive Poisson's ratio. Our study revealed that auxetic sensors have excellent sensitivity performance until the shifting strain due to having negative Poisson's ratio, and after that, their sensitivity performance is going to be weak due to having positive Poisson's ratio. In the present work, silicone rubber as the substrate material was used. This is a very soft material and made it possible to have low shifting strain resulting in perfect sensitivity performance for low-strain applications. The presented sensor has applications in many fields which are in low-strain conditions such as measuring the Vocal Cord Dysfunction (VCD), wrist pulse, or even earth vibration. (C) 2020 Elsevier B.V. All rights reserved.