Strain and temperature sensors made from fishing lines

Abstract

Soft and flexible sensors are demanded in a wide variety of wearables and soft-robotic applications. We designed and developed novel integrated strain and temperature sensors using super-coiled transparent polymer fibres as an optical waveguide by exploiting changes in macro-bending optical losses induced by strain or heat. Polymers used in this research such as nylon and fluorocarbon are shaped as super-coils. The customized optical couplings were designed that can sustain tension induced by axial strain force or thermal stress (entropic spring effect). A customized method of transmission and measurement of the optical signal transferred through a super-coiled polymeric waveguide was designed to reduce attenuation losses. Transmitted optical signals were recorded in the range of −65 dBm to −45 dBm. Changes in the measured transmitted optical signal were recorded and compared for transparent mono-filament nylon fibre fishing line and fluorocarbon fibre fishing line. The trends of the measured parameters registered during the testing period showed a variation of ∼2%, good linearity and repeatability, however with minor hysteresis in the range of ∼ 4 % for nylon and the range of ∼ 2.5 % for fluorocarbon. Limited optical characteristics of these materials were compensated and substituted by high sensitivity introduced by a small macro-bend radius. These sensing devices combine high sensitivity with large comparative strain and a wide range of temperatures. Polymers used in this research exhibit the potential for use in SCP waveguide-based soft robotic sensors. Measured reaction times validate the potential of these sensors in measurements of moderate or slow speed processes. These sensing devices also combine a simple manufacturing process that uses abundant and cost-effective materials with a wide array of potential applications.