Effects of the textile-sensor interface on stitched strain sensor performance

The influence of the textile substrate on the performance of a textile-based strain sensor has not been well understood or characterized in many wearable sensor evaluations. The underlying textile has its own anisotropic mechanical behaviors due to its woven or knit fabrication process, and introduces non-trivial structural influences on integrated wearable strain sensors. This study considers stitched strain sensors of two stitch geometries, fabricated on two different knit fabrics, with the sensor stitched in different orientations with respect to the knit structure. The resulting mechanical and electrical performance is characterized under cyclic extension, as the angle of extension (relative to the fabric) is also incrementally changed. The results illustrate a shift from linear to non-linear mechanical behavior as fabric stiffness increases, and variations in behavior between stitch geometries. Results show that force direction and sensor placement both introduce variability in calculated elastic modulus, which affect sensor modeling (e.g. predicting applied force from sensor response). A novel stitch geometry (the chainstitch sensor) is characterized as having a higher gauge force and lower transverse sensitivity factor than the coverstitch sensor. This work offers insight into the textile-sensor interface and design implications for development of textile-based sensors.