Design, Development and Characterization of Textile Stitch-Based Piezoresistive Sensors for Wearable Monitoring

Conductive textiles have a range of applications including sports, military, automobiles and healthcare. In this study, textile-based piezoresistive sensors were designed and developed using flexible conductive threads stitched on fabric. The sensor is a multi-layer structure, including fabric, a flexible conductive sheet and a semi-rigid material. This work aimed to create new knowledge in the field of e-textiles using stitching as a new scalable fabrication technique to develop wearable piezoresistive sensors. Unlike other methods, stitching has the advantage to create free-form sensor designs. The sensors were developed using different thread lengths and stitch designs to study their impact on sensitivity, working range and response time. Replicability was assured by developing and testing several sensors with the same physical characteristics. Each sensor was characterized by gradually loading and unloading pressure from 0 kPa to 14 kPa. The sensor was also subjected to cyclic loading for 3000 cycles to evaluate its fatigue behavior. After the extensive characterization, the developed sensor was embedded inside a garment and used to measure small pressure changes exerted by human muscles. Experiments showed that the piezoresistive sensor is capable of monitoring breathing rate through ribcage and step counting through hamstring muscle. This wearable, low cost and easy to develop sensor was then machine washed for ten cycles to check its performance after washing. The characteristics of high sensitivity, repeatability, excellent response time and flexibility provide a high possibility for the developed sensor to fit on various wearable applications.