Development of smart e-textile wearables by advanced technocal embroidery

Applications of wearable electronic textiles (e-textiles) in smart clothing have attracted considerable attention on account of their immense potential to monitor vital signals, such as electrocardiogram (ECG) and respiratory rate. Embroidery is one of the most preferred ways to create e-textiles because the technique allows for flexible patterns, dimensional accuracy, mass production, and cost-effective production. However, the parameter design of embroidery with conductive yarns not only affects the aesthetics of the product but also results in incompetent electrical performance, such as short out of interconnects because the jammed stitches. This thesis proposes embroidery techniques for the design and construction of stretchable interconnects, electrodes and strain sensors used for ECG and respiration signals monitoring. The thesis focuses on several key aspects for design and fabrication of smart e-textile wearables. 1) After comparing needle thread loop formation performance of various commercial conductive yarns, the analysis of conductive tracks with multi-direction lock-stitch embroidery indicated embroidery direction and stitch length significantly affect size shrinkage, stitch length and embroidery speed significantly affect resistance of conductive tracks. Stretchable interconnects are designed with zigzag and horseshoe shaped structures, which fabricated by lock-stich and TFP embroidery techniques, respectively. The horseshoe-shaped interconnect proposed in this study (R =5mm and θ=45°) shows significant elongation over 130% and maintain stable resistance during stretching. 2) The electrodes are embroidered by silver-coated conductive yarns with different embroidery patterns, filling density and sizes. The skin contact impedance at 1 Hz, and signal quality of ECG monitoring compared with Ag/AgCl electrodes are evaluated. The EP2 pattern electrode shows the lowest surface resistance under 2.5 kPa wearing pressure since the conductive threads overlapped in filling stitch structures. 3) The embroidered strain sensors combining conductive yarns and elastane threads are designed in conjunction with lock-stitch and TFP embroidery techniques. The electromechanical performance of optimal sensor shows 32.4 GF at 40% elongation, less electro-mechanical hysteresis and stable stretching-releasing performance within 1000 cycles. The sensor has sufficient capability to clearly detect normal breathing and deeply slow breathing patterns. 4) Based on the design concept of embroidered electrodes and strain sensors, a wearable smart band prototype for physiological signal monitoring is developed. Wearing pressure at 1.5 kPa can ensure the quality of ECG and respiratory signals in body static and dynamic measurement conditions. Additionally, the walking tests demonstrate that the smart band under 1.5 kPa wearing pressure was able to measure representative respiratory and ECG waveform features, body temperature and humidity at various levels of treadmill speed. The outcome from this research provides guidelines for development and fabrication of tailored smart e-textiles wearables for health care with highly efficient embroidery techniques.