Embroidery Circuits for Textile Touch Sensors and Wearable Interfaces

The main objective of incorporating e-textile components into garments is to augment the functionality and interactivity of clothing. However, integrating electronic textiles (e-textiles) into objects or garments involves various challenges, especially regarding the creation of new usage concepts, applications, and defining specifications for embedded circuits. Herein, we investigate the implementation of embroidered capacitive sensors for use in wearable human-machine interfaces by utilizing various combinations of conductive yarns and embroidery patterns to enhance circuit conductivity. Embroidered conductive tracks underwent fifteen consecutive standard washing cycles and were evaluated for resistance and simulated touch repeatability using custom-built setups. Tracks made from silver-coated yarns showed a greater decrease in conductivity compared to those made from stainless steel, attributed to partial removal of silver from their surfaces as indicated by SEM and EDS analysis. Under optimal conditions, the zigzag pattern with increased embroidery density on both the upper and lower surfaces of the fabric, utilizing nylon@Ag yarn, exhibited the lowest resistance value (R $= 0.38~\Omega $ /cm), thereby demonstrating the highest suitability as an electrical signal conducting element. The developed approach enables tailoring electrical properties to accommodate cost variations of conductive yarns across different fabric sections, and an estimated cost for a prototype implementation per distinct yarn combinations is also presented. Two prototypes with capacitive touchpads, buttons, Wi-Fi, and Bluetooth were developed as human-machine interfaces. They demonstrated a 200 ms response time and 2.3 pF capacitance change upon touch, showing promise for healthcare and assistive technology applications.