Interconnection of Highly Flexible Carbon Threads Suitable for Wearable Strain Monitoring using Ultrasonic Plastic Welding

The paper deals with the contacting of highly flexible carbon threads spun by polyamide (PAD) embedded in an elastic fabric suitable for strain monitoring and testing of interconnection reliability. These carbon threads are suitable as strain sensors due to their high flexibility, their electrical resistance is dependent on stretching and it is possible to integrate them into textiles and thus create wearable textile strain sensors. Interconnection of the carbon threads to the textile or flexible substrates is important for smart textile applications. The initial impulse for this study was a creation of a user-friendly interconnection of a conventional electronic with an arm sleeve with integrated carbon threads for strain monitoring. Carbon threads were connected to conductive textile ribbons by ultrasonic plastic welding. The conductive ribbon can be used as a busbar for interconnecting the textile sensor (made of carbon threads) and the conventional electronics module (e.g. wearable evaluation unit, Bluetooth, or Internet of things module). The contacts made by ultrasonic welding were further stressed using a cyclic stretch test, the reliability of this interconnection and the rate of dependence of electrical resistance on stretching were verified.