Samenvatting

The flexible strain sensors have been a topic of interest for multiple studies in the past years. These sensors are soft, bendable mechanisms, which can be applied to substrates through printing or other means. They can indicate longitudinal strain through resistance change, which means that they can be used for a variety of applications in the healthcare industry, the performance wear industry, or for electronic skins and soft robotics. Nevertheless, the current challenges, facing the fabrication of such devices are many. They exhibit large hysteresis, noise, non-linearity, lack of cyclic durability, etc. The majority of these can be overcome with complex algorithms, but this comes at a cost, and the challenge to produce a strain sensor with excellent performance remains.
This research explores the state-of-the-art of flexible strain sensors and delves deeper into the topic by processing silicone/carbon-based sensors, meant to be integrated in motion tracking wearables. Silicone elastomers have excellent stretchability, outstanding mechanical, chemical and thermal stability, and good synergism with carbon. On the other hand, carbon black has high intrinsic conductivity, and does not require complex processing. The developed conductive silicone composite was coated on stretchable textile knits, suitable for performance activities. The sensors were characterized through scanning electron microscope (SEM), and a tensile tester with a voltage supply unit.
Arguably the best electromechanical performances was exhibited by the 1x1 rib knitted, polyester/elastane blend. Its gauge factor (GF) over strain was 6.7 at 5% strain, 4.8 at 10% strain, and 3.9 at 20% strain. Its curve could be approximated with a polynomial of third order, where R 2 = 0.999. Its hysteresis values were 0.28 for the resistance, and 0.42 for the stress at 20% strain. If tested for its durability and characterized further with regards to its drift, the composite could be screen printed on a wearable, on a place where it could measure the movement of the joint flexures, encapsulated, and be worn in a real life scenario.
Garments embedded with electronics are very environmentally costly since they cannot be upcycled. Nevertheless, to offset some of its impact, the produced motion tracking wearable could be made from standardized patterns, which would allow maintenance through detachment and reattachment of specific components to prolong its life. Afterwards, the garment can be recycled mechanically and used for filling or insulation.