Suitability of knitted fabrics as elongation sensors subject to structure, stitch dimension and elongation direction

The area of smart textiles has recently attracted more and more attention. One of the challenges in this domain is the development of textile sensors, such as textile electrodes, pressure sensors, elongation sensors, etc., mostly containing conductive yarn and/or conductive coating. One possibility to build a textile elongation sensor which can, for example, be utilized as a breathing sensor in a smart shirt, is using knitted fabrics created from conductive yarns, which often show a strong dependence of the electric resistance on the elongation. Due to the typical wearing out of knitted fabrics, however, the time-dependent behavior of a stretched fabric must also be taken into account. The article thus shows the results of elongation-dependent and time-dependent resistance measurements on knitted fabrics, produced from different yarns in various structures and stitch dimensions, elongated in different orientations with respect to the course direction. The results of our study show that full cardigan with medium stitch size is better suited for use as an elongation sensor than double face fabrics or other stitch sizes. These findings are not influenced by the stainless steel fraction in the conduction yarn, while mixing this yarn with a non-conductive one causes undesired signal deviations.