Textile-based weft knit strain sensor: Experimental investigation of the effect of stretching on electrical conductivity and electromagnetic shielding

Recently, the research and development of textile-based sensors have attracted considerable attention. Changes in electrical conductivity (EC) and electromagnetic (EM) shielding effectiveness (SE) during external stimuli are the most frequently studied output. In this study, the EC and EM SE of an electro-conductive 1 x 1 rib knitted fabric made of metal-coated yarn were investigated during uniaxial and biaxial stretching. According to a theoretical survey, 2 main mechanisms are expected to influence the EC of the fabric under mechanical stress: the contact resistance at the junction of two yarns at low levels of applied force and the electrical resistance (ER) of yarn at high stress. Therefore, the electromechanical properties of single, single-loop, and multiloop yarns were also explored to explain the knitted fabric behavior during uniaxial and biaxial stretching. The SE of the knitted fabric varied from 63 to 47 dB based on the type and level of stretching. Using tests with yarns and crocheted chains, we confirmed that the effect of contact points and resistance on the entire ER textile unit prevails at low deformations. Further, the SE increased almost linearly with deformation during wale-wise stretching. The SE results correlate well with the ER values, which reflect the contact and longitudinal resistances of the knitted fabric. The higher the ER, the lower the SE. Notably, the porosity, which changes during stretching, needs to be considered in estimating SE. It was experimentally confirmed that the knit electro-conducite fabric could be used as a wireless strain sensors.