The effect of tensile deformation of knitted fabrics on their electromagnetic shielding ability, electrical resistance, and porosity

Nowadays, electrically conductive textile materials are widely used also for sensing applications in addition to being used as antistatic, electromagnetic shielding, for creating smart textiles, etc. The main aim of this paper is to study the effect of tensile deformation applied on knitted fabrics on their electromagnetic shielding ability, electrical resistance, and porosity to gain knowledge for the construction of textile-based wireless strain sensors. For the experiment, silver-coated yarn was chosen to produce knitted fabrics with two different patterns and three levels of stitch densities. The uniaxial and biaxial deformation was applied to samples and at the same time, the change of electromagnetic shielding ability, electric resistance, and porosity of the sample set was evaluated. It can be summarized, that the vertical stretch has the highest positive effect on the electromagnetic shielding ability and the maximum shielding sensitivity is 12 % compared to other deformation types. In general, the electrical resistance decreases during increased stretch due to the increasing number of contacts between electrically conductive yarns, which causes a decrease in the contact resistance and also a decrease in total electrical resistance. The highest positive effect on the porosity of samples represents biaxial deformation. The finding that the overall shielding efficiency is positively influenced by the electrical conductivity of the sample and at the same time negatively influenced by the increasing porosity during tensile deformation was the motivation to construct a simple regression model for the prediction of the electromagnetic shielding ability of the sample during its extension.