Electrical parameters of conductive structures for smart textiles

Abstract

The growing need for supportive and performance-enhancing garments has led to the rapid induction of smart textiles in the military sector. Smart textiles aim to reduce the weight of battery packs, electronic gadgets, connecting cables, etc. If a soldier wearing a ‘Smart Shirt’ gets injured during a war, the information on the wound and the soldier’s condition would be immediately transmitted to a medical triage unit near the battlefield [1]. The increasing adoption of smart textiles for military applications and operations is saving lives and changing the ways that militaries worldwide operate. Military clothing plays an essential role in protecting soldiers from warfare and combat elements. Textile structures were designed and made by weaving and knitting technologies using conductive yarns (Shieldex, Statex, Filix, Agis, etc.) in order to integrate into the block diagram a primary haemostasis device intended for combatants on the battlefields. The surface resistance of the fabrics with metallic yarns was measured by means of a device, consisting of two parallel linear electrodes, placed at a distance of 30 mm.The device measured resistance in Ohm for a known surface of the tested material (sq = 6,45 cm2). As such, the results were expressed in Ohm / sq. We have the following physical relations for the electrical resistance RS (1) and the electrical resistivity of a certain material ρS(2) [2]:R_S= U/I_S (1)ρ_S= R_S (D∙g)/L (2)With the following notations: U – voltage applied, IS – measured electric current intensity, L – length of the fabric, placed between the two electrodes, D – width of the fabric and g thickness of the fabric.ρ= U/I∙(D∙g)/L=R∙ (D∙g)/L [Ω.m]The electrical conductivity of the fabrics was computed with relation (3).σ= 1/ρ (3)The results of the computations show that the textile structure with AGIS LIB 40 has the highest conductivity of 32808.16 S/m, followed by the structure with AGIS 100 D yarn, of 11233.33 S/m, Agis 200D – 6916 S/m and Statex with a conductivity of 5626 S/m, respectively Shieldex with 5390.14 S/m. The Lloyd material testing equipment coupled with a data acquisition unit-DAQ (white box) was used for the simultaneous variation of elasticity and electrical conductivity of textile structures. The lowest value of the electrical resistance was obtained by the knit structure made only of conductive (yarn 1). In this case, the min./max value at the strain 5% was: 2,72 Ω/m/12,18 Ω/m and at the strain 40%: 0,56 Ω/m/37,17 Ω/m. These values are in the limit of linear electrical resistance of the yarn (76 Ω/m) [3]. The prediction of the parameter values was estimated by determining the linear regression line with the regression coefficients, R2, and the calculated correlation coefficient. The cases resistivity=f(time), resistivity=f(load), resistivity=f(strain) is represented. The only case where it seems that there are no disturbing values (noise) is the one with 30% elongation, there is also a fairly good correlation between the values.