Elektricky vodivé pletené struktury se zvýšeným stíněním elektromagnetického rušení

Sundaramoorthy Palanisamy, M.Tech.

Doctoral thesis

Knitted Conductive Fabrics With Enhanced Electromagnetic Interference Shielding

Abstract:

The work deals with the development of electrically conductive knitted fabrics and their deformation characteristics. The effect of deformation on changes in electrical characteristics is measured by the high-frequency electromagnetic radiation (EM) shielding method. EM radiation of these frequencies penetrates electrically non-conductive materials and is reflected or absorbed by electrically conductive materials. This makes it possible to monitor the change in electrical resistance of textiles, which characterizes the deformation of the sample in tension. This work is divided into two basic parts: a part of the analysis of electrically conductive yarn and a part of the production and analysis of electrically conductive knitted fabrics. In the yarn analysis part, a conductive commercially available silver-plated polyamide yarn (Statex Inc., Bremen) with a fineness of 60 tex containing 36 filaments with a specific electrical resistance of 68?14 /m and a tensile strength of 47 cN/tex was used. To simulate the electrical resistance of the yarn related with its length and to simulate the effect of contact resistance, three different yarn configurations (single yarn (SY), single loop yarn (SLY) and multiloop yarn (MLY)) were used. Electrical resistance was tested for all yarn arrangements. The tensile strength of the yarn arrangements was analyzed by tensile stress at a strain rate of 50 mm/min. Multiloop yarn has been found to have higher strength than other forms of yarn. Changes in electrical resistance during tensile stress were evaluated using Arduino resistance circuit probes that were connected to the jaws of the tensile strength tester and real-time values were recorded using a MATLAB programming language program. It was confirmed that the electrical resistance decreases as the number of loops increases. In the subsequent part of the work, two patterns of knitwear were produced on a flat knitting machine, a plain "single jersey" and a 1x1 ribbed "double jersey". Three different densities were produced in each design: low, medium and high. The effectiveness of the electromagnetic shielding (SE) of knitted fabrics was tested using a frequency range of 30 MHz to 1.5 GHz according to the ASTM D4935-18 standard. It was found that the higher the sample density, the higher the SE. The double jersey had a higher SE than the single jersey and the difference was around 15 dB at 1.5 GHz frequency. The thickness of the knitted fabric and the porosity have decreased due to the increase in stitch density. A special device with four independent jaws was used for tensile deformation of knitted samples in one direction (transverse and longitudinal) and in two directions (biaxial). The knitted fabrics were stretched up to 25% strain and electromagnetic shielding, electrical resistance and porosity were measured. "Single Jersey" shielding efficiency has an increasing trend in all stretching directions. The effectiveness of the double Jersey shield has an increasing trend in vertical stretching, but horizontal and biaxial deformation initially reduces the shielding effectiveness. The porosity and electrical resistance results against stretching of the knitted fabric in all directions were also analyzed. The reason for changes in fabric behavior was analyzed using data from the electromechanical survey of simple yarn formations. A stochastic model based on multiple regression analysis and using partial regression graphs was proposed to predict the effectiveness of electromagnetic shielding of knitted fabrics based on knowledge of their electrical conductance/resistance and porosity.

Abstract:

The work deals with the development of electrically conductive knitted fabrics and their deformation characteristics. The effect of deformation on changes in electrical characteristics is measured by the high-frequency electromagnetic radiation (EM) shielding method. EM radiation of these frequencies penetrates electrically non-conductive materials and is reflected or absorbed by electrically conductive materials. This makes it possible to monitor the change in electrical resistance of textiles, which characterizes the deformation of the sample in tension. This work is divided into two basic parts: a part of the analysis of electrically conductive yarn and a part of the production and analysis of electrically conductive knitted fabrics. In the yarn analysis part, a conductive commercially available silver-plated polyamide yarn (Statex Inc., Bremen) with a fineness of 60 tex containing 36 filaments with a specific electrical resistance of 68?14 /m and a tensile strength of 47 cN/tex was used. To simulate the electrical resistance of the yarn related with its length and to simulate the effect of contact resistance, three different yarn configurations (single yarn (SY), single loop yarn (SLY) and multiloop yarn (MLY)) were used. Electrical resistance was tested for all yarn arrangements. The tensile strength of the yarn arrangements was analyzed by tensile stress at a strain rate of 50 mm/min. Multiloop yarn has been found to have higher strength than other forms of yarn. Changes in electrical resistance during tensile stress were evaluated using Arduino resistance circuit probes that were connected to the jaws of the tensile strength tester and real-time values were recorded using a MATLAB programming language program. It was confirmed that the electrical resistance decreases as the number of loops increases. In the subsequent part of the work, two patterns of knitwear were produced on a flat knitting machine, a plain "single jersey" and a 1x1 ribbed "double jersey". Three different densities were produced in each design: low, medium and high. The effectiveness of the electromagnetic shielding (SE) of knitted fabrics was tested using a frequency range of 30 MHz to 1.5 GHz according to the ASTM D4935-18 standard. It was found that the higher the sample density, the higher the SE. The double jersey had a higher SE than the single jersey and the difference was around 15 dB at 1.5 GHz frequency. The thickness of the knitted fabric and the porosity have decreased due to the increase in stitch density. A special device with four independent jaws was used for tensile deformation of knitted samples in one direction (transverse and longitudinal) and in two directions (biaxial). The knitted fabrics were stretched up to 25% strain and electromagnetic shielding, electrical resistance and porosity were measured. "Single Jersey" shielding efficiency has an increasing trend in all stretching directions. The effectiveness of the double Jersey shield has an increasing trend in vertical stretching, but horizontal and biaxial deformation initially reduces the shielding effectiveness. The porosity and electrical resistance results against stretching of the knitted fabric in all directions were also analyzed. The reason for changes in fabric behavior was analyzed using data from the electromechanical survey of simple yarn formations. A stochastic model based on multiple regression analysis and using partial regression graphs was proposed to predict the effectiveness of electromagnetic shielding of knitted fabrics based on knowledge of their electrical conductance/resistance and porosity.

Keywords

Bezdrátový snímač deformace, stříbrem povrstvená polyamidová příze, pevnost v tahu, příze s jednou smyčkou, příze s více smyčkami, hladká pletenina, 1x1 žebrová pletenina, ploché pletací stroje, elektromagnetická stínící účinnost, porozita pleteniny, elektrický odpor, and dvouosé tahové namáhání.

Language used: English

Date on which the thesis was submitted / produced: 7. 3. 2023

Thesis defence

• Supervisor: Ing. Veronika Tunáková, Ph.D.

Technical University of Liberec

Faculty of Textile Engineering

Doctoral programme / field:
Textile Engineering / Textile Technics and Materials Engineering