Ilda Kazani

Stability and Efficiency of Screen-Printed Wearable and Washable Antennas

Wearable antennas, integrated into garments, are prone to get dirty. Therefore, for the first time in literature, washable antennas are proposed by covering textile antennas by a breathable thermoplastic polyurethane coating, protecting the antennas against water absorption and corrosion. The washability of coated wearable antennas produced by screen printing conductive ink onto a textile substrate is compared to coated wearable antennas based on an electrotextile, analyzing performance in terms of their reflection coefficient and radiation efficiency before and after washing. The combination of screen printing and coating provides stable antenna performance with sufficiently high radiation efficiency after several washing cycles.

Van Der Pauw method for measuring resistivities of anisotropic layers printed on textile substrates

Electrically conducting layers have been screen printed on woven textile substrates. Using the Van Der Pauw method for electrical resistivity measurements in thin layers, it was observed that the screen-printed layers showed anisotropic behavior. In order to be able to interpret the measurements correctly, a mathematical analysis of the measuring method has been established. From the experimental results one is then able to find the relation between the electrical resistivity in the warp versus the weft direction.

Comparative study on the mechanical properties of elastic, electro-conductive hybrid yarns and their input materials

The development of electro-conductive yarns and the characterization of their conductive properties has gained importance over the past years. However, for their later application, not only the electro-conductive properties of the yarns are important, but also their mechanical characteristics. Hence, this paper presents an analysis of the mechanical behaviour of elastic, electro-conductive hybrid yarns. The yarns comprised an elastic core yarn and electro-conductive winding yarns. Studying the mechanical properties of the hybrid yarns, as well as their corresponding input yarns, it could be proven that the overall good strength and elongation behaviour of the hybrid yarns was depended on the properties of the input yarns, as well as on the yarns’ production parameters.

Performance study of screen-printed textile antennas after repeated washing

Abstract The stability of wearable textile antennas after 20 reference washing cycles was evaluated by measuring the reflection coefficient of different antenna prototypes. The prototypes’ conductive parts were screen-printed on several textile substrates using two different silver-based conductive inks. The necessity of coating the antennas with a thermoplastic polyurethane (TPU) coating was investigated by comparing coated with uncoated antennas. It is shown that covering the antennas with the TPU layer not only protects the screen-printed conductive area but also prevents delamination of the multilayered textile fabric substrates, making the antennas washable for up to 20 cycles. Furthermore, it is proven that coating is not necessary for maintaining antenna operation and this up to 20 washing cycles. However, connector detachment caused by friction during the washing process was the main problem of antenna performance degradation. Hence, other flexible, durable methods should be developed for establishing a stable electrical connection.

Dry cleaning of electroconductive layers screen printed on flexible substrates

Smart textiles and wearable textile systems are up to now a growing research field, with a view to applications such as monitoring vital signs or environmental parameters through garments. These developments require new materials such as electroconductive textiles. As a result, research into screen printing of conductive silver inks onto textiles has emerged. In this study, screen printing is used to print four kinds of silver-based conductive inks on a flexible foam and a nonwoven substrate. The screen printing method is chosen because it is a low cost and user friendly technique to obtain flexible and lightweight conductive fabrics. For the evaluation of the electrical properties the square resistance of the printed fabrics is measured after repeated dry cleaning cycles. The printed textiles studied here show good electrical properties after printing (< 0.05 Ω/□). However, after 60 dry cleaning cycles, the conductivity decreased considerably. Consequently, in order to improve washability, a protective polyurethane layer was put on top of the printed samples. In this case, the resistivity remained below 2.3 Ω/□ after 60 dry cleaning cycles.

Washable Screen Printed Textile Antennas

The wireless communication systems are applied in different applications such as computers, mobile phones, satellites and antennas for off-body communication. A lot of efforts were made to have the antennas in a smaller size, flat and with better performance. In the last decade the rigid antennas are replaced with textile in order to be flexible and to be integrated into garments in order to have wearable textile systems. The textile antennas can find use in medical, military and first responders monitoring. The conductivity of the antennas can be achieved by using coated textile materials which are available in the market, conductive threads for embroidery or conductive inks. When using the conductive coated textile it is necessary to cut the patch in the desired pattern but using a simple cutting tool sometimes is not very precise and accurate. Thus in our study we decide to screen print with silver conductive inks on Polyester and Cotton/Polyester substrates. The screen printed antennas are than washed in order to conform that antennas for off-body communication integrated in garments can be easily washed five times.

Electrical circuit model of elastic and conductive yarns produced by hollow spindle spinning

Abstract The implementation of electronic textiles which are capable of being applied as electrodes, sensors or heating elements is crucial in several fields of application, ranging from automotive to sports, from rehabilitation to art and design. However, current electronic textiles often suffer from poor mechanical properties, low drape and unstable electroconductive characteristics. One possibility to overcome these shortcomings is to introduce the electroconductive properties at a fibre or yarn level by combining traditional fibres and yarns with metal wires or metalised yarns. In this paper, we describe the production of multicomponent yarns which combine electroconductive properties with elasticity, drape and mechanical strength. We discuss the electroconductive properties of the yarns produced with hollow spinning technology. An electrical model based on Kirchhoff’s law was designed and validated with the abovementioned measurements.

About the collinear four-point probe technique´s inability to measure the resistivity of anisotropic electroconductive fabrics:

The sheet resistance of electrically conducting screen-printed surfaces can be measured with different techniques such as Van Der Pauw or four-point probe. As electroconductive textile materials show anisotropic behaviour we investigate the possibility of using the four-point probe method to measure the anisotropic properties of the electric conductivity. It was proved both theoretically and experimentally that no anisotropy can be detected with the collinear contacts of the four-point probe.

Investigation of the influence of heat transfer on screen printed textile conductor

Two different textile substrates were screen printed with silver-based inks in order to be electrically conductive. In every textile four conductors were printed with different widths in order to investigate the influence of heat transfer on each conductor. This was done, by using the thermo graphic camera and through the evaluation of each conductors profile. It was found that the conductors printed on the white textile had higher values of heat transfer compared to the other conductors printed on the dark textiles.

Influence of dry cleaning on the electrical resistance of screen printed conductors on textiles

Abstract Electrically conducting inks were screen printed on various textile substrates. The samples were dry cleaned with the usual chemicals in order to investigate the influence of the mechanical treatment on the electrical conductivity. It was found that dry cleaning has a tremendous influence on this electrical conductivity. For several samples, it is observed that the electrical resistance increases with the square of the number of dry cleaning cycles. In order to explain this observation a theoretical model and a numerical simulation have been carried out, by assuming that dry cleaning cycles introduce a crack in the conducting layer. The theoretical analysis and the numerical analysis both confirmed the experimental observations.