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The possibility of printing conductive ink on textiles is progressively researched due to its potential benefits in manufacturing functional wearable electronics and improving wearing comfort. However, few studies have reported the effect of conductive ink formulation on electrodes directly screen-printed on flexible substrates, especially printing UV curable conductive ink on common textiles. In this work, a novel UV curable nano-silver ink with short-time curing and low temperature features was developed to manufacture the fully flexible and washable textile-based electrodes by screen printing. The aim of this study was to determine the influence of ink formulation on UV-curing speed, degree of conversion, morphology and electrical properties of printed electrodes. Besides, the application demonstration was highlighted. The curing speed and adhesion of ink was found depending dominantly on the type of prepolymer and the functionality of monomer, and the type of photoinitiator had a decisive effect on the curing speed, degree of double bond conversion and morphology of printed patterns. The nano-silver content is key to guarantee the suitable screen-printability of conductive ink and therefore the uniformity and high conductivity of textile-based electrodes. Optimally, an ink formulation with 60 wt% nano-silver meets the potential application requirements. The electrode with 1.0 mm width showed significantly high electrical conductivity of 2.47 × 106 S/m, outstanding mechanical durability and satisfactory washability. The high-performance of electrodes screen-printed on different fabrics proved the feasibility and utility of UV curable nano-silver ink. In addition, the application potential of the conductive ink in fabricating electronic textiles (e-textiles) was confirmed by using the textile-based electrodes as the cathodes of silver-zinc batteries. We anticipate the developed UV curable conductive ink for screen-printing on textiles can provide a novel design opportunity for flexible and wearable e-textile applications.

The thickness and dielectric properties (dielectric constant and loss tangent) of fabric substrate play a key role in the design and properties of wearable antennas. Related research shows that a thicker substrate with a low dielectric constant and high loss tangent can enhance the bandwidth of antennas. Here, sewing multiple fabrics together was a good way to increase the thickness while maintaining flexibility, but it is hard to control the dielectric properties because of the lack of the relationship between the dielectric properties and that of the components. Although previous works have established the equivalent capacitance model of sewed multilayer fabric, they cannot obtain its dielectric properties completely. In this work, based on the circuit model proposed by Chin and Lee, the equivalent capacitance and resistance models of sewed multilayer fabric were established to predict its loss tangent. The sewed multilayer fabrics were fabricated and measured by split post dielectric resonator at 1.11 GHz to validate the model. From the comparison of the predicted and measured loss tangents of sewed multilayer fabrics, it was found that the predicted loss tangents agreed well with the experimental results. It is believed that the proposed model is beneficial to the rapid and rational configuration of the components for multilayer fabric according to thickness and dielectric properties of the components, and will provide a theoretical basis for the design of multilayer flexible electronic substrate.

To reveal the engineering relationship among the electrical properties of embroidered conductive lines, the electrical properties and arrangements of conductive yarns, it is necessary to establish their equivalent resistance model. Embroidered conductive lines in textiles are usually fabricated by single-layer (conductive and nonconductive yarn used as upper and lower yarn) or double-layer embroidery technology (conductive yarns used as upper and lower yarn). Several researchers have proposed the simple resistance model for single-layer embroidered conductive line based on geometric structure of single conductive yarn in fabric. However, the double-layer conductive line has the contact resistance periodically interlaced by the upper and lower conductive yarns, and it made its equivalent circuit different from that of single-layer conductive line. In this work, a geometric model was built to describe the trace of conductive yarn in fabric, and in combination with Wheatstone Bridge theory, was applied to establish the equivalent resistance models of double-layer conductive lines with a certain width, consisted of various courses. First, the equivalent resistance model of double-layer conductive lines consisting of single course was proposed to calculate the contact resistance. Then, to obtain the electrical resistance of double-layer conductive lines with a certain width, the equivalent resistance model was extended from single course to multiple courses ([Formula: see text]). Finally, to validate the proposed equivalent resistance model, double-layer conductive lines with different embroidery parameters (stitch length and stitch spacing) on nonwoven fabric were fabricated and evaluated. The experimental results revealed that the proposed model accurately predicted the resistances of double-layer conductive lines.

The conductivity of screen printing films at microwave frequency is one of the most important properties of conductive ink when applied in printed electronics. However, the existing methods of conductivity characterization at microwave frequency focus on homogeneous metal films or semiconductors, which are not suitable for conductive composite materials with poor thickness uniformity, like screen printing films. In this research, by applying a classic stripline ring resonator, a rigorous electromagnetic model was set up, and the conductivity of the screen printing film was able to be deduced by comparison between the measurement and simulation results. As a result, the equivalent conductivity of the film is 2 × 106 S/m at 1–3 GHz, which is a little higher than its average direct current conductivity of 1.82 × 106 S/m. This method has been proved to be feasible in measuring the conductivity of screen printing films at microwave frequency. Furthermore, it has great potential in the characterization of other printed conductive composite materials on rough surfaces, like textiles.

Measuring the dielectric properties of the fabric is much important when it is used as a substrate material for flexible electronic devices. However, the classical resonant cavity is not accurate f...

Nowadays, fabric-based antennas, resonators, and sensors are attracting significant attention due to their excellent comfortability and flexibility compared with the rigid commercial printed circuit boards (PCBs). Both the dielectric constant ( ε r ) and dielectric loss tangent ( tan δ ) of substrate materials have a great influence on their frequency response characteristics. However, the effect of dielectric loss is usually ignored, since traditional radio frequency (RF) devices are fabricated on commercial PCBs with much lower tan δ . As the differences of dielectric loss vary widely with different fabric materials, it is of great significance to explore the influence of dielectric loss on the frequency response characteristics. Therefore, this paper systematically studied the influence of substrate properties on RF performance of microstrip multiresonator. Firstly, the models of microstrip multiresonators with different ε r and tan δ were created by HFSS simulation. By parametrically sweeping, it showed that the tan δ was the key factor for the notch depth. And the larger the tan δ , the bigger the electromagnetic loss of the material, resulting in a smaller notch depth of the resonator. Then, three representative materials with different orders of magnitude of tan δ (AD-450: 0.002, FR-4: 0.015, and denim fabric: 0.114) were chosen to verify the simulation. The results showed that the common fabric-based resonator has poor RF characteristics for their big dielectric loss compared with those of commercial PCBs. This study is of great significance for designing wearable electronic devices with flexible substrate materials with large dielectric loss.

One-step printing of electrically conductive inks on textiles is one of the simplest and most prospective methods to manufacture functional wearable electronics. However, the high surface roughness and porous structure as well as poor temperature endurance of most textiles have become the major challenges for the realization of printed electronic textiles (E-textiles). To solve these issues, the UV curable conductive ink with fast curing and low temperature characteristics was formulated to fabricate the flexible fabric-based conductive patterns using screen printing method. The specific focus was spent on investigating the effect of ink composition on curing speed, film forming ability, morphological characteristics and electrical properties of conductive patterns directly printed on fabric substrates. Firstly, we determined the necessity of defoamer for the formation of uniform and continuous printed textile-based patterns, and optimized the film forming ability of UV-curing ink by exploring the defoamer performance. Then, the ink curing speed was found heavily depending on the different types and contents of photoinitiators. Finally, the nano-silver loading showed critical influence to the screen-printability and the electrical properties of printed patterns. An ink formulation with 60 wt% nano-silver, 4 wt% photoinitiator (1173), and 0.2 wt% defoamer (BYK-555) showed satisfactory screen printability, and the conductive patterns with 1.0 mm width exhibited a remarkably low resistivity of 4.04 × 10−5 Ω cm. Moreover, the high performance of the conductive pattern screen-printed on four different fabrics by the formulated UV curable conductive ink further demonstrated its application potential. The results showed that uniformity and electrical properties of printed patterns were directly related to the weaving method, texture characteristic, and roughness of the textiles. We believe these results will provide basic guidance for the formulation design of conductive ink and facilitate the utility of textiles-based wearable electronics.