Electronic Textile Applications Research Articles

Electrical and electrothermal characterization of silver-coated Vectran and Amberstrand yarns for wearable heating

The development and manufacturing of conductive fibers, yarns, and fabrics is increasing exponentially due to their multiple applications in wearable electronic textiles in sensors, actuators, data processing, communication, and energy storage. This paper investigated the electrical and electrothermal properties of Liberator 40 yarns and Amberstrand 166 conductive yarns for application in wearable heating textiles. The aim of the study was to find a flexible material for protective wearable resistive heating cloths in cold environments. The analytical results demonstrate that the Liberator 40 conductive yarn gave better heating performance than the Amberstrand 166 conductive yarn due to its electrothermal characteristics. In addition, Liberator 40 conductive yarn had higher long-term durability, washing resistance, and thermal stability than Amberstrand 166 conductive yarn. The average surface temperature of both the Liberator 40 and Amberstrand 166-based wearable heating fabrics was 40°C and 34.5°C at a 9 V DC power supply, respectively. Therefore, both the conductive yarns are suitable to be applied as resistive heating elements for localized wearable heating textiles.

Stretchable Fibers with Highly Conductive Surfaces and Robust Electromechanical Performances for Electronic Textiles.

One-dimensional conductive fibers that can simultaneously accommodate multiple deformations are crucial materials to enable next-generation electronic textile technologies for applications in the fields of healthcare, energy harvesting, human-machine interactions, etc. Stretchable conductive fibers (SCFs) with high conductivity on their external structure are important for their direct integration with other electronic components. However, the dilemma to achieve high conductivity and concurrently large stretchability is still quite challenging to resolve among conductive fibers with a conductive surface. Here, a three-layer coaxial conductive fiber, which can provide robust electrical performance under various deformations, is reported. A dual conducting structure with a semisolid metallic layer and a stretchable composite layer was designed in the fibers, providing exceptional conductivity and mechanical stability under mechanical strains. The conductive fiber achieved an initial conductivity of 2291.83 S cm-1 on the entire fiber and could be stretched up to 600% strains. With the excellent electromechanical properties of the SCF, we were able to demonstrate different electronic textile applications including physiological monitoring, neuromuscular electrical stimulation, and energy harvesting.

LEGO-like Assembly of Fibrous Modules for Display Textiles.

Due to their promising advantages over classical rigid devices, the development of display textiles has exciting potential for various fields, including sensor technology, healthcare, and communication. To realize display textiles, it is necessary to prepare light-emitting building blocks at the fiber level and then weave or knit them to form the desired textile structures. However, from a practical viewpoint, it is difficult to continuously weave functional fibers containing light-emitting devices using conventional textile technologies. To address this issue, we introduced fibrous modules that can be assembled like LEGO blocks to realize textile displays. A unique feature of this work is that the light-emitting pixels are generated through a simple contact between modular electrochemiluminescent (ECL) fibers. Each fiber is composed of a single metallic wire coated with a gel-type ECL electrolyte that is formed by using a simple dip-coating method in ambient air. The sticky nature of the gel electrolyte enables the construction of light-emitting pixels through the simple physical contact of two or more fiber modules without the need for external pressure or heating. The diversity of this technology offers in terms of fibrous module arrangements and assembly can provide various options for designing the geometries of light-emitting pixels. We have implemented this technique to demonstrate not only a 1 × 1 pixel but also 3 × 3 pixels with an irregular shape. These results demonstrate that the unique strategy for display devices developed in this work provides a feasible approach for various electronic and optical textile applications.

The Design and Development of Woven Textile Solar Panels.

Over the past few years, alternative power supplies to either supplement or replace batteries for electronic textile and wearable applications have been sought, with the development of wearable solar energy harvesting systems gaining significant interest. In a previous publication the authors reported a novel concept to craft a yarn capable of harvesting solar energy by embedding miniature solar cells within the fibers of a yarn (solar electronic yarns). The aim of this publication is to report the development of a large-area textile solar panel. This study first characterized the solar electronic yarns, and then analyzed the solar electronic yarns once woven into double cloth woven textiles; as part of this study, the effect of different numbers of covering warp yarns on the performance of the embedded solar cells was explored. Finally, a larger woven textile solar panel (510 mm × 270 mm) was constructed and tested under different light intensities. It was observed that a PMAX = 335.3 ± 22.4 mW of energy could be harvested on a sunny day (under 99,000 lux lighting conditions).

Stretchable and wash durable reactive silver ink coatings for electromagnetic interference shielding, Joule heating, and strain sensing textiles

In this paper, we demonstrate a highly conductive, stretchable, and wash-durable fabric for a variety of electronic textile applications such as electromagnetic interference (EMI) shielding, Joule heating, and strain sensing by utilizing a chemical etchant pretreatment that promotes covalent bonding, a reactive silver ink with conformal in situ silver reduction, and the use of a polymer coating for a protective barrier. Reactive ink coated on polyethylene terephthalate (PET) knitted textiles exhibit an average EMI shielding efficiency of 74.8 dB in the X band (frequency range of 8–12 GHz) and 76.6 dB in the Ku band (12–18 GHz). The conductive textiles show high Joule heating performance, where a temperature of 152 °C can be achieved at only 1.3 V DC applied voltage. This Joule heating performance is maintained after stretching and washing. Furthermore, the textile may be used for strain sensing and monitoring human movement. As prepared silver films do not degrade after 1000 stretching cycles at 50 % strain and maintain EMI SE higher than 70 dB after 300 min washing. The demonstrated textiles may be used for wearable electronics, personal medical devices, and next generation communications.

3D Printing of Conductive Flexible Filaments for E-Textile Applications

Electronic textiles (e-textiles) can incorporate conductive materials at all levels of integration, from fibers to yarns to fabric itself. There are many ways to connect the textile elements to electronic components with interconnect mechanisms from mechanical gripping to welding, to gluing, to printing, to embroidery, knitting, and weaving. 3D printing method offers the possibility of creating flexible and stretchable interconnects for e-textiles applications. This study explored 3D printing of flexible conductive filaments on fabric to create interconnects for hard electrical components as well as transmission lines and switches for electronic textile applications. NinjaTek Eel and Palmiga TPU based conductive filaments were printed on polyester knit fabric. Electrical characterization measurements as well as visual and haptic analysis of printed samples were conducted. The results showed that TPU based flexible conductive filaments offer possibilities of direct 3D printing onto textiles for electronic textile applications.

Solderable conductive paste for electronic textiles

Background: In recent years, electronic textiles (e-textiles) have attracted widespread attention due to their versatility, but still lack a good packaging technique. Soldering, one of the electronic packaging technologies, has been widely used to provide electronic joints with good electrical and mechanical properties. However, direct soldering on e-textiles has to overcome several problems, such as melting at high soldering temperature and non-solderability of printed conductive patterns.Methods: The thermal stability and wettability of the resin were enhanced by adjusting the formulation to provide a base polymeric adhesive material. The formulated polymeric resin was then mixed with 85 wt% metal fillers to reach good conductivity after curing. A surfactant was also added to enhance particle dispersion and lowered the paste viscosity to screen print complicated conductive patterns on textile materials.Significant findings: The printed thin film showed good solderability with a low wetting angle for solder melt. A layer of intermetallic compound (Cu6Sn5) was found between solder and solderable patterns, which provided a great adhesion strength and peel strength on fabrics. Solder joints on the printed conductive adhesive also showed great shear strength. The solderable paste was printed into a heating grid on textiles to show good electrical interconnectivity with solder joints. In summary, this study provides a general guideline for the preparation of solderable paste and can be extended for other packaging applications in electronic textiles.

Influence of Knitting and Material Parameters on the Quality and Reliability of Knitted Conductor Tracks

Many electronic textile (e-textile) applications require a stretchable basis, best achieved through knitted textiles. Ideally, conductive structures can be directly integrated during the knitting process. This study evaluates the influence of several knitting and material parameters on the resistance of knitted conductive tracks after the knitting process and after durability testing. The knitting speed proves to be of little influence, while the type of conductive thread used, as well as the knitting pattern both impact the resistance of the knitted threads and their subsequent reliability considerably. The presented research provides novel insights into the knitting process for conductive yarns and possible applications and shows that choosing suitable material and processing methods can improve the quality and robustness of knitted e-textiles.

Robust and Highly Conductive PEDOT:PSS:Ag Nanowires/Polyethyleneimine Multilayers Based on Ionic Layer-by-Layer Assembly for E-Textiles and 3D Electronics

This study shows the production of robust and highly conductive multilayers through the layer-by-layer (LBL) assembly of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS):Ag nanowires and counterionic compounds, including monomeric tris(2-aminoethyl)amine and chitosan and polyethylenimine (PEI). These materials provide a strong electrostatic interaction with PEDOT:PSS and enable a reliable interface between the layers during the LBL process. Systematic chemical and electrical analyses of the multilayers reveal that the use of PEI results in the highest electrical conductivity (2034 S cm–1 at six LBL cycles) and interfacial adhesion (8.9 mN at the tearing stress). Furthermore, the use of PEI generates a powerful interconnection for electrical circuit patterns with low contact resistance (∼5 Ω) and robust mechanical durability during the water-assisted welding process. Finally, we successfully show the use of this material in electronic textile applications and 3D electronics based on water-assisted welding and transfer printing technology to confirm its feasibility for use in device applications.

Electronic Textiles Based on Highly Conducting Poly(vinyl alcohol)/Carbon Nanotube/Silver Nanobelt Hybrid Fibers.

Highly stable conducting fibers have attracted significant attention in electronic textile (e-textile) applications. Here, we fabricate highly conducting poly(vinyl alcohol) (PVA) nanocomposite fibers with high thermal and chemical stability based on silver nanobelt (AgNB)/multiwalled carbon nanotube (MWCNT) hybrid materials as conducting fillers. At 20 vol % AgNB/MWCNT, the electrical conductivity of the fiber dramatically increased (∼533 times) from 3 up to 1600 S/cm after thermal treatment at 300 °C for 5 min. Moreover, PVA/AgNB/MWCNT fiber resists the harsh conditions of good solvents for PVA as well as high temperatures over the melting point of PVA, whereas pure PVA fiber is unstable in these environments. The significantly enhanced electrical conductivity and chemical stability can be realized through the post-thermal curing process, which is attributed to the coalescence between adjacent AgNBs and additional intensive cross-linking of PVA. These remarkable characteristics make our conducting fibers suitable for applications in e-textiles such as water leakage detectors and wearable heaters. In particular, heating behavior of e-textiles by Joule heating can accelerate the desorption of physically trapped moisture from the fiber surface, resulting in the fully reversible operation of water leakage monitoring. This smart e-textile sensor based on highly stable and conductive composite fibers will pave the way for diverse e-textile applications.

Smart-Fabric-Based Supercapacitor with Long-Term Durability and Waterproof Properties toward Wearable Applications.

The rapid development of wearable electronics and smart textiles has dramatically motivated the generation of flexible textile-based supercapacitors (SCs). However, the rapid evaporation of water moisture in gel electrolyte substantially limits the working durability and performance enhancements of the flexible devices. Therefore, a high-performance multifunctional textile-based SC with long-term durability is highly desired. Herein, a poly(vinyl alcohol) (PVA)/polyacrylamide (PAM) composite gel electrolyte was developed to fabricate multifunctional device with water-retaining and water-proofing properties based on multidimensional hierarchical fabric. And the assembled SC based on composite gel exhibited a superior water-retaining property and long-term working durability (93.29% retention rate after operation for 15 days), whereas the performance of SC based on pure PVA gel declined sharply and only 43.2% capacitance remained. In addition, the assembled SC exhibited enhanced specific capacitance of 707.9 mF/cm2 and high energy density of 62.92 μWh/cm2 and maintained a good stability of 80.8% even after 10 000 cyclic tests. After water repellency treatment, the integrated device immersed in water could still work normally. What's more, the assembled devices could be charged by a portable hand generator, which could be potentially applied for field rescue and military applications. We foresee that this strategy would be a potential route to prepare high-performance multifunctional textile-based SCs for wearable electronic systems and smart textile applications.

Conductive cotton fabric using laser pre-treatment and electroless plating

This paper presents the fabrication and characterization of laser-treated conductive cotton fabrics by means of copper metallization techniques. The physical properties of the laser-treated knitted samples were examined in terms of thickness, durability, and abrasion impact. Furthermore, the surface topography of the laser-treated substrates was analyzed using a scanning electron microscope (SEM) before and after the coating process and samples demonstrated remarkably uniform deposition of copper metal nanoparticles on the surface of the fabric. An energy dispersing spectroscopy (SEM-EDX) analysis was carried out to determine the elemental composition on the surface of the substrate after the electroless metallization method. The study found that laser-treated samples showed better resistance to wear compared to untreated fabric samples. Since abrasion resistance is key property in electronic textile applications, laser-treated samples could, therefore, be ideal candidates for electronic textile applications. As a result, laser treatment has been shown to be successful in improving the abrasion resistance of conductive textile fabrics.

Bath Electrospinning of Continuous and Scalable Multifunctional MXene-Infiltrated Nanoyarns.

Electroactive yarns that are stretchable are desired for many electronic textile applications, including energy storage, soft robotics, and sensing. However, using current methods to produce these yarns, achieving high loadings of electroactive materials and simultaneously demonstrating stretchability is a critical challenge. Here, a one-step bath electrospinning technique is developed to effectively capture Ti3 C2 Tx MXene flakes throughout continuous nylon and polyurethane (PU) nanofiber yarns (nanoyarns). With up to ≈90 wt% MXene loading, the resulting MXene/nylon nanoyarns demonstrate high electrical conductivity (up to 1195 S cm-1 ). By varying the flake size and MXene concentration, nanoyarns achieve stretchability of up to 43% (MXene/nylon) and 263% (MXene/PU). MXene/nylon nanoyarn electrodes offer high specific capacitance in saturated LiClO4 electrolyte (440 F cm-3 at 5 mV s-1 ), with a wide voltage window of 1.25 V and high rate capability (72% between 5 and 500 mV s-1 ). As strain sensors, MXene/PU yarns demonstrate a wide sensing range (60% under cyclic stretching), high sensitivity (gauge factor of ≈17 in the range of 20-50% strain), and low drift. Utilizing the stretchability of polymer nanofibers and the electrical and electrochemical properties of MXene, MXene-based nanoyarns demonstrate potential in a wide range of applications, including stretchable electronics and body movement monitoring.

Long wavy copper stretchable interconnects fabricated by continuous microcorrugation process for wearable applications

AbstractContinuous microcorrugation processes have been developed to form long vertical wavy structures of copper (Cu) foil electrodes for the development of long stretchable interconnects of wearable devices and electronic textiles. Vertical wavy stretchable interconnects in previous studies suffer from low uniformity and limited size due to their wrinkling process with prestretched rubber substrate. Therefore, we propose a continuous metal foil forming process where a long flat Cu foil is continuously deformed into a wavy shape between two three‐dimensional printed gears. 5‐μm Cu foils were corrugated into a wavy structure with waves having 620‐μm pitch and 270‐μm height by the microcorrugation process. The fabricated wavy Cu interconnects showed a 40% stretchability. After microcorrugation, the interconnects were embedded in silicone rubber to protect them from mechanical scratch and improve their elasticity. The interconnects exhibited a 60% stretchability. Finally, a 25 cm‐long stretchable light emitting diodes (LEDs) ribbon with a stretchability over 20% was demonstrated by connecting the LEDs with our wavy Cu interconnects for electronic textile applications. The results demonstrate the effectiveness of our microcorrugation process in the fabrication of long uniform vertical interconnects.

Significant enhancement of out-coupling efficiency for yarn-based organic light-emitting devices with an organic scattering layer

Yarn-based organic light-emitting devices (YOLEDs) have emerged as candidates for potential applications in electronic textiles and wearable electronics. However, the efficiency of YOLEDs is lower than that of conventional OLEDs based on glass substrates because of the loss of light in the interface between the yarn and the organic layers. This paper reports an enhanced out-coupling efficiency when Norland Optical Adhesive 63 (NOA63): Bathophenanthroline (Bphen) particles are used as an organic scattering layer (OSL) for applications in high-efficiency YOLEDs. The RMS roughness of the yarn/OSL/PEDOT:PSS structures (4.3 nm) is drastically reduced in comparison with that of yarn (19.7 nm). Furthermore, the transmittance intensities at 515 nm of yarn with and without an OSL containing Bphen particles are 87% and 82%, respectively, and the luminance of YOLEDs with Bphen particles in the OSL (194.1 cd/cm2) is 41.7 cd/cm2 larger than that without Bphen particles (152.4 cd/cm2) due to the scattering of light from those particles. Moreover, at 515 nm, the electroluminescence (EL) intensity of YOLEDs with Bphen particles in the OSL is 1.3 times larger than that of the YOLEDs without the particles. This successful demonstration of enhanced luminescence and enhanced EL for YOLEDs based on an OSL containing Bphen particles indicates a potential for applications of YOLEDs in next-generation wearable display systems.

Highly conductive wet-spun PEDOT:PSS fibers for applications in electronic textiles

PEDOT:PSS fibers with outstanding electrical and mechanical properties were fabricated and their use in a variety of electronic textile applications was demonstrated.

Recent developments in flexible photodetectors based on metal halide perovskite

AbstractFlexible photodetectors (FPDs) have been receiving increasing attention in recent years because of their potential applications in electronic eyes, bioinspired sensing, smart textiles, and wearable devices. Moreover, metal halide perovskites (MHPs) with outstanding optical and electrical properties, good mechanical flexibility, low‐cost and low‐temperature solution‐processed fabrication have become promising candidates as light harvesting materials in FPDs. Herein, we comprehensively review the developments of FPDs based on MHPs reported recently. This review firstly provides an introduction with respect to the performance parameters and device configurations of perovskite photodetectors, followed by the specific requirements of FPDs including substrate and electrode materials. Next, chemical compositions, structures and preparation methods of MHPs are presented. Then, the FPDs on the basis of single‐component perovskite and hybrid structure perovskite are discussed, subsequently, self‐powered flexible perovskite photodetectors were presented. In the end, conclusions and challenges are put forward in the field of FPDs based on perovskites.image

Smart and robust electrospun fabrics of piezoelectric polymer nanocomposite for self-powering electronic textiles

The present work designs a piezoelectric nanogenerator (PENG) based on the electrospun nanofibers of the piezoelectric polymer, polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), by uniformly drawing the spun membranes containing cellulose nanocrystals (CNC, 2 wt%) and the Fe-doped nano ZnO (2 wt%). The hybrid nanocomposite fibers were made in double layers, with CNC/PVDF-HFP composite on one side and the Fe-doped ZnO/PVDF-HFP on the other side. This ferroelectric polymer composite exhibited maximum peak-to-peak output voltage of 12 V with a current density, 1.9 μAcm−2, which are respectively higher by 60 and 2.3 times compared to the neat polymer fibers. The PENG is tested for its energy harvesting ability by exposing it to different environments such as ultrasound vibrations and human body movements during hand tapping, elbow movements and by attaching with the textile fabrics. While the finger tapping generated peak-to-peak output voltage of 6.5 V, elbow movements resulted in 5.5 V generation. In all sorts of movements, the nanogenerator shows good output performance indicating its compatibility with textile materials. The mechanical properties, breakdown strength and dielectric properties of the material are also in accordance with its possible applications in wearable electronic textiles.

Textile-based triboelectric nanogenerators with high-performance via optimized functional elastomer composited tribomaterials as wearable power source

Wearable power sources with high performance are attracting intensive attention, owing to their great potential in new-generation wearable electronics. Herein, we proposed a composited fabric with flexible functional elastomer layers (FEL@CF) and employed it as a negative tribomaterial in triboelectric nanogenerators (TENGs). The FEL@CF consists of a low-temperature vulcanized silicone (LTV) electrification layer, CNTs/Ecoflex nanocomposite layer, super-soft Ecoflex layer and conductive fabric substrate, which play critical roles on the output enhancement of FEL@CF-based TENG (abbreviated as FEL@CF-TENG). The effect of the thickness of the Ecoflex layer and CNTs content in the nanocomposite layer on the electrical performance of FEL@CF-TENG were systematically investigated. The FEL@CF with 180 μm thick Ecoflex layer and 1.6 wt% CNTs content was realized as an optimal sample to obtain optimum output signals. The high outputs (~490 V, ~43 μA, ~70 nC, 1.6 mW/cm2) were obtained from the optimal FEL@CF-TENG (2.5 × 2.5 cm2) under small force (~16 N) and low frequency (~1.5 Hz). The flexible FEL@CF-TENG can power for wearable electronics by harvesting biomechanical energy and operate in dual-electrodes mode (FEL@CF-DTENG) or single-electrode mode (FEL@CF-STENG). Especially, the power glove made of FEL@CF-STENG can contact with various daily-used objects for human motion energy harvesting. The durability and washability of FEL@CF-TENGs were also performed, exhibiting excellent stability even under harsh and complex conditions. All these merits of the FEL@CF-TENG not only provide a promising strategy for exploring high-performance wearable power source but also show great potential for applications in portable electronics and electronic textiles.

A New Architecture for Fibrous Organic Transistors Based on a Double-Stranded Assembly of Electrode Microfibers for Electronic Textile Applications.

Herein, a unique device architecture is proposed for fibrous organic transistors based on a double-stranded assembly of electrode microfibers for electronic textile applications. A key feature of this work is that the semiconductor channel of the fiber transistor comprises a twist assembly of the source and drain electrode microfibers that are coated by an organic semiconductor. This architecture not only allows the channel dimension of the device to be readily controlled by varying the thickness of the semiconductor layer and the twisted length of the two electrode microfibers, but also passivates the device without affecting interconnections with other electrical components. It is found that the control of crystalline nanostructure of the semiconductor layer is critical for improving both the production yield of the device and the charge-carrier transport in the device. The resulting fibrous organic transistors show a high output current of over -5 mA at a low operation voltage of -1.3 V and a good on/off current ratio of 105 . The device performance is maintained after repeated bending deformation and washing with a strong detergent solution. Application of the fibrous organic transistors to switch current-driven LED devices and detection of electrocardiography signals from a human body are demonstrated.