Wearable Research Articles

Restricted growth of polyaniline nanofiber arrays between holey graphene sheets on carbon cloth towards improved charge storage capacity

The rapid−growing demand for flexible and wearable electronics has driven increased interest in developing porous electrodes with outstanding charge storage capacity especially areal capacity for polymeric and hybrid supercapacitors. Herein, unique porous polyaniline/holey graphene/carbon cloth (PANI/HG/CC) composite electrodes were constructed by combining rapid frozen interfacial polymerization and layer−by−layer spraying to restrict the growth of PANI nanofiber arrays between carbon−based materials. Benefiting from rapid charge transport, more electroactive sites and improved electrolyte penetration provided by hierarchical porous structure and highly oriented PANI nanofibers in the composite (P − G) by growing directly PANI array on the CC and applying graphene sheets as interlayer and cover layer, an areal specific capacitance of 3.22 F cm−2 at 5 mA cm−2 was achieved. A maximum areal energy density of up to 104.86 μWh cm−2, and excellent capacity retention of 89.5 % at 20 mA cm−2 after 5000 cycles also were achieved for flexible symmetric all−solid−state supercapacitor. Furthermore, the zinc−ion hybrid supercapacitor (P − G||Zn) assembled with P − G cathode and Zn anode could display a capacity of 217.7 mAh g−1 at 0.2 A g−1, and the maximum energy density of 130.6 Wh kg−1 at the power density of 120 W kg−1.

EKFNet: Edge-based Kalman filter network for real-time EEG signal denoising.

Signal denoising methods based on deep learning have been extensively adopted on Electroencephalogram(EEG) devices. However, they are unable to deploy on edge-based portable or wearable (P/W) electronics due to the high computational complexity of the existed models. To overcome such issue, we propose an edge-based lightweight Kalman filter network (EKFNet) that does not require manual prior knowledge estimation.
Approach: Specifically, we construct a multi-scale feature fusion (MSFF) module to capture multi-scale feature information and implicitly compute the prior knowledge. Meanwhile, we design an adaptive gain estimation (AGE) module that incorporates long short-term memory (LSTM) and sequential channel attention module (CAM) to dynamically predict the Kalman gain. Furthermore, we present an optimization strategy utilizing operator fusion and constant folding to reduce the model's computational overhead and memory footprint.
Main results: Experimental results show that the EKFNet reduces the sum of the square of the distances by at least 12% and improves the cosine similarity by at least 2.2% over the state-of-the-art methods. Besides, the model optimization shortens the inference time by approximately 3.3×. The code of our EKFNet is available at https://github.com/cathnat/EKFNet.
Significance: By integrating Kalman filter with deep learning, the approach addresses the parameter-setting challenges in traditional algorithms while reducing computational overhead and memory consumption, which exhibits a good tradeoff between algorithm performance and computing power.

A Universal Strategy for Synthesis of Large-Area and Ultrathin Metal Oxide/rGO Film Towards Scalable Fabrication of High-Performance Wearable Microsupercapacitors.

High-performance wearable microsupercapacitor (MSC) as energy storage components is highly desirable for developing self-powering wearable electronics. However, synthesis of MSC electrode film concurrently possessing large area, ultrathin thickness, and high areal energy storage capability is still challenging. Herein, a universal strategy is reported to synthesize large-area and ultrathin metal oxide nanoparticles (MONPs)/reduced graphene oxide (rGO) hybrid-structured films by attaching self-assembled film of a wide range of MONPs onto self-assembled rGO film and subsequent carbonization. Combining a template-assisted patterning strategy and a floating film salvaging process, flexible symmetric and asymmetric MSCs based on MONPs@C/rGO films can be easily prepared in large areas. MONP agglomeration is avoided and its pseudocapacitive behavior is well utilized, thereby realizing a high areal specific capacitance of 9.32 mF cm-2 in Fe3O4@C/rGO-based symmetric MSC at a film thickness of only 275 nm, corresponding to a high volumetric specific capacitance of 338.9 F cm-3. Moreover, the MnO@C/rGO‖Fe3O4@C/rGO-based asymmetric MSC delivers a high volumetric energy density of 69.8 mWh cm-3. The MSCs also demonstrate their efficient power supply in wearable self-powering systems. This work provides a new route for scalable preparation of high-performance wearable MSCs, and also enables customizable fabrication and performance tuning of MSCs.

Polyelectrolyte complex membranes for zinc-ion cathode by polymerization of polyaniline

Although lithium batteries dominate the rechargeable battery market, concern over safety and material supply have motivated scientists to develop non-lithium-based alternative such as zinc-ion batteries (ZIBs). This work focuses on the development of polyelectrolyte complex-based cathode for ZIBs using a mild aqueous electrolyte such as ZnCl2 instead of KOH and to be further developed into wearable electronics. Composite polyelectrolyte complex electrodes with carbon black and polyaniline (PANI), or manganese oxide (MnO2) as active materials were prepared. The membranes were then further modified by electropolymerization of PANI to enhance the battery performance. Results show that electropolymerization leads to a threefold increase in ZIB performance with increased current density, power density, and specific energy capacity. Zinc chloride (ZnCl2; 1 m) was used as a mild electrolyte instead of potassium chloride (KOH; 6 m) leading to a reduced performance yet allowing for potential use in skin contact and wearable electronics. All the membranes were assembled into ZIB and tested using the battery testing machine. Scanning electron microscopy was used to observe the morphology of the electropolymerized PANI while attenuated total reflection Fourier transform infrared spectroscopy was used to confirm the chemical nature of PANI.

Solution-processed fabric-based Ag electrodes for wearable top-emitting organic light-emitting devices

Flexible fabric-based top-emitting organic light-emitting devices (Fa-TEOLEDs) have garnered significant attention due to their tremendous potential in wearable electronics. However, fabricating cost-effective high-quality metal reflection electrodes on fabric still poses a formidable challenge. Herein, flexible fabric-based Ag reflection electrodes, which possess a sheet resistance of ∼0.15 Ω/sq and a reflectance of ∼94.7 %, along with excellent environmental and mechanical stability, were fabricated through the innovative combination of fast silver mirror reaction and template-stripping processes. Adopting the fabric-based Ag electrodes, ultra-flexible red, green and blue Fa-TEOLEDs with ultrathin emitting layers present the remarkable current efficiencies of 39.4 cd/A, 119.0 cd/A and 44.8 cd/A, respectively. Impressively, the Fa-TEOLEDs show excellent mechanical flexibility and durability, retaining ∼88.1 % of the original luminance after 700 bending cycles at a bending radius of 2 mm. This substantial advancement marks a crucial stride forward in the design of high-quality metal reflection electrodes and the advancement of Fa-TEOLEDs for wearable electronics.

Applications of organic solar cells in wearable electronics

Applications of organic solar cells in wearable electronics

Giant piezoelectricity in fluoropolymer fiber mats achieved by corona poling in water

Polymer piezoelectrics hold great potential for energy harvesting and wearable electronics. Efforts have been dedicated to enhancing piezoelectric coefficients and thermostability for several decades, but most of these have not been successful. In this report, we demonstrate a straightforward way to achieve high piezoelectric coefficients and output voltages while maintaining high thermostability at temperatures over 110 °C. Poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] 80/20 mol.% nanofiber mats (made by electrospinning) with extremely high crystallinity and Curie temperatures were obtained via a two-step annealing process, from which large ferroelectric domains were formed in extended-chain crystals. After corona poling using water, which is a high dielectric constant medium, giant piezoelectricity (apparent d33 = 1020 ± 20 pC/N) and high output voltages (29.9 ± 0.5 V) were achieved. It is found that the dimensional effect induced significant polarization changes, which is the key requirement for piezoelectricity. Our finding in this work paves a way to further improve high-performance polymer piezoelectrics.

One-pot construction of all-in-one flexible asymmetrical supercapacitors for extreme-condition applications

All-in-one flexible energy storage devices hold great application potential in the flexible and wearable electronics by virtue of unique configuration, however, still face severe challenges including complex fabrication steps, single variety of symmetrical supercapacitors and limited scenario application. For the first time, we propose a facile one-pot approach to fabricate all-in-one flexible asymmetrical supercapacitors (AFASCs) through magnetic driving localization of magnetic FeOOH anode away from MnO2 cathode in the electrolyte containing ethylene vinyl alcohol copolymers toward multi-scenario application. Distinctly different from the reported all-in-one approaches, this one-pot approach dramatically simplifies fabrication steps and especially extends more variety of electroactive materials for asymmetrical supercapacitors and even aqueous battery systems. A well-integrated configuration without any interfaces forms in the FeOOH/MnO2 AFASCs with low interfacial resistance, high areal capacitance, good cyclic stability and remarkable energy density. Significantly, the FeOOH/MnO2 AFASCs achieve superhigh capacitance retention not only in long-term bending and twisting deformations, but also under various extreme conditions including cutting, rolling, hammering, puncturing, sewing, soaking and washing in the water, as well as low temperature. Furthermore, the FeOOH/MnO2 AFASCs are demonstrated to power wearable smart bracelet, health monitoring, intelligent positioning system and running pod. Those findings can open up a new approach for one-pot construction of all-in-one flexible energy storage devices to meet future needs of flexible and wearable electronic devices under harsh working conditions.

All-cellulose triboelectric textile with complete biodegradability for eco-friendly smart wearable electronics

All-cellulose triboelectric textile with complete biodegradability for eco-friendly smart wearable electronics

Silk-Polyurethane Composite based flexible electrochemical biosensing platform for pathogen detection

The upcoming era of flexible and wearable electronics necessitates the development of low-cost, flexible, biocompatible substrates amenable to the fabrication of active devices such as electronic devices, sensors and transducers. While natural biopolymers such as Silk are robust and biocompatible, long-term flexibility is a concern due to the inherent brittle nature of soft Silk thin films. This work elucidates the preparation and characterization of Silk-polyurethane (Silk-PU) composite film that provides long-duration flexibility. More importantly, an electrochemical biosensing platform is developed by creating a three-electrode system using a screen-printing technique. The solvents in the Ink had little impact on the film. As a proof of concept, the detection of E. coli, a highly infectious pathogen, was demonstrated using screen-printed electrodes (SPEs) modified with gold nanoparticles. This method effectively detected E. coli across a wide range of concentrations, with a detection limit of 0.12 CFU/mL. The entire surface functionalization and detection process did not impact the Silk-PU substrate. Even after rigorous bending tests, the results were consistent, demonstrating the robustness and flexibility of the Silk-PU film. The platform demonstrated is scalable and amenable for multi-pathogen detection as it not only can integrate several working electrodes, each catering to detection of a particular pathogen, but also serve as a platform for lab-on-chip devices wherein PDMS-based microfluidics can be seamlessly integrated along with the proposed platform.

Metal coordination bond and rough interface enhanced triboelectric nanogenerator aiming for multiple complex conditions

Triboelectric nanogenerator (TENG) is widely used in the fields of sustainable green energy harvesting, self-powered motion parameter and tactile sensing, However, it still fails to meet the requirements under various complex conditions, such as low temperatures, self healing after destruction, punching, long-term placement, soaking in acid or alkali solution, scorch, continuous work. Herein, based on metal coordination, Zr4+ ions are introduced to enhance the first network k-carrageenan (k-CG) for achieving double enhancement in mechanics and electricity of the gel electrode layer, poly (N-hydroxyl acrylamide)/k-CG (PKZ) double network organic conductive gel enhanced by multiple hydrogen bonds and metal coordination bond is designed, and the gel exhibits high tensile strength, high conductivity, fast self-recovery, excellent self-repairing and low-temperature resistance. Based on simple sandpaper templates with different mesh numbers Ecoflex film with rough surfaces is designed for efficient triboelectric contact interface, and TENG with PKZ double network organic conductive gel as electrode layer is constructed, and possesses excellent resistant to multiple complex conditions. With high short-circuit current, open-circuit voltage and output power, the TENG is capable of powering electronic devices, and it can also be sensitive and stable sensing in writing recognition, real-time monitoring of motion parameters involving acceleration, speed and distance. The TENG is stable and reliable for sustainable green energy harvesting, motion parameter and tactile sensing in multiple complex environments. Thus, we provide novel ideas for designing energy harvesting and sensing for future wearable electronics under multiple complex conditions.

Artificial neural network assisted omnidirectional strain sensors for human motion perception

Flexible resistance strain sensors gain tremendous attentions in emerging fields such as wearable sensing, electronic skins and human–machine interfaces due to its excellent stretchability and sensitivity. However, due to the coupling of strain along both principal and perpendicular axes, conventional uniaxial strain sensors face challenges in recognizing multi-directional strain which naturally occurs in practical applications. In this work, we present the omnidirectional strain sensors comprised of multiple-stacked oriented conductive layers and harness the artificial neural network (ANN) to assist recognizing strain information with high accuracy. Each conductive layer consists of a patterned multi-walled carbon nanotubes mixture coated on a soft substrate, exhibiting remarkable sensitivity with a gauge factor of 4.18 along the principal direction. When centrally aligning two or three layers along different directions, the assembled structures can monitor the multi-directional electronic resistance changes under deformations, enabling the recognition of both strain direction and amplitude. The ANN model used three-dimensional resistance data as input to perform a multi-class classification task, with strain amplitude and direction as the outputs. The hidden layers employed the ReLU activation function, while the output layer utilized the SoftMax activation function. The model was compiled with the sparse_categorical_crossentropy loss function and optimized using the Adam optimizer. Its performance was evaluated based on prediction accuracy. The strain prediction accuracy is above 98 % with the assistance of an ANN model. The triple-layer configuration can perceive the human wrist motions such as rotation and bending, exhibiting high potential in applications such as multidimensional wearable electronics.

Advances in Wearable Smart Chemical Sensors for Health Monitoring

The advancement of wearable technology has entered a new phase, leading to the creation of various wearable sensors due to the rise of technologies like IoT and AI. Wearable chemical sensors are essential components of wearable electronics and hold significant promise in monitoring health. This review reports on the recent achievements and advantages of portable smart chemical sensing for health monitoring and discusses portable chemical sensing using frictional/piezoelectric electrochemical generators, photovoltaics and thermal power accumulators. This paper also evaluates the potential of wearable chemical sensors for health monitoring.

Comments on “EAKE-WC: Efficient and Anonymous Authenticated Key Exchange Scheme for Wearable Computing”

Comments on “EAKE-WC: Efficient and Anonymous Authenticated Key Exchange Scheme for Wearable Computing”

Yarn‐to‐Yarn Surface Area and Roughness as Structural Engineering Tools for Optimizing the Electrical Output of Triboelectric Nanogenerators: Geometrical and Experimental Verification

AbstractThis paper investigates the performance of woven triboelectric nanogenerators (W‐TENGs) fabricated with different fabric patterns, specifically plain, twill, and hopsack weaves, using wool and polyester yarns. It is intended to enhance the electrical output and efficiency of W‐TENGs for potential applications in wearable electronics by optimizing the weaving pattern. Results indicate that W‐TENGs with twill 2/2 and hopsack 2/2 patterns exhibit superior electrical outputs, attributed to their higher contact surface area and roughness. The twill 2/2 pattern demonstrates the highest electrical output, generating an open‐circuit voltage of 4.7 V, a short‐circuit current of 4 µA, and a transferred charge of 0.35 µC. This study also highlights the critical role of surface area and dielectric material roughness in determining the output performance of triboelectric structures. A theoretical model is developed to calculate the real contact surface area of the woven fabrics with different patterns. Statistical analysis reveals significant relationships between surface roughness parameters and electrical performance. Dynamic testing under varying contact forces and frequencies demonstrates the practical applicability and robustness of the W‐TENGs. Furthermore, the devices exhibit excellent durability, maintaining stable performance over extended periods. This research provides new insights into fabric design strategies for optimizing energy harvesting in wearable devices.

A Wearable Triboelectric Nanogenerator Based on Polyester-Paper Cloth for Mechanical Energy Harvesting and Running Motion Sensing.

Paper-based triboelectric nanogenerators (P-TENGs) have recently garnered significant attention in wearable electronics. However, traditional P-TENGs are constrained by the inherent strength limitations of paper. Hence, we reported a novel polyester-paper cloth-based triboelectric nanogenerator (PP-TENG) designed for mechanical energy harvesting and running motion monitoring. Compared to paper, polyester-paper cloth has higher durability and tear resistance. The PP-TENG capitalizes on the unique fluffy internal structure of polyester-paper cloth, imparting high sensitivity to pressure variations. Experimental results demonstrate that the PP-TENG achieves an open-circuit voltage (Voc) of 466.64 V, a short-circuit current (Isc) of 48.73 μA, and a transfer charge (Qsc) of 90 nC. Its maximum output power reaches 930.26 μW when connected to a 40 MΩ load. These impressive metrics underscore the potential of PP-TENG in energy harvesting applications, particularly for wearable electronic devices. The device's integration into the soles of athletic socks showcases its practical utility, providing real-time monitoring of runners' gait and step count. This integration not only enhances the functionality of sportswear but also offers valuable data for performance analysis and injury prevention, marking a significant advancement in wearable technology and intelligent textiles. This research provide a promising path for self-powered wearable sensors and flexible electronics applications.

Lightweight energy harvesting backpack achieved with a slingshot-inspired flexible accelerator

The energy harvesting backpack (EHB) has been recognized as a sustainable power source for wearable electronics, but its daily applications have been hindered by the rigid and heavy frame and accelerator structure. Therefore, a flexible and lightweight design strategy for EHBs is proposed based on a slingshot-inspired flexible accelerator (FA). The proposed FA accomplishes the speed acceleration for harvester actuation by rapidly releasing accumulated elastic potential energy. Then, a 1.9 kg electromagnetic EHB with the FA (FA-EEHB) is modeled, tested, and applied to wearable electronics. Actuated by 3.0 Hz ultralow-frequency vibrations, the FA-EEHB with a 2.0 kg payload can generate 215.1 mW output power, which is over eight times the 26.6 mW output of an EHB without FA. With a small payload of 1.0 kg, the FA-EEHB can work well over a large traveling speed range from 4 km/h to 9 km/h. The application experiment of the FA-EEHB was conducted at 5 km/h traveling speed with a 2.0 kg payload to demonstrate the ability to continuously power a lamp, charge a smartphone, and sustain a tracking and positioning system. This study provides a distinctive strategy for the flexible and lightweight design of EHBs with small payloads.

Hydrogen bond cross-linked photo-healable multifunctional phase change materials for thermal management

Phase change materials (PCMs) are extensively employed in the realm of electronic device thermal management due to their remarkable ability to absorb heat while maintaining temperature stability. However, the lack of versatility has greatly hindered their applications in flexible wearable electronics and similar fields. Herein, we designed a dynamic, flexible, anti-flaming, ultrafast healable and recyclable supramolecular poly(urethane-urea) phase change material (PUSePCM). The synergistic effects of dynamic hydrogen-bond network and rapid diselenide metathesis endowed a rapid self-healing within 30 s and recycle capability. The PUSePCM could also attach to various metal surfaces and was further used as flexible interface materials in thermal management applications. With the silver microparticles content of ≥30 vol%, the resultant composite can significantly reduce the work temperature of a chip by about 10 °C. This research not only provides a new approach for creating phase-change materials with dynamic, flexible, self-healing, and recyclable performance, but also offers the applications for damage tolerable thermal management interface.

Constructing ultrahigh capacitance (Co,Mn)(Co,Mn)2O4/Ni(OH)2 electrode for boosted all-solid-state fiber asymmetric supercapacitors

To meet the practical demands of flexible fiber-shaped supercapacitors (FSSCs) for wearable electronics, it's crucial to develop electrodes with both high energy density and flexibility. In this work, an ultrahigh capacitance (Co,Mn)(Co,Mn)2O4/Ni(OH)2 (CMO/Ni(OH)2) fiber electrode is designed. The (Co,Mn)(Co,Mn)2O4 (CMO) nanosheets possessing large specific surface area and enriched active sites, which can be served as nano-substrate for the electrodeposition of Ni(OH)2. This special structure facilitates the exposure of more electroactive sites and accelerate rapid electrons transfer, resulting in boosted electrochemical performance. Benefiting from these advantages, the area capacitance of the CMO/Ni(OH)2 electrode is up to 4787.6 mF cm−2 at 1 mA cm−2, which is approximately 15 times higher than that of the CMO (311 mF cm−2), and 6.7 times higher than that of the Ni(OH)2 (718 mF cm−2). Coupled with activated carbon (AC) electrode, the assembled all-solid-state CMO/Ni(OH)2//AC FSSCs demonstrate a high energy density of 89.45 μW h cm−2 at 1505 μW cm−2, along with great flexibility and stability. Moreover, these devices can be integrated into clothes, and electronic watch, serving as an energy supply. This work offers a novel approach to designing high-performance fiber electrode for wearable flexible energy storage devices.

Optimization studies on output stabilization time and graphene oxide concentration in graphene-based flexible micro-supercapacitor.

Miniature energy storage devices are vital for developing flexible and wearable electronics. This paper discusses the fabrication of flexible laser-induced graphene-based micro-supercapacitors (MSCs) using a layered polyimide film and graphene oxide as the precursor for laser scribing. The areal capacitance of the MSCs was assessed daily after applying a H₂SO₄/PVA gel electrolyte. The capacitance displayed a substantial increase in the early days before stabilizing at a consistent value. The stabilization time was evaluated through systematic experimentation conducted over ten consecutive days. The experiments showed that the capacitance stabilized after six days. Various concentrations of graphene oxide were used to assemble the MSCs, and their performance was evaluated to determine the optimal concentration. The electrochemical impedance spectroscopy revealed that the supercapacitor fabricated with the optimum concentration of graphene oxide exhibited the lowest resistance. The optimized MSC displayed an areal capacitance of 10.07 mF/cm2 at a current density of 13 µA/cm2. The device could maintain a reliable output at different bending states and retain 87.9% of its original capacitance after 5000 charge-discharge cycles, highlighting its suitability for flexible and self-powered systems.