Wearable Energy Harvesting Research Articles

Copper Iodide on Spacer Fabrics as Textile Thermoelectric Device for Energy Generation.

The integration of electronic functionalities into textiles for use as wearable sensors, energy harvesters, or coolers has become increasingly important in recent years. A special focus is on efficient thermoelectric materials. Copper iodide as a p-type thermoelectrically active, nontoxic material is attractive for energy harvesting and energy generation because of its transparency and possible high-power factor. The deposition of CuI on polyester spacer fabrics by wet chemical processes represents a great potential for use in textile industry for example as flexible thermoelectric energy generators in the leisure or industrial sector as well as in medical technologies. The deposited material on polyester yarn is investigated by electron microscopy, x-ray diffraction and by thermoelectric measurements. The Seebeck coefficient was observed between 112 and 153 µV/K in a temperature range between 30 °C and 90 °C. It is demonstrated that the maximum output power reached 99 nW at temperature difference of 65.5 K with respect to room temperature for a single textile element. However, several elements can be connected in series and the output power can be linear upscaled. Thus, CuI coated on 3D spacer fabrics can be attractive to fabricate thermoelectric devices especially in the lower temperature range for textile medical or leisure applications.

Green-in-green biohybrids as transient biotriboelectric nanogenerators

Green self-powered devices based on biodegradable materials have attracted widespread attention. Here, we propose the construction of the transient biotriboelectric nanogenerator (TENG) using green-in-green bionanocompoites. The green-in-green nanocomposites, cellulose nanocrystal (CNC)/polyhydroxybutyrate (PHB), are prepared with a high-pressure molding method. The CNC promotes the degradation and enhances the dielectric constant of CNC/PHB. It further allows for the significant improvement of the triboelectric output of CNC/PHB-based TENG. The voltage output and current output of CNC/PHB-based TENG are 5.7 and 12.5 times higher than those of pristine PHB-based TENG, respectively. Also, the bio-TENG exhibits admirable signal stability in over 20000 cycles. Despite the high hardness of CNC/PHB, a soft but simple-structured arch sensor is successfully assembled using CNC/PHB-based TENG. It can attain the precise real-time monitoring of various human motions. This study may provide new insights into the design/fabrication of green functional materials, and initiate the next wave of innovations in eco-friendly self-powered devices.

A wearable collaborative energy harvester combination of frequency-up conversion vibration, ambient light and thermal energy

In this study, a wearable multi-source collaborative energy harvester (MC-EH) is proposed to overcome the problem that a single-source EH is unstable from time to time. A customized ring monocrystalline silicon photovoltaic (PV) cell on the surface of energy harvester (EH) is used to harvest ambient light energy. The thermoelectric generator (TEG) converts the thermal energy of the temperature difference into electrical energy. A Macro-Fiber Composite (MFC) constitutes piezoelectric frequency up-conversion rotating structure, which harvest the low frequency vibration energy. The advantages of designed MC-EH are that energy of human body and environment can be fully harvested. Due to the difficulty in extracting small voltage generated by TEG independently, MC-EH was improved that it can extract thermal energy in the process of vibration energy extraction efficiently by the interface circuit. Results showed that maximum output power of harvester was about 4.48 mW, power density was 1.5 × 10−4 W/cm3. MC-EH can work efficiently in different human movement states and environments conditions. Therefore, MC-EH may provide electric energy for wearable device. Three energy harvesting systems are integrated into one compact structure by MC-EH, forming the advantages and originality of MC-EH that brought a case study of EH.

Enhanced electrical conductivity into PA6 thermoelectric fabric modified by PEDOT-Tosylate for efficient heat harvesting

Thermoelectric (TE) fabric can be seamlessly integrated into garments to power portable electronic devices by harvesting body heat. Hence, a flexible PEDOT-Tos/PDA/PA6 thermoelectric fabric was successfully prepared by depositing polydopamine (PDA) on polyamide 6 (PA6) fabric and exploiting the interaction between PDA and PEDOT-Tosylate (PEDOT-Tos). The resistance of TE fabric was only 10.56 Ω/□, which was superior to most of the reported PA6 composite fabrics. Finally, a wearable flexible TE device was prepared by using PEDOT-Tos/PDA/PA6 fabrics. When worn on the arm, it can generate an output voltage of 2.4 mV, which indicated that the TE fabric had a potential application in wearable energy harvesting devices.

Direct-current, long-lasting and highly efficient electret energy harvesting from ultra-low-frequency motions using toothed clutch mechanism

Generally, most wearable energy harvesters generate only a small amount of electrical energy from the low-frequency motions of human body and immediately stop working when the activity ends, resulting in low energy extraction efficiency. Here, we propose an electret rotatory energy harvester (e-REH) with a mechanical tooth-clutch transmission system, converting the ultra-low-frequency irregular human motion (< 0.1 Hz) into a high-speed and long-lasting rotation for boosted energy conversion efficiency. The tooth-clutch transmission system is designed with a compact integration of a linear-to-rotation unit, a tooth-clutch transmission unit and an energy storage unit to generate continuous, stable and highly efficient electrical output. Triggered by impulse excitation of gentle hand tapping, the flywheel can continuously rotate for about 45 s inertially, and the maximum speed of the flywheel can reach about 1500 rpm, indicating the frequency is increased up to 4500 times from 0.022 Hz to 100 Hz. In addition, by introducing the multi-layer phase-shift electrode design, a constant direct-current output with a crest factor down to 1.09 is obtained by the phase coupling effect, avoiding the complicated signal processing circuit. Experimental results show the fabricated e-REH can produce an overall coupling current of 22.1 μA and average output power of 3.95 mW. Thanks to the lightweight, compact and high-efficient transmission design, the e-REH is further integrated into a shoe for wearable energy harvesting and self-powered underground environmental monitoring applications. The research is of considerable significance to the practical applications of e-REH in powering sensors and building self-powered wearable sensor networks.

Fast optimize arm wearable piezoelectric energy harvesters via artificial neural network

• Using artificial neural networks to optimize piezoelectric devices allows skipping the construction of physical models. • The ball impact energy harvesting device is more suitable for human energy harvesting. • Considering different optimization algorithms can effectively improve the predictive power of artificial neural networks. • It is necessary to adjust the initial learning rate of the algorithm. Converting actions of human’s body into electrical energy via wearable energy harvesters is an exciting area. This study presents a ball impact piezoelectric energy converter consisting of two circular ceramic piezoelectric sheets to obtain energy from arm swing. 2264 sets of data were measured to train the artificial neural network (ANN) modes. The performance of ANN optimized by three different algorithms (Nadam, Adamax, and Adadelta) was compared and discussed. Treadmill experiments verified and confirmed the prediction results from ANN, an effective voltage of 11.3 V was demonstrated at a running speed of 9 km/h. Our results show that ANN can speed up the optimizing process for designing better energy harvesters.

Highly sensitive strain sensor and self-powered triboelectric nanogenerator using a fully physical crosslinked double-network conductive hydrogel

Stretchable and conductive hydrogels have broad application prospects in various portable and wireless electronic devices and sensors. However, most hydrogels used to construct strain sensors and triboelectric nanogenerators (TENGs) suffer from poor mechanical properties and lack of adhesion till this day. To address these issues, fully physical crosslinked PVA/P(AM-co-AA)-Fe3+ double-network hydrogel (DN gel) was prepared. The unique DN structure endows the hydrogels with excellent mechanical properties (2.1 MPa tensile stress, 6.5 MJ/m3 toughness, 0.4 MPa elastic modulus) and the strong adhesion on various material surfaces. The DN gel as a strain sensor shows high sensitivity (GF = 2.3) and wide sensing range of 1–300%. In addition, the TENG based on PVA/P(AM-co-AA)-Fe3+ (PP-TENG) with an area of 2 × 2 cm2 exhibits attractive electrical output properties, including a maximum open-circuit voltage (VOC) of 238 V, a short circuit current (ISC) of 1.2 μA, and a short-circuit transferred charge (QSC) of 37 nC at a fixed frequency of 2 Hz. Moreover, their applications in highly sensitive strain sensor to effectively distinguish complex human activities and transmit encrypted information, as well as self-powered TENG to power commercial light-emitting diodes and calculator are described. It is foreseen that the as-prepared stretchable and conductive hydrogels have great potential in wearable electronic devices, human-health care, and energy harvesting systems.

Zirconium metal-organic framework and hybridized Co-NPC@MXene nanocomposite-coated fabric for stretchable, humidity-resistant triboelectric nanogenerators and self-powered tactile sensors

High-performance triboelectric nanogenerators (TENGs) have become more attractive for energy harvesting and self-powered sensing applications. Herein, a stretchable, humidity-resistant, and high-performance multilayered TENG (M-TENG) is newly developed for self-powered biomotion and tactile sensing applications by using a zirconium metal-organic framework (MOF-525)@Ecoflex nanocomposite with a layer of Ecoflex@cobalt-nanoporous carbon (Co-NPC)@MXene. The MOF-525 improved TENG’s performance four times due to homogeneous porosity and high charge accumulation. The porous structure of the Co-NPC functions as charge traps, promoting high charge-trapping capability, while the MXene nanosheets operate as microcapacitors, improving transport-ions inside the Ecoflex@Co-NPC@MXene nanocomposite (charge-trapping and charge-transport). When the Ecoflex@Co-NPC@MXene nanocomposite was added as an intermediate layer, it captured triboelectric charges from the charge-generating layer and accumulated more negative charges, improving the M-TENG performance by 13 times. A 3D-printed microstructure is apprehended to the surface to increase contact area and humidity-resistant. Besides, knitted fabrics provide flexible electrodes due to their excellent stretchability. The as-prepared M-TENG showed excellent performance, including a power density of 25.7 W/m2, sensitivity (149 V/KPa), humidity-resistant, and stretchability (245%) which are superior to the previously reported TENGs. By exploiting the outstanding stretchability of the M-TENG and its ultra-high sensitivity to mechanical stimuli, practical applications were successfully demonstrated in low-frequency wearable biomotion monitoring, biomechanical energy harvesting, high-precision character recognition, and as a self-powered tactile sensor. Furthermore, the real-time sensing capability was demonstrated via the LabVIEW interface and virtual-reality car games control by tracing the finger. Therefore, this work is anticipated to open exciting opportunities for wearable energy harvesters, self-powered sensing systems, and human-machine interfaces.

A Review on Wearable Electrospun Polymeric Piezoelectric Sensors and Energy Harvesters

AbstractIn recent years, wearable sensors and energy harvesters have shown great potential for a wide range of applications in personalized healthcare, robotics, and human–machine interfaces. Among different types of materials used in wearable electronics, piezoelectric materials have gained enormous attention due to their exclusive ability to harvest energy from ambient sources. Piezoelectric materials can be utilized as sensing elements in wearable sensors while harvesting biomechanical energy. Electrospun piezoelectric polymer nanofibers are extensively investigated due to their high flexibility, ease of processing, biocompatibility, and higher piezoelectric property (in contrast to their corresponding cast films). However, as compared to piezoceramic materials, they mostly exhibit relatively lower piezoelectric coefficients. Therefore, considerable efforts have been devoted to improving the piezoelectricity of electrospun polymer nanofibers recently, resulting in significant advances. This review presents a broad overview of these advances including new material, structure designs as well as new strategies to enhance piezoelectricity of electrospun polymer nanofibers. The challenges in achieving high mechanical performance as well as high piezoelectricity are particularly discussed. The main motivation of this review is to examine these challenges and highlight effective approaches to achieving high‐performance piezoelectric sensors and energy harvesters for wearable technologies.

(Digital Presentation) Enhanced Streaming Vibration Potential By Silane-Modificated Mxene/PVA Hydrogel for High-Performance Flexible Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) play a vital role in self-powered electronics, based on their superior energy harvesting ability and simple construction. In this work, polyvinyl alcohol (PVA) hydrogel is fabricated, exhibiting a three-dimensional (3D) network structure that allows PVA chains to be covered by a large amount of water. Combining MXene nanosheets with the hydrogel TENG, the composite improves the ion transport of the hydrogel and provides the streaming vibration potential (SVP) mechanism. This composite effectively enhances the output performance of hydrogel TENG. Furthermore, this work adopts different functional groups of silane (APTES, CPTMS, FOTS) to modify the surface work function of MXene nanosheets. The surface modification increases the charge density at the interface between MXene and water inside the hydrogel, improving the electrical output performance and mechanical sensitivity of MXene hydrogel TENG (MH-TENG). The result demonstrates that the electrical output performance of MH-TENGs modified by 1H,1H,2H,2H-Perfluorooctyltriethoxysilane (FOTS) is approximately two times larger (output-voltage~85 V/output-current~240 nA) than pristine hydrogel TENG (output-voltage~40 V/output-current~100 nA). The MH-TENG behaves unlimited potential in the use of flexible electronics, such as movement monitoring electronics, strength sensors on the paddle, and wearable energy harvesting devices in the future.

Lead-Free Transparent Flexible Piezoelectric Nanogenerator for Self-Powered Wearable Electronic Sensors and Energy Harvesting through Rainwater

Lead-Free Transparent Flexible Piezoelectric Nanogenerator for Self-Powered Wearable Electronic Sensors and Energy Harvesting through Rainwater

Flexible fabric-based GaAs thin-film solar cell for wearable energy harvesting applications

GaAs photovoltaic (PV) cells have been extensively studied for flexible energy harvesting devices due to their merits such as thin-film feasibility, flexibility, and high-efficiency. However, GaAs-based thin-film PV cells have a limitation for the applications in wearable platform since they are not compatible with fabric carrier. To handle this problem, we report thin-film transfer technique that involves a sacrificial layer with a double-layer structure, an Au–Au bonding technique, a Cr/Au bilayer to induce metal stress, and an etchant for fast epitaxial lift-off (ELO). In addition, a polyimide layer attached underneath the fabric substrate not only protects the fragile epi layer but also accelerates the lateral etching via spontaneous bending. The application of these techniques enables the successful transfer of GaAs thin-film PV epi structures onto fabric platform without degrading crystal quality. Fabric-based GaAs PV cells are fabricated via the standard PV cell fabrication process. The platform expansion of GaAs thin-film techniques has great potential for large-scale commercialization. • III-V epi-layers onto fabric substrate can be realized without degrading crystal quality. • The GaAs solar cells are directly integrated with fabric platform. • High efficiencies over 17.49% can be achieved on fabric platform. • Fabric-based GaAs solar cells present the stable output power with high flexibility.

Adaptable and Wearable Thermocell Based on Stretchable Hydrogel for Body Heat Harvesting

AbstractThe application of traditional inorganic thermoelectric materials to wearable energy harvesters has been hindered by the rigid bulkiness, while flexible organic conductive polymers have been long troubled by their intrinsic low thermopower. An ideal solution that possesses the merits of the two thermoelectric materials is desperately needed for practical application. Here it is demonstrated that a polyacrylamide (PAAm)‐based ultra‐stretchable hydrogel can be selected as a superior candidate matrix for flexible and stretchable thermocells to adapt to the curved surface of the human body and deformation of the ankle. Fe(ClO4)3/Fe(ClO4)2 is selected as n‐type ion pair for their comparable thermoelectric performance to K3[Fe(CN)6]/K4[Fe(CN)6]. The p‐n pair hydrogel electrolytes show a voltage output of 29 mV and current output of 8.5 Am−2 with an average maximum power density of 0.66 mW K−2 m−2 for each p‐n cell (ΔT = 10 K). By integrating with the graphite paper electrode, a body‐conformal and portable thermocell device, employing the hydrogel electrolytes, is fabricated and reached a voltage output of 0.16 V with 14 pairs of p‐n cells (ΔT = 4.1 K). This commercially‐effective blueprint demonstrates the bright future of hydrogel‐based ionic thermocell in daily wearable scenarios.

An annular tubular wearable piezoelectric-electromagnetic hybrid vibration energy harvester driven by multi magnetic beads

Wearable devices are widely applied because of the rapid development of semiconductor devices and integrated circuit technology. People hoped to enhance their senses through various wearable devices. However, the application is currently limited by the operating time of electrochemical batteries. This paper presents an annular tubular wearable piezoelectric-electromagnetic hybrid vibration energy harvester driven by multi magnetic beads for harvesting energy from the arm swing motion. The structure consists of a piezoelectric beam, magnetic beads and a set of coils. Specifically, piezoelectric energy harvesting (PEH) converts vibration energy into electrical energy by using a new macro-fiber composite (MFC). Magnetic beads and coils form an electromagnetic energy harvester (EMEH).Two energy harvesting units are coupled by magnetic beads. The magnetic beads can not only induce the coil to generate electrical energy, but also excite the piezoelectric beam. Two conversion mechanisms extract energy simultaneously through one excitation.Experimental results show that the device can harvest the vibration energy generated by human activity under different types of human motion, such as slow walking, fast walking and running. The integration between PEH and EMEH not only extends the operating bandwidth, but also makes it easy for ultra-low frequency energy harvesting. The prototype harvester that could power a number of portable electronic devices shows great potential.

A wearable textile-based pneumatic energy harvesting system for assistive robotics.

Wearable assistive, rehabilitative, and augmentative devices currently require bulky power supplies, often making these tools more of a burden than an asset. This work introduces a soft, low-profile, textile-based pneumatic energy harvesting system that extracts power directly from the foot strike of a user during walking. Energy is harvested with a textile pump integrated into the insole of the user’s shoe and stored in a wearable textile bladder to operate pneumatic actuators on demand, with system performance optimized based on a mechano-fluidic model. The system recovered a maximum average power of nearly 3 W with over 20% conversion efficiency—outperforming electromagnetic, piezoelectric, and triboelectric alternatives—and was used to power a wearable arm-lift device that assists shoulder motion and a supernumerary robotic arm, demonstrating its capability as a lightweight, low-cost, and comfortable solution to support adults with upper body functional limitations in activities of daily living.

Bias and Motivation of Energy Monitoring during Exercise under Scientometric Perspective

The thermodynamics is of great value for better practical applications of Internet of Things (IoT). With the development of IoT, Wearable Energy Harvester can provide more abundant measurement methods for human engineering and human heat. However, how close the relationship is between traditional individual thermal measurement and emerging technologies remains a topic that has not been paid attention to. Therefore, this paper first sorts and summarizes the literature of human calorimetry and then shows the cross field of Wearable Energy Harvester and traditional research using graph theory. Specifically, this paper presents the evolution of the research field in the form of dual-map overlays by characterizing the network structure and measuring the structural transformation of the knowledge network. With Web of Science as the data source and CiteSpace 5.0 software as the tool to make a knowledge graph for quantitative statistics, it is found that the research hotspot of individual energy expenditure is in the physiological field. The starting point of individual thermal energy monitoring technology represented by Wearable Energy Harvester is to aid with human health. However, as time progresses, although the development of this field still focuses on the fields of chemical industry and materials, it has gradually become closely related to multiple disciplines such as the monitoring of thermal energy during high-intensity sports training.

Wearable Piezoelectric Energy Harvesting From Human Gait: Modeling and Experimental Validation

Wearable devices with a flexible and stretchable form factor enable novel and attractive applications. The promising outlook for these devices is hindered by their limited battery capacity constrained by size and other physical limitations. Motion energy harvesting can alleviate these challenges and reduce dependency on batteries. Despite this potential, a definitive capacity for wearable motion energy harvesting has yet to be identified. To facilitate the exploration of this capacity, we propose an analytical model for the energy harvesting potential of a wearable piezoelectric energy harvester placed on the knee joint. In addition, we validate the proposed model extensively with a prototype piezoelectric energy harvester. Our results show that the proposed model estimates the harvested power with less than 5% mean absolute percentage error for all gait speeds and various transducer configurations. In addition, the proposed harvester can generate 161 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> power at 5 mph. We further show that this amount can sustain a 35 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> load.

A Multibeam and Surface Plasmonic Clothing With RF Energy-Localized Harvester for Powering Battery-Free Wireless Sensor

A wearable radio-frequency (RF) energy-localized harvester with multiple antennas and spoof surface plasmon (SSP) structure for multibeam radiation is presented to power the Bluetooth sensor module. The harvester contains four separate antennas connected by SSP waveguides, while the loop is applied to excite the structure to generate multibeam radiation and improve energy harvesting. The radiative waves will be harvested and converted into surface waves on the SSP waveguides, then, confined in a localized area of the structure through the evanescent field interactions between the current of SSP and the loop in a contactless way. More importantly, it is free of RF connectors and soldering works on the interface between the energy harvester and clothing. In addition, the wearable energy harvester is entirely made of flexible materials, such as conductive fabrics, polyimide, and nylon fabrics in a compact and low-profile structure. The loop can easily be integrated with the rectify circuit and power management unit (PMU) to provide direct-current (dc) power for different kinds of wireless sensor modules. In this design, the harvested power can support a battery-free Bluetooth temperature and humidity sensor with a power density of 2.75 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The complete system-level demonstration of RF energy harvesting shows the potential to power small electronic devices for wearable applications.

Constructing A/B-Side Heterogeneous Asynchronous Structure with Ag2Se Layers and Bushy-like PPy toward High-Performance Flexible Photo-Thermoelectric Generators.

The enthusiasm for environmental energy harvesting has triggered a boom in research on photo-thermoelectric generators (PTEGs), and the relevant applications are mainly focused on self-energy supply sensors owing to the limitations of their output performances. For this purpose, high-output hierarchical heterogeneous PTEGs were constructed by assembling separately optimized thermoelectric (TE) and photothermal (PT) layers. The pressure and temperature conditions of Ag2Se films during the pressing process were first explored, and the sample with the optimal performance and least defects was selected as the TE layer. At the same time, different morphologies of polypyrrole (PPy) PT layers were electrochemically synthesized. It is found that the three-dimensional structure of Bushy-PPy could effectively improve the light absorption and thus enhance the PT conversion performance. The final assembled PTEG can produce an output voltage of -9.03 mV and an output power of 3.53 μW under the irradiation of a near-infrared light source of 300 mW cm-2 without a cooling source, and it can also achieve considerable output power under visible light irradiation of different intensities. Combining its high retentions of electrical conductivity (99%) and output performance (97%) after 1000 bending-tension cycles, it is proven to be a promising next-generation wearable flexible energy harvesting device.

Toward 3D double-electrode textile triboelectric nanogenerators for wearable biomechanical energy harvesting and sensing

Textile-based triboelectric nanogenerators (T-TENGs) have attracted much attention nowadays because of their excellent flexibility and wearability in biomechanical energy harvesting and sensing. However, T-TENGs prepared by current methods of layer-by-layer stacking, stitching, or coating on the surface of fabric still have some problems such as poor comfort, complicated preparation processes, and easy peeling of coating materials. Herein, a 3D double-electrode and machine-knittable fabric TENG (3D-FTENG) with integrated positive and negative triboelectric materials and electrode materials is proposed by coated core-spun yarn and programmable spacer fabric technologies. The triboelectric materials and electrodes of 3D-FTENG are made of thermoplastic polyurethane (TPU) coated and polydimethylsiloxane (PDMS) coated Ag-cotton core-spun yarns. With structural design, three 3D-FTENGs with the same surface structures but different intermediate structures are designed and prepared, and the influence of intermediate structures on performance of 3D-FTENG is further studied. The power density of 3D-FTENG with the crisscross structure as intermediate layer reach up to 200.93 mW/m2. The 3D-FTENG is also soft, comfortable, high air permeable and washable. The output electric performance can be maintained after washing cycles and 50,000 cyclic tests. The 3D-FTENG can not only power small electronic products but also monitor human motions, demonstrating good potentials in wearable electronics.