A universal self-charging system driven by random biomechanical energy for sustainable operation of mobile electronics

Piezoelectric Energy Harvester Technologies: Synthesis, Mechanisms, and Multifunctional Applications

Piezoelectric energy harvesters have gained significant attention in recent years due to their ability to convert ambient mechanical vibrations into electrical energy, which opens up new possibilities for environmental monitoring, asset tracking, portable technologies and powering remote "Internet of Things (IoT)" nodes and sensors. This review explores various aspects of piezoelectric energy harvesters, discussing the structural designs and fabrication techniques including inorganic-based energy harvesters (i.e., piezoelectric ceramics and ZnO nanostructures) and organic-based energy harvesters (i.e., polyvinylidene difluoride (PVDF) and its copolymers). The factors affecting the performance and several strategies to improve the efficiency of devices have been also explored. In addition, this review also demonstrated the progress in flexible energy harvesters with integration of flexibility and stretchability for next-generation wearable technologies used for body motion and health monitoring devices. The applications of the above devices to harvest various forms of mechanical energy are explored, as well as the discussion on perspectives and challenges in this field.

Elastic Self-Recovering Hybrid Nanogenerator for Water Wave Energy Harvesting and Marine Environmental Monitoring

To achieve large-scale development of triboelectric nanogenerators (TENGs) for water wave energy harvesting and powering the colossal sensors widely distributed in the ocean, facile and scalable TENGs with high output are urgently required. Here, an elastic self-recovering hybrid nanogenerator (ES-HNG) is proposed for water wave energy harvesting and marine environmental monitoring. The elastic skeletal support of the ES-HNG is manufactured using three-dimensional (3D) printing technology, which is more conducive to the large-scale integration of the ES-HNG. Moreover, the combination of a TENG and an electromagnetic generator (EMG) optimizes the utilization of device space, leading to enhanced energy harvesting efficiency. Experimental results demonstrate that the TENG achieves a peak power output of 42.68 mW, and the EMG reaches a peak power output of 4.40 mW. Furthermore, various marine environment monitoring sensors, such as a self-powered wireless meteorological monitoring system, a wireless alarm system, and a water quality monitoring pen, have been successfully powered by the sophisticated ES-HNG. This work introduces an ES-HNG for water wave energy harvesting, which demonstrates potential in marine environment monitoring and offers a new solution for the sustainable development of the marine internet of things.

Achieving Self-Reinforcing Triboelectric-Electromagnetic Hybrid Nanogenerator by Magnetocaloric and Magnetization Effects of Gadolinium

Triboelectric-electromagnetic hybrid nanogenerator (TEHG) has emerged as a promising technology for distributed energy harvesting. However, currently reported hybrid generators are straightforward combinations of two functional components. Moreover, inevitable heat from friction intensifies material abrasion and degrades the performance of polymer-based triboelectric nanogenerators (TENGs). Here, a self-reinforcing TEHG (SR-TEHG) that harnesses the magnetocaloric and magnetization effects of gadolinium (Gd), is proposed. The synergy between TENG and electromagnetic generator (EMG) renders them an indivisible unit. Leveraging Gd's magnetocaloric effect, an efficient heat transfer mechanism is constructed to cool the tribolayer and strengthen the device's electrical stability. After 80 h of continuous operation, the optimized TENG occupies a charge decay rate of only 0.32% per hour, significantly outperforming most existing TENGs. Additionally, Gd's magnetization effect boosts the power of EMG by ≈80.84%. This work provides a universal solution in hybrid generators where internal components reinforce each other, achieving a synergistic effect of 1 + 1 > 2.

Sodium Niobate Nanowires Embedded PVA-Hydrogel-Based Triboelectric Nanogenerator for Versatile Energy Harvesting and Self-Powered CO Gas Sensor

The surging demand for sustainable energy solutions and adaptable electronic devices has led to the exploration of alternative and advanced power sources. Triboelectric Nanogenerators (TENGs) stand out as a promising technology for efficient energy harvesting, but research on fully flexible and environmental friendly TENGs still remain limited. In this study, an innovative approach is introduced utilizing an ionic-solution modified conductive hydrogel embedded with piezoelectric sodium niobate nanowires-based Triboelectric Nanogenerator (NW-TENG), offering intrinsic advantages to healthcare and wearable devices. The synthesized NW-TENG, with a 12.5 cm2 surface area, achieves peak output performance, producing ≈840 V of voltage and 2.3 µC of charge transfer, respectively. The rectified energy powers up 30 LEDs and a stopwatch; while the NW-TENG efficiently charges capacitors from 1µF to 100 µF, reaching 1 V within 4 to 65 s at 6 Hz. Integration with prototype carbon monoxide (CO) gas sensor transform the device into a self-powered gas sensory technology. This study provides a comprehensive understanding of nanowire effects on TENG performance, offering insights for designing highly flexible and environmentally friendly TENGs, and extending applications to portable self-powered gas sensors and wearable devices.

Self-Charging Power System Empowered by Bismuth Halide Perovskite-Based Hybrid Nanogenerator and Lithium-ion Battery

Halide perovskite, renowned for its multifunctional properties, shows considerable promise for realizing self-charging power systems. In this study, a lead-free methylammonium bismuth iodide (MA3Bi2I9) perovskite is used to create a self-charging power unit (SPU). This involves constructing a hybrid piezoelectric-triboelectric nanogenerator (Hybrid-TENG) and utilizing MA3Bi2I9 for energy storage as an anode in a lithium-ion battery (LIB). Initially, MA3Bi2I9 nanorods are synthesized and composited with a polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene polymer. The dielectric and mechanical properties of composite films having perovskite loading content are investigated. The optimized Hybrid-TENG exhibits superior performance, generating a voltage of 537 V, current density of 13.2 µA cm- 2, and maximum power density of 3.04 mW cm-2, which can be attributed to the high piezoelectric coefficient of MA3Bi2I9 nanorods (≈20.6 pm V-1). A MA3Bi2I9 thin film, serving as an electrode in LIB, demonstrates a high specific capacity of 2378.9 mAh cm-3 (578.8 mAh g-1) with a capacity retention of ≈87.5% over 100 cycles, underscoring its stable performance. Furthermore, a Hybrid-TENG is employed to charge the MA3Bi2I9-based LIB, thus realizing an SPU for driving portable electronics. This study highlights the promising potential of perovskites for developing efficient nanogenerators and LIBs, paving the way for sustainable energy solutions in small-scale electronics.

Deep-Learning-Assisted Sensor with Multiple Perception Capabilities for an Intelligent Driver Assistance Monitoring System

Driver assistance systems can help drivers achieve better control of their vehicles while driving and reduce driver fatigue and errors. However, the current driver assistance devices have a complex structure and severely violate the privacy of drivers, hindering the development of driver assistance technology. To address these limitations, this article proposes an intelligent driver assistance monitoring system (IDAMS), which combines a Kresling origami structure-based triboelectric sensor (KOS-TS) and a convolutional neural network (CNN)-based data analysis. For different driving behaviors, the output signals of the KOS-TSs contain various features, such as a driver's pressing force, pressing time, and sensor triggering sequence. This study develops a multiscale CNN that employs different pooling methods to process KOS-TS data and analyze temporal information. The proposed IDAMS is verified by driver identification experiments, and the results show that the accuracy of the IDAMS in discriminating eight different users is improved from 96.25% to 99.38%. In addition, the results indicate that IDAMS can successfully monitor driving behaviors and can accurately distinguish between different driving behaviors. Finally, the proposed IDAMS has excellent hands-off detection (HOD), identification, and driving behavior monitoring capabilities and shows broad potential for application in the fields of safety warning, personalization, and human-computer interaction.

Observation of Ultrahigh Photoconductivity in DNA-MoS2 Nano-Biocomposite

A nano-biocomposite film with ultrahigh photoconductivity remains elusive and critical for bio-optoelectronic applications. A uniform, well-connected, high-concentration nanomaterial network in the biological matrix remains challenging to achieve high photoconductivity. Wafer-scale continuous nano-biocomposite film without surface deformations and cracks plays another major obstacle. Here ultrahigh photoconductivity is observed in deoxyribonucleic acid-molybdenum disulfide (DNA-MoS2) nano-biocomposite film by incorporating a high-concentration, well-percolated, and uniform MoS2 network in the ss-DNA matrix. This is achieved by utilizing DNA-MoS2 hydrogel formation, which results in crack-free, wafer-scale DNA-MoS2 nano-biocomposite films. Ultra-high photocurrent (5.5 mA at 1 V) with a record-high on/off ratio (1.3 × 106) is observed, five orders of magnitude higher than conventional biomaterials (≈101) reported so far. The incorporation of the Wely semimetal (Bismuth) as an electrical contact exhibits ultrahigh photoresponsivity (2.6 × 105 A W-1). Such high photoconductivity in DNA-MoS2 nano-biocomposite could bridge the gap between biology, electronics, and optics for innovative biomedicine, bioengineering, and neuroscience applications.

Biomimetic Exogenous "Tissue Batteries" as Artificial Power Sources for Implantable Bioelectronic Devices Manufacturing

Implantable bioelectronic devices (IBDs) have gained attention for their capacity to conformably detect physiological and pathological signals and further provide internal therapy. However, traditional power sources integrated into these IBDs possess intricate limitations such as bulkiness, rigidity, and biotoxicity. Recently, artificial "tissue batteries" (ATBs) have diffusely developed as artificial power sources for IBDs manufacturing, enabling comprehensive biological-activity monitoring, diagnosis, and therapy. ATBs are on-demand and designed to accommodate the soft and confining curved placement space of organisms, minimizing interface discrepancies, and providing ample power for clinical applications. This review presents the near-term advancements in ATBs, with a focus on their miniaturization, flexibility, biodegradability, and power density. Furthermore, it delves into material-screening, structural-design, and energy density across three distinct categories of TBs, distinguished by power supply strategies. These types encompass innovative energy storage devices (chemical batteries and supercapacitors), power conversion devices that harness power from human-body (biofuel cells, thermoelectric nanogenerators, bio-potential devices, piezoelectric harvesters, and triboelectric devices), and energy transfer devices that receive and utilize external energy (radiofrequency-ultrasound energy harvesters, ultrasound-induced energy harvesters, and photovoltaic devices). Ultimately, future challenges and prospects emphasize ATBs with the indispensability of bio-safety, flexibility, and high-volume energy density as crucial components in long-term implantable bioelectronic devices.

The Role of Artificial Intelligence of Things in Achieving Sustainable Development Goals: State of the Art

With the environmental and societal changes, the achievement of sustainable development goals (SDGs) and the realization of sustainability in general is now more important than ever. Through a bibliometric analysis and scientific mapping analysis, this study aims to explore and provide a review regarding the role of artificial intelligence (AI), the Internet of Things (IoT), and artificial intelligence of things (AIoT) in realizing sustainable development and achieving SDGs. AIoT can be defined as the combination of AI with IoT to create more efficient and data-driven interconnected, intelligent, and autonomous IoT systems and infrastructure that use AI methods and algorithms. The analysis involved 9182 documents from Scopus and Web of Science (WoS) from 1989 to 2022. Descriptive statistics of the related documents and the annual scientific production were explored. The most relevant and impactful authors, articles, outlets, affiliations, countries, and keywords were identified. The most popular topics and research directions throughout the years and the advancement of the field and the research focus were also examined. The study examines the results, discusses the main findings, presents open issues, and suggests new research directions. Based on the results of this study, AIoT emerged as an important contributor in ensuring sustainability and in achieving SDGs.

High-Performing and Capacitive-Matched Triboelectric Implants Driven by Ultrasound

In implantable bioelectronics, which aim for semipermanent use of devices, biosafe energy sources and packaging materials to protect devices are essential elements. However, research so far has been conducted in a direction where they cannot coexist. Here, the development of capacitance-matched triboelectric implants driven is reported by ultrasound under 500 mW cm-2 safe intensity and realize a battery-free, miniatured, and wireless neurostimulator with full titanium (Ti) packaging. The triboelectric implant with high dielectric composite, which has ultralow output impedance, can efficiently deliver sufficient power to generate the stimulation pulse without an energy-storing battery, despite ultrasound attenuation due to the Ti, and has the highest energy transmission efficiency among those reported so far. In vivo study using a rat model demonstrated that the proposed device system is an effective solution for relieving urinary symptoms. These achievements provide a significant step toward permanently implantable devices for controlling human organs and treating various diseases.

Self-Powered Sensing in Wearable Electronics─A Paradigm Shift Technology

With the advancements in materials science and micro/nanoengineering, the field of wearable electronics has experienced a rapid growth and significantly impacted and transformed various aspects of daily human life. These devices enable individuals to conveniently access health assessments without visiting hospitals and provide continuous, detailed monitoring to create comprehensive health data sets for physicians to analyze and diagnose. Nonetheless, several challenges continue to hinder the practical application of wearable electronics, such as skin compliance, biocompatibility, stability, and power supply. In this review, we address the power supply issue and examine recent innovative self-powered technologies for wearable electronics. Specifically, we explore self-powered sensors and self-powered systems, the two primary strategies employed in this field. The former emphasizes the integration of nanogenerator devices as sensing units, thereby reducing overall system power consumption, while the latter focuses on utilizing nanogenerator devices as power sources to drive the entire sensing system. Finally, we present the future challenges and perspectives for self-powered wearable electronics.

A Flexible Pressure Sensor Based on Graphene/Epoxy Resin Composite Film and Screen Printing Process

At present, flexible pressure-sensitive materials generally have problems with weak adhesion and poor wear resistance, which easily result in friction failure when used for plantar pressure detection. In this study, a flexible pressure sensor with the advantages of a wide detection range, fast recovery, and good abrasive resistance was designed and prepared based on the screen printing process. The pressure-sensitive unit with a structural size of 5 mm× 8 mm was a functional material system due to the use of graphene and epoxy resin. The influence of the different mass ratios of the graphene and epoxy resin on the sensing properties was also studied. The test results showed that when the mass ratio of graphene to epoxy resin was 1:4, the response time and recovery time of the sensing unit were 40.8 ms and 3.7 ms, respectively, and the pressure detection range was 2.5-500 kPa. The sensor can detect dynamic pressure at 0.5 Hz, 1 Hz, 2 Hz, 10 Hz, and 20 Hz and can withstand 11,000 cycles of bending. In addition, adhesion tests showed that the high viscosity of the epoxy helped to improve the interlayer bond between the pressure-sensitive materials and the flexible substrate, which makes it more suitable for plantar pressure detection environments, where friction is common.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Improving the Output Efficiency of Triboelectric Nanogenerator by a Power Regulation Circuit

Triboelectric nanogenerator (TENG) is a promising technology for harvesting energy from various sources, such as human motion, wind and vibration. At the same time, a matching backend management circuit is essential to improve the energy utilization efficiency of TENG. Therefore, this work proposes a power regulation circuit (PRC) suitable for TENG, which is composed of a valley-filling circuit and a switching step-down circuit. The experimental results indicate that after incorporating a PRC, the conduction time of each cycle of the rectifier circuit doubles, increasing the number of current pulses in the TENG output and resulting in an output charge that is 1.6 fold that of the original circuit. Compared with the initial output signal, the charging rate of the output capacitor increased significantly by 75% with a PRC at a rotational speed of 120 rpm, significantly improving the utilization efficiency of the TENG's output energy. At the same time, when the TENG powers LEDs, the flickering frequency of LEDs is reduced after adding a PRC, and the light emission is more stable, which further verifies the test results. The PRC proposed in this study can enable the energy harvested by the TENG to be utilized more efficiently, which has a certain promoting effect on the development and application of TENG technology.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Moisture-Enabled Germination of Heat-Activated Bacillus Endospores for Rapid and Practical Bioelectricity Generation: Toward Portable, Storable Bacteria-Powered Biobatteries

Small-scale battery-like microbial fuel cells (MFCs) are a promising alternative power source for future low-power electronics. Controllable microbial electrocatalytic activity in a miniaturized MFC with unlimited biodegradable energy resources would enable simple power generation in various environmental settings. However, the short shelf-life of living biocatalysts, few ways to activate the stored biocatalysts, and extremely low electrocatalytic capabilities render the miniature MFCs unsuitable for practical use. Here, heat-activated Bacillus subtilis spores are revolutionarily used as a dormant biocatalyst that can survive storage and rapidly germinate when exposed to special nutrients that are preloaded in the device. A microporous, graphene hydrogel allows the adsorption of moisture from the air, moves the nutrients to the spores, and triggers their germination for power generation. In particular, forming a CuO-hydrogel anode and an Ag₂ O-hydrogel cathode promotes superior electrocatalytic activities leading to an exceptionally high electrical performance in the MFC. The battery-type MFC device is readily activated by moisture harvesting, producing a maximum power density of 0.4 mW cm^-2 and a maximum current density of 2.2 mA cm^-2 . The MFC configuration is readily stackable in series and a three-MFC pack produces enough power for several low-power applications, demonstrating its practical feasibility as a sole power source.

From Piezoelectric Nanogenerator to Non-Invasive Medical Sensor: A Review

Piezoelectric nanogenerators (PENGs) not only are able to harvest mechanical energy from the ambient environment or body and convert mechanical signals into electricity but can also inform us about pathophysiological changes and communicate this information using electrical signals, thus acting as medical sensors to provide personalized medical solutions to patients. In this review, we aim to present the latest advances in PENG-based non-invasive sensors for clinical diagnosis and medical treatment. While we begin with the basic principles of PENGs and their applications in energy harvesting, this review focuses on the medical sensing applications of PENGs, including detection mechanisms, material selection, and adaptive design, which are oriented toward disease diagnosis. Considering the non-invasive in vitro application scenario, discussions about the individualized designs that are intended to balance a high performance, durability, comfortability, and skin-friendliness are mainly divided into two types: mechanical sensors and biosensors, according to the key role of piezoelectric effects in disease diagnosis. The shortcomings, challenges, and possible corresponding solutions of PENG-based medical sensing devices are also highlighted, promoting the development of robust, reliable, scalable, and cost-effective medical systems that are helpful for the public.

An Environmental-Inert and Highly Self-Healable Elastomer Obtained via Double-Terminal Aromatic Disulfide Design and Zwitterionic Crosslinked Network for Use as a Triboelectric Nanogenerator

Due to the ongoing development of portable/mobile electronics, sources to power have received widespread attention. Compared to chemical batteries as power sources, triboelectric nanogenerators (TENGs) possess lots of advantages, including the ability to harvest energy via human motions, flexible structures, environment-friendliness, and long-life characteristics. Although many self-healable TENGs are reported, the achievement of a muscle-like elasticity and the ability to recover from inevitable damage under extreme conditions (such as a high/low temperature and/or humidity) remain a challenge. Herein, a "double-terminal aromatic disulfide" on a structure with zwitterions as branched chains is reported to engineer the high-efficient self-healable elastomer for application in a flexible TENG. The as-designed material exhibits a repeatable elastic recovery (at 250% elongation) and a self-healing efficiency with an ultimate tensile stress of 96% over 2 h, representing an improvement on previously reported disulfide-based elastomers. The elastomer can autonomously recover by 50% even at a subzero temperature of -30 °C within 24 h. The elastomer-based TENG, as a self-driven sensor for detecting human behavior, is demonstrated to exhibit stable outputs and self-healing in the temperature range of -30 to 60 °C, and so is expected to promote the development of self-powered electronics for next-generation human-machine communications.

Impedance Coupled Voltage Boosting Circuit for Polyvinylidene Fluoride Based Energy Harvester

Polyvinylidene fluoride (PVDF) is an emerging method for energy harvesting by fluid motion with superior flexibility. However, the PVDF energy harvester, which has a high internal impedance and generates a low voltage, has a large power transmission loss. To overcome this problem, we propose an impedance-coupled voltage-boosting circuit (IC-VBC) that reduces the impedance of the PVDF energy harvester and boosts the voltage. SPICE simulation results show that IC-VBC reduces the impedance of the PVDF energy harvester from 4.3 MΩ to 320 kΩ and increases the output voltage by 2.52 times. We successfully charged lithium-ion batteries using the PVDF energy harvester and IC-VBC with low-speed wind power generation.

Multidiscipline Applications of Triboelectric Nanogenerators for the Intelligent Era of Internet of Things

In the era of 5G and the Internet of things (IoTs), various human-computer interaction systems based on the integration of triboelectric nanogenerators (TENGs) and IoTs technologies demonstrate the feasibility of sustainable and self-powered functional systems. The rapid development of intelligent applications of IoTs based on TENGs mainly relies on supplying the harvested mechanical energy from surroundings and implementing active sensing, which have greatly changed the way of human production and daily life. This review mainly introduced the TENG applications in multidiscipline scenarios of IoTs, including smart agriculture, smart industry, smart city, emergency monitoring, and machine learning-assisted artificial intelligence applications. The challenges and future research directions of TENG toward IoTs have also been proposed. The extensive developments and applications of TENG will push forward the IoTs into an energy autonomy fashion.

Self-powered image array composed of touch-free sensors fabricated with semiconductor nanowires

We successfully develop a self-powered image array (IA) composed of 16 touch-free sensors (TFSs) fabricated with semiconductor InN nanowires (NWs) as a response medium. Without using a power supply, the InN-NW TFS can detect the position of a human hand 30 cm away from the device surface. It also distinguishes different materials such as polyimide, Al foil, printing paper, latex, and polyvinyl chloride in non-contact mode at a distance of 1 cm. The self-powered TFS-IA clearly distinguishes square-shaped transparent polydimethylsiloxane film attached to the back of a human hand positioned 5 cm from the device, indicating the possibility for detecting changes in the surface texture of human skin, such as skin burns or skin cancer. The performance of the self-powered TFS and TFS-IA is attributed to high electrostatic induction of InN NWs by external triboelectricity resulting from the simple movement of the target object, which differs markedly from conventional sensors designed to detect variations in the temperature or light essentially using a power supply.

Toward a New Era of Sustainable Energy: Advanced Triboelectric Nanogenerator for Harvesting High Entropy Energy

Widely distributed across the environment, irregular micro-nano mechanical high entropy energy (HEE) is a new promising recoverable energy, in which the development of matched harvesting technology is imperative to fit in with the requirements of booming sustainable energy in the new era. The triboelectric nanogenerator (TENG) is a very efficient technology for harvesting micro-nano HEE, especially when converting irregular, low-frequency, weak mechanical energy into electricity. Here, the latest advancements are comprehensively reviewed in using TENGs for sustainable energy, sensing, and other applications. The fundamental theory and overwhelming superiority of TENG is systematically analyzed as a sustainable energy with four representative domains: micro-nano distributed power sources, self-powered sensing systems, direct high-voltage power sources, and large-scale blue energy. The review is concluded with a discussion of the challenges of leveraging TENGs for sustainable energy engineering. The striving directions of TENG technologies are proposed with a concentration on basic research and commercialization for the new ear of 5G and Internet of Things.

Triboelectric nanogenerators as wearable power sources and self-powered sensors

Smart wearable technologies are augmenting human bodies beyond our biological capabilities in communication, healthcare and recreation. Energy supply and information acquisition are essential for wearable electronics, whereas the increasing demands in multifunction are raising the requirements for energy and sensor devices. The triboelectric nanogenerator (TENG), proven to be able to convert various mechanical energies into electricity, can fulfill either of these two functions and therefore has drawn extensive attention and research efforts worldwide. The everyday life of a human body produces considerable mechanical energies and, in the meantime, the human body communicates mainly through mechanical signals, such as sound, body gestures and muscle movements. Therefore, the TENG has been intensively studied to serve as either wearable sources or wearable self-powered sensors. Herein, the recent finding on the fundamental understanding of TENGs is revisited briefly, followed by a summary of recent advancements in TENG-based wearable power sources and self-powered sensors. The challenges and prospects of this area are given as well.

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.

Ferromagnetic-Based Charge-Accumulation Triboelectric Nanogenerator With Ultrahigh Surface Charge Density

An encouraging micro-energy harvesting technology, the triboelectric nanogenerator (TENG), has been proven to transfer ambient environmental micro-energy into electricity, but a low surface charge density results in low performance and limits the practical application of TENG. Here, a ferromagnetic-based charge-accumulation TENG (FC-TENG) is proposed with ultrahigh surface charge density and performances. The FC-TENG introduces a ferromagnetic media to enhance the output charge by magnetization effect. Meanwhile, the charge can also be continuously accumulated by the charge pump effects. Based on these two effects, an ultra-high surface charge density of 2.85 mC m^-2 is obtained under ambient atmospheric conditions using an ultra-thin PET film (3 µm) and deposited Permalloy ferromagnetic electrodes. Meanwhile, the surface charge density of the FC-TENG can always maintain more than 1.5 mC m^-2 , even if the relative humidity arrives at 90%. This work provides a prospective technical mode to enhance the surface charge density of TENG, which would shed a new insight and guidance on the high-performance TENG for various environmental conditions such as the ocean, industrial manufacturing, aerospace, and rail traffic.

Nanogenerator-Based Wireless Intelligent Motion Correction System for Storing Mechanical Energy of Human Motion

As it is urgently needed to address the energy consumption and health care problems caused by population growth, the field of sustainable energy collection and storage equipment as well as intelligent health care for monitoring human motion behavior has received wide attention and achieved rapid development. However, the portable intelligent systems that integrate them have not been widely discussed. In this work, we propose a design of a nanogenerator-based wireless intelligent motion correction system, combining triboelectric nanogenerator technology with wireless intelligent host computer signal processing and visualization systems. Under the condition of no external power supply, a noninvasive triboelectric nanogenerator (FL-TENG) sensor integrated system stores the mechanical energy due to human movement behavior and drives wireless micro-electronic devices to realize the human–computer interaction application of the intelligent system. In the conducted test, the reported instantaneous output of an ordinary clap action was around 241V. For a variety of physical exercise types being monitored, it can accurately determine human movement behavior and perform error correction and scoring for movement techniques. Additionally, using hydrogel as an electrode improves the service life and stability of the device. Therefore, this flexible and convenient design concept is beneficial to the development and utilization of sustainable energy and sports activities. In addition, it extends the application prospects of FL-TENG in self-powered sensing systems.

Coaxial Spring-Like Stretchable Triboelectric Nanogenerator Toward Personal Healthcare Monitoring

Stretchable triboelectric nanogenerators have attracted increasing interests in the field of Internet of Things and sensor network. Therefore, great efforts have been made to realize the stretchability of electronic devices via elaborated material configurations and ingenious device designs. In this work, a flexible and stretchable TENG is developed with a coaxial spring-like structure. The unique structure allows it to generate electrical energy for different degrees of stretching deformations. Its output demonstrates good response to the strain and frequency of the mechanical deformation. At the same time, it exhibits excellent stability and washability. The TENG can be worn on the human fingers, elbow, and knee to monitor the body activities. Furthermore, a self-powered temperature sensor system is fabricated by integrating the TENG with a temperature sensor to identify the operating ambient temperature in real time. A combination of this flexible and stretchable TENG with body motions and a temperature sensor brings a novel insight into wearable functional electronics and user-friendly health monitoring, which has an important basic research significance and practical application value in biometric systems.

Harvesting circuits for triboelectric nanogenerators for wearable applications

Internet of Things (IoT) and recently Internet of Nano Things (IoNT) bear the promise of new devices able to communicate and assist our daily lives toward wearable technologies which demand a versatile integration such as in wireless body networks (WBN), sensing, and health monitorization. These must comply with stringent constraints on energy usage. Dimensions and complexity intensify the need for small and maintenance-free power sources. Environment energy harvesting and storage is an important approach to sustain operation for a long time. Triboelectric nanogenerators (TENGs) arise as a strong and promising solution to power the new field of outcoming self-sustainable devices, implantable, and wearable devices. They can transform mechanical energy in different modes, have simple structures, and use vulgar and sustainable materials. This paper makes a review about TENGs technology, construction, materials, operation, and focus on strategies for harvesting circuits. Main challenges like efficiency, reliability, energy storage, and sustainability are discussed.

Underwater Monitoring Networks Based on Cable-Structured Triboelectric Nanogenerators

The importance of ocean exploration and underwater monitoring is becoming vital, due to the abundant biological, mineral, energy, and other resources in the ocean. Here, a self-powered underwater cable-based triboelectric nanogenerator (TENG) is demonstrated for underwater monitoring of mechanical motion/triggering, as well as searching and rescuing in the sea. Using a novel double-layer winding method combined with ferroelectric polarization, a self-powered cable-structured sensor with a stable electrical output has been manufactured, which can accurately respond to a variety of external mechanical stimuli. A self-powered cable sensing network woven using smart cables can comprehensively transmit information, such as the plane position and dive depth of a submersible. More precisely, it can analyze its direction of movement, speed, and path, along with transmitting information such as the submersible's size and momentum. The developed self-powered sensor based on the cable-based TENG not only has low cost and simple structure but also exhibits working accuracy and stability. Finally, the proposed work provides new ideas for future seabed exploration and ocean monitoring.

Recent Progress of Switching Power Management for Triboelectric Nanogenerators

Based on the coupling effect of contact electrification and electrostatic induction, the triboelectric nanogenerator (TENG) as an emerging energy technology can effectively harvest mechanical energy from the ambient environment. However, due to its inherent property of large impedance, the TENG shows high voltage, low current and limited output power, which cannot satisfy the stable power supply requirements of conventional electronics. As the interface unit between the TENG and load devices, the power management circuit can perform significant functions of voltage and impedance conversion for efficient energy supply and storage. Here, a review of the recent progress of switching power management for TENGs is introduced. Firstly, the fundamentals of the TENG are briefly introduced. Secondly, according to the switch types, the existing power management methods are summarized and divided into four categories: travel switch, voltage trigger switch, transistor switch of discrete components and integrated circuit switch. The switch structure and power management principle of each type are reviewed in detail. Finally, the advantages and drawbacks of various switching power management circuits for TENGs are systematically summarized, and the challenges and development of further research are prospected.

Flexible Triboelectric Nanogenerators Based on Electrospun Poly(vinylidene fluoride) with MoS2/Carbon Nanotube Composite Nanofibers

With the miniaturization of wearable smart devices, the demand for portable and sustainable power sources is increasing. Herein, a flexible and lightweight triboelectric nanogenerator (PMC-TENG) was fabricated with MoS₂/carbon nanotube (MC)-doped PVDF as the friction substrate based on electrospinning for harvesting random body motion energy under complex mechanical deformations. The charge density on the friction surface of PVDF nanofibers was found to increase significantly as the introduced electron acceptor of the MC composite, and nylon as a clothing material for another friction layer simplifies the structure of the device. Upon optimization of the electrospinning preparation process, the output voltage of the prepared PMC-TENG can reach >300 V and the instantaneous power can reach 0.484 mW (∼6 cm × 6 cm). At the same time, the PMC-TENG remains stable over 3000 cycles and has the ability to charge a capacitor. The flexible device demonstrates an excellent capability of converting mechanical energy to electrical energy. Therefore, this study has good prospects for application in the field of power supply for portable electronic devices and others.

Bioinspired Triboelectric Nanosensors for Self-Powered Wearable Applications

The sustainable operation of wearable sensors plays an important role in continuous and longtime health monitoring. Conventional batteries, which are bulky and rigid, do not satisfy these requirements and, rather, cause additional economic burdens and environmental problems by regular replacement of power sources. This article provides a review on an alternative solution in the form of self-powered devices that can harvest energy from the surrounding environment to support the operation of the wearable sensor. The Review starts with an introduction of the self-powered triboelectric nanosensors (TENSs) and its two independent modules: the energy harvester and the sensing module. The Review continues with the TENS-related bioinspired designs for wearable applications, while providing a bird's-eye view of their characteristics and applications. The ongoing challenges and prospects for providing personal healthcare with self-powered TENS are presented and discussed.

p-n Junction Based Direct-Current Triboelectric Nanogenerator by Conjunction of Tribovoltaic Effect and Photovoltaic Effect

Triboelectric nanogenerators (TENGs) have attracted much interest in recent years, due to its effectiveness and low cost for converting high-entropy mechanical energy into electric power. The traditional TENGs generate an alternating current, which requires a rectifier to provide a direct-current (DC) power supply. Herein, a dynamic p-n junction based direct-current triboelectric nanogenerator (DTENG) is demonstrated. When a p-Si wafer is sliding on a n-GaN wafer, carriers are generated at the interface and a DC current is produced along the direction of the built-in electric field, which is called the tribovoltatic effect. Simultaneously, an UV light is illuminated on the p-n junction to enhance the output. The results indicate that the current increases 13 times and the voltage increases 4 times under UV light (365 nm, 28 mW/cm²) irradiation. This work demonstrates the coupling between the tribovoltaic effect and the photovoltaic effect in DTENG semiconductors, promoting further development for energy harvesting in mechanical energy and photon energy.

An Electret/Hydrogel-Based Tactile Sensor Boosted by Micro-Patterned and Electrostatic Promoting Methods with Flexibility and Wide-Temperature Tolerance

With the rising demand for wearable, multifunctional, and flexible electronics, plenty of efforts aiming at wearable devices have been devoted to designing sensors with greater efficiency, wide environment tolerance, and good sustainability. Herein, a thin film of double-network ionic hydrogel with a solution replacement treatment method is fabricated, which not only possesses excellent stretchability (>1100%) and good transparency (>80%), but also maintains a wide application temperature range (-10~40 °C). Moreover, the hydrogel membrane further acts as both the flexible electrode and a triboelectric layer, with a larger friction area achieved through a micro-structure pattern method. Combining this with a corona-charged fluorinated ethylene propylene (FEP) film, an electret/hydrogel-based tactile sensor (EHTS) is designed and fabricated. The output performance of the EHTS is effectively boosted by 156.3% through the hybrid of triboelectric and electrostatic effects, which achieves the open-circuit peak voltage of 12.5 V, short-circuit current of 0.5 μA, and considerable power of 4.3 μW respectively, with a mentionable size of 10 mm × 10 mm × 0.9 mm. The EHTS also demonstrates a stable output characteristic within a wide range of temperature tolerance from -10 to approximately 40 °C and can be further integrated into a mask for human breath monitoring, which could provide for a reliable healthcare service during the COVID-19 pandemic. In general, the EHTS shows excellent potential in the fields of healthcare devices and wearable electronics.

Hybrid Triboelectric-Electromagnetic Nanogenerators for Mechanical Energy Harvesting: A Review

Motion-driven electromagnetic-triboelectric energy generators (E-TENGs) hold a great potential to provide higher voltages, higher currents and wider operating bandwidths than both electromagnetic and triboelectric generators standing alone. Therefore, they are promising solutions to autonomously supply a broad range of highly sophisticated devices. This paper provides a thorough review focused on major recent breakthroughs in the area of electromagnetic-triboelectric vibrational energy harvesting. A detailed analysis was conducted on various architectures including rotational, pendulum, linear, sliding, cantilever, flexible blade, multidimensional and magnetoelectric, and the following hybrid technologies. They enable highly efficient ways to harvest electric energy from many forms of vibrational, rotational, biomechanical, wave, wind and thermal sources, among others. Open-circuit voltages up to 75 V, short-circuit currents up to 60 mA and instantaneous power up to 144 mW were already achieved by these nanogenerators. Their transduction mechanisms, including proposed models to make intelligible the involved physical phenomena, are also overviewed here. A comprehensive analysis was performed to compare their respective construction designs, external excitations and electric outputs. The results highlight the potential of hybrid E-TENGs to convert unused mechanical motion into electric energy for both large- and small-scale applications. Finally, this paper proposes future research directions toward optimization of energy conversion efficiency, power management, durability and stability, packaging, energy storage, operation input, research of transduction mechanisms, quantitative standardization, system integration, miniaturization and multi-energy hybrid cells.

From contact electrification to triboelectric nanogenerators

Although the contact electrification (CE) (or usually called 'triboelectrification') effect has been known for over 2600 years, its scientific mechanism still remains debated after decades. Interest in studying CE has been recently revisited due to the invention of triboelectric nanogenerators (TENGs), which are the most effective approach for converting random, low-frequency mechanical energy (called high entropy energy) into electric power for distributed energy applications. This review is composed of three parts that are coherently linked, ranging from basic physics, through classical electrodynamics, to technological advances and engineering applications. First, the mechanisms of CE are studied for general cases involving solids, liquids and gas phases. Various physics models are presented to explain the fundamentals of CE by illustrating that electron transfer is the dominant mechanism for CE for solid-solid interfaces. Electron transfer also occurs in the CE at liquid-solid and liquid-liquid interfaces. An electron-cloud overlap model is proposed to explain CE in general. This electron transfer model is extended to liquid-solid interfaces, leading to a revision of the formation mechanism of the electric double layer at liquid-solid interfaces. Second, by adding a time-dependent polarization termPscreated by the CE-induced surface electrostatic charges in the displacement fieldD, we expand Maxwell's equations to include both the medium polarizations due to electric field (P) and mechanical aggitation and medium boundary movement induced polarization term (Ps). From these, the output power, electromagnetic (EM) behaviour and current transport equation for a TENG are systematically derived from first principles. A general solution is presented for the modified Maxwell's equations, and analytical solutions for the output potential are provided for a few cases. The displacement current arising fromε∂E/∂t is responsible for EM waves, while the newly added term ∂Ps/∂t is responsible for energy and sensors. This work sets the standard theory for quantifying the performance and EM behaviour of TENGs in general. Finally, we review the applications of TENGs for harvesting all kinds of available mechanical energy that is wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tires, wind, flowing water and more. A summary is provided about the applications of TENGs in energy science, environmental protection, wearable electronics, self-powered sensors, medical science, robotics and artificial intelligence.

Moisture-induced autonomous surface potential oscillations for energy harvesting

A variety of autonomous oscillations in nature such as heartbeats and some biochemical reactions have been widely studied and utilized for applications in the fields of bioscience and engineering. Here, we report a unique phenomenon of moisture-induced electrical potential oscillations on polymers, poly([2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide-co-acrylic acid), during the diffusion of water molecules. Chemical reactions are modeled by kinetic simulations while system dynamic equations and the stability matrix are analyzed to show the chaotic nature of the system which oscillates with hidden attractors to induce the autonomous surface potential oscillation. Using moisture in the ambient environment as the activation source, this self-excited chemoelectrical reaction could have broad influences and usages in surface-reaction based devices and systems. As a proof-of-concept demonstration, an energy harvester is constructed and achieved the continuous energy production for more than 15,000 seconds with an energy density of 16.8 mJ/cm2. A 2-Volts output voltage has been produced to power a liquid crystal display toward practical applications with five energy harvesters connected in series.

Triboelectric Nanogenerator-Based Sensor Systems for Chemical or Biological Detection

The rapid advances in the Internet of things and wearable devices have created a massive platform for sensor systems that detect chemical or biological agents. The accelerated development of these devices in recent years has simultaneously aggravated the power supply problems. Triboelectric nanogenerators (TENGs) represent a thriving renewable energy technology with the potential to revolutionize this field. In this review, the significance of TENG-based sensor systems in chemical or biological detection from the perspective of the development of power supply for biochemical sensors is discussed. Further, a range of TENGs are classified according to their roles as power supplies and/or self-powered active sensors. The TENG powered sensor systems are further discussed on the basis of their framework and applications. The working principles and structures of different TENG-based self-powered active sensors are presented, along with the classification of the sensors based on these factors. In addition, some representative applications are introduced, and the corresponding challenges are discussed. Finally, some perspectives for the future innovations of TENG-based sensor systems for chemical/biological detection are discussed.

High-Performance Flexible Self-Powered Photodetectors Utilizing Spontaneous Electron and Hole Separation in Quasi-2D Halide Perovskites

Although there are recent advances in many areas of quasi-2D halide perovskites, photodetectors based on these materials still cannot achieve satisfactory performance for practical applications where high responsivity, fast response, self-powered nature, and excellent mechanical flexibility are urgently desired. Herein, utilizing one-step spin-coating method, self-assemble quasi-2D perovskite films with graded phase distribution in the order of increasing number of metal halide octahedral layers are successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained and then employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibits impressive performance with the responsivity up to 444 mA W^-1 and ultrashort response time down to 52 µs. With a bias voltage of 1.5 V, the device responsivity becomes 3463 mA W^-1 with the response speed as fast as 24 µs. Importantly, the device's mechanical flexibility is greatly enhanced since the photocurrent prefers flowing through the metal halide octahedral layers between the top and bottom contact electrodes in the vertical device structure, being more tolerant to film damage. These results evidently indicate the potential of graded quasi-2D perovskite phases for next-generation optoelectronic devices.

A universal managing circuit with stabilized voltage for maintaining safe operation of self-powered electronics system

Harvesting mechanical energy via a triboelectric nanogenerator (TENG) is a promising strategy for solving energy problems. However, it is necessary to develop an effective and safe energy managing circuit for preventing high voltage breaking electronic devices. Here, a universal managing circuit is developed to optimize TENG's output performance, which for the first time allows the TENG to safely power various sensor systems with a safe and stable voltage. Based on the circuit, TENG's output can be transformed into a stable voltage with tunable amplitude, while an enhanced short-circuit current of 94 mA with an energy loss lower than 5% is achieved. For demonstrations, three different types of TENGs, respectively, targeting at ocean energy, wind energy, and walking energy have been prepared to reveal the capability of the circuit. This study offers a strategy to greatly enhance the output performance of TENGs to provide useful guidance for constructing self-powered and distributed sensor systems.

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UMC is designed for a TENG to maintain stable voltage with a lower resistance

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UMC provides a short-circuit current of 94 mA with an energy loss lower than 5%

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UMC can completely avoid the breakdown of electronic devices due to TENG's high voltage

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Three self-powered sensor systems have been successfully established

Tribo-Induced Smart Reflector for Ultrasensitive Self-Powered Wireless Sensing of Air Flow

Air-flow sensing is essential in broad applications of weather forecasting, ocean monitoring, gas leakage alarming, and health monitoring. However, in severe environments where electrical power supply and cable connection are not available, the sensing of air flow in a self-powered way is a challenging issue. In this work, we reported a tribo-induced smart reflector to achieve the self-powered wireless sensing of the air flow by combining an aerodynamics-driven triboelectric nanogenerator (TENG) and a silver-coated polymer network liquid crystal. Upon being driven by the air flow, the developed reflector performed specular and diffused reflectance without and with charging by the TENG, respectively, enabling wireless sensing through mechanical-electrical-optical signal conversion. In the developed sensing paradigm, the sensing module can be fully self-powered without the need of signal pre-amplification, which is electrically separated from the light source and detection modules without cable connections. The applications of self-powered wireless wind speed sensing and breath monitoring were performed to demonstrate the effectiveness of the developed paradigm toward self-powered wireless sensing nodes in the internet of things.

Hierarchical Honeycomb-Structured Electret/Triboelectric Nanogenerator for Biomechanical and Morphing Wing Energy Harvesting

Flexible, compact, lightweight and sustainable power sources are indispensable for modern wearable and personal electronics and small-unmanned aerial vehicles (UAVs). Hierarchical honeycomb has the unique merits of compact mesostructures, excellent energy absorption properties and considerable weight to strength ratios. Herein, a honeycomb-inspired triboelectric nanogenerator (h-TENG) is proposed for biomechanical and UAV morphing wing energy harvesting based on contact triboelectrification wavy surface of cellular honeycomb structure. The wavy surface comprises a multilayered thin film structure (combining polyethylene terephthalate, silver nanowires and fluorinated ethylene propylene) fabricated through high-temperature thermoplastic molding and wafer-level bonding process. With superior synchronization of large amounts of energy generation units with honeycomb cells, the manufactured h-TENG prototype produces the maximum instantaneous open-circuit voltage, short-circuit current and output power of 1207 V, 68.5 μA and 12.4 mW, respectively, corresponding to a remarkable peak power density of 0.275 mW cm^-3 (or 2.48 mW g^-1) under hand pressing excitations. Attributed to the excellent elastic property of self-rebounding honeycomb structure, the flexible and transparent h-TENG can be easily pressed, bent and integrated into shoes for real-time insole plantar pressure mapping. The lightweight and compact h-TENG is further installed into a morphing wing of small UAVs for efficiently converting the flapping energy of ailerons into electricity for the first time. This research demonstrates this new conceptualizing single h-TENG device's versatility and viability for broad-range real-world application scenarios.

Progress in micro/nano sensors and nanoenergy for future AIoT-based smart home applications

Self-sustainable sensing systems composed of micro/nano sensors and nano-energy harvesters contribute significantly to developing the internet of things (IoT) systems. As one of the most promising IoT applications, smart home relies on implementing wireless sensor networks with miniaturized and multi-functional sensors, and distributed, reliable, and sustainable power sources, namely energy harvesters with a variety of conversion mechanisms. To extend the capabilities of IoT in the smart home, a technology fusion of IoT and artificial intelligence (AI), called the artificial intelligence of things (AIoT), enables the detection, analysis, and decision-making functions with the aids of machine learning assisted algorithms to form a smart home based intelligent system. In this review, we introduce the conventional rigid microelectromechanical system (MEMS) based micro/nano sensors and energy harvesters, followed by presenting the advances in the wearable counterparts for better human interactions. We then discuss the viable integration approaches for micro/nano sensors and energy harvesters to form self-sustainable IoT systems. Whereafter, we emphasize the recent development of AIoT based systems and the corresponding applications enabled by the machine learning algorithms. Smart home based healthcare technology enabled by the integrated multi-functional sensing platform and bioelectronic medicine is also presented as an important future direction, as well as wearable photonics sensing system as a complement to the wearable electronics sensing system.

A Stretchable, Self-Healable Triboelectric Nanogenerator as Electronic Skin for Energy Harvesting and Tactile Sensing

Electronic skin that is deformable, self-healable, and self-powered has high competitiveness for next-generation energy/sense/robotic applications. Herein, we fabricated a stretchable, self-healable triboelectric nanogenerator (SH-TENG) as electronic skin for energy harvesting and tactile sensing. The elongation of SH-TENG can achieve 800% (uniaxial strain) and the SH-TENG can self-heal within 2.5 min. The SH-TENG is based on the single-electrode mode, which is constructed from ion hydrogels with an area of 2 cm × 3 cm, the output of short-circuit transferred charge (Qsc), open-circuit voltage (Voc), and short-circuit current (Isc) reaches ~6 nC, ~22 V, and ~400 nA, and the corresponding output power density is ~2.9 μW × cm⁻² when the matching resistance was ~140 MΩ. As a biomechanical energy harvesting device, the SH-TENG also can drive red light-emitting diodes (LEDs) bulbs. Meanwhile, SH-TENG has shown good sensitivity to low-frequency human touch and can be used as an artificial electronic skin for touch/pressure sensing. This work provides a suitable candidate for the material selection of the hydrogel-based self-powered electronic skin.

Smart Wearable Sensors Based on Triboelectric Nanogenerator for Personal Healthcare Monitoring

Accurate monitoring of motion and sleep states is critical for human health assessment, especially for a healthy life, early diagnosis of diseases, and medical care. In this work, a smart wearable sensor (SWS) based on a dual-channel triboelectric nanogenerator was presented for a real-time health monitoring system. The SWS can be worn on wrists, ankles, shoes, or other parts of the body and cloth, converting mechanical triggers into electrical output. By analyzing these signals, the SWS can precisely and constantly monitor and distinguish various motion states, including stepping, walking, running, and jumping. Based on the SWS, a fall-down alarm system and a sleep quality assessment system were constructed to provide personal healthcare monitoring and alert family members or doctors via communication devices. It is important for the healthy growth of the young and special patient groups, as well as for the health monitoring and medical care of the elderly and recovered patients. This work aimed to broaden the paths for remote biological movement status analysis and provide diversified perspectives for true-time and long-term health monitoring, simultaneously.

Triboelectric Effect Enabled Self-Powered, Point-of-Care Diagnostics: Opportunities for Developing ASSURED and REASSURED Devices

The use of rapid point-of-care (PoC) diagnostics in conjunction with physiological signal monitoring has seen tremendous progress in their availability and uptake, particularly in low- and middle-income countries (LMICs). However, to truly overcome infrastructural and resource constraints, there is an urgent need for self-powered devices which can enable on-demand and/or continuous monitoring of patients. The past decade has seen the rapid rise of triboelectric nanogenerators (TENGs) as the choice for high-efficiency energy harvesting for developing self-powered systems as well as for use as sensors. This review provides an overview of the current state of the art of such wearable sensors and end-to-end solutions for physiological and biomarker monitoring. We further discuss the current constraints and bottlenecks of these devices and systems and provide an outlook on the development of TENG-enabled PoC/monitoring devices that could eventually meet criteria formulated specifically for use in LMICs.

Triboelectric nanogenerators for human-health care

Since the world's first triboelectric nanogenerator (TENG) was proposed in 2012, numerous TENG-based devices and equipment have sprung up in various fields. In particular, TENG has great potential in the field of human-health care due to its small size, self-powered and low cost. With the continuous deepening of TENG research, its structure, function and technical concept are becoming more and more abundant. In order to summarize the progress and development status of TENG in health care, based on the different types of applications subdirection, this paper reviews the TENG-based research work of this field in recent eight years. The characteristics of various types of TENG-based applications and their corresponding technologies are introduced and analyzed, under the comparison of their structure and performance. This review is dedicated to provide reference and inspiration for the future development and innovation of TENG for health care.