A Packaged Self-Powered System with Universal Connectors Based on Hybridized Nanogenerators

A Flexible Self-Powered Noncontact Sensor with an Ultrawide Sensing Range for Human-Machine Interactions in Harsh Environments

Noncontact human-machine interactions (HMIs) provide a hygienic and intelligent approach to communicate between humans and machines. However, current noncontact HMIs are generally hampered by the interaction distance, and they lack the adaptability to environmental interference such as high humidity conditions. Here, we explore a self-powered electret-based noncontact sensor (ENS) with moisture-resisting ability and ultrawide sensing range exceeding 2.5 m. A megascopic air-bubble structure is designed to enhance charge-storage stability and charge-recovery ability of the ENS based on the heterocharge-synergy effect in electrets. Besides, multilayer electret films are introduced to strengthen the electric field by utilizing the electrostatic field superposition effect. Thanks to the above improved performances of the ENS, we demonstrate various noncontact HMI applications in harsh environments, including noncontact appliances, a moving trajectory and accidental fall tracking system, and a real-time machine learning-assisted gesture recognition system with accuracy as high as 99.21%. This research expands the way for noncontact sensor design and may further broaden applications in noncontact HMIs.

Implantable Triboelectric Nanogenerators for Self-Powered Cardiovascular Healthcare

Triboelectric nanogenerators (TENGs) have gained significant traction in recent years in the bioengineering community. With the potential for expansive applications for biomedical use, many individuals and research groups have furthered their studies on the topic, in order to gain an understanding of how TENGs can contribute to healthcare. More specifically, there have been a number of recent studies focusing on implantable triboelectric nanogenerators (I-TENGs) toward self-powered cardiac systems healthcare. In this review, the progression of implantable TENGs for self-powered cardiovascular healthcare, including self-powered cardiac monitoring devices, self-powered therapeutic devices, and power sources for cardiac pacemakers, will be systematically reviewed. Long-term expectations of these implantable TENG devices through their biocompatibility and other utilization strategies will also be discussed.

Unique Contact Point Modification Technique for Boosting the Performance of a Triboelectric Nanogenerator and Its Application in Road Safety Sensing and Detection

A triboelectric nanogenerator (TENG) is a potential technique that can convert waste kinetic energy to electrical energy by contact separation followed by electrostatic induction. Herein, a unique contact point modification technique has been reviewed carefully via the enlargement of the effective surface area of the tribo layer by using a simple and scalable printing method. In this study, the zinc sulfide (ZnS) nanostructure morphology has been introduced directly on an aluminum electrode (Al) as a tribo positive layer by a modified hydrothermal method and different line patterns directly printed on overhead projector (OHP) transparent sheets by a monochrome laser printer as a tribo negative layer to increase the effective contact area and work-function difference between two tribo layers. This dual parameter results in ∼11 times increment in the open-circuit output voltage (∼420 V) and ∼17 times increment in the short-circuit current density (∼83.33 mA m^-2) compared to the normal one. Furthermore, with the proposed surface modification technique, an ultrahigh instantaneous output power density of ∼3.9 W m^-2 at a load resistance of 2 MΩ was easily achieved. The direct energy conversion efficiency reached up to 66.67% at 2 MΩ load, which is very high compared to other traditional TENGs. Further, the fabricated TENG demonstrated efficacy in novel road safety sensing applications in hilly areas to control vehicle movement. Therefore, the current idea of surface engineering using a laser printer will be helpful for energy-harvesting enthusiasts to develop more efficient nanogenerators for higher energy conversions.

An Advanced Strategy to Enhance TENG Output: Reducing Triboelectric Charge Decay

The Internet of Things (IoT) is poised to accelerate the construction of smart cities. However, it requires more than 30 billion sensors to realize the IoT vision, posing great challenges and opportunities for industries of self-powered sensors. Triboelectric nanogenerator (TENG), an emerging new technology, is capable of easily converting energy from surrounding environment into electricity, thus TENG has tremendous application potential in self-powered IoT sensors. At present, TENG encounters a bottleneck to boost output for large-scale commercial use if just by promoting triboelectric charge generation, because the output is decided by the triboelectric charge dynamic equilibrium between generation and decay. To break this bottleneck, the strategy of reducing triboelectric charge decay to enhance TENG output is focused. First, multiple mechanisms of triboelectric charge decay are summarized in detail with basic theoretical principles for future research. Furthermore, recent advances in reducing triboelectric charge decay are thoroughly reviewed and outlined in three aspects: inhibition and application of air breakdown, simultaneous inhibition of air breakdown and triboelectric charge drift/diffusion, and inhibition of triboelectric charge drift/diffusion. Finally, challenges and future research focus are proposed. This review provides reference and guidance for enhancing TENG output.

A hybrid piezoelectric and triboelectric nanogenerator with lead-free BZT-BCT/PDMS composite and PVA film for scavenging mechanical energy

A hybrid piezo/triboelectric nanogenerator (H/P-TENG) is designed for mechanical energy harvesting using polymer ceramic composite films; polydimethylsiloxane/Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (PDMS/BZT-BCT) and polyvinyl alcohol (PVA). A lead-free BZT-BCT piezoelectric ceramic was prepared via solid-state method and blended into PDMS to form a series of polymer-ceramic composite films, ranging from 5% to 30% by weight. The films were forward/reverse poled with corona poling and their electrical properties were compared to non-poled samples. The H/P-TENG constructed with forward-poled 15 wt% BZT-BCT in PDMS achieved the highest open-circuit voltage, V _oc of 127 V, short-circuit current density, J _sc of 67 mA m^-2, short-circuit charge density, Q _sc of 118 μC m^-2, and peak power density of 7.5 W m^-2, an increase of 190% over pristine PDMS-based TENG. It was discovered that incorporating BZT-BCT into the PDMS matrix improved the triboelectric properties of PDMS. The overlapping electron cloud (OEC) model was used to explain the enhancement and the effect of poling direction of the PDMS/BZT-BCT composite used in H/P-TENG, providing fundamental knowledge of the influence of piezoelectric polarisation on contact electrification.

Discrete Molecular Copper(II) Complex for Efficient Piezoelectric Energy Harvesting Above Room-Temperature

Developing robust, wearable, and biocompatible energy harvesting devices with bulk oxides (ceramics and perovskites) is extremely hard to achieve due to their zero mechanical flexibility, heavy metal toxicity, and tunability of properties. Alternatively, discrete inorganic complexes can be an excellent choice to overcome the above-stated issues, thanks to appropriate molecular engineering. Herein, we report an above-room-temperature ferroelectric discrete molecular complex [Cu(L-phe)(bpy)(H₂ O)]PF₆ ⋅H₂ O (1) which is suitable for piezoelectric energy harvesting due to its large values of piezoelectric co-efficient (d₃₃ =10 pm V^-1 ) and spontaneous polarization (P_s =1.3 μC cm^-2 ). Among the devices prepared with the composite films of polyvinyl alcohol (PVA) and various weight % composition of 1, the 10 Wt % composite shows the highest output voltage of 8 V, a power density of 0.85 μW cm^-2 , and output current of 5 μA, which is highest for any discrete inorganic complex reported to date.

Progress of Advanced Devices and Internet of Things Systems as Enabling Technologies for Smart Homes and Health Care

In the Internet of Things (IoT) era, various devices (e.g., sensors, actuators, energy harvesters, etc.) and systems have been developed toward the realization of smart homes/buildings and personal health care. These advanced devices can be categorized into ambient devices and wearable devices based on their usage scenarios, to enable motion tracking, health monitoring, daily care, home automation, fall detection, intelligent interaction, assistance, living convenience, and security in smart homes. With the rapidly increasing number of such advanced devices and IoT systems, achieving fully self-sustained and multimodal intelligent systems is becoming more and more important to realize a sustainable and all-in-one smart home platform. Hence, in this Review, we systematically present the recent progress of the development of advanced materials, fabrication techniques, devices, and systems for enabling smart home and health care applications. First, advanced polymer, fiber, and fabric materials as well as their respective fabrication techniques for large-scale manufacturing are discussed. After that, functional devices classified into ambient devices (at home ambiance such as door, floor, table, chair, bed, toilet, window, wall, etc.) and wearable devices (on body parts such as finger, wrist, arm, throat, face, back, etc.) are presented for diverse monitoring and auxiliary applications. Next, the current developments of self-sustained systems and intelligent systems are reviewed in detail, indicating two promising research directions in this field. Last, conclusions and outlook pinpointed on the existing challenges and opportunities are provided for the research community to consider.

A Novel Porous PDMS-AgNWs-PDMS (PAP)-Sponge-Based Capacitive Pressure Sensor

The development of capacitive pressure sensors with low cost, high sensitivity and facile fabrication techniques is desirable for flexible electronics and wearable devices. In this project, a highly sensitive and flexible capacitive pressure sensor was fabricated by sandwiching a porous PAP sponge dielectric layer between two copper electrodes. The porous PAP sponge dielectric layer was fabricated by introducing highly conductive silver nanowires (AgNWs) into the PDMS sponge with 100% sucrose as a template and with a layer of polydimethylsiloxane (PDMS) film coating the surface. The sensitivity of the PAP sponge capacitive pressure sensor was optimized by increasing the load amount of AgNWs. Experimental results demonstrated that when the load amount of AgNWs increased to 150 mg in the PAP sponge, the sensitivity of the sensor was the highest in the low-pressure range of 0–1 kPa, reaching 0.62 kPa−1. At this point, the tensile strength and elongation of sponge were 1.425 MPa and 156.38%, respectively. In addition, the specific surface area of PAP sponge reached 2.0 cm2/g in the range of 0–10 nm pore size, and showed excellent waterproof performance with high elasticity, low hysteresis, light weight, and low density. Furthermore, as an application demonstration, ~110 LED lights were shown to light up when pressed onto the optimized sensor. Hence, this novel porous PAP-sponge-based capacitive pressure sensor has a wide range of potential applications in the field of wearable electronics.

A Triboelectric Nanogenerator Based on Sodium Chloride Powder for Self-Powered Humidity Sensor

Recently, the research of distributed sensor networks based on triboelectric technology has attracted extensive attention. Here, we reported a new triboelectric nanogenerator based on sodium chloride powder (S-TENG) to obtain mechanical energy. The polytetrafluoroethylene (PTFE) film and sodium chloride powder layer serve as the triboelectric pair. After testing and calculation, the internal resistance of S-TENG is 30 MΩ, and the output power of S-TENG (size: 6 cm × 6 cm) can arrive at the maximum value (about 403.3 µW). Furthermore, the S-TENG can achieve the open circuit voltage (V_oc) of 198 V and short-circuit current (I_sc) of 6.66 µA, respectively. Moreover, owing to the moisture absorption of sodium chloride powder, the S-TENG device also has the function of the humidity sensor. This work proposed a functional TENG device, and it can promote the advancement of self-powered sensors based on the TENG devices.

Triboelectric Nanogenerators for Therapeutic Electrical Stimulation

Current solutions developed for the purpose of in and on body (IOB) electrical stimulation (ES) lack autonomous qualities necessary for comfortable, practical, and self-dependent use. Consequently, recent focus has been placed on developing self-powered IOB therapeutic devices capable of generating therapeutic ES for human use. With the recent invention of the triboelectric nanogenerator (TENG), harnessing passive human biomechanical energy to develop self-powered systems has allowed for the introduction of novel therapeutic ES solutions. TENGs are especially effective at providing ES for IOB therapeutic systems given their bioconformability, low cost, simple manufacturability, and self-powering capabilities. Due to the key role of naturally induced electrical signals in many physiological functions, TENG-induced ES holds promise to provide a novel paradigm in therapeutic interventions. The aim here is to detail research on IOB TENG devices applied for ES-based therapy in the fields of regenerative medicine, neurology, rehabilitation, and pharmaceutical engineering. Furthermore, considering TENG-produced ES can be measured for sensing applications, this technology is paving the way to provide a fully autonomous personalized healthcare system, capable of IOB energy generation, sensing, and therapeutic intervention. Considering these grounds, it seems highly relevant to review TENG-ES research and applications, as they could constitute the foundation and future of personalized healthcare.

Boosting the Power and Lowering the Impedance of Triboelectric Nanogenerators through Manipulating the Permittivity for Wearable Energy Harvesting

Triboelectric nanogenerators (TENGs), which hold great promise for sustainably powering wearable electronics by harvesting distributed mechanical energy, are still severely limited by their unsatisfactory power density, small capacitance, and high internal impedance. Herein, a materials optimization strategy is proposed to achieve a high performance of TENGs and to lower the matching impedance simultaneously. A permittivity-tunable electret composite film, i.e., a thermoplastic polyurethane (TPU) matrix with polyethylene glycol (PEG) additives and polytetrafluoroethylene (PTFE) nanoparticle inclusions, is employed as the triboelectric layer. Through optimizing the dielectric constant of the composite, the injected charge density and internal capacitance of the TENG are significantly enhanced, thus synergistically boosting the output power and reducing the impedance of the TENG. The optimal output power reaches 16.8 mW at an external resistance of 200 kΩ, showing a 17.3 times enhancement in output power and a 90% decline in matching impedance. This work demonstrates a significant progress toward the materials optimization of a triboelectric generator for its practical commercialization.

Flourishing energy harvesters for future body sensor network: from single to multiple energy sources

Body sensor network (bodyNET) offers possibilities for future disease diagnosis, preventive health care, rehabilitation, and treatment. However, the eventual realization demands reliable and sustainable power sources. The flourishing energy harvesters (EHs) have provided prominent techniques for practically addressing the concurrent energy issue. Targeting for a specific energy source, wearable EHs with a sole conversion mechanism are well investigated. Hybrid EHs integrating different effects for a single source or multi-sources are attaining growing attention, for they provide another degree of freedom concerning a higher-level energy utility. Merging EHs with other functional electronics, diversified functional self-sustainable systems are developed, paving the way for the accomplishment of bodyNET. This review introduces the evolution of wearable EHs from a single effect to hybridized mechanisms for multiple energy sources and wearable to implantable self-sustainable systems. Last, we provide our perspectives on the future development of hybrid EHs to be more competitive with conventional batteries.

Triboelectric Nanogenerators and Hybridized Systems for Enabling Next-Generation IoT Applications

In the past few years, triboelectric nanogenerator-based (TENG-based) hybrid generators and systems have experienced a widespread and flourishing development, ranging among almost every aspect of our lives, e.g., from industry to consumer, outdoor to indoor, and wearable to implantable applications. Although TENG technology has been extensively investigated for mechanical energy harvesting, most developed TENGs still have limitations of small output current, unstable power generation, and low energy utilization rate of multisource energies. To harvest the ubiquitous/coexisted energy forms including mechanical, thermal, and solar energy simultaneously, a promising direction is to integrate TENG with other transducing mechanisms, e.g., electromagnetic generator, piezoelectric nanogenerator, pyroelectric nanogenerator, thermoelectric generator, and solar cell, forming the hybrid generator for synergetic single-source and multisource energy harvesting. The resultant TENG-based hybrid generators utilizing integrated transducing mechanisms are able to compensate for the shortcomings of each mechanism and overcome the above limitations, toward achieving a maximum, reliable, and stable output generation. Hence, in this review, we systematically introduce the key technologies of the TENG-based hybrid generators and hybridized systems, in the aspects of operation principles, structure designs, optimization strategies, power management, and system integration. The recent progress of TENG-based hybrid generators and hybridized systems for the outdoor, indoor, wearable, and implantable applications is also provided. Lastly, we discuss our perspectives on the future development trend of hybrid generators and hybridized systems in environmental monitoring, human activity sensation, human-machine interaction, smart home, healthcare, wearables, implants, robotics, Internet of things (IoT), and many other fields.

Multieffect Coupled Nanogenerators

With the advent of diverse electronics, the available energy may be light, thermal, and mechanical energies. Multieffect coupled nanogenerators (NGs) exhibit strong ability to harvest ambient energy by integrating various effects comprising piezoelectricity, pyroelectricity, thermoelectricity, optoelectricity, and triboelectricity into a standalone device. Interaction of multitype effects can promote energy harvesting and conversion by modulating charge carriers' behaviour. Multieffect coupled NGs stand for a vital group of energy harvesters, supporting the advances of an electronic device and promoting the resolution of energy crisis. The matchless versatility and high reliability of multieffect coupled NGs make them main candidates for integration in complicated arrays of the electronic device. Multieffect coupled NGs can also be employed as a variety of self-powered sensors due to their rapid response, high accuracy, and high responsivity. This article reviews the latest achievements of multieffect coupled NGs. Fundamentals mainly including basic theory and materials of interest are covered. Advanced device design and output characteristics are introduced. Potential applications are described, and future development is discussed.

Recent Progress in Hybridized Nanogenerators for Energy Scavenging

As the world's demand for alternative energy increases, the development of green energy harvesters becomes ever more important. As a result, the creation of triboelectric (TENG), piezoelectric (PENG), and pyroelectric nanogenerators, electromagnetic generators (EMG), solar cells, and electrochemical cells is attracting interest in an effort to convert mechanical, thermal, magnetic, solar, and chemical energy into electricity. In order to take advantage of the ambient energies from our surrounding environment, the design of hybridized generator units that can simultaneously scavenge energy in a variety of forms continues to develop. These systems are being considered to satisfy the energy needs of a range of electronic devices and adapt to a variety of working environments. This review demonstrates the latest progress in hybridized nanogenerators in accordance with their structure, operating principle, and applications. These studies demonstrate new approaches to developing hybrid techniques and novel assemblies for efficiently harvesting environmental energy from a number of sources.

Self-powered cardiovascular electronic devices and systems

Cardiovascular electronic devices have enormous benefits for health and quality of life but the long-term operation of these implantable and wearable devices remains a huge challenge owing to the limited life of batteries, which increases the risk of device failure and causes uncertainty among patients. A possible approach to overcoming the challenge of limited battery life is to harvest energy from the body and its ambient environment, including biomechanical, solar, thermal and biochemical energy, so that the devices can be self-powered. This strategy could allow the development of advanced features for cardiovascular electronic devices, such as extended life, miniaturization to improve comfort and conformability, and functions that integrate with real-time data transmission, mobile data processing and smart power utilization. In this Review, we present an update on self-powered cardiovascular implantable electronic devices and wearable active sensors. We summarize the existing self-powered technologies and their fundamental features. We then review the current applications of self-powered electronic devices in the cardiovascular field, which have two main goals. The first is to harvest energy from the body as a sustainable power source for cardiovascular electronic devices, such as cardiac pacemakers. The second is to use self-powered devices with low power consumption and high performance as active sensors to monitor physiological signals (for example, for active endocardial monitoring). Finally, we present the current challenges and future perspectives for the field.

Emerging Implantable Energy Harvesters and Self-Powered Implantable Medical Electronics

Implantable energy harvesters (IEHs) are the crucial component for self-powered devices. By harvesting energy from organisms such as heartbeat, respiration, and chemical energy from the redox reaction of glucose, IEHs are utilized as the power source of implantable medical electronics. In this review, we summarize the IEHs and self-powered implantable medical electronics (SIMEs). The typical IEHs are nanogenerators, biofuel cells, electromagnetic generators, and transcutaneous energy harvesting devices that are based on ultrasonic or optical energy. A benefit from these technologies of energy harvesting in vivo, SIMEs emerged, including cardiac pacemakers, nerve/muscle stimulators, and physiological sensors. We provide perspectives on the challenges and potential solutions associated with IEHs and SIMEs. Beyond the energy issue, we highlight the implanted devices that show the therapeutic function in vivo.

"Self-Matched" Tribo/Piezoelectric Nanogenerators Using Vapor-Induced Phase-Separated Poly(vinylidene fluoride) and Recombinant Spider Silk

Flexible biocompatible mechanical energy harvesters are drawing increasing interest because of their high energy-harvesting efficiency for powering wearable/implantable devices. Here, a type of "self-matched" tribo-piezoelectric nanogenerators composed of genetically engineered recombinant spider silk protein and piezoelectric poly(vinylidene fluoride) (PVDF)-decorated poly(ethylene terephthalate) (PET) layers is reported. The PET layer serves as a shared structure and electrification layer for both piezoelectric and triboelectric nanogenerators. Importantly, the PVDF generates a strong piezo-potential that modifies the surface potential of the PET layer to match the electron-transfer direction of the spider silk during triboelectrification. A "vapor-induced phase-separation" process is developed to enhance the piezoelectric performance in a facile and "green" roll-to-roll manufacturing fashion. The devices show exceptional output performance and energy transformation efficiency among currently existing energy harvesters of similar sizes and exhibit the potential for large-scale fabrication and various implantable/wearable applications.

Fiber/Fabric-Based Piezoelectric and Triboelectric Nanogenerators for Flexible/Stretchable and Wearable Electronics and Artificial Intelligence

Integration of advanced nanogenerator technology with conventional textile processes fosters the emergence of textile-based nanogenerators (NGs), which will inevitably promote the rapid development and widespread applications of next-generation wearable electronics and multifaceted artificial intelligence systems. NGs endow smart textiles with mechanical energy harvesting and multifunctional self-powered sensing capabilities, while textiles provide a versatile flexible design carrier and extensive wearable application platform for their development. However, due to the lack of an effective interactive platform and communication channel between researchers specializing in NGs and those good at textiles, it is rather difficult to achieve fiber/fabric-based NGs with both excellent electrical output properties and outstanding textile-related performances. To this end, a critical review is presented on the current state of the arts of wearable fiber/fabric-based piezoelectric nanogenerators and triboelectric nanogenerators with respect to basic classifications, material selections, fabrication techniques, structural designs, and working principles, as well as potential applications. Furthermore, the potential difficulties and tough challenges that can impede their large-scale commercial applications are summarized and discussed. It is hoped that this review will not only deepen the ties between smart textiles and wearable NGs, but also push forward further research and applications of future wearable fiber/fabric-based NGs.

Body-Integrated Self-Powered System for Wearable and Implantable Applications

The human body has an abundance of available energy from the mechanical movements of walking, jumping, and running. Many devices such as electromagnetic, piezoelectric, and triboelectric energy harvesting devices have been demonstrated to convert body mechanical energy into electricity, which can be used to power various wearable and implantable electronics. However, the complicated structure, high cost of production/maintenance, and limitation of wearing and implantation sites restrict the development and commercialization of the body energy harvesters. Here, we present a body-integrated self-powered system (BISS) that is a succinct, highly efficient, and cost-effective method to scavenge energy from human motions. The biomechanical energy of the moving human body can be harvested through a piece of electrode attached to skin. The basic principle of the BISS is inspired by the comprehensive effect of triboelectrification between soles and floor and electrification of the human body. We have proven the feasibility of powering electronics using the BISS in vitro and in vivo. Our investigation of the BISS exhibits an extraordinarily simple, economical, and applicable strategy to harvest energy from human body movements, which has great potential for practical applications of self-powered wearable and implantable electronics in the future.

Ultrahigh Output Piezoelectric and Triboelectric Hybrid Nanogenerators Based on ZnO Nanoflakes/Polydimethylsiloxane Composite Films

We demonstrated a hybrid nanogenerator (NG) exploiting both piezoelectric and triboelectric effects induced from ZnO nanoflakes (NFs)/polydimethylsiloxane (PDMS) composite films through a facile, cost-effective fabrication method. This hybrid NG exhibited not only high piezoelectric output current owing to the enhanced surface piezoelectricity of the ZnO NFs but also high triboelectric output voltage owing to the pronounced triboelectrification of Au-PDMS contact, producing a peak-to-peak output voltage of ∼470 V, a current density of ∼60 μA·cm^-2, and an average power density of ∼28.2 mW·cm^-2. Without additional energy storage devices, the hybrid NGs with an area of 3 × 3 cm² instantaneously lit up 180 commercial green light-emitting diodes through periodic hand compression. This approach may provide an innovative design for constructing high-performance and portable energy harvesting devices with enhanced power output, scavenging ambient mechanical energy from human motions in our daily life.

Implantable Energy-Harvesting Devices

The sustainable operation of implanted medical devices is essential for healthcare applications. However, limited battery capacity is a key challenge for most implantable medical electronics (IMEs). The human body abounds with mechanical and chemical energy, such as the heartbeat, breathing, blood circulation, and the oxidation-reduction of glucose. Harvesting energy from the human body is a possible approach for powering IMEs. Many new methods for developing in vivo energy harvesters (IVEHs) have been proposed for powering IMEs. In this context energy harvesters based on the piezoelectric effect, triboelectric effect, automatic wristwatch devices, biofuel cells, endocochlear potential, and light, with an emphasis on fabrication, energy output, power management, durability, animal experiments, evaluation criteria, and typical applications are discussed. Importantly, the IVEHs that are discussed, are actually implanted into living things. Future challenges and perspectives are also highlighted.

Capsule Triboelectric Nanogenerators: Toward Optional 3D Integration for High Output and Efficient Energy Harvesting from Broadband-Amplitude Vibrations

The technology of triboelectric nanogenerators (TENGs) has made great progress as a promising approach to generating electricity from ambient vibration energy. However, finding a way to generate enough electrical output efficiently from vibrations with a broadband of amplitudes is crucial when the relatively low current output of existing TENGs and the existence of natural vibrations with diverse amplitudes are considered. In this work, a freestanding and lightweight triboelectric nanogenerator with a capsule structure (namely, a capsule TENG) is demonstrated with an aim toward optional 3D integration and the efficient harvesting of energy from vibrations with a broadband of amplitudes. The capsule TENGs can be easily integrated to form 1D, 2D, and 3D structures to realize high electrical output. Under ideal conditions, the total output power of an integrated capsule-TENG pack can be approximately estimated as p × n², where p is the peak output power per capsule TENG and n is the number of capsule TENGs. When capsule TENGs with hybrid structures, such as different lengths of the capsule tube and different numbers of paired electrodes, are assembled, energy can be more efficiently harvested from vibrations with a broadband of amplitudes. A total of three parameters (the active area-to-volume ratio, the power-to-volume ratio, and the power-to-weight ratio), which are important parameters for 3D-integrated TENGs, are proposed. The results of this research show that capsule TENGs are versatile devices that can potentially be used for the efficient harvesting of ambient vibration energy.

Poly(dimethylsiloxane)/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High-Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation

Herein, we report the successful synthesis of poly(dimethylsiloxane)/ZnO nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for a high-performance energy-harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 μA cm^-2, resulting in an ultrahigh power density of 6.22 mW cm^-2. Furthermore, we have evaluated the performance of the PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy-storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance, flexible, wearable energy-harvesting devices.

A One-Structure-Based Multieffects Coupled Nanogenerator for Simultaneously Scavenging Thermal, Solar, and Mechanical Energies

Rapid advances in various energy harvesters impose the challenge on integrating them into one device structure with synergetic effects for full use of the available energies from the environment. Here, a multieffect coupled nanogenerator based on ferroelectric barium titanate is reported. It promotes the ability to simultaneously scavenging thermal, solar, and mechanical energies. By integration of a pyroelectric nanogenerator, a photovoltaic cell, and a triboelectric-piezoelectric nanogenerator in one structure with only two electrodes, multieffects interact with each other to alter the electric output, and a complementary power source with peak current of ≈1.5 µA, peak voltage of ≈7 V, and platform voltage of ≈6 V is successfully achieved. Compared with traditional hybridized nanogenerators with stacked architectures, the one-structure-based multieffects coupled nanogenerator is smaller, simpler, and less costly, showing prospective in practical applications and represents a new trend of all-in-one multiple energy scavenging.

Toward Wearable Self-Charging Power Systems: The Integration of Energy-Harvesting and Storage Devices

One major challenge for wearable electronics is that the state-of-the-art batteries are inadequate to provide sufficient energy for long-term operations, leading to inconvenient battery replacement or frequent recharging. Other than the pursuit of high energy density of secondary batteries, an alternative approach recently drawing intensive attention from the research community, is to integrate energy-generation and energy-storage devices into self-charging power systems (SCPSs), so that the scavenged energy can be simultaneously stored for sustainable power supply. This paper reviews recent developments in SCPSs with the integration of various energy-harvesting devices (including piezoelectric nanogenerators, triboelectric nanogenerators, solar cells, and thermoelectric nanogenerators) and energy-storage devices, such as batteries and supercapacitors. SCPSs with multiple energy-harvesting devices are also included. Emphasis is placed on integrated flexible or wearable SCPSs. Remaining challenges and perspectives are also examined to suggest how to bring the appealing SCPSs into practical applications in the near future.

Recent Progress on Piezoelectric and Triboelectric Energy Harvesters in Biomedical Systems

Implantable medical devices (IMDs) have become indispensable medical tools for improving the quality of life and prolonging the patient's lifespan. The minimization and extension of lifetime are main challenges for the development of IMDs. Current innovative research on this topic is focused on internal charging using the energy generated by the physiological environment or natural body activity. To harvest biomechanical energy efficiently, piezoelectric and triboelectric energy harvesters with sophisticated structural and material design have been developed. Energy from body movement, muscle contraction/relaxation, cardiac/lung motions, and blood circulation is captured and used for powering medical devices. Other recent progress in this field includes using PENGs and TENGs for our cognition of the biological processes by biological pressure/strain sensing, or direct intervention of them for some special self-powered treatments. Future opportunities lie in the fabrication of intelligent, flexible, stretchable, and/or fully biodegradable self-powered medical systems for monitoring biological signals and treatment of various diseases in vitro and in vivo.

High-Performance Piezoelectric Nanogenerators with Imprinted P(VDF-TrFE)/BaTiO3 Nanocomposite Micropillars for Self-Powered Flexible Sensors

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO₃ ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO₃ nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm^-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO₃ nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.

A piezoelectric micro generator worked at low frequency and high acceleration based on PZT and phosphor bronze bonding

Recently, piezoelectric energy harvesters (PEHs) have been paid a lot of attention by many researchers to convert mechanical energy into electrical and low level vibration. Currently, most of PEHs worked under high frequency and low level vibration. In this paper, we propose a micro cantilever generator based on the bonding of bulk PZT wafer and phosphor bronze, which is fabricated by MEMS technology, such as mechanical chemical thinning and etching. The experimental results show that the open-circuit output voltage, output power and power density of this fabricated prototype are 35 V, 321 μW and 8664 μW cm⁻³ at the resonant frequency of 100.8 Hz, respectively, when it matches an optimal loading resistance of 140 kΩ under the excitation of 3.0 g acceleration. The fabricated micro generator can obtain the open-circuit stable output voltage of 61.2 V when the vibration acceleration arrives at 7.0 g. Meanwhile, when this device is pasted on the vibrating vacuum pump, the output voltage is about 11 V. It demonstrates that this novel proposed device can scavenge high vibration level energy at low frequency for powering the inertial sensors in internet of things application.

Self-Powered, One-Stop, and Multifunctional Implantable Triboelectric Active Sensor for Real-Time Biomedical Monitoring

Operation time of implantable electronic devices is largely constrained by the lifetime of batteries, which have to be replaced periodically by surgical procedures once exhausted, causing physical and mental suffering to patients and increasing healthcare costs. Besides the efficient scavenging of the mechanical energy of internal organs, this study proposes a self-powered, flexible, and one-stop implantable triboelectric active sensor (iTEAS) that can provide continuous monitoring of multiple physiological and pathological signs. As demonstrated in human-scale animals, the device can monitor heart rates, reaching an accuracy of ∼99%. Cardiac arrhythmias such as atrial fibrillation and ventricular premature contraction can be detected in real-time. Furthermore, a novel method of monitoring respiratory rates and phases is established by analyzing variations of the output peaks of the iTEAS. Blood pressure can be independently estimated and the velocity of blood flow calculated with the aid of a separate arterial pressure catheter. With the core-shell packaging strategy, monitoring functionality remains excellent during 72 h after closure of the chest. The in vivo biocompatibility of the device is examined after 2 weeks of implantation, proving suitability for practical use. As a multifunctional biomedical monitor that is exempt from needing an external power supply, the proposed iTEAS holds great potential in the future of the healthcare industry.

In Vivo Self-Powered Wireless Cardiac Monitoring via Implantable Triboelectric Nanogenerator

Harvesting biomechanical energy in vivo is an important route in obtaining sustainable electric energy for powering implantable medical devices. Here, we demonstrate an innovative implantable triboelectric nanogenerator (iTENG) for in vivo biomechanical energy harvesting. Driven by the heartbeat of adult swine, the output voltage and the corresponding current were improved by factors of 3.5 and 25, respectively, compared with the reported in vivo output performance of biomechanical energy conversion devices. In addition, the in vivo evaluation of the iTENG was demonstrated for over 72 h of implantation, during which the iTENG generated electricity continuously in the active animal. Due to its excellent in vivo performance, a self-powered wireless transmission system was fabricated for real-time wireless cardiac monitoring. Given its outstanding in vivo output and stability, iTENG can be applied not only to power implantable medical devices but also possibly to fabricate a self-powered, wireless healthcare monitoring system.