Mechanical Energy Harvesting Technology Research Articles

A generalized model for a triboelectric nanogenerator energy harvesting system

A triboelectric nanogenerator (TENG) energy harvesting system involves at least three components: the mechanical source that inputs mechanical energy to drive TENGs, the TENG device itself as an energy converter, and an external electrical circuit that output the energy from TENGs. Multiple theoretical models have been developed for structural optimization design and maximum power output, yet there has been less emphasis on dynamic modelling of the entire energy harvesting system. This work presents attempts to establish such system-level models that encompass both mechanical and electrical systems. Special consideration is paid to the dynamic contact problem in this generalized model, since dynamic response of impacts can significantly affect the electric outputs. To address contact constraint problems, the penalty function method is utilized to handle non-smoothness and discontinuity. Subsequently, this research specifies how to improve the maximum energy conversion efficiency, and suggest optimal executive strategies for maximizing the energy output through a thorough parametric study. The anticipated outcome is that the generalized model will not only guide optimization design and predict the dynamic characteristics of the energy harvesting system but also assess the potential feasibility of mechanical energy harvesting technology across diverse application domains.

The Potential of Electrospinning to Enable the Realization of Energy-Autonomous Wearable Sensing Systems.

The market for wearable electronic devices is experiencing significant growth and increasing potential for the future. Researchers worldwide are actively working to improve these devices, particularly in developing wearable electronics with balanced functionality and wearability for commercialization. Electrospinning, a technology that creates nano/microfiber-based membranes with high surface area, porosity, and favorable mechanical properties for human in vitro and in vivo applications using a broad range of materials, is proving to be a promising approach. Wearable electronic devices can use mechanical, thermal, evaporative and solar energy harvesting technologies to generate power for future energy needs, providing more options than traditional sources. This review offers a comprehensive analysis of how electrospinning technology can be used in energy-autonomous wearable wireless sensing systems. It provides an overview of the electrospinning technology, fundamental mechanisms, and applications in energy scavenging, human physiological signal sensing, energy storage, and antenna for data transmission. The review discusses combining wearable electronic technology and textile engineering to create superior wearable devices and increase future collaboration opportunities. Additionally, the challenges related to conducting appropriate testing for market-ready products using these devices are also discussed.

Overview of Advanced Micro-Nano Manufacturing Technologies for Triboelectric Nanogenerators

In the era of the Internet of Things, various electronics play an important role in information interaction, in which the power supply is an urgent problem to be solved. Triboelectric nanogenerator (TENG) is an emerging mechanical energy harvesting technology that can serve as a power source for electronics, which is developing towards high performance, miniaturization and integration. Herein, the advanced micro-nano manufacturing technologies are systematically reviewed for TENGs. First, film preparation such as physical vapor deposition, chemical vapor deposition, electrochemical deposition, electrospinning and screen printing for triboelectric layers are introduced and discussed. Then, surface processing, such as soft lithography, laser ablation, inductively coupled plasma and nanoimprint for micro-nano structures on the surface of triboelectric layers are also introduced and discussed. In addition, micro-electromechanical system fabrication for TENG devices such as acoustic and vibration sensors, is introduced, and their current challenges are analyzed. Finally, the challenges of the advanced micro-nano manufacturing technologies for the TENGs are systematically summarized, and further development is prospected.

Tunable Tribovoltaic Effect via Metal–Insulator Transition

Tribovoltaic direct-current (DC) nanogenerator made of dynamic semiconductor heterojunction is emerging as a promising mechanical energy harvesting technology. However, fundamental understanding of the mechano-electronic carrier excitation and transport at dynamic semiconductor interfaces remains to be investigated. Here, we demonstrated for the first time, that tribovoltaic DC effect can be tuned with metal-insulator transition (MIT). In a representative MIT material (vanadium dioxide, VO2), we found that the short-circuit current (ISC) can be enhanced by >20 times when the material is transformed from insulating to metallic state upon static or dynamic heating, while the open-circuit voltage (VOC) turns out to be unaffected. Such phenomenon may be understood by the Hubbard model for Mott insulator: orders' magnitude increase in conductivity is induced when the nearest hopping changes dramatically and overcomes the Coulomb repulsion, while the Coulomb repulsion giving rise to the quasi-particle excitation energy remains relatively stable.

Design and Test of a Spoke-like Piezoelectric Energy Harvester.

With the development of industry IoT, microprocessors and sensors are widely used for autonomously transferring information to cyber-physics systems. Massive quantities and huge power consumption of the devices result in a severe increment of the chemical batteries, which is highly associated with problems, including environmental pollution, waste of human/financial resources, difficulty in replacement, etc. Driven by this issue, mechanical energy harvesting technology has been widely studied in the last few years as a great potential solution for battery substitution. Therefore, the piezoelectric generator is characterized as an efficient transformer from ambient vibration into electricity. In this paper, a spoke-like piezoelectric energy harvester is designed and fabricated with detailed introductions on the structure, materials, and fabrication. Focusing on improving the output efficiency and broadening the pulse width, on the one hand, the energy harvesting circuit is optimized by adding voltage monitoring and regulator modules. On the other hand, magnetic mass is adopted to employ the magnetic field of repulsive and upper repulsion–lower attraction mode. The spoke-like piezoelectric energy harvester suggests broadening the frequency domain and increasing the output performance, which is prepared for wireless sensors and portable electronics in remote areas and harsh environments.

Supercapacitor-Inspired Triboelectric Nanogenerator Based on Electrostatic Double Layer

Triboelectric nanogenerator (TENG) is an efficient mechanical energy harvesting technology that relies on the coupling effects of contact electrification and electrostatic induction. Here, inspired by the principles of electrical double layer and supercapacitor (SC), we present a newly designed TENG based on electrostatic double layer formed by electrostatic charges adsorbing on the surface of the dielectric layer coated on the electrodes. We built three-dimensional electrodes using polyurethane sponge and silver nanowires, by mimicking the structure and mechanism of SC. After electrochemical polarization charging or corona charging, a thirteen times enhancement of output power was achieved. Furthermore, a whole compressible self-charging power system composed of TENG and SC was fabricated to sustainably drive electric devices. These findings show a proof-of-concept TENG based on electrostatic double layer, and provide new opportunities for chemical principles to promote energy conversion.

Promoting smart cities into the 5G era with multi-field Internet of Things (IoT) applications powered with advanced mechanical energy harvesters

Along with the arrival of the 5G era, sustainable and renewable energy supplies have become urgent demands towards plentifully distributed devices utilized for constructing smart cities. On the one hand, although the low-entropy fossil energies are constantly transformed into high-entropy energies and consumed through various batteries, the large-scale combustion inevitably brings a huge carbon footprint and severe climate changes. On the other hand, mechanical energies are widely distributed in the urban environment in types of vibrations and rotations, and natural areas in types of water waves, rainfalls, and winds. With the development of mechanical energy harvesting technologies like triboelectric, piezoelectric, electromagnetic, etc., various mechanical energy harvesters with optimized structures and selected materials, including triboelectric nanogenerator (TENG), piezoelectric nanogenerator (PENG), electromagnetic generator (EMG), etc., have been demonstrated for efficiently extracting electric power from ubiquitous existed mechanical energy sources like wind, water waves/flows, raindrops, vibrations, human motions, organs, and so on. With a comprehensive review of energy harvesting-assisted Internet of Things (IoT) applications among smart environmental monitoring (wind, ocean, and agriculture), smart transportations (drivers, vehicles, ships, roads, and bridges), smart homes (windows, floors, accessories, and human-machine interfaces), smart healthcare (wearable/portable devices, and implantable devices), the concept of smart cities are being promoted to conform with requirements of carbon neutrality and environment-friendly. Moreover, by combining developed self-powered sensor nodes, self-sustainable wireless sensor nodes, and self-charging energy storage units, the concept of IoT will be reinforced by increasing 5G endpoints and accelerates digitalization in smart cities. • A comprehensive investigation of mechanical energy harvesting technologies from principle to materials is provided. • Progresses among smart environmental monitoring, smart transportations, smart homes, and smart healthcare are reviewed. • Strategies of smart cities improved with energy harvesting assisted wireless sensor nodes/networks are discussed. • Emerging research fronts about energy harvesting technologies supporting smart cities are summarized.

Theoretical and experimental investigation into the asymmetric external charging of Triboelectric Nanogenerators

Triboelectric Nanogenerator (TENG) is a mechanical energy harvesting technology with the potential to autonomously power future wearable and portable electronics. Triboelectric charging is the major phenomenon governing the power generation and efficiency of a TENG. Studies on TENG, thus far, have focussed on the symmetric triboelectric charging with equal amounts of triboelectric charges with opposite polarities distributed on its two contact surfaces, especially for the purpose of theoretical modelling and simulations. Our work presents a fundamental study on the asymmetric triboelectric charging with unequal quantities of charges on TENG contact surfaces obtained through an external charging method, as an effective technique to enhance its power generation. For the first time, a theoretical model which can simulate the outputs of an asymmetrically charged TENG is derived using the distance-dependent electric field concept and experimentally verified, providing a detailed understanding of this phenomenon. The asymmetric charging is experimentally demonstrated to enhance the average power outputs of TENGs containing dissimilar contact surfaces (469% improvement) and identical contact surfaces (6076% improvement). Therefore, this study introduces a method to use identical triboelectric materials as TENG contact surfaces and generate comparable outputs to triboelectrically dissimilar materials, which significantly enhances the material range compatible for TENGs. Furthermore, we provide an insight into materials transfer characteristics between TENG contact surfaces and its impact on the non-linear external charging behaviour, revealing several crucial parameters which affect the efficiency and consistency of a TENG. Finally, this work elaborates on the TENG surface contaminations during experimental practices and the importance of TENG fabrication and characterisation procedures towards their long-term applications.

Investigation on the adhesive contact and electrical performance for triboelectric nanogenerator considering polymer viscoelasticity

The triboelectric nanogenerator (TENG) is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane (PDMS) is widely used. Micro-/nano-textures are often fabricated on the PDMS surface to enhance the electrical performance of TENG. As the contact region decreases to micro/nano scale, the adhesive forces become dominant. However, there is still a lack of contact mechanics model considering both material viscoelasticity and the adhesive forces to guide the surface texture design. In this paper, the explicit data-fitting formulas based on the fractional derivative Zener model are firstly derived to identify the viscoelastic constitutive parameters, which can not only avoid the influence of the initial contact point, but also ensure the accurate conversion between the creep compliance and the relaxation modulus function. Then a viscoelastic-adhesive contact model based on the fitted constitutive parameters is established, and the numerical algorithms such as bi-conjugate stabilized (Bi-CGSTAB) method and fast Fourier transform (FFT) technique are employed to analyze the effects of material viscoelasticity and texture sizes on the contact and electrical performance. It is shown that, compared with results from the elastic-adhesive contact model, the contact area ratio based on the viscoelastic-adhesive contact model is significantly larger, which is much closer to the experimental results. Among the selected sizes of pyramid texture, the higher electrical performance can be obtained from the textures with a smaller pitch and a larger width under the heavier applied load. This study can provide a theoretical reference for the design of viscoelastic surface texture of TENG.

Comparison of applied torque and energy conversion efficiency between rotational triboelectric nanogenerator and electromagnetic generator

SummaryTriboelectric nanogenerator (TENG) is regarded as an equally important mechanical energy harvesting technology as electromagnetic generator (EMG). Here, the input mechanical torques and energy conversion efficiencies of the rotating EMG and TENG are systematically measured, respectively. At constant rotation rates, the input mechanical torque of EMG is balanced by the friction resisting torque and electromagnetic resisting torque, which increases with the increasing rotation rate due to Ampere force. While the input mechanical torque of TENG is balanced by the friction resisting torque and electrostatic resisting torque, which is nearly constant at different rotation rates. The energy conversion efficiency of EMG increases with the increasing input mechanical power, while that of the TENG remains nearly constant. Compared with the EMG, the TENG has a higher conversion efficiency at a low input mechanical power, which demonstrates a remarkable merit of the TENG for efficiently harvesting weak ambient mechanical energy.

Y-ZnO Microflowers Embedded Polymeric Composite Films to Enhance the Electrical Performance of Piezo/Tribo Hybrid Nanogenerators for Biomechanical Energy Harvesting and Sensing Applications

Nowadays, hybrid nanogenerators (HNGs) have attracted much interest in mechanical energy-harvesting technology because of their assertable advantages in self-powered portable electronic devices. Ho...

Pumping up the charge density of a triboelectric nanogenerator by charge-shuttling

As an emerging technology for harvesting mechanical energy, low surface charge density greatly hinders the practical applications of triboelectric nanogenerators (TENGs). Here, a high-performance TENG based on charge shuttling is demonstrated. Unlike conventional TENGs with static charges fully constrained on the dielectric surface, the device works based on the shuttling of charges corralled in conduction domains. Driven by the interaction of two quasi-symmetrical domains, shuttling of two mirror charge carriers can be achieved to double the charge output. Based on the mechanism, an ultrahigh projected charge density of 1.85 mC m−2 is obtained in ambient conditions. An integrated device for water wave energy harvesting is also presented, confirming its feasibility for practical applications. The device provides insights into new modes of TENGs using unfixed charges in domains, shedding a new light on high-performance mechanical energy harvesting technology.

Mechanical Energy Harvesting Taxonomy for Industrial Environments: Application to the Railway Industry

Traditional industry is experiencing a worldwide evolution with Industry 4.0. Wireless sensor networks (WSNs) have a main role in this evolution as an essential part of data acquisition. The way in which WSNs are powered is one of the main challenges to face if industry wants to achieve the digital transformation. Energy harvesting technologies are one of the possible solutions to this challenge. The main purpose of this paper is to present a novel method to taxonomize knowledge in the field of mechanical energy harvesting to enhance the use of energy harvesting technologies in industrial applications. The methodology is based on the analysis of key parameters and performance metrics for existing technologies. The taxonomy is applied to rail axles in order to select the energy harvesting technology that is more appropriate for this specific location, demonstrating the potential of mechanical energy harvesting technologies (MEHTs) for the railway industry, as a use case of industrial environment. In addition, the taxonomy allows to identify the upcoming challenges for research purposes while analyzing the compatibility among mechanical energy harvesting technologies in order to create hybrid harvesters.

Versatile surface for solid–solid/liquid–solid triboelectric nanogenerator based on fluorocarbon liquid infused surfaces

ABSTRACT The triboelectric nanogenerator (TENG) is a recent mechanical energy harvesting technology that has been attracting significant attention. Its working principle involves the combination of triboelectrification and electrostatic induction. The TENG can harvest electrical energy from both solid–solid and liquid–solid contact TENGs. Due to their physical difference, triboelectric materials in the solid–solid TENG need to have high mechanical properties and the surface of the liquid–solid contact TENG should repel water. Therefore, the surface of the TENG must be versatile for applications in both solid–solid and liquid–solid contact environments. In this work, we develop a solid–solid/liquid–solid convertible TENG that has a slippery liquid-infused porous surface (SLIPS) at the top of the electrode. The SLIPS consists of a HDFS coated hierarchical Al(OH)3 structure and fluorocarbon liquid. The convertible TENG developed in this study is capable of harvesting electricity from both solid–solid and liquid–solid contacts due to the high mechanical property of Al(OH)3 and the water-based liquid repelling nature of the SLIPS. When the contact occurs in freestanding mode, electrical output was generated through solid–solid/liquid–solid sliding motions. The convertible TENG can harvest electricity from both solid–solid and liquid–solid contacts; thus, it can be a unified solution for TENG surface fabrication.

Sunlight‐Triggerable Transient Energy Harvester and Sensors Based on Triboelectric Nanogenerator Using Acid‐Sensitive Poly(phthalaldehyde)

AbstractTransient electronics that disintegrate via material dissolution or depolymerization under certain stimuli have great potential in biomedical and military applications. The triboelectric nanogenerator (TENG), an emerging mechanical energy harvesting technology with great flexibility in material choices, is promising in offering transient power sources. Previously reported transient energy harvesters using biodegradable polymers require solution‐based degradation and have limited applications in non‐biological scenarios. A short time span, sunlight‐triggered degradable TENG is developed. The main substrate includes an acid‐sensitive poly(phthalaldehyde) (PPHA), a photoacid generator (PAG), and a photosensitizer (PS). Through photo‐induced electron transfer, the ultraviolet radiation absorbed by the PS is transferred to the PAG to generate photoacids that trigger the depolymerization of PPHA. Transient TENG‐based mechanical energy harvesters and touch/acoustic sensors are successfully demonstrated by embedding silver nanowires onto the PPHA‐based films. The fabricated devices degrade rapidly under winter sunlight. The degradation rate can be further tuned via changing the ratio of photosensitive agents. This work not only broadens the applicability of TENG as transient power sources and sensors, but also extends the use of transient functional polymers toward advanced energy and sensing applications.

Modified energy harvesting figures of merit for stress- and strain-driven piezoelectric systems

Piezoelectrics are an important class of materials for mechanical energy harvesting technologies. In this paper we evaluate the piezoelectric harvesting process and define the key material properties that should be considered for effective material design and selection. Porous piezoceramics have been shown previously to display improved harvesting properties compared to their dense counterparts due to the reduction in permittivity associated with the introduction of porosity. We further this concept by considering the effect of the increased mechanical compliance of porous piezoceramics on the energy conversion efficiency and output electrical power. Finite element modelling is used to investigate the effect of porosity on relevant energy harvesting figures of merit. The increase in compliance due to porosity is shown to increase both the amount of mechanical energy transmitted into the system under stress-driven conditions, and the stress-driven figure of merit, FoM33X, despite a reduction in the electromechanical coupling coefficient. We show the importance of understanding whether a piezoelectric energy harvester is stress- or strain-driven, and demonstrate how porosity can be used to tailor the electrical and mechanical properties of piezoceramic harvesters. Finally, we derive two new figures of merit based on the consideration of each stage in the piezoelectric harvesting process and whether the system is stress- (FijX), or strain-driven (Fijx).

Performance enhancement of triboelectric nanogenerators based on polyvinylidene fluoride/graphene quantum dot composite nanofibers

Wearable mechanical energy harvesting technologies have been achieved much attention for the wireless sustainable power source applications. In this study, we have fabricated polyvinylidene fluoride (PVDF)/graphene quantum dot (GQD) composite nanofibers (NFs), which showed improved triboelectric nanogenerator (TENG) performance. PVDF/GQD composite NFs were fabricated by an electrospinning method. Structural and chemical investigations show that the GQDs were embedded in the PVDF NFs and promoted the formation of polar β-phase when an optimal amount of GQDs was incorporated. The PVDF/GQD NFs showed strong photoluminescence at a wavelength of 453 nm, which was attributed to the electronic transitions in the GQDs. As the GQD content increased from 0 to 5 vol%, the maximum output power from TENG devices increased from 35 to 97 μW but decreased with further additions of GQDs. The enhancement and degradation of the TENG performance with increasing the GQD contents were due to the enhanced formation of polar β-phase and the detrimental effect of conductive GQDs for charge trapping, respectively.

Direct-Current Rotary-Tubular Triboelectric Nanogenerators Based on Liquid-Dielectrics Contact for Sustainable Energy Harvesting and Chemical Composition Analysis

Ambient mechanical energy harvesting technology introduces a promising solution to alleviate expanding energy demands on a sustainable basis, of which the drawbacks should attract attention for further advances. In this work, a liquid-dielectrics interface based triboelectric nanogenerator (TENG) with direct-current output is reported as an energy harvester and a chemical sensor, with advantages of feasible fabrication, anti-wearing durability, and low energy consumption. The TENG consisting of an fluorinated ethylene propylene (FEP) tube and Cu electrodes is designed into a ring structure, with two electric brushes bilaterally anchored that converts an alternating-current output into direct-current output. The liquids and copper pellets as the fluid-state dielectrics are prefilled to generate triboelectric charges with an FEP tube. The relevant parameters of TENG are initially optimized, enabling a satisfactory output under rotating excitations. Furthermore, the inherent impacts of various liquids on the output performance of TENG are comprehensively studied, based on which chemical analysis system is developed. Meanwhile, the design for TENG with pellets is also modified for output-current enhancement. Finally, an assembled TENG has been demonstrated not only for energy harvesting without rectification but also for chemical detecting in liquid composition and moisture content analysis. The proposed TENG renders a more-efficient method for energy harvesting and greatly expands its application in direct-current self-powered systems.

Lead-Free Perovskite Nanowire-Employed Piezopolymer for Highly Efficient Flexible Nanocomposite Energy Harvester.

In the past two decades, mechanical energy harvesting technologies have been developed in various ways to support or power small-scale electronics. Nevertheless, the strategy for enhancing current and charge performance of flexible piezoelectric energy harvesters using a simple and cost-effective process is still a challenging issue. Herein, a 1D-3D (1-3) fully piezoelectric nanocomposite is developed using perovskite BaTiO3 (BT) nanowire (NW)-employed poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) for a high-performance hybrid nanocomposite generator (hNCG) device. The harvested output of the flexible hNCG reaches up to ≈14 V and ≈4 µA, which is higher than the current levels of even previous piezoceramic film-based flexible energy harvesters. Finite element analysis method simulations study that the outstanding performance of hNCG devices attributes to not only the piezoelectric synergy of well-controlled BT NWs and within P(VDF-TrFE) matrix, but also the effective stress transferability of piezopolymer. As a proof of concept, the flexible hNCG is directly attached to a hand to scavenge energy using a human motion in various biomechanical frequencies for self-powered wearable patch device applications. This research can pave the way for a new approach to high-performance wearable and biocompatible self-sufficient electronics.

Studying about applied force and the output performance of sliding-mode triboelectric nanogenerators

Triboelectric nanogenerator (TENG) as a powerful mechanical energy harvesting technology has major applications as micro/nano-power source, for self-powered sensors and even large-scale blue energy, which would impact the world likely development for the future. In this work, a theoretical model for the sliding-mode TENG with considering the external force applied onto the TENG was presented. Through approximate analytical equations derivation, the output characteristics of TENG with arbitrary load resistance were calculated, including the output power and energy. Based on the relationships between the output characteristics and load resistance or sliding velocity, the force applied on the sliding component of TENG and the friction force were investigated for two cases, i.e., without load resistor and with load resistor. Also, the influences of the resistance and sliding velocity on the forces were investigated. Furthermore, the corresponding experiments were carried out to measure the force applied on the TENG as well as the output performance of the fabricated sliding-mode TENG. The experimental results are in good agreement with the theoretical predictions, which can effectively reveal the principle of applied force on the TENG and facilitate the understanding of the relationship between the power, energy and applied force.