Triboelectric Energy Harvesting Research Articles

An Efficient Power Management System Using Dynamically Configured Multiple Triboelectric Nanogenerators and Dual‐Parameter Maximum Power Point Tracking

AbstractTriboelectric nanogenerators (TENGs) have shown great potential as sustainable energy sources with the advantages of a lightweight, low cost, simple fabrication, and small size. Nevertheless, schemes for efficient power extraction from TENGs remains difficult, partly because of their short, high‐voltage (HV) pulse output. The available power from a single TENG is not usually enough for practical applications. An efficient power management system for TENGs using a dynamically reconfigured combining method and dual‐parameter maximum power point tracking (MPPT) is proposed. A series to parallel/parallel to series (SPPS) adaptive control method, which dynamically reconfigures the connection of multiple TENGs, efficiently combines the outputs. An MPPT method, which adjusts the dual parameters in a closed‐loop, provides a wide range for matching the high output impedance (≈MΩ) of TENGs. The proposed technique is implemented using a 416 nW energy harvester interface integrated circuit (EHI‐IC), realized using a 180 nm, 48 V Bipolar‐CMOS‐DMOS (BCD) process. Measured results show that the proposed approach achieves a 159‐fold improvement in power extraction compared to the results without EHI‐IC. Finally, a triboelectric energy harvesting ball (T‐EHB), which combines 12 TENG pairs for multi‐axis excitation, and several examples of device powering are presented using the T‐EHB.

Layer-by-Layer Self-Assembled Thin Films for Triboelectric Energy Harvesting under Harsh Conditions

With the rapid growth in triboelectric nanogenerator (TENG) technology, selecting appropriate tribomaterial (TM) with high electrical output performance and a cheap fabrication technique is vital for sustainable nanogenerator operations. Thus, we prepared an electrostatic bonded thin poly(diallyldimethylammonium chloride) and poly(4-styrene-sulfonic acid) multilayered-based film as a potential positive TM via facile and cheap layer-by-layer (LbL) self-assembly fabrication technique. The high electrical output performance of the LbL-TENGs depends on the number of BL films was optimized by changing the number of bilayers (BLs) from 10 to 50. The 30 BL TENG shows a significant voltage of 189 V and a current density of 17 mA m–2 under the harsh environment of 65% RH, indicating the sustainability of the LbL-TENG device. Furthermore, the single-electrode mode of the optimized TENG exhibited an impressive TENG performance of 215 V and 79 mA m–2 and lit up 39 green light-emitting diodes just by tapping the TENG by hand.

Cost-effective fabrication approaches for improving output performance of triboelectric energy harvesters

This study exploits conductive nickel/copper nonwoven polyester as a new triboelectric material and proves its effectiveness in improving the electrical characteristics of triboelectric energy harvesters and reducing production costs. The tribo-surface charge density as another influencing factor in the triboelectric nanogenerators (TENGs) output performance has also been addressed via pre-implanting charges into the surface of polytetrafluoroethylene (PTFE) film using a compact, small, and inexpensive boost step-up power module as an innovative tool. The open-circuit voltage and short-circuit current of eight TENGs are examined to assess the effect of the triboelectric materials, surface morphology, and charge-implantation process on the TENG performance. Sandpaper is used as a stamp to induce micro/nanostructures on the PTFE surface, and its surface charge density is improved using the proposed boost step-up power module. The main purpose of this study is not to provide a new structure for the TENG; this study provides a feasible way to reduce fabrication costs and increase the output performance of triboelectric energy harvesters.

Book-Shaped All-in-One Piezo-Triboelectric Energy Harvester Module with Enhanced Current Characteristics As an Eco-Friendly Energy Source

A book-shaped all-in-one energy harvester module with a piezo-triboelectric hybrid structure as a next-generation eco-friendly energy source was manufactured based on flexible piezoceramic nanofibers with enhanced current characteristics obtained by controlling the added amount of carbon black (CB). To prepare flexible piezoceramic nanofibers with favorable current properties, 0.78Bi0.5Na0.5TiO3−0.22SrTiO3 (BNT-ST) piezoelectric ceramics were composited with CB, a highly conductive material, and then electrospun with a poly(vinylidene fluorideco–trifluoroethylene) polymer. The prepared CB/BNT-ST nanofibers were modularized into piezoelectric energy harvester modules (PEHMs) with interdigitated electrodes, yielding an improved output performance with a high voltage of 10.1 V and high current of 2.02 nA. A book-shaped triboelectric energy harvester module (TEHM) was manufactured with polydimethylsiloxane on one side and the CB/BNT-ST nanofibers on the other side, affording an improved output performance with a high voltage of 391 V and high current of 130 μA. A book-shaped all-in-one hybrid energy harvester module (HEHM) was then manufactured by fitting PEHMs at both ends of the book-shaped TEHMs. As a result of optimizing the output performance by connecting HEHM multiple layers, a high voltage and current of 1043 V and 579 μA were observed, respectively, and charging of a 1.0 μF capacitor was completed in 25 s. Furthermore, in simulated energy harvesting experiments using the all-in-one HEHM, LED light bulbs were clearly illuminated in real time, and an electronic calculator was operated without charging. This work suggests the application potential of the all-in-one HEHM as the next generation of eco-friendly flexible energy sources.

Toxic Gas-Free Synthesis of Extremely Negative Triboelectric Sulfur Copolymer Blends Via Phase Separation of Fluorine-Rich Polymers

Recently, we reported surface fluorination of sulfur-based polymers to introduce a new class of extremely negative triboelectric material. However, the direct surface fluorination requires the use of toxic fluorine gas. In this study, we report the toxic gas-free synthesis of extremely negative triboelectric sulfur-rich polymers via the phase separation of a fluorine-rich polymer, poly(2,3,4,5,6-pentafluorostyrene) (PPFS), from sulfur copolymers. PPFS was physically mixed in situ during the inverse vulcanization of elemental sulfur, a by-product of petroleum refining to prepare the polymer blends. Hot pressing of the blends into films induced the phase separation of the hydrophobic PPFS; subsequently, PPFS migrates to the hydrophobic air interface to minimize the interfacial energy. A triboelectric nanogenerator (TENG) based on the phase separated blend films presented long-term stable voltage and current outputs that are 8-fold and 9-fold higher, respectively, than those of a TENG based on polytetrafluoroethylene (PTFE), a well-known extremely negative triboelectric polymer. We also demonstrate the ability of a TENG based on an 81.1 cm2-sized blend film to power 400 series-connected blue LEDs of 3.3 V; a triboelectric open-circuit voltage output of 1362.4 V is obtained under a minimal force of 30 N. The demonstrated phase-separation strategy for fluorine-rich polymers will thus provide insights for achieving low-cost, environment-friendly, and high-performance triboelectric energy harvesting.

Self-Powered Load Sensing Circuitry for Total Knee Replacement.

There has been a significant increase in the number of total knee replacement (TKR) surgeries over the past few years, particularly among active young and elderly people suffering from knee pain. Continuous and optimal monitoring of the load on the knee is highly desirable for designing more reliable knee implants. This paper focuses on designing a smart knee implant consisting of a triboelectric energy harvester and a frontend electronic system to process the harvested signal for monitoring the knee load. The harvester produces an AC signal with peak voltages ranging from 10 V to 150 V at different values of knee cyclic loads. This paper demonstrates the measurement results of a PCB prototype of the frontend electronic system fabricated to verify the functionality and feasibility of the proposed approach for a small range of cycling load. The frontend electronic system consists of a voltage processing unit to attenuate high peak voltages, a rectifier and a regulator to convert the input AC signal into a stabilized DC signal. The DC voltage signal provides biasing for the delta-sigma analog-to-digital converter (ADC). Thus, the output of the triboelectric harvester acts as both the power signal that is rectified/regulated and data signal that is digitized. The power consumption of the proposed PCB design is approximately 5.35 μW. Next, the frontend sensor circuitry is improved to accommodate a wider range of cyclic load. These results demonstrate that triboelectric energy harvesting is a promising technique for self-monitoring the load inside knee implants.

Energy Harvesting Materials and Structures for Smart Textile Applications: Recent Progress and Path Forward.

A major challenge with current wearable electronics and e-textiles, including sensors, is power supply. As an alternative to batteries, energy can be harvested from various sources using garments or other textile products as a substrate. Four different energy-harvesting mechanisms relevant to smart textiles are described in this review. Photovoltaic energy harvesting technologies relevant to textile applications include the use of high efficiency flexible inorganic films, printable organic films, dye-sensitized solar cells, and photovoltaic fibers and filaments. In terms of piezoelectric systems, this article covers polymers, composites/nanocomposites, and piezoelectric nanogenerators. The latest developments for textile triboelectric energy harvesting comprise films/coatings, fibers/textiles, and triboelectric nanogenerators. Finally, thermoelectric energy harvesting applied to textiles can rely on inorganic and organic thermoelectric modules. The article ends with perspectives on the current challenges and possible strategies for further progress.

3D Printed Double Roller-Based Triboelectric Nanogenerator for Blue Energy Harvesting.

The ocean covers 70% of the earth’s surface and is one of the largest uncultivated resources still available for harvesting energy. The triboelectric energy harvesting technology has the potential to effectively convert the ocean’s “blue energy” into electricity. A half-cylinder structure including rollers floating on the water has already been used, in which the pendulum motion of the rollers is driven by the waveform. For the stable motion of the rollers, the printed surface of the device was treated with acetone for attaining hydrophilicity. The electrical outputs with the proposed device were enhanced by increasing the contact surface area by simply implementing the double roller structure with double side-covered electrodes. With the optimized structure, the maximum power density reached a value of 69.34 µW m−2 at a load resistance of 200 MΩ with the device’s high output durability. Finally, the fabricated device was also applied to the artificial water waves to demonstrate the possibility of using this device in the ocean. By simply modifying the electrode structure and adding a roller, this device demonstrated the ability to generate over 160% of electrical output with the same covered area of the ocean by the triboelectric nanogenerators (TENGs) and potential ocean application.

Probing Contact Electrification: A Cohesively Sticky Problem.

Contact electrification and the triboelectric effect are complex processes for mechanical-to-electrical energy conversion, particularly for highly deformable polymers. While generating relatively low power density, contact electrification can occur at the contact-separation interface between nearly any two polymer surfaces. This ubiquitousness of surfaces enables contact electrification to be an important phenomenon to understand energy conversion and harvesting applications. The mechanism of charge generation between polymeric materials remains ambiguous, with electron transfer, material (also known as mass) transfer, and adsorbed chemical species transfer (including induced ionization of water and other molecules) all being proposed as the primary source of the measured charge. Often, all sources of charge, except electron transfer, are dismissed in the case of triboelectric energy harvesters, leading to the generation of the "triboelectric series", governed by the ability of a polymer to lose, or accept, an electron. Here, this sole focus on electron transfer is challenged through rigorous experiments, measuring charge density in polymer-polymer (196 polymer combinations), polymer-glass (14 polymers), and polymer-liquid metal (14 polymers) systems. Through the investigation of these interfaces, clear evidence of material transfer via heterolytic bond cleavage is provided. Based on these results, a generalized model considering the cohesive energy density of polymers as the critical parameter for polymer contact electrification is discussed. This discussion clearly shows that material transfer must be accounted for when discussing the source of charge generated by polymeric mechanical energy harvesters. Thus, a correlated physical property to understand the triboelectric series is provided.

Energy Harvesting Untethered Soft Electronic Devices (Adv. Healthcare Mater. 17/2021)

Human–Machine Interfaces In article number 2002286, Seung Hwan Ko and co-workers review the cutting edge of wearable devices. Recent development of untethered devices consists of a range of cutting-edge technologies such as electromagnetic, triboelectric, and thermoelectric energy harvesting. Recent advances in bio-fuel-based electronics show numerous solutions to the remaining practical issues of continuous measurement without an external power source. Key advancements in untethered devices in various power sources are introduced with their principles and working mechanisms.

Theoretical investigation and experiment of a disc-shaped triboelectric energy harvester with a magnetic bistable mechanism

Triboelectric energy harvesting has emerged as a promising route to scavenge ambient mechanical energy for cost-effective, clean and sustainable electricity. Disc-shaped triboelectric energy harvesters are suitable for two kinds of mechanical energy sources: continuous rotation and vibration. A majority of current studies about disc-shaped triboelectric energy harvesters focus on scavenging energy in continuous rotation, but there is a lack of investigations on angular vibration, especially in structural dynamics. In this work, a new disc-shaped triboelectric energy harvester with a bistable mechanism enabled by two repulsive magnets is developed for harvesting vibration energy. There are two discs in the harvester, one stationary and the other undergoing angular oscillation. Both have segmented triboelectric films on their contact surfaces. The magnetic bistable mechanism is utilized for the first time in a disc-shaped triboelectric energy harvester for efficiency enhancement. A comprehensive theoretical model coupling both structural dynamic and electric dynamic domains is established. A comparison between the coupled and uncoupled models reveals that the ET between electrodes can be ignored. Numerical simulations are carried out to investigate the effect of the potential wells due to the two magnets, basins of attractors and the influence of damping from the perspective of structural dynamics. A prototype is fabricated for experimental investigations, which demonstrate that the harvester with the bistable mechanism can achieve a better performance than the corresponding harvester without the bistable mechanism, and the output voltage of the harvester increases with the increase of excitation amplitude. Theoretical and experimental comparisons about the electric outputs between the triboelectric films with different segmentation structures reveal that increasing the number of sectors on the films effectively improves the harvesting efficiency. This work establishes a link between the structural dynamics and electric dynamics for the vibration-based disc-shaped triboelectric energy harvester, providing guidelines for its design and fabrication.

A study on the design parameters for water–solid triboelectric energy harvesting with a channel device

This study demonstrates a channel device to harvest energy from water flow in a channel, which can fix the water droplet’s shape and speed. By using this device configuration, design parameters like material thickness, water droplet’s speed and length, and electrode length were able to analyze independently. An electrical output is generated when different Teflon thicknesses coated on the top and bottom electrodes of the channel. The device with the overall thinnest Teflon layers can produce the highest short circuit current of 2.346 ± 0.018 nA and open-circuit voltage of 2.01 ± 0.01 V. Furthermore, the short circuit current increases with the water droplet speed in the channel. However, short circuit current output remains unchanged when the electrode and the water droplet’s length changes. For potential device application, the channel device can produce a direct current – like short circuit current output with a long duration (~1s) of constant current (Ipk = 2.358 nA). This was achieved simply by using a long electrode and water droplet length of 25 mm. The findings in this study not only provide information to understand the design parameters in water–solid triboelectric energy harvesting devices but also helpful for future device design to generate a constant current output.

A new Mylar-based triboelectric energy harvester with an innovative design for mechanical energy harvesting applications

In this paper, an innovative origami structure is deployed to create a novel, flexible, lightweight, and low-cost triboelectric nanogenerator (Miura-Ori-TENG). For the first time, Mylar film is used as a supporting and flexible spring-like structure to develop the first Mylar-based origami TENG, eliminating the need for any external auxiliary system to ensure continuous operation of the TENG. Subsequently, a self-powered power management circuit with a novel self-controlled switching mechanism is designed and implemented for direct use of Miura-Ori-TENG electrical output and maximizing the harvested energy. The performance of the Miura-Ori-TENG and power management circuit are evaluated under different practical conditions. The open-circuit voltage and short-circuit current reached 308.6 V and 55.5 µA, respectively, with a peak power of 5.1 mW under a linear reciprocating motion with an operating frequency of 4 Hz. Moreover, open-circuit voltage, short-circuit current, and instant output power of 1050 V, 131 µA, and 40 mW are obtained using footsteps during human walking. Furthermore, in a 1000 µF capacitor charging experiment using the proposed power management circuit, the stored energy increased up to 117.5 times compared to a direct charging experiment. In order to prove that the Miura-Ori-TENG, in combination with the proposed power management circuit, could be used as a power source in many applications, its ability to charge the capacitors and rechargeable batteries and drive the electronics is shown with proof-of-concept demonstrations. The results of this study demonstrated potential applications of the Miura-Ori-TENG in converting rotational, vibrational, and impact kinetic energies into electrical energy, as well as the outstanding performance of the proposed power management circuit in managing the harvested energy.

A capsule-structured triboelectric energy harvester with stick-slip vibration and vibro-impact

Despite great progress made in triboelectric energy harvesting, most investigations are purely about experiments and/or manufacturing. There is a serious lack of in-depth theoretical studies of the underlying vibration and its effects on power yield. In this paper, a novel triboelectric energy harvester is presented and its non-smooth structural dynamics and electrical performance are studied. This first theoretical study of a capsule-structured triboelectric energy harvester includes a mathematical model coupling the structural dynamics and electric dynamics, which integrates in-plane sliding mode and contact-separation mode. The influences of friction properties on sliding surfaces, electrostatic force, initial slider position, excitation level and harvester dimensions, are investigated. The performance of this harvester is not limited by its frequency bandwidth, whose average power increases from 10.3 μW at 3 Hz to 69.4 μW at 14 Hz. Impact/chatter events are found to improve power yield, for example, there is a dramatic increase of 20 μW at 6 Hz due to impact induced by a slight increase of excitation amplitude. Additionally, the internal capsule length plays a subtle role and a length beyond a certain value causes a sharp fall of power yield. These findings enable innovative designs and provide fabrication guidelines of triboelectric energy harvesters.

Technique for Measuring Power across High Resistive Load of Triboelectric Energy Harvester.

This paper proposed a more-accurate-than-conventional measurement technique for determining electrical power across exceptionally high-impedance of triboelectric energy harvester (TEH). The key idea of this proposed technique was to measure the voltage across an introduced, parallelly-connected resistor divider to the oscilloscope instead of the voltage across the harvester. An experiment was set up to verify the measurement accuracy performance of this technique against the ideal theoretical values. The maximum percentage error found was only 2.30%, while the conventional measurement technique could not be used to measure voltage across high impedance TEH at all because the readings were not accurate, i.e., the measurement error would be at least over 10%. Therefore, we concluded that this proposed technique should always be used instead of the conventional measurement technique for power measurement of any TEH. A suggestion that we would like to offer to researchers investigating or developing a TEH is that, in using our measurement technique, a good starting point for a load to probe resistance ratio is 1:10, a ratio that worked well for our TEH test bench that we developed.

Effect of Dielectric Material and Package Stiffness on the Power Generation in a Packaged Triboelectric Energy Harvesting System for Total Knee Replacement.

The objectives of this study are to experimentally investigate the effects of the dielectric material and the package stiffness on the durability and the efficiency of a previously developed triboelectric-based instrumented knee implant prototype. The proposed smart knee implant may provide useful information about prosthesis health and its functionality after a total knee replacement (TKR) by routine monitoring of tibiofemoral load transfer without the need for any external power source. The triboelectric powered load sensing by the proposed TKR system needs to be functional throughout the entire life of a knee replacement. The power output of the triboelectric system depends on the surface charge generations and accumulations on its dielectric material, and the force that transmits through its housing into the tribo-materials. The properties of the dielectric material and the package stiffness can significantly influence the reliability of the proposed device. For such a TKR system, a compliant mechanism with the ideal material selection can improve its state of the art. We investigated the performance of three vertical contact mode triboelectric generators made with three different dielectric materials: polydimethylsiloxane (PDMS), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE). To investigate the effect of package stiffness, we tested two Ti-PDMS-Ti harvesters inside a polyethylene and a Ti6Al4V package. At 1500 N of sinusoidal loads, the harvesters could generate 67.73 μW and 19.81 μW of mean apparent power in parallel and single connections in the polyethylene package, which was 32 and 17 times greater than the power recorded in the Ti assembly, respectively.

Triboelectric Energy Harvester Based on Stainless Steel/MoS2 and PET/ITO/PDMS for Potential Smart Healthcare Devices.

The smart healthcare devices connected with the internet of things (IoT) for medical services can obtain physiological data of risk patients and communicate these data in real-time to doctors and hospitals. These devices require power sources with a sufficient lifetime to supply them energy, limiting the conventional electrochemical batteries. Additionally, these batteries may contain toxic materials that damage the health of patients and environment. An alternative solution to gradually substitute these electrochemical batteries is the development of triboelectric energy harvesters (TEHs), which can convert the kinetic energy of ambient into electrical energy. Here, we present the fabrication of a TEH formed by a stainless steel substrate (25 mm × 15 mm) coated with a molybdenum disulfide (MoS2) film as top element and a polydimethylsiloxane (PDMS) film deposited on indium tin oxide coated polyethylene terephthalate substrate (PET/ITO). This TEH has a generated maximum voltage of 2.3 V and maximum output power of 112.55 μW using a load resistance of 47 kΩ and a mechanical vibration to 59.7 Hz. The proposed TEH could be used to power potential smart healthcare devices.

Fully elastic multilayered triboelectric energy harvester made of polymer thin films and elastic tubes

This paper presents a triboelectric energy harvester that can be stacked in multiple layers and fabricated using an elastic hollow tube, polymer film, and conductive tape. Using the compression deformation characteristic of the elastic tube, the proposed device can stably generate high average powers at large displacements and generate energy even at small vibrations, where the two materials are not entirely separated. The proposed device was fabricated by attaching a conductive tape to the film and a self-assembled monolayer coating. Peak-to-peak values of 33.5 V and 11.5 μA were measured when a force of 50 N at 4 Hz was applied to a single-layer device. When the device was pressed by 1 mm in advance, the outputs decreased to 19.2 V and 6.6 μA. A three-layer device exhibited the same open-circuit voltage, whereas the maximum short-circuit current was measured to be 33 μA, approximately three times higher. When the device was operated in the full contact–separation mode, the maximum power was measured to be 837 µW, whereas when a 1 mm preload state was maintained, the measured power was 419 µW.

A Fully Energy-Autonomous Temperature-to-Time Converter Powered by a Triboelectric Energy Harvester for Biomedical Applications

This article presents a fully energy-autonomous temperature-to-time converter (TTC), entirely powered up by a triboelectric nanogenerator (TENG) for biomedical applications. Existing sensing systems either consume too much power to be sustained by energy harvesting or have poor accuracy. Also, the harvesting of low-frequency energy input has been challenging due to high reverse leakage of a rectifier. The proposed dynamic leakage suppression full-bridge rectifier (DLS-FBR) reduces the reverse leakage current by more than 1000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> , enabling harvesting from sparse and sporadic energy sources; this enables the TTC to function with a TENG as the sole power source operating at <1-Hz human motion. Upon harvesting 0.6 V in the storage capacitor, the power management unit (PMU) activates the low-power TTC, which performs one-shot conversion of temperature to pulsewidth. Designed for biomedical applications, the TTC enables a temperature measurement range from 15 °C to 45 °C. The energy-autonomous TTC is fabricated in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> 1P6M CMOS technology, consuming 0.14 pJ/conversion with 0.014-ms conversion time.

Tailoring the triboelectric output of poly-L-lactic acid nanotubes through control of polymer crystallinity

Triboelectric devices capable of harvesting ambient mechanical energy have attracted attention in recent years for powering biomedical devices. Typically, triboelectric energy harvesters rely on contact-generated charges between pairs of materials situated at opposite ends of the triboelectric series. However, very few biocompatible polymeric materials exist at the ‘tribopositive’ end of the triboelectric series. In order to further explore the use of triboelectric energy harvesting devices within the body, it is necessary to develop more biocompatible tribopositive materials and look into ways to improve their triboelectric performance in order to enhance the harvested power output of these devices. Poly-L-lactic acid (PLLA) is a tribopositive biocompatible polymer, frequently used in biomedical applications. Here, we present a way to improve the triboelectric output of nanostructured PLLA through fine control of its crystallinity via a customised template-assisted nanotube (NT) fabrication process. We find that PLLA NTs with higher values of crystallinity (∼41%) give rise to a threefold enhancement of the maximum triboelectric power output as compared to NTs of the same material and geometry but with lower crystallinity (∼13%). Our results thus pave the way for the production of a viable polymeric and biocompatible tribopositive material with improved power generation, for possible use in implantable triboelectric nanogenerators.