Power Management Circuit Research Articles

A Synergistically Enhanced Triboelectric-Electromagnetic Hybrid Generator Enabled by Multifunctional Amorphous Alloy for Highly Efficient Self-Powered System.

Triboelectric-electromagnetic hybrid generator (TEHG) has emerged as an effective technology for mechanical energy harvesting. However, the independent operation of triboelectric nanogenerator (TENG) and electromagnetic generator (EMG), along with tribo-materials wear and magnetic field divergence, constrain the device's overall performance. To address these challenges, a synergistically enhanced TEHG (SE-TEHG) is proposed based on the multifunctional amorphous alloy. Following detailed material analyses, Fe72Si8B20 is selected as the synergistic layer for its low surface roughness, high Vickers-hardness, amorphous structure, and high magnetization. Compared to Al, this material not only boosts TENG's output current and current retention rate by 28.75% and 85.24%, but also improves EMG's output power by 51.05%. In constructing a self-powered system with TEHG, a significant impedance discrepancy exists between the energy harvester (with matched impendence of 16 MΩ for TENG and 110 kΩ for EMG) and the application end. Without power management circuits, the demonstrated self-powered variable impedance system achieves an energy utilization efficiency that is 2.98 times greater than the conventional constant impedance system. The integration of multifunctional materials to realize strong-coupling hybrid generators, combined with the customization of variable impedance systems, set a milestone in efficient mechanical energy harvesting and utilization.

Significantly Enhanced Output Performance of Triboelectric Nanogenerators via Charge Storage and Release Strategy.

As a novel energy harvesting technology, bettering the output performance of triboelectric nanogenerators (TENGs) is vital. Although quite a number methods to increase charge density have been proposed, challenges such as high impedance matching and low output current persist, severely limit the energy utilization efficiency of TENGs. Here, a new power management circuit (PMC) is proposed that through charge storage and release strategy. This circuit first excites the surface charge of the TENG using the charge excitation circuit, and then releases the stored charge through a self-triggered switch. Compared to a standard TENG, the output current of the TENG with this PMC is increased by a factor of 1108, the impedance is decreased from 100 MΩ to 10 kΩ, and the energy utilization efficiency is markedly improved. This work affords a reference for enhancing the output performance of TENG, reducing impedance, and broading the utility attainable of TENGs.

Hybrid Wind‐Solar Self‐Powered Detector System Using a Triboelectric‐Photovoltaic Generator for Smart Agriculture

The growth of crops is affected by factors such as temperature, humidity, and salinity, so it is critical to monitor these indicators through detectors in smart agriculture. Collecting renewable energy in the farmland environment to power the detector will provide a feasible approach. Therefore, a triboelectric‐photovoltaic hybrid generator (WS‐TPHG) is proposed to collect solar and wind energy efficiently. The generator structure includes a photovoltaic panel (PV) and a wind‐driven triboelectric nanogenerator (W‐TENG). The switching function of the power supply can be realized through the power management circuit. In the case of sufficient light, the detector is powered by PV steadily, and in the case of insufficient light, the detector is powered by W‐TENG via the switching function. The PV can supply a stable voltage of 8.1 V, and the open‐circuit voltage (VOC) of W‐TENG can reach 478.6 V at 180 rpm. The results verify that the detection of temperature, humidity, and salinity can be successfully achieved through the detector which is powered by WS‐TPHG. In this article, the potential application of WS‐TPHG is demonstrated in farmland to provide a solution for the sustainable development of agriculture.

AI-enhanced backpack with double frequency-up conversion vibration energy converter for motion recognition and extended battery life

With growing interest in physical activities, wearable device sales have been increasing each year due to their help in tracking movement. However, keeping these devices running for a long time is still a key challenge. This paper presents an AI-enhanced backpack equipped with a hybrid vibration energy converter that integrates piezoelectric (PE) and electromagnetic (EM) technologies, featuring a double frequency-up conversion (FUC) mechanism. The PE unit enables efficient motion recognition, while the EM unit extends battery life via kinetic energy harvesting. The double FUC mechanism boosts human motion signal strength and resolution by converting sub-Hertz frequencies to hundreds of Hertz. This makes the device particularly effective in environments with performance constraints and interference. By adopting deep learning techniques, the system maintains a high motion recognition accuracy of 97.33 % even under low data sampling rates and significant noise interference. The EM unit effectively harvests kinetic energy, generating an average output power of 4.5 mW during activities such as running at 4.5 Hz, despite of the device’s compact size. Additionally, a power management circuit with human motion-stimulated switch optimizes battery life by managing the system’s sleep and active states. This innovative energy management approach ensures that during human activity, the system conserves energy by remaining in sleep state for at least 30 % of the time, significantly extending battery life and enhancing the backpack’s suitability for outdoor applications.

Analysis and Application of Poly(vinyl alcohol) (PVA) and Polyacrylonitrile (PAN) Nanofiber Membrane-Based Triboelectric Nanogenerators.

The triboelectric property of materials is used to harvest energy from intentional or nonintentional sources of vibration. Contact mode freestanding dielectric based nanogenerators (CFTENGs) have many advantages when compared with other modes of triboelectric nanogenerators. The property of dielectric materials plays an important role in the energy harvesting process. In this work, we aim to fabricate nanofiber membranes of poly(vinyl alcohol) (PVA) and polyacrylonitrile (PAN) and study their properties for CFTENGs. The morphology and porosity of both membranes were tested experimentally. The mechanical property is modeled with a representative volume element (RVE) technique to understand its deflection behavior. In addition, an electromechanical model is developed to predict and analyze the behavior of those membranes in the energy conversion process. Our research reveals that the PAN dielectric layer achieves a maximum open circuit voltage of 192 kV compared to the PVA dielectric layer (2.2 kV) in the CFTENG system. In comparison, the dielectric layer of the PAN nanofiber membrane reflects its flexibility to generate electrical energy in a CFTENG with the effect of contact electrification and electrostatic induction under various sources of unused energies for a wide range of applications. Moreover, the same methodology is applied to various sources of vibration, and their performance is reported. With an appropriate power management circuit, we can design a PAN membrane-based TENG for various applications.

Aurivillius-Type SrBi4Ti4O15/PGA Composite Film-Based Flexible Triboelectric Nanogenerators for Energy Harvesting/Storage and Multipurpose Tap-Indication Transducer Applications.

Recent advancements in flexible triboelectric nanogenerators (TENGs) have widely focused on converting mechanical energy into electrical energy to power small wearable electronic gadgets and sensors. To effectively achieve this, an efficient energy-converted power management circuit is required. Herein, we report on Aurivillius-type strontium bismuth titanate (SrBi4Ti4O15) nanoparticles (SBT NPs)-loaded polyglucosamine (PGA) composite film-based flexible TENG to be used for energy harvesting/storage and biomechanical applications. Initially, SBT NPs were synthesized and then, different weight concentrations were loaded into PGA. The TENG devices were fabricated using different wt % composite films (SBT/PGA) and polydimethylsiloxane as positive and negative triboelectric layers, respectively, and aluminum was used as a conductive electrode attached to two tribo films. To evaluate the electrical output from the device, contact-separation operation mode was used. An optimized TENG consisting of 2 wt % SBT/PGA composite film produced the maximum electrical output voltage and current of approximately ∼239 V and ∼7.5 μA, respectively. Efficient TENG energy harvesting and storage circuits have been proposed for storing charges in capacitors and for operating electronic gadgets. The optimized TENG was employed to generate electrical energy from various biomechanical movements. Thereafter, the biodegradability of the composite film was also tested. The fabricated films were completely biodegraded within a few hours. Furthermore, the TENG was utilized as a tap-indication transducer for multipurpose switching applications.

Investigating superior performance by configuring bimetallic electrodes on fabric triboelectric nanogenerators (F-TENGs) for IoT enabled touch sensor applications

Fabric Triboelectric Nanogenerators (F-TENGs) are increasingly becoming more significant in wearable monitoring and beyond. These devices offer autonomous energy generation and sensing capabilities, by replacing conventional batteries in flexible wearables. Despite the substantial effort, however, achieving high output with optimal stability, durability, comfort, and washability poses substantial challenges, so we have yet to see any practical commercial uses of these materials. This study focuses on output and investigates the impacts of mono and bimetallic composite fabric electrode configurations on the output performance of F-TENGs. Our findings showcase the superiority of bimetallic configurations, particularly those incorporating Copper (Cu) with Nickel (Ni), over monometallic (Cu only) electrodes. These configurations demonstrate remarkable results, exhibiting a maximum instantaneous voltage, current, and power density of ∼ 199 V (a twofold increase compared to monometallic configurations), ∼22 μA (a threefold increase compared to monometallic configurations), and 2992 mW/m², respectively. Notably, these bimetallic configurations also exhibit exceptional flexibility, shape adaptability, structural integrity, washability, and mechanical stability. Furthermore, the integration of passive component-based power management circuits significantly enhances the performance capabilities of the F-TENGs, highlighting the essential role of power management circuits and electrode selection in optimizing F-TENGs. In addition, we have developed a complete IoT-enabled touch sensor system using CuNi-BEF EcoFlex layered F-TENGs for precise detection of soft and hard touches. This advanced system enhances robotic functionality, enabling nuanced touch understanding essential for precision tasks and fostering more intuitive human-machine interactions.

Durable Multilayered Sleeve-Structured Hybrid Nanogenerator for Efficient Water Wave Energy Harvesting.

The state-of-the-art triboelectric nanogenerator (TENG) technology has numerous advantages and creates new prospects for the rapid development of the Internet of Things (IoT) in marine environments. Here, to accelerate the application process of TENG, an elaborately designed multilayered sleeve-structured hybrid nanogenerator (M-HNG) is developed to efficiently and persistently harvest marine energy. The M-HNG integrates an electromagnetic nanogenerator (EMG) with four coils and a multilayered sleeve-structured TENG (MS-TENG) with three freestanding layer units to increase spatial utilization efficiency. Moreover, rabbit fur strips are introduced to enhance the output performance and strengthen the durability of TENG. Therefore, the MS-TENG has high durability due to its soft-contact structure, maintaining its performance even after 240,000 cycles. When a 1000 μF capacitor is charged by M-HNG utilizing a power management circuit (PMC), the stored energy is increased from 2.62 mJ to 140.11 mJ, representing a significant improvement of 52-fold. The M-HNG triggered by water waves has successfully powered various small electronic devices, including 1200 LED lights, nine thermo-hygrometers, a water quality testing pen, and water level alarms. The proposed M-HNG effectively harvests low-frequency water wave energy, introducing an innovative concept for constructing a hybrid TENG with enhanced density and durability.

Construction of small size and high output triboelectric nanogenerator by multi-layer-stacking and charge excitation

Abstract The triboelectric nanogenerator (TENG) has been considered a low-frequency mechanical energy collection and conversion device in the modern era. The reasonable stack structure of TENG is an effective method to boost its electric output performance within a limited space. Nevertheless, relying solely on the stacking structure, the TENG is unable to produce excessive output due to the low contact electrification capability of its materials. Hence, there are still significant challenges in enhancing the output performance of stacked TENGs. We propose a multi-layer-stack TENG (M-TENG) with two zigzag-shaped (Z-shaped) multilayer units interleaving and stacking with each other, which enormously enlarges the effective utilization area. Furthermore, a voltage multiplier circuit (VMC) incorporating a Zener diode allows the transfer charge to approach the critical threshold and maintain a stable output. The transfer charge and current of M-TENG integrated with a VMC can reach 1.52 μC and 86 μA, respectively, with the maximum output of the TENG being 8.65 mW (5 MΩ). To prove it as a self-power device, M-TENG excited by a VMC is employed to power 912 light-emitting diodes (LEDs) and three temperature and humidity sensors with a power management circuit (PMC), respectively. This work offers a new method for optimizing stacking-layer TENG electric output performance in a narrow space.

Fully Integrated Direct Current Triboelectric Nanogenerators Coupled with Charge Pump and Electric Field Enhancing Effect Enabling Improved Output Performance

AbstractDirect‐current triboelectric nanogenerators (DC‐TENGs) arising from electrostatic breakdown have garnered significant attention due to their advantages of rectification‐free operation, constant current output, and high output power density. Previous studies have primarily concentrated on improving its performance through structural design and parameter optimization, neglecting the potential benefits of external charge excitation. Here, a facile and universal strategy coupling charge pump and electric field enhancing effect with DC‐TENG (CE‐DC‐TENG) is proposed to improve the output performance of DC‐TENG. An alternating current TENG is used as the charge pump. A field‐enhancing conductive layer, which is introduced under the main DC‐TENG, is connected with the pump TENG to accumulate the charge and enhance the electric field for electrostatic breakdown. The effectiveness of this method is demonstrated by linear and rotary sliding mode TENGs. Furthermore, a fully integrated rotary sliding mode CE‐DC‐TENG is designed and fabricated, and it exhibits impressive performance with a 13‐fold higher power density of 1.56 W m−2 compared to conventional DC‐TENG. Moreover, it can directly power small electronics or be combined with a designed power management circuit for more efficient energy conversion. This work presents a new design strategy for improving the performance of DC‐TENG and facilitating its practical applications.

From natural abundant silk to TENG; from biowaste to carbon supercap: A natural sustainable approach of active energy storage

Integrating an energy harvester and energy storage into a single unit, without connecting any external source, has gathered substantial attention for its ability to convert and store energy in a single device. This study introduces an innovative, self-sustaining power cell called the self-power supercapacitor (SPSC). The SPSC consists of two triboelectric nanogenerators (TENG) and a carbon based supercapacitor cell sandwiched between two TENGs. The SPSC utilizes the energy produced by two TENGs and stores it directly in the supercapacitor, bypassing the requirement of power management circuits. This energy storage process is achieved using tribo-electrochemical methodology. The supercapacitor consists of activated porous carbon obtained from natural biowaste, infused with an ionic liquid electrolyte gel. Each TENG is constructed using a blend of naturally abundant Silk with PVA and PVDF as triboelectric components and exhibit a maximum voltage of 800 V with an instantaneous output power density of 598 mW/cm2. In addition, the self-power supercapacitor effectively gets charged to a voltage of 0.8 V after continuous tapping of 100 s Due to the huge active surface area of the activated carbon electrodes, the device attains a specific capacitance of 43.75 mF/cm2. The assessed specific energy and specific power of the assembled SPSC device were 3.89 mWh/cm2 and 666.67 mW/cm2, respectively when subjected to tapping operations. The self-power supercapacitor cell also has the ability to power a range of portable electronics, such as LED. This research evidences the competence of charging the supercapacitor of SPSC system using TENGs without the need for an external parameter.

Standalone Stretchable Biophysical Sensing System Based on Laser Direct Write of Patterned Porous Graphene/Co3O4 Nanocomposites.

Skin-interfaced wearable sensors can continuously monitor various biophysical and biochemical signals for health monitoring and disease diagnostics. However, such devices are typically limited by unsatisfactory and unstable output performance of the power supplies under mechanical deformations and human movements. Furthermore, there is also a lack of a simple and cost-effective fabrication technique to fabricate and integrate varying materials in the device system. Herein, we report a fully integrated standalone stretchable biophysical sensing system by combining wearable biophysical sensors, triboelectric nanogenerator (TENG), microsupercapacitor arrays (MSCAs), power management circuits, and wireless transmission modules. All of the device components and interconnections based on the three-dimensional (3D) networked graphene/Co3O4 nanocomposites are fabricated via low-cost and scalable direct laser writing. The self-charging power units can efficiently harvest energy from body motion into a stable and adjustable voltage/current output to drive various biophysical sensors and wireless transmission modules for continuously capturing, processing, and wirelessly transmitting various signals in real-time. The novel material modification, device configuration, and system integration strategies provide a rapid and scalable route to the design and application of next-generation standalone stretchable sensing systems for health monitoring and human-machine interfaces.

Direct Current Triboelectric Nanogenerator Based on Contact Electrification, Air Breakdown, Electrostatic Induction, and Charge Leakage for Self‐powered Applications

AbstractDiverging from air breakdown‐based triboelectric nanogenerators (TENGs), recent TENG designs present high output power density without requiring precise control over discharge channels. However, existing researches predominantly ascribe its direct current output to electrostatic induction, disregarding the critical factor of charge leakage. This oversight hampers efforts to improve device performance, especially in material selection and optimization. Here, the generation of direct current signals ultimately stems from material charge leakage and spatial electrostatic induction is illustrated. Through theoretical analysis, visualization, and experimental measurement of four phenomena in the device, a quadruple‐effect mechanoelectrical conversion mechanism is established to refine the material selection rule. Under this guideline, the output power density is increased by 34.42% in contrast to the electrostatic induction direct current TENG. For practical applications, a power management circuit is utilized to boost the device's charging rate by up to 18 times. Furthermore, the high voltage of the device can activate discharge‐type UV tubes, demonstrating great potential in developing self‐powered wastewater treatment systems. The multiple charge behaviors proposed in this work, along with the material selection rule, lay a solid foundation for achieving high output power density in direct current TENGs.

Wind-driven suspended triboelectric-electromagnetic hybrid generator with vibration elimination for environmental monitoring in the high-voltage power transmission line

The sustainable development of the high-voltage power transmission system puts forward more significant requirements IoT sensor network. Currently, a large number of the IoT sensors are installed on the high-voltage transmission lines, and environmental wind energy harvesting around the outdoor power transmission lines enables a promising and feasible solution to supply distributed sensors. However, the traditional floor-mounted wind energy nanogenerator with high requirements for placement and fixation is no longer applicable to the suspension scenario of the high-voltage power transmission lines. In this work, a wind-driven suspended triboelectric-electromagnetic hybrid generator (WS-TEHG) is designed as a suspended wind cup with a three-layered integrated structure, which can be integrated with the damping structure that hanged and installed on the power transmission line, demonstrating the simultaneously achieving high efficiency wind energy harvesting and the operation stability of the device. After the structural and material optimization, WS-TEHG can achieve efficient energy collection under wide-range of the wind speed from 2.6 to 17.3 m s−1, whose TENG and EMG produced instantaneous peak power from 0.2 to 7.9 mW and 0.6–85.1 mW, respectively. Moreover, a standardized power management based on LTC 3588-based double-channel circuit was established to co-manage the outputs of the two generating modules in the hybrid generator and enhance the continuous stability of the standardized voltage output, demonstrating a shorter undervoltage charge accumulation, a faster start-up process, a lower power consumption compared with the traditional power management. Finally, a self-powered environmental monitoring system by a WS-TEHG equipped with a standardized power management circuit was developed to provide the weather and climate information around the power transmission lines, thereby demonstrating a potential and feasible for large-scale self-powered application in the field of the high-voltage power transmission lines.

Droplet Energy Harvesting System Based on Total-Current Nanogenerator.

The droplet-based nanogenerator (DNG) is a highly promising technology for harvesting high-entropy water energy in the era of the Internet of Things. Yet, despite the exciting progress made in recent years, challenges have emerged unexpectedly for the AC-type DNG-based energy system as it transitions from laboratory demonstrations to real-world applications. In this work, we propose a high-performance DNG system based on the total-current nanogenerator concept to address these challenges. This system utilizes the water-charge-shuttle architecture for easy scale-up, employs the field effect to boost charge density of the triboelectric layer, adopts an on-solar-panel design to improve compatibility with solar energy, and is equipped with a novel DC-DC buck converter as power management circuit. These features allow the proposed system to overcome the existing bottlenecks of DNG and empower the system with superior performances compared with previous ones. Notably, with the core architecture measuring only 15 cm × 12.5 cm × 0.3 cm in physical dimensions, this system reaches a record-high open-circuit voltage of 4200 V, capable of illuminating 1440 LEDs, and can charge a 4.7 mF capacitor to 4.5 V in less than 24 min. In addition, the practical potential of the proposed DNG system is further demonstrated through a self-powered, smart greenhouse application scenario. These demonstrations include the continuous operation of a thermohygrometer, the operation of a Bluetooth plant monitor, and the all-weather energy harvesting capability. This work will provide valuable inspiration and guidance for the systematic design of next-generation DNG to unlock the sustainable potential of distributed water energy for real-world applications.

From interface effect to bulk effect: Probing the capacitive coupling enhancement mechanism to achieve high performance DC droplet-based nanogenerator

The DC droplet-based nanogenerator (DNG) technology has opened up a new avenue for high-entropy water energy harvesting. However, the conventional DC DNG relies on the interface effect to generate a limited surface charge density, which severely restricts its electrical performance. Here, inspired by the MOS transistors, a novel total current DNG (TC-DNG) platform with back-gate modulation structure is developed, successfully realizing the transform from interface effect to bulk effect. By using the rationally patterned DNG as triboelectric probe, an intriguing capacitive coupling enhancement mechanism is discovered. With such a mechanism, the nanogenerator could employ both the capacitive coupling effect of the back-gate electrode and the self-exciting effect of droplet charge-shuttles to achieve a significantly enhanced performance in both charge transfer and voltage output. As a result, this TC-DNG provides a transferred charge of 30 nC per droplet and an output voltage of 800 V and is capable of illuminating 480 high-brightness LEDs without using any power management circuit. In addition, this TC-DNG could easily adapt to a wide range of application scenarios owing to the interchangeability of the back-gate material. This work could inspire further innovations in energy transfer mechanism and harvesting technology at the liquid-solid interface.

A hybrid wind and raindrop energy harvesting operating on Savonius turbine

In offshore environments, abundant wind and rainfall resources await development, representing significant untapped energy potential for powering Internet of Things (IoT) devices. Triboelectric Nanogenerators (TENGs) are particularly suited for capturing continuous motion in offshore environments, presenting a reliable solution for sustainable energy generation in IoT applications. Herein, we propose a wind-droplet hybrid generator (WDHG) tailored for adaptive environmental energy harvesting, explicitly targeting the demanding conditions prevalent in offshore environments. The WDHG combines the efficiency of a helical Savonius TENG with the versatility of an interdigitated electrode TENG, enabling simultaneous wind and rain energy harvesting. The helical Savonius TENG exhibits superior aerodynamic performance, producing an output power ranging from 0.39 to 2.10 mW with wind speeds increasing from 0.75 to 6.84 m/s. Additionally, the droplet TENG generates a power output of 35.90 mW/m2 under rainfall at 70 mm/min. Optimizations include not only the comparative analysis of helical Savonius turbines and the variation in pole-pair numbers but also adjustments in fluorinated ethylene propylene (FEP) film thickness and electrode gap length for interdigitated electrode, alongside the development of a tailored power management circuit (PMC) featuring dual bridge rectifiers, a buck circuit module, and a smart load switch. The PMC enables continuous operation of a low-powered digital thermohygrometer under conditions of 4.5 m/s wind speed, and drives a 20-second wake BLE server under 7.2 m/s wind speeds. Integration of the WDHG with offshore wind and raindrop extends energy harvesting capabilities, exhibiting a great potential of providing reliable power source for IoT devices.

Autonomously Self‐healing, Adhesive, and Stretchable Triboelectric Nanogenerator Using Multifunctional Hydrogel‐Elastomer Double Layer with a Power Management Circuit

AbstractTriboelectric nanogenerators (TENGs) are promising candidates replacing conventional batteries in wearable devices, owing to their self‐powering properties. Although TENGs can convert mechanical energy into electrical energy, excessive mechanical stresses can degrade their performance. Moreover, conformal adhesion to skin is required to improve its performance in wearable devices. Here, a stretchable, adhesive, and self‐healing single‐electrode TENG with a multifunctional hydrogel‐elastomer double layer is developed. Carbon nanotubes (CNTs)‐doped hydrogel is used as the electrode. Subsequently, the electrode is covered with an Ecoflex elastomer that acted as a triboelectrification layer. The soft tissue‐like properties of the hydrogel allow conformal adhesion to nonplanar skin, whereas the dynamic polymer network of the hydrogel endows toughness and ability to self‐heal (within 5 min) against external damage. The TENG demonstrates an output voltage and current peak at 180 V and 0.8 µA. Moreover, it can generate a maximum power peak at 37.8 mW m−2, which is sufficient to power small electronics like stopwatches and light‐emitting diodes, with a power management circuit. The proposed TENG devices can function as telecommunication touch panels via Morse code. Thus, this study presents a promising approach for advancing the flexible power supplies and self‐powered sensors that can be applied to wearable devices.

Power Scavenging Microsystem for Smart Contact Lenses.

On-the-eye microsystems such as smart contacts for vision correction, health monitoring, drug delivery, and displaying information represent a new emerging class of low-profile (≤ 1mm) wireless microsystems that conform to the curvature of the eyeball surface. The implementation of suitable low-profile power sources for eye-based microsystems on curved substrates is a major technical challenge addressed in this paper. The fabrication and characterization of a hybrid energy generation unit composed of a flexible silicon solar cell and eye-blinking activated Mg-O2 metal-air harvester capable of sustainably supplying electrical power to smart ocular devices are reported. The encapsulated photovoltaic device provides a DC output with a power density of 42.4 µW cm-2 and 2.5mW cm-2 under indoor and outdoor lighting conditions, respectively. The eye-blinking activated Mg-air harvester delivers pulsed power output with a maximum power density of 1.3mW cm-2. A power management circuit with an integrated 11 mF supercapacitor is used to convert the harvesters' pulsed voltages to DC, boost up the voltages, and continuously deliver ≈150 µW at a stable 3.3V DC output. Uniquely, in contrast to wireless power transfer, the power pack continuously generates electric power and does not require any type of external accessories for operation.

A Dual-Mode Triboelectric Nanogenerator for Efficiently Harvesting Droplet Energy.

Triboelectric nanogenerator (TENG) is a promising solution to harvest the low-frequency, low-actuation-force, and high-entropy droplet energy. Conventional attempts mainly focus on maximizing electrostatic energy harvest on the liquid-solid surface, but enormous kinetic energy of droplet hitting the substrate is directly dissipated, limiting the output performance. Here, a dual-mode TENG (DM-TENG) is proposed to efficiently harvest both electrostatic energy at liquid-solid surface from a droplet TENG (D-TENG) and elastic potential energy of the vibrated cantilever from a contact-separation TENG (CS-TENG). Triggered by small droplets, the flexible cantilever beam, rather than conventional stiff ones, can easily vibrate multiple times with large amplitude, enabling frequency multiplication of CS-TENG and producing amplified output charges. Combining with the top electrode design to sufficiently utilize charges at liquid-solid interface, a record-high output charge of 158 nC is realized by single droplet. The energy conversion efficiency of DM-TENG is 2.66-fold of D-TENG. An array system with the specially designed power management circuit is also demonstrated for building self-powered system, offering promising applications for efficiently harvesting raindrop energy.