Matching Load Resistance Research Articles

Design and test of liquid sloshing piezoelectric energy harvester

The energy harvester based on the piezoelectric effect can convert the vibration energy in the environment into electricity to power the network nodes. In order to broaden the effective frequency bandwidth of the piezoelectric energy harvester and reduce the resonant frequency of the system, a liquid slosh-type piezoelectric energy harvester is proposed in this paper. Based on the theory of the piezoelectric effect, the mechanical model and electromechanical coupling model of the piezoelectric energy harvester were established, and the dynamic characteristics of the liquid slosh piezoelectric energy harvester were analyzed. Based on theoretical model and experimental test, the liquid slosh piezoelectric energy harvester is studied. By making a prototype and building a vibration experiment platform, the energy capture characteristics of the piezoelectric energy harvester were tested experimentally. The experimental results show that when the external excitation frequency is close to the first resonant frequency, the maximum output power of the liquid sloshing piezoelectric energy harvester is 0.068 mW, and the optimal matched impedance is 440 kΩ. When the external excitation frequency is close to the second resonant frequency, the maximum output power of the liquid sloshing piezoelectric energy harvester is 0.178 mW, and the optimal matching load resistance is 600 kΩ. Compared with the traditional cantilever beam piezoelectric energy harvester, the liquid slosh piezoelectric energy harvester has a lower resonant frequency and achieves two resonant peaks in the range of 1–20 Hz, which greatly widens the effective frequency bandwidth and improves the energy capture efficiency of the piezoelectric energy harvester.

Harnessing energy from hand-shaking vibration for electronics through a magnetic rolling pendulum bistable energy harvester

Converting the kinetic energy of human movement into electricity provides a solution for the power supply of portable electronics for communication, medical treatment, positioning, search-and-rescue, etc. Due to the characteristics of high sensitivity and snap-through, a magnetic rolling pendulum bistable energy harvester (MRP-BEH) based on magnetic-spring mechanism is proposed for scavenging energy from handshaking vibration. The harvester possessing the advantage of small damping exploits the rolling oscillation of a suspended magnet. By establishing the electromechanical model, numerical outcomes of the MRP-BEHs with different potential well depths are investigated through the response under constant and sweep frequency excitations. Particularly, the complex dynamic behaviors are characterized by basins of attraction and bifurcation diagrams. A prototype is fabricated, and experiments are undertaken under harmonic and handshaking excitations. Experimental results are consistent with numerical simulations, and excitation of 0.5 g witnesses a broadband frequency range from 5.18 Hz to 10.02 Hz for the harvester with proper system parameters. Regarding the excitation of handshaking, an instantaneous maximum power of 21.9 mW and an average power of 4.21 mW is achieved with matched load resistance. By boosting the output voltage with a transformer, the charging and discharging experiments of capacitors for powering various electronics demonstrate the broad application prospects of the harvester. This research, in a nutshell, broadens the methodology for achieving bistable oscillation and introduces a fresh perspective for designing high-efficiency energy harvesters attuned to human motion.

An analytical model for wearable thermoelectric generators harvesting body heat: An opportunistic approach

Wearable thermoelectric generators (WTEGs) have the potential to transform body heat into electrical energy, thereby establishing a sustainable power reservoir for wearable electronics and offering a promising alternative to traditional chemical batteries. This paper presents an opportunistic analytical model that investigates the energy conversion performance of a human skin-WTEG system. The model incorporates a one-dimensional bioheat transport equation to account for metabolic heat generation within skin tissue and heat exchange resulting from the blood perfusion, while a comprehensive three-dimensional analysis of the WTEG captures convective heat dissipation occurring between the WTEG and ambient surroundings. Analytical solutions for the temperature profile and power density of WTEGs are obtained, along with an approximate closed-form expression for the matched load resistance. The results demonstrate the significant impact of blood perfusion and convective heat dissipation on the WTEG performance. The optimal fill factor and height of thermoelectric couples for maximum power output are also determined. This model will assist in predicting and optimizing the performance of WTEG devices in practical applications.

Energy harvesting analysis of wearable thermoelectric generators integrated with human skin

This paper proposes a novel configuration for wearable thermoelectric generators (W-TEGs) in which the fill material only encloses each thermoelectric leg with a specific size. An analytical model for the presented W-TEG integrated with human skin is developed. Numerical results show that the metabolic heat generation can be neglected, but the maximum power density of W-TEG will be underestimated by 30.72% if the influence of heat exchange induced by blood perfusion is not considered. The matched load resistance, the optimal fill factor and optimal length of thermoelectric legs corresponding to maximum power output of W-TEG are also obtained. The matched load resistance ratio and optimal fill factor of the W-TEG are 1.4090 and 10.01%, respectively, which are quite different from the values of classical thermoelectric generators (TEGs). The study further indicates that the performance of W-TEG can be improved by increasing the contact pressure at skin/W-TEG interface. Additionally, the impact of heat convection at lateral surfaces of thermoelectric legs should be taken into account to accurately estimate the power output of W-TEG. The optimization parameters presented in this paper may pave a way for achieving higher performance of W-TEG with actual applications.

MXene effectively enhances the electron-withdrawing (EW) ability and dielectric properties of PVDF-TrFE nanofibers for triboelectric nanogenerators

Functional fillers can improve the triboelectric characteristics of polyvinylidene difluoride (PVDF)-based material, a typical triboelectric nanogenerator (TENG) negative dielectric layer material. MXene fillers can significantly enhance the triboelectric characteristics of PVDF-based negative dielectric layers by dielectric modulation. However, the effect of MXene as a highly electronegative filler on the electron-withdrawing (EW) ability of PVDF/MXene composite films is frequently ignored. In this work, polyvinylidene fluoride-trifluoro-ethylene (PVDF-TrFE)/MXene (Ti3C2Tx) composite nanofibers films (PMNFs) are prepared by electrospinning. When the MXene content is 0.8 wt%, PMNFs-based TENG achieves a maximum output power density of 250 mW/m2 at a matching external load resistance of 4 MΩ and a maximum open-circuit voltage (VOC) of 85 V, 2.66 times higher than that of the PVDF-TrFE-based TENG. Enhancing the EW ability and the dielectric properties by adding MXene are considered and proven by examining the work function (WF) and dielectric constant (and loss), respectively. Finally, we design a tremor-based TENG by PMNFs and develope a novel respiratory monitor to achieve real-time respiratory monitoring, which should offer fresh perspectives on creating respiratory monitoring devices.

Dynamic modeling and experimental validation of a low frequency piezoelectric vibration energy harvester via secondary excitation of pressured fluid

A low frequency piezoelectric energy harvester using secondary excitation of pressured fluid is proposed in this paper to scavenge low frequency vibration energy in ambient environments. This harvester was characterized by an indirect vibration-to-electric energy converter via transferring the pressure energy of pressured liquid medium. A series of simulations and experiments were conducted to prove the good performance and the feasibility of this novel structure in low-frequency high-intensity vibration. The results showed that the diameter of damping orifice, initial system backpressure and proof mass brought strong influences on the resonance frequency and output voltage. Meanwhile, according to experiments, it was found that the resonance frequency was decreased with the decreasing liquid backpressure. In this case, lowest resonance frequency of 19 Hz was achieved under the condition of 10-kg proof mass and 0.2-MPa liquid backpressure. Also, there were the optimal proof mass and backpressure to maximize the generated voltage, respectively. Moreover, in the impedance matching experiments, the maximum output power reached 1.35mW at the matching load resistance of 18kΩ.

Triboelectric Nanogenerator-Based Near-Field Electrospinning System for Optimizing PVDF Fibers with High Piezoelectric Performance

Electrospinning is an effective method to prepare polyvinylidene fluoride (PVDF) piezoelectric fibers with a high-percentage β phase. However, as an energy conversion material for micro- and nanoscale diameters, PVDF fibers have not been widely used due to their disordered arrangement prepared by traditional electrospinning. Here, we designed a near-field electro-spinning (NFES) system driven by a triboelectric nanogenerator (TENG) to prepare PVDF fibers. The effects of five important parameters (PVDF concentration, needle inner diameter, TENG pulse DC voltage (TPD-voltage), flow rate, and drum speed) on the β phase fraction of PVDF fiber were optimized one by one. The results showed that the electrospun PVDF fibers had uniform diameter and controllable parallel arrangement. The β phase content of the optimized PVDF fiber reached 91.87 ± 0.61%. For the bending test of a single PVDF fiber piezoelectric device, when the strain is 0.098%, the electric energy of the single PVDF fiber device of NFES reaches 7.74 pJ and the energy conversion efficiency reaches 13.5%, which is comparable to the fibers prepared by the commercial power-driven NFES system. In 0.5 Hz, the best matching load resistance of a PVDF single fiber device is 10.6 MΩ, the voltage is 6.1 mV, and the maximum power is 3.52 pW. Considering that TENG can harvest micromechanical energy in the low frequency environment, the application scenario of the NFES system can be extended to the wild or remote mountainous areas without traditional high-voltage power supply. Therefore, the electrospun PVDF fibers in this system will have potential applications in high-precision 3D fabrication, self-powered sensors, and flexible wearable electronic products.

Dynamical modeling and parametric analysis of an electret-based wave energy converter

Carbon neutrality and the Internet of Underwater Things have injected new impetus into the development of wave energy converters (WECs) albeit most of WEC projects have ended in failure due to low cost-effectiveness. Hereupon we present the dynamical modeling and parametric analysis of a novel electret-based WEC that has a distinct power take-off system compared to the conventional ones and has exhibited high power density in our previous study. Linear wave theory and Morison equation are applied for wave field and forces, respectively. WEC motions parallel with incident waves are modeled, and the electrical subsystem of the generator is treated as a current source and a capacitor. With these simplifications, the governing equations of the nonlinear and non-smooth electromechanical system are obtained and then numerically solved using an event-driven algorithm. The new power take-off system is experimentally validated. We find that the power output varies nonlinearly with wave parameters under regular wave excitation but linearly under irregular ones, and that superharmonic resonance can significantly enhance energy conversion performance at relatively low frequencies, based on which the optimum parameters are obtained. A peak average power of around 2 mW (at a matched load resistance) is generated from each generator encapsulated in the WEC of a diameter of 15 cm. The findings shed light on the characteristics of electret-based WECs and provide support for the development of wave energy farm; moreover, the methodologies of modeling and analysis can be extended to the design and optimization of the scaleups of the proposed electret-based WEC.

Energy harvesting from flexion motion using a flexible piezoelectric ring

In this study, we studied the performance of a ring-type energy harvester mounted on a finger flexion structure. We fabricated the harvester using a piezoelectric material, polyvinylidene fluoride, on a polydimethylsiloxane substrate. In addition, we used a finger flexion model composed of a 3D printed component and silicone (Ecoflex 00-30) to mimic the flexion motion of the human finger. We analyzed the relationship between the bending angle of the finger flexion structure and the electrical response of the ring-type energy harvester using visual results and voltage output measurements. Moreover, we conducted a parametric study to determine the effect of the design parameters of the harvester by changing the thickness and width of the piezoelectric material (polyvinylidene fluoride), the thickness of the silicone substrate (polydimethylsiloxane), and the notch orientation of the ring-shaped harvester. We found that the optimized dimensions of the ring-type energy harvester are the thickness and width of PVDF, the thickness of PDMS, and notch orientation of 28 μm, 15 mm, 1.5 mm, and 180°, respectively. Furthermore, a series of experiments were conducted under various bending angles and input frequencies, and the experimental and theoretical output powers were assessed and analyzed. We observed that the harvesting power was maximized at the matched load resistance to the impedance of the piezoelectric material and found a maximum harvesting power of approximately 230 nW.

A waterwheel hybrid generator with disk triboelectric nanogenerator and electromagnetic generator as a power source for an electrocoagulation system

Electrocoagulation (EC) method has emerged as a state-of-the-art water purifying technology. Here, a self-powered EC system is proposed using a waterwheel hybrid generator (W-HG) based on disk-type triboelectric nanogenerator (D-TENG) and electromagnetic generator (EMG). D-TENG consists of a rotator and stator based on printed circuit board (PCB) technology. With electrospinning and sintering process for polytetrafluoroethylene (PTFE) as a dielectric layer of the D-TENG, the fabricated membrane exhibits superhydrophobic property with a water contact angle of 160.5°, which allows the device to show self-cleaning property and to operate at high relative humidity. Additionally, a fractal-design based switched-capacitor-converter (FSCC) is utilized with the high-frequency and high-output based D-TENG to operate commercial electronic devices. The hybridized W-HG exhibits 1.75 mW of the average power at the matching load resistance of 400 Ω. An energy conversion efficiency of the device between rotational input energy and electrical output energy marks at 8.75%. The D-TENG and EMG are combined with a rotating waterwheel to demonstrate their ability to power an EC purification system. A power management integrated circuit (PMIC) is utilized with the D-TENG for high current input to the EC module. Finally, the W-HG successfully purifies wastewater with a high removal ratio above 95% for 18 h.

Natural cotton-based triboelectric nanogenerator as a self-powered system for efficient use of water and wind energy

With the challenges of the energy crisis and related environmental issues, the development and utilization of renewable energy have become a mandatory requirement for the sustainable development of modern society. Recently, triboelectric nanogenerators (TENGs) have been widely utilized in renewable energy sources harvesting, such as solar power, wind power, hydropower and so on. Here, a wheel-disk-shaped TENG based on natural pollution-free cotton is reported for simultaneously harvesting wind and water energy. 8.9 µA of short-circuit current and 782 V of open-circuit voltage are obtained by cotton assemble triboelectric nanogenerator (C-TENG) under a rotation speed of 210 r/min. The maximum peak power can reach 1.89 mW at a matched load resistance of 330 MΩ. Moreover, C-TENG can be used as a self-powered system to power electronic devices and sensing wind speed. This work not only presents a feasible solution for sustainable and clean energy harvesting, but also provides a reliable self-powered sensor for environmental monitoring.

Design, Manufacture and Test of Piezoelectric Cantilever-Beam Energy Harvesters with Hollow Structures.

This article presents a single-crystal piezoelectric energy harvester (PEH) with a trapezoidal hollow hole that can obtain high energy density at low frequency. Harvesters with a hollow structure were fabricated through a series of manufacturing processes such as thermocompression bonding, screen printing and laser cutting. Finite element analysis (FEA) and experimental results showed that using low modulus brass instead of stainless steel as the PEH substrate enhances the voltage output of the device, and the hollow design greatly increases the overall stress level and power density. In addition, the developed PEH with a trapezoidal hole obtained the best output performance; when the acceleration, resonance frequency and matched load resistance were 0.5 g, 56.3 Hz and 114 kΩ, respectively, the peak voltage was 17 V and the power density was 2.52 mW/cm3. Meanwhile, compared with the unhollowed device, the peak voltage and maximum power density of the proposed PEH were increased by 30.7% and 24.4%, respectively, and the resonance frequency was reduced by 7%. This study verified the feasibility of the optimized design through simulation and experimental comparison.

Designing and Fabricating a Prototype of the Elastic Thermoelectric Generator

The elastic thermoelectric generator (ETEG) was fabricated by using 27 couples of n-Bi2Te3 and p-Sb2Te3 bulk thermoelectric materials in size of 3 × 3 × 5 mm3 on silicone substrate and using copper plate for electrodes. It was found that the open circuit voltage shows maximum value of 46.74 mV at temperature difference 13.85 K. External load resistances were apply in the measurement and varies for obtaining the maximum output power. The matched load resistance is 0.22 Ω obtaining maximum power about 3.46 mW at temperature difference difference of 13.85 K. The output power, voltage and current were increased with temperature difference increasing and show maximum values about 35.19 mW, 27.82 mV and 126.36 mA at temperature difference 12.75 K.

Nonlinear multi-mode electromagnetic insole energy harvester for human-powered body monitoring sensors: Design, modeling, and characterization

The current research in wearable electronics is trending towards miniaturization, portability, integration, and sustainability, with the harvesting of biomechanical energy seen as a promising route to improve the sustainability of these wearable electronics. Efforts have been made to prolong operational life of these harvesters, to overcome energy dissipation, lowering resonant frequency, attaining multi-resonant states as well as widening frequency bandwidth of these biomechanical energy harvesters. Herein, an electromagnetic insole energy harvester (EMIEH), capable of efficiently harvesting low-frequency biomechanical energy, has been designed, fabricated and experimentally tested. The core component in the device is the vibrating circular spiral spring, holding two magnets as the driving force on the central platform of the circular spiral spring, and just in-line with the upper and lower wound coils. It has been shown that the harvester exhibits higher sensitivity to low-frequency external vibrations than conventional cantilever-based designs, and hence allows low impact energy harvesting such as harvesting energy from walking, running and jogging. The experimentally-tested four resonant frequencies occurred at 8.9 Hz, 28 Hz, 50 Hz, and 51 Hz. At the first resonant frequency of 8.9 Hz under base acceleration of 0.6 g, the lower electromagnetic generator can deliver a peak power of 664.36 µW and an RMS voltage of 170 mV to a matching load resistance of 43.5 Ω. The upper electromagnetic generator can contribute an RMS voltage of 85 mV, corresponding to the peak power of 175 µW across 41 Ω under the same experimental condition. Finally, the harvester has been integrated into the shoe and it is able to charge a 100 µF capacitor up to 1 Volt for about 8 minutes foot movement. The result has remarkable significance in the development of wireless body monitoring sensors applications.

Electret Nanogenerators for Self-Powered, Flexible Electronic Pianos

Traditional electronic pianos mostly adopt a gantry type and a large number of rigid keys, and most keyboard sensors of the electronic piano require additional power supply during playing, which poses certain challenges for portable electronic products. Here, we demonstrated a fluorinated ethylene propylene (FEP)-based electret nanogenerator (ENG), and the output electrical performances of the ENG under different external pressures and frequencies were systematically characterized. At a fixed frequency of 4 Hz and force of 4 N with a matched load resistance of 200 MΩ, an output power density of 20.6 mW/cm2 could be achieved. Though the implementation of a signal processing circuit, ENG-based, self-powered pressure sensors have been demonstrated for self-powered, flexible electronic pianos. This work provides a new strategy for electret nanogenerators for self-powered sensor networks and portable electronics.

Ultra-robust and broadband rotary hybridized nanogenerator for self-sustained smart-farming applications

The practical realization of nanogenerators for realistic applications of scavenging sustainable energy is still challenging due to their limited output performance and mechanical durability. Herein, a contactless mode triggering-based ultra-robust rotary hybridized nanogenerator (CMTUr-HNG) for efficiently harvesting wind- and water-flows in natural environments is reported. By implementing a soft magnetic-coupled triggering strategy, the hybrid electromagnetic-triboelectric nanogenerator shows high output performance under a broad range of rotational motions (50–1000 rpm) with excellent robustness. The electrospun nanofibers materials greatly improve the triboelectric performance while the electromagnetic structure is optimized by finite element method simulations. Therefore, the as-fabricated CMTUr-HNG delivers a maximum hybrid power of 40.65 mW at a matching load resistance, while triboelectric and electromagnetic generators show a high output power density of 1568 mW/kg and 386 mW/kg at 500 rpm, respectively. The robustness of CMTUr-HNG is confirmed by a durability test for 8.5 h (≈2,000,000 cycles) at 1000 rpm. As a feasible application, a self-powered wireless smart-farm monitoring system has been successfully implemented using the CMTUr-HNG, thereby demonstrating the immense potential of harvesting rotational energy for future autonomous sensing technologies. • Miniaturized hybridized (electromagnetic-triboelectric) nanogenerator for effectively harvesting rotational energy. • Soft magnetic-coupled triggering strategy for ultra-robust triboelectric nanogenerators. • High output performance under a broad range of rotational motions (50-1000 rpm). • Implementing nanofiber-based tribo-layers increase the charge density by 5.7 times. • Successful demonstration of a self-powered wireless smart-farm monitoring system.

Electrospun PVDF-TrFE/MXene Nanofiber Mat-Based Triboelectric Nanogenerator for Smart Home Appliances.

Understanding of the triboelectric charge accumulation from the view of microcapacitor formation plays a critical role in boosting the output performance of the triboelectric nanogenerator (TENG). Here, an electrospun nanofiber-based TENG (EN-TENG) using a poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)/MXene nanocomposite material with superior dielectric constant and high surface charge density is reported. The influence of dielectric properties on the output performance of the EN-TENG is investigated theoretically and experimentally. The fabricated EN-TENG exhibited a maximum power density of 4.02 W/m2 at a matching external load resistance of 4 MΩ. The PVDF-TrFE/MXene nanocomposite improved the output performance of the EN-TENG fourfold. The EN-TENG successfully powered an electronic stopwatch and thermo-hygrometer by harvesting energy from human finger tapping. Moreover, it was utilized in smart home applications as a self-powered switch for controlling electrical home appliances, including fire alarms, fans, and smart doors. This work presents an effective and innovative approach toward self-powered systems, human-machine interfaces, and smart home applications.

High‐performance flexible piezoelectric nanogenerator based on necklace‐like PZT particle chains

SummaryFlexible piezoelectric nanogenerators (F‐PENG) as a clean, green power generation device have attracted much attention. Dielectrophoresis (DEP) was used to prepare flexible piezoelectric nanogenerators with necklace‐like oriented structure. The results showed that the oriented structure significantly improved the electrical output performance of F‐PENG by enhancing the stress and free charge transmission. For the F‐PENG with 8 vol% oriented PZT particle, open‐circuit voltage and short‐circuit current reached 176 V and 35 μA and an instantaneous power of up to 2 mW was collected for an optimal matched load resistance of 6 MΩ. Output voltage and current increase by 135% and 133%, respectively, compared with the F‐PENG with random structure. Meanwhile, the finite element simulation results also confirmed the superiority of this oriented structure. There was a clear linear relationship between the output voltage and pressure, and the sensitivity was 1.13 N/V. The oriented PZT particle‐based F‐PENG with excellent electrical output performance has great application prospects in the fields of green power generation and self‐powered building monitoring system.

A Novel MXene/Ecoflex Nanocomposite‐Coated Fabric as a Highly Negative and Stable Friction Layer for High‐Output Triboelectric Nanogenerators

AbstractThe triboelectric material properties and mechanical stability of the contact layer are vital to achieving durable triboelectric nanogenerators (TENGs) with high output performance. Herein, a novel MXene/Ecoflex nanocomposite is introduced as a promising triboelectric material because of its highly negative triboelectric properties and mechanical stability. The MXene/Ecoflex nanocomposite with a fabric‐based waterproof TENG (FW‐TENG) is fabricated and designed to universally harvest energy from various human motions as well as the natural environment (rain and wind). The fabricated FW‐TENG delivers a maximum output peak power of 3.69 mW and a power density of 9.24 W m−2, respectively, at a matching load resistance of 4.5 MΩ under a frequency of 4.5 Hz and a force of 8 N. Furthermore, the applicability of this device in various products is investigated. The FW‐TENG can protect against a crash caused by rainy and humid weather. An FW‐TENG‐based self‐powered smart active device that detects motion on a carpet is demonstrated and is equipped with sleep monitoring motion sensors. The FW‐TENG not only has self‐powered benefits and excellent mechanical amenability but is also exceptionally reliable and stable against water intrusion, which are important characteristics to realize next‐generation wearable/portable technologies.

Optimization of structural parameters for rotary freestanding-electret generators and wind energy harvesting

Electret generators have been invented as a promising technology to harvest ambient mechanical energy for powering electrics. This paper discusses the structural optimization of rotary freestanding electret generators (FEGs) for enhancing the output power. The influences of the structural parameters on outputs including the maximum average output power and the matched load resistance are investigated theoretically, with and without the consideration of the parasitic capacitance. The theoretical results are verified through experiments. In addition, a figure-of-merit (FOM) is proposed to evaluate the output performance of rotary electrostatic generators including electret generators and triboelectric nanogenerators. The maximum average power of the optimum FEG achieves 18.3 mW at 1000 rpm, which is 31% higher than that of the previous unoptimized FEG with the same diameter and net charge density. The FEG with a wind turbine can be activated at the wind speed of 0.8 m/s and works continuously at speed of 0.6 m/s. The generator produces an average power of 9.1 mW at the wind speed of 2.7 m/s, indicating the potential of the FEG for wind energy harvesting, especially in low-speed wind.