Open-circuit Output Voltage Research Articles

Observation of the Marcus Inverted Region of Electron Transfer from Asymmetric Chemical Doping of Pristine (n,m) Single-Walled Carbon Nanotubes.

The concept of electrical energy generation based on asymmetric chemical doping of single-walled carbon nanotube (SWNT) papers is presented. We explore 27 small, organic, electron-acceptor molecules that are shown to tune the output open-circuit voltage (VOC) across three types of pristine SWNT papers with varying (n,m) chirality distributions. A considerable enhancement in the observed VOC, from 80 to 440 mV, is observed for SWNT/molecule acceptor pairs that have molecular volume below 120 Å3 and lowest unoccupied molecular orbital (LUMO) energies centered around -0.8 eV. The electron transfer (ET) rate constants driving the VOC generation are shown to vary with the chirality-associated Marcus theory, suggesting that the energy gaps between SWNT and the LUMO of acceptor molecules dictate the ET process. When the ET rate constants and the maximum VOC are plotted versus the LUMO energy of the acceptor organic molecule, volcano-shaped dependencies, characteristic of the Marcus inverted region, are apparent for three distinct sources of SWNT papers with modes in diameter distributions of 0.95, 0.83, and 0.75 nm. This observation, where the ET driving force exceeds reorganization energies, allows for an estimation of the outer-sphere reorganization energies with values as low as 100 meV for the (8,7) SWNT, consistent with a proposed image-charge modified Born energy model. These results expand the fundamental understanding of ET transfer processes in SWNT and allow for an accurate calculation of energy generation through asymmetric doping for device applications.

Improved dielectric and touch sensing performance of surface modified zinc ferrite (ZF)/Polyvinylidene fluoride (PVDF) composite

The continuous demand of fabricating self-powered body implantable devices have raised the development of new lead free polymer-ceramic composites. Herein, we have fabricated Zinc Ferrite (ZF)/Polyvinylidene Fluoride (PVDF) composite by simple solution casting technique. The inherent difficulty of compatibility between two phases (polymer and ceramic) for homogeneous film was addressed by addition of two different modifiers: Sodium dodecyl sulphate (SDS) and Tetraethyl orthosilicate (TEOS). Similarity in the piezo/ferro electrical properties between the externally poled unmodified nanocomposite with that of the surface modified composites were observed which were basically attributed to higher dispersion of nanoparticles in the polymer matrix and improved interfacial interaction between organic and inorganic matrix. It indicates that a self polarization effect has been induced in the surface modified composites. The mechanism for the interaction between two phases was discussed on the basis of zeta potential results and spectroscopic analysis. Further, external poled MSDS-ZF(C)-PVDF composite offered the highest energy storage density (0.25 Jcm−3), whereas poled TEOS modified ZF-PVDF composite exhibited an output open circuit voltage of 2.2V with power density of 3.7μWcm−3 under repeated single finger touch.

Highly sensitive, self-powered and wearable electronic skin based on pressure-sensitive nanofiber woven fabric sensor

The wearable electronic skin with high sensitivity and self-power has shown increasing prospects for applications such as human health monitoring, robotic skin, and intelligent electronic products. In this work, we introduced and demonstrated a design of highly sensitive, self-powered, and wearable electronic skin based on a pressure-sensitive nanofiber woven fabric sensor fabricated by weaving PVDF electrospun yarns of nanofibers coated with PEDOT. Particularly, the nanofiber woven fabric sensor with multi-leveled hierarchical structure, which significantly induced the change in contact area under ultra-low load, showed combined superiority of high sensitivity (18.376 kPa−1, at ~100 Pa), wide pressure range (0.002–10 kPa), fast response time (15 ms) and better durability (7500 cycles). More importantly, an open-circuit voltage signal of the PPNWF pressure sensor was obtained through applying periodic pressure of 10 kPa, and the output open-circuit voltage exhibited a distinct switching behavior to the applied pressure, indicating the wearable nanofiber woven fabric sensor could be self-powered under an applied pressure. Furthermore, we demonstrated the potential application of this wearable nanofiber woven fabric sensor in electronic skin for health monitoring, human motion detection, and muscle tremor detection.

Stochastic resonance energy harvesting for a rotating shaft subject to random and periodic vibrations: influence of potential function asymmetry and frequency sweep

Stochastic resonance is referred to as a physical phenomenon that is manifest in nonlinear systems whereby a weak periodic signal can be significantly amplified with the aid of inherent noise or vice versa. In this paper, stochastic resonance is considered to harvest energy from two typical vibrations in rotating shafts: random whirl vibration and periodic stick-slip vibration. Stick-slip vibrations impose a constant offset in centrifugal force and distort the potential function of the harvester, leading to potential function asymmetry. A numerical analysis based on a finite element method was conducted to investigate stochastic resonance with potential function asymmetry. Simulation results revealed that a harvester with symmetric potential function generates seven times higher power than that with asymmetric potential function. Furthermore, a frequency-sweep analysis also showed that stochastic resonance has hysteretic behavior, resulting in frequency difference between up-sweep and down-sweep excitations. An electromagnetic energy harvesting system was constructed to experimentally verify the numerical analysis. In contrast to traditional stochastic resonance harvesters, the proposed harvester uses magnetic force to compensate the offset in the centrifugal force. System identification was performed to obtain the parameters needed in the numerical analysis. With the identified parameters, the numerical simulations showed good agreement with the experiment results with around 10% error, which verified the effect of potential function asymmetry and frequency sweep excitation condition on stochastic resonance. Finally, attributed to compensating the centrifugal force offset, the proposed harvester generated nearly three times more open-circuit output voltage than its traditional counterpart.

Structural Optimization for Wideband Flexoelectric Energy Harvester Using Bulk Paraelectric Ba0.6Sr0.4TiO3

Flexoelectricity is a phenomenon which allows all crystalline dielectric materials to exhibit strain-induced polarization. With recent articles reporting giant flexoelectric coupling coefficients for various ferroelectric materials, this field must be duly investigated for its application merits. In this study, a wide-band linear energy harvesting device has been proposed using Ba0.6Sr0.4TiO3 ceramic. Both structural and material parameters were scrutinized for an optimized approach. Dynamic analysis was performed using finite element modeling to evaluate several important parameters including beam deflection, open circuit voltage and net power output. It was revealed that open circuit voltage and net power output lack correlation. Further, power output lacks a dependency on optimized width ratios, with the highest power output of 0.07 μW being observed for a width ratio of 0.33 closely followed by ratios of 0.2 and 0.5 (∼0.07 μW) each. The resulting power was generated at discrete (resonant) frequencies lacking a broadband structure. A compound design with integrated beams was proposed to overcome this drawback. The finalized design is capable of a maximum power output of >0.04 μW with an operational frequency of 90–110 Hz, thus allowing for a higher power output in a broader frequency range.

Synthesis of poly(vinylidenefluoride-trifluoroethylene)-0.65Pb(Mg 1/3 Nb 2/3 )O 3 -0.35PbTiO 3 -reduced graphene oxide-composite sheet and its application to flexible energy harvesting

Abstract Here the synthesis and the optimization of piezoelectric materials by varying the reduced graphene oxide (RGO) contents in the poly(vinylidenefluoride-trifluoroethylene)-0.65Pb(Mg 1/3 Nb 2/3 )O 3 -0.35PbTiO 3 (P(VDF-TrFE)-PMN-PT) composite and their application to low-pressure and low-frequency energy harvesting have been reported. Among the synthesized piezoelectric compositions, the PPMR5 (P(VDF-TrFE)-PMN-PT-RGO (RGO = 0.5%)) sample exhibits a maximum dielectric constant of 60 and a relatively high dielectric loss of 0.0654 at 1 kHz. Additionally, flexible piezoelectric energy harvester (FPEH) made off PPMR5 sheet reveals highest output performance under mechanical deformation. The fabricated FPEH demonstrate a maximum open-circuit output voltage of 8 V (pk-pk) and a short-circuit current of 3.5 μA (pk-pk) at an external applied force of 2N. Furthermore, the FPEH exhibits an output power density of 6.5 μW/cm 2 at 1 MΩ load resistance. The fabricated device was also exposed to several pressing-releasing cycles to confirm its stability. The device shows excellent stability even after 1000 pressing-releasing cycles. Finally, our fabricated FPEH can be a promising energy source for futuristic flexible electronics.

Self-Powered Viscosity and Pressure Sensing in Microfluidic Systems Based on the Piezoelectric Energy Harvesting of Flowing Droplets.

The rapid development of microscaled piezoelectric energy harvesters has provided a simple and highly efficient way for building self-powered sensor systems through harvesting the mechanical energy from the ambient environment. In this work, a self-powered microfluidic sensor that can harvest the mechanical energy of the fluid and simultaneously monitor their characteristics was fabricated by integrating the flexible piezoelectric poly(vinylidene fluoride) (PVDF) nanofibers with the well-designed microfluidic chips. Those devices could generate open-circuit high output voltage up to 1.8 V when a droplet of water is flowing past the suspended PVDF nanofibers and result in their periodical deformations. The impulsive output voltage signal allowed them to be utilized for droplets or bubbles counting in the microfluidic systems. Furthermore, the devices also exhibited self-powered sensing behavior due to the decreased voltage amplitude with increasing input pressure and liquid viscosity. The drop of output voltage could be attributed to the variation of flow condition and velocity of the droplets, leading to the reduced deformation of the piezoelectric PVDF layer and the decrease of the generated piezoelectric potential.

A two-degree-of-freedom piezoelectric energy harvester with stoppers for achieving enhanced performance

Environmental vibrations often exist in a broadband form. To have a robust performance over a wide frequency range, vibration energy harvesters need to be designed to be insensitive to excitation frequencies. In this paper, we propose a novel two-degree-of-freedom (DOF) piezoelectric energy harvester (PEH) with stoppers that introduce nonlinear dynamic interaction between the two DOFs. First, the mechanical model of the 2DOF system with stoppers is developed by emulating the impact behavior as a piecewise linear stiffness and the working principle is explained. Subsequently, the analytical solution of the system with piecewise linear stiffness is derived using the averaging method and the dynamic response of the system is obtained and confirms its wide bandwidth property. Finally, by integrating the mechanical system with a piezoelectric transducer, the energy harvesting performance of the proposed 2DOF PEH with stoppers is numerically evaluated. The open circuit voltage response of the proposed system is compared with that of the conventional linear 2DOF and 1DOF PEHs. A parametric study reveals the effect of the stopper distance on the energy harvesting performance in terms of both the bandwidth and open circuit voltage output. The superiority of the proposed system in terms of both power output and operation bandwidth is demonstrated.

Electrospinning aligned and random environmental-friendly BCTZ nanowires for high-performance energy harvester

Abstract Being able to harvest energy from many kinds of motions, such as touching, tapping, bending, etc., novel energy harvester (NEH) has gained a lot of interests nowadays. In this work, NEHs were fabricated with 0.5Ba(Zr 0.2 Ti 0.8 )O 3 −0.5(Ba 0.7 Ca 0.3 )TiO 3 nanowires (BCTZ NWs), both aligned (A-BCTZ NWs) and random (R-BCTZ NWs). The BCTZ NWs were prepared by electrospinning. XRD pattern revealed BCTZ NWs’ pure perovskite structure. Excellent electric properties with output open-circuit voltage of 3 V and short-circuit current of 50 nA were obtained for A-BCTZ NWs based NEH. EDS, Raman and FESEM were also used to characterize the morphology and structure of BCTZ NWs.

Performance-boosted triboelectric textile for harvesting human motion energy

Developing flexible, lightweight and sustainable power sources is an important route to provide electricity for portable electronics. Here, we demonstrate a high-performance double-layer–stacked triboelectric textile (DTET) for harvesting human motion energy. Both the Ni-coated polyester conductive textile and the silicone rubber were adopted as effective triboelectric materials. A high output open-circuit voltage of 540V and a short-circuit current of 140µA can be obtained from the DTET with the size of 5 ×5cm2, corresponding to a high peak surface power density of 0.892mW/cm2 at a load resistance of 10 MΩ. The output peak signal of the DTET can be used as a trigger signal of a movement sensor to design movement monitoring equipment. With only the energy harvested from walking, running or flapping, the DTET can directly light up 100 light-emitting diodes (LEDs) connected serially, and drive portable electronics, such as competition timer, digital clock and electronic calculator, which indicate the potential and broad application prospects in biological health monitoring, outdoor exploration, troop marching and portable electronics.

Frequency Dependent Behavior of a Dynamo-Type HTS Flux Pump

The high-T c superconductor (HTS) dynamo is a type of superconducting flux pump that can inject a dc current into a superconducting magnet coil, without requiring physical connection to an external power supply. Here, we report experimental results from an HTS dynamo employing 46-mm wide coated conductor stator wire. We characterize the output of the device as a function of frequency, and show the effect of slitting the stator wire into two or three parallel equivalent strips. At operating frequencies above ~100 Hz, we observe that the internal resistance and open-circuit voltage ceases to increase linearly with frequency, and that the short-circuit current is greatly reduced. Experimental waveform data of the output open-circuit voltage enables us to identify three distinct and different signature waveforms, which mark the low-frequency, midfrequency, and high-frequency operating regimes. These regimes appear to arise due to the saturation of circulating currents within the stator wire, followed by a rise in temperature of the wire. We conclude that dissipation due to circulating currents plays an important role in depressing the output of this wide stator device at high frequencies. This effect is in marked contrast to results previously reported for a similar HTS dynamo employing narrower stator wires.

A new broadband energy harvester using propped cantilever beam with variable overhang

Design of piezoelectric energy harvester for a wide operating frequency range is a challenging problem and is currently being investigated by many researchers. Widening the operating frequency is required, as the energy is harvested from ambient source of vibration which consists of spectrum of frequency. This paper presents a new technique to increase the operating frequency range which is achieved by designing a harvester featured by a propped cantilever beam with variable over hang length. The proposed piezoelectric energy harvester is modeled analytically using Euler Bernoulli beam theory and the effectiveness of the harvester is demonstrated through experimentation. The results from analytical model and from experimentation reveal that the proposed energy harvester generates an open circuit output voltage ranging from 36.43 V to 11.94 V for the frequency range of 27.24 Hz to 48.47 Hz. The proposed harvester produces continuously varying output voltage and power in the broadened operating frequency range.

Flexible piezoelectric nanogenerator in wearable self-powered active sensor for respiration and healthcare monitoring

A wearable self-powered active sensor for respiration and healthcare monitoring was fabricated based on a flexible piezoelectric nanogenerator. An electrospinning poly(vinylidene fluoride) thin film on silicone substrate was polarized to fabricate the flexible nanogenerator and its electrical property was measured. When periodically stretched by a linear motor, the flexible piezoelectric nanogenerator generated an output open-circuit voltage and short-circuit current of up to 1.5 V and 400 nA, respectively. Through integration with an elastic bandage, a wearable self-powered sensor was fabricated and used to monitor human respiration, subtle muscle movement, and voice recognition. As respiration proceeded, the electrical output signals of the sensor corresponded to the signals measured by a physiological signal recording system with good reliability and feasibility. This self-powered, wearable active sensor has significant potential for applications in pulmonary function evaluation, respiratory monitoring, and detection of gesture and vocal cord vibration for the personal healthcare monitoring of disabled or paralyzed patients.

Design and analysis of a multi-step piezoelectric energy harvester using buckled beam driven by magnetic excitation

In this paper, a multi-step buckled beam piezoelectric energy harvester driven by magnetic force is proposed. To convert ambient mechanical vibration into electrical energy with increased operational frequency bandwidth and power density, the harvester utilizes a combination of multi-step mechanism and bistable structure. A multi-step mechanism in the form of a magnet array with staggered magnetic poles has been designed for the energy harvesting system to obtain a wide working bandwidth. A buckled beam as a bistable structure enables the harvester to demonstrate a high-voltage output. A theoretical model is developed to characterize the multi-step piezoelectric energy harvester. Both simulations and experiments on the fabricated experimental device are carried out to validate the design and analysis of the multi-step piezoelectric energy harvester. The experimental results indicate that output open circuit voltage of the harvester is 4.4V. The harvester generates a peak power of 5.0μW across resistive load of 3.3 MΩ at the frequency of 3.0Hz. The results show that the device can cause stable output voltage under wideband excitations. Furthermore, under the multi-step mechanism, the magnet array with staggered magnetic poles increases the output voltage of the harvester by 25.0% compared to the unidirectional magnetic pole arrangement.

Three-dimensional piezoelectric energy harvester with spring and magnetic coupling

This letter proposes a three-dimensional piezoelectric energy harvester (3D PEH) that enables energy scavenging from vibrations in arbitrary directions. The proposed harvester comprises a spring, a primary beam, an inner beam, and two magnetic masses. The beams capture vibrations along their surface normal directions, and the spring, which acts as a mechanical energy buffer, is used to sense vibrations that occur parallel to the length direction of the inner beam. Magnetic coupling is introduced to perform frequency up-conversion and thus transfer vibration energy from the inner beam to the primary beam. As a benefit of the proposed structure, the 3D PEH can sense and convert all vibration energies occurring within the 3D space. When compared with use of the same beams in a linear configuration, the peak voltage of the proposed configuration is more than 3 V, and the bandwidths of voltages exceeding 5 V are wider by more than 3 Hz. Simultaneously, the primary beam resonant frequency is reduced by more than 6 Hz. Experimental results indicate that the proposed 3D PEH offers the advantages of higher open-circuit output voltages and wider frequency bandwidths at a lower resonant frequency.

Enabling a wind energy harvester based on ZnO thin film as the building skin

In this paper, a wind energy harvester, which can be used as building skin, is developed. In order to overcome the defects of traditional wind energy harvester, such as expensive and crisp, the developed harvester is designed as a circular silicon plate with several symmetrically distributed rectangular cavities which were covered with ZnO (Zinc oxide) thin film. It is verified whether the designed harvester can function in turbulence flow by theoretical analysis and finite element analysis. The acoustic measurement illustrated that the output of designed device is linear to the frequency. And, the wind fluid experiments suggested that the thin film can vibrate under a low wind velocity 1m/s and is easy to vibrate in wind turbulence. The maximum output power density is 23.39nW/cm2 with a maximum open circuit output voltage 2.81V. All of characteristics of designed harvester enable that it can be used as the building skin to harvest wind energy.

Comparative Study with a Unique Arrangement to Tap Piezoelectric Output to Realize a Self Poled PVDF Based Nanocomposite for Energy Harvesting Applications

AbstractIn this research paper we present a comparative study on the enhanced piezoelectric performance between Carbon Nanotubes (CNT)/PVDF nanocomposite as well as Iron‐Reduced Graphene Oxide (Fe‐RGO)/PVDF nanocomposite. The enhanced performance is realized by a unique device structure, in which the bottom electrode is physically not in contact with the piezoelectric film until external excitation is applied. FTIR characterization shows the enhancement of polar crystallization phases due to electrostatic interactions in PVDF by the addition of CNT and Fe‐RGO. Raman Spectroscopy indicates the formation of good quality Fe‐RGO nanosheets and also shows high crystalline quality of CNTs. Raman Spectroscopy identifies the interaction between CNTs and Fe‐RGO nanosheets with the polymer that supports the piezoelectric current generation mechanism. Conductivity measurements show that addition of CNT and Fe‐RGO in PVDF increases the conductivity of the nanocomposite films. The CNT/PVDF and Fe‐RGO/PVDF piezoelectric energy harvesting device produced an open circuit output voltage of 2.5 V and 1.2 V respectively. A short circuit rectified current of nearly 700 nA and 300 nA was detected by the CNT/PVDF and Fe‐RGO/PVDF based piezoelectric energy harvesting device.

Enhanced performance of ZnO microballoon arrays for a triboelectric nanogenerator

In recent years, triboelectric nanogenerators (TENGs), harvesting energy from the environment as a sustainable power source, have attracted great attention. Currently, many reports focus on the effect of surface modification on the electrical output performance of the TENG. In this work, we have fabricated vertically grown ZnO microballoon (ZnOMB) arrays on top of pyramid-featured PDMS patterned film, contacted with PTFE film to construct the TENG. The electrical output performances of the designed TENG are presented under external forces with different frequencies. The corresponding output open-circuit voltage with ZnOMBs could reach about 57 V the current density about 59 mA m−2 at 100 Hz, which was about 2.3 times higher than without any ZnO. The global maximum of the instantaneous peak power could reach 1.1 W m−2 when the external load resistance was about 2 MΩ. Furthermore, the electrical output of the fabricated device could light 30 commercial LED bulbs without any rectifier circuits or energy-storage elements. This clearly suggests that this kind of surface modification can dramatically enhance the output performance of the TENG. Moreover, the design of TENG demonstrated here can be applied to various energy harvesting applications.

Synthesis of Orthorhombic Perovskite-Type ZnSnO3 Single-Crystal Nanoplates and Their Application in Energy Harvesting.

In recent years, lead-free piezoelectric nanogenerators have attracted much attention because of their great potential for harvesting energy from the environment. Here, we report the first synthesis of two-dimensional (2D) single-crystal ZnSnO3 hexagon nanoplates and the fabrication of ZnSnO3 nanoplate-based nanogenerators. The orthorhombic perovskite-structured ZnSnO3 nanoplates with (111) facets of the exposed plate surface are successfully synthesized via a one-step hydrothermal reaction. Piezoelectric nanogenerators are then fabricated using the as-synthesized single-crystal ZnSnO3 nanoplates and poly(dimethylsiloxane) (PDMS). A d33 value as high as 49 pC/N for the ZnSnO3@PDMS composite was obtained without any electrical poling process, which demonstrates that the single-crystal ZnSnO3 nanoplates have a single-domain structure. To the best of our knowledge, this d33 value is also the highest among lead-free piezoelectric composites. A bending strain can induce the piezoelectric nanogenerator (PENG) to generate a large, stable, and sustainable output open circuit voltage of 20 V and a short circuit current of 0.6 μA, which are higher than many other PENGs. The output signals are sufficient to light a single light-emitting diode (LED), which shows the great potential of the material for scavenging mechanical energy from moving entities, such as road vehicles, railway vehicles, and humans.

Temperature dependence of a magnetically levitated electromagnetic vibration energy harvester

Electromagnetic vibration energy harvesters including magnetically levitated devices where opposing magnets are used to form the spring have been well documented. The strength of the magnets naturally has a large influence on the dynamic characteristics and output power of such harvesters. However, it can be affected by ambient temperatures which vary from applications to applications. This paper presents investigation into the performance of a magnetically levitated electromagnetic energy harvester under various ambient temperatures. Parameters investigated include magnetic flux density, resonant frequency, damping ratio, open circuit output voltage, velocity of the relative motion and the load resistance. Both simulation and experimental results show that these properties vary with ambient temperatures. The magnetic flux density reduces as the temperature increases which results in lower resonant frequency, lower relative velocity, lower open circuit output voltage and higher damping ratio. Varying resonant frequencies with temperature can lead to harvesters being de-tuned from the target vibration frequency. Decreasing magnetic field strength and increased damping ratios will also reduce output power even if the harvester’s resonant frequency still matches the environmental vibration frequency. The power transferred to the electrical load will be reduced due to the variation in the optimal load resistance with temperature. This means the harvester is no longer matched to achieve the maximum harvested power. The specified maximum operating temperature of the magnets was found to lead to partial demagnetisation. When cycling from room to the maximum specified temperature, the magnetic field was initially found to fall but remained constant thereafter. Harvesters were found to operate beyond the specified maximum operating temperature of the magnet, but suffer from a reduced magnetic strength.