Conventional Energy Harvester Research Articles

Silk Materials Light Up the Green Society

The revolutionary and pioneering advancements of silk materials in recent years have provided numerous opportunities for the great trend of sustainable green energy. Working as an eco‐friendly replacement for conventional energy harvester or storage device, silk‐based energy sources that get intensive attention are regarded as new solutions in flexible human‐integrated applications. Compared with other synthetic polymers, silk materials present outstanding biocompatibility, biodegradability, and many other attractive properties owing to the natural protein composition, various modification methods, large‐scale green production, and superior fabrication techniques. Herein, recent progress and ongoing challenges posed by the utilization and translation of silk materials in green energy application are discussed.

Multimodal pizza-shaped piezoelectric vibration-based energy harvesters

Energy harvesting from ambient vibration through piezoelectric devices has received a lot of attention in recent years from both academia and industry. One of the main challenges is to develop devices capable of adapting to diverse sources of environmental excitation, being able to efficiently operate over a broadband frequency spectrum. This work proposes a novel multimodal design of a piezoelectric energy harvesting system to harness energy from a wideband ambient vibration source. Circular-shaped and pizza-shaped designs are employed as candidates for the device, comparing their performance with classical beam-shaped devices. Finite element analysis is employed to model system dynamics using ANSYS Workbench. An optimization procedure is applied to the system aiming to seek a configuration that can extract energy from a broader frequency spectrum and maximize its output power. A comparative analysis with conventional energy harvesting systems is performed. Numerical simulations are carried out to investigate the harvester performances under harmonic and random excitations. Results show that the proposed multimodal harvester has potential to harness energy from broadband ambient vibration sources presenting performance advantages in comparison to conventional single-mode energy harvesters.

A new concept of frequency-excitation-up conversion to improve the yield of linear piezoelectric generators

A new and novel frequency-excitation up-conversion (FEUC) mechanism achieved by converting low-frequency excitation into friction-induced vibration (FIV) is proposed to improve the output power of linear piezoelectric energy harvesters at ultra-low ambient frequencies. For comparison, a conventional resonant energy harvester and an impact-driven energy harvester are created, the output power is measured at the resonant frequency under a 0.5 g driving acceleration. Then, a friction system driven by reciprocating sliding and capable of generating FIV is established. The driving reciprocating is equivalent to the low-frequency ambient vibration, and a single piezoelectric cantilever beam is added to the friction system for energy recovery. The results show that, compared with the impact-driven energy harvester, the vibration frequency can be increased hundreds of times, and the excitation level can be improved several orders of magnitude by the friction nonlinearities. The impedance of the energy harvester is reduced significantly due to a sharp increase in the vibration frequency. In addition, the open-circuit voltage amplitude is not substantially lowered due to the significantly increased excitation level, even though the piezoelectric cantilever beam operates in a high-frequency condition and in the absence of resonance. Therefore, the output power is dramatically improved. The effectiveness and superiority of the FEUC strategy proposed in this work has been demonstrated.

Magnetic Field Energy Harvesting with a Lead-Free Piezoelectric High Energy Conversion Material

This article presents a high-performance lead-free piezoelectric energy harvester (LPEH) system for magnetic field. It based on a Ba0.85Ca0.15Ti0.90Zr0.10O3 + CuO 0.3 wt% (BCTZC0.3) composite was fabricated by sintering at 1450 °C. The BCTZC0.3 composite, which has an enhanced high energy conversion constant (d33×g33), shows improved piezoelectric power-generation performance when compared with conventional piezoelectric energy harvesters. The BCTZC0.3-based LPEH produces instantaneous maximum power of 8.2 mW and an energy density of 107.9 mW/cm3 in a weak magnetic field of 250 μT. This system can be used to charge a capacitor and operate a wireless sensor network (WSN) system to provide temperature sensing and radio-frequency (RF) transmission in a 250 μT magnetic field. The proposed LPEH is a promising green-energy device for potentially self-powering WSN systems when applied.

Efficiency enhancement of electromagnetic energy harvesters for high‐rise buildings

Because the vibration of buildings and bridges is often small in amplitude, low in frequency, and wide in frequency bandwidth, designing a conventional energy harvester with the natural frequency low enough to coincide with the low excitation usually accompany with very large mass and volume. However, it is very important to use portable energy harvester (usually with higher natural frequency) to obtain energy for wireless devices. If portable energy harvesters were used directly on high-rise buildings, the efficiency would be very low. To solve this problem, we propose a simple device to implement portable energy harvester in high-rise building application environment with a high efficiency. It is an intermediate spring-mass system to be installed between the energy harvester and the underlying building. The crux of this device is to enhance the vibration amplitude of the oscillating mass of energy harvesters, so that more energy can be harvested. By changing the degree of freedom (DOF) and stiffness of the intermediate device, the performance of energy harvester can be drastically enhanced. The effects of the parameters of the device for the harvesting performance have been identified using the Lyapunov method, and the conclusion has been verified using four earthquake ground motions. Applications to 100-story buildings are used to demonstrate the efficiency of the proposed intermediate device. In the illustrative examples, this device can increase the generated energy of linear electromagnetic energy harvester (EMEH) up by several hundred times.

A Multi-Mode Broadband Vibration Energy Harvester Composed of Symmetrically Distributed U-Shaped Cantilever Beams.

Using the piezoelectric effect to harvest energy from surrounding vibrations is a promising alternative solution for powering small electronic devices such as wireless sensors and portable devices. A conventional piezoelectric energy harvester (PEH) can only efficiently collect energy within a small range around the resonance frequency. To realize broadband vibration energy harvesting, the idea of multiple-degrees-of-freedom (DOF) PEH to realize multiple resonant frequencies within a certain range has been recently proposed and some preliminary research has validated its feasibility. Therefore, this paper proposed a multi-DOF wideband PEH based on the frequency interval shortening mechanism to realize five resonance frequencies close enough to each other. The PEH consists of five tip masses, two U-shaped cantilever beams and a straight beam, and tuning of the resonance frequencies is realized by specific parameter design. The electrical characteristics of the PEH are analyzed by simulation and experiment, validating that the PEH can effectively expand the operating bandwidth and collect vibration energy in the low frequency. Experimental results show that the PEH has five low-frequency resonant frequencies, which are 13, 15, 18, 21 and 24 Hz; under the action of 0.5 g acceleration, the maximum output power is 52.2, 49.4, 61.3, 39.2 and 32.1 μW, respectively. In view of the difference between the simulation and the experimental results, this paper conducted an error analysis and revealed that the material parameters and parasitic capacitance are important factors that affect the simulation results. Based on the analysis, the simulation is improved for better agreement with experiments.

A universal single electrode droplet-based electricity generator (SE-DEG) for water kinetic energy harvesting

Harvesting water kinetic energy is a prospective way to obtain sustainable power. However, conventional water energy harvesting technologies are restricted by specific operating locations and fabrication materials. These techniques urgently need to be improved and supplemented with new methods. Here, we report a novel and universal single electrode droplet-based electricity generator (SE-DEG) that allows converting water droplet kinetic energy into electricity power on any surfaces of artificial or natural materials such as PTFE, glass, wood, aloe, cicada wing, stone and etc. This functionality is endowed by a special configuration characterized by the location of the electrode on the top of dielectric material rather than underlying as in the conventional triboelectric nanogenerator (TENG). Such special configuration can effectively harness the triboelectric charges generated without going through the electrostatic induction process between bottom electrode and the surface in the case of TENG. We envision that SE-DEGs represent a new dimension in ability to harvest abundant hydrodynamic energy everywhere. • A universal SE-DEG represents a new dimension in ability to harvest abundant hydrodynamic energy everywhere. • The universal preparation makes the operating locations and fabrication materials of the generator unrestricted. • The design of the electrode can harness the triboelectric charges without going through electrostatic induction process.

Analytical and experimental investigation of stepped piezoelectric energy harvester

Conventional Piezoelectric Energy Harvesters (CPEH) have been extensively studied for maximizing their electrical output through material selection, geometric and structural optimization, and adoption of efficient interface circuits. In this paper, the performance of Stepped Piezoelectric Energy Harvester (SPEH) under harmonic base excitation is studied analytically, numerically and experimentally. The motivation is to compare the energy harvesting performance of CPEH and SPEHs with the same characteristics (resonant frequency). The results of this study challenge the notion of achieving higher voltage and power output through incorporation of geometric discontinuities such as step sections in the harvester beams. A CPEH consists of substrate material with a patch of piezoelectric material bonded over it and a tip mass at the free end to tune the resonant frequency. A SPEH is designed by introducing a step section near the root of substrate beam to induce higher dynamic strain for maximizing the electrical output. The incorporation of step section reduces the stiffness and consequently, a lower tip mass is used with SPEH to match the resonant frequency to that of CPEH. Moreover, the electromechanical coupling coefficient, forcing function and damping are significantly influenced because of the inclusion of step section, which consequently affects harvester's output. Three different configurations of SPEHs characterized by the same resonant frequency as that of CPEH are designed and analyzed using linear electromechanical model and their performances are compared. The variation of strain on the harvester beams is obtained using finite element analysis. The prototypes of CPEH and SPEHs are fabricated and experimentally tested. It is shown that the power output from SPEHs is lower than the CPEH. When the prototypes with resonant frequencies in the range of 56-56.5 Hz are tested at 1 m/s2, three SPEHs generate power output of 482 μW, 424 μW and 228 μW when compared with 674 μW from CPEH. It is concluded that the advantage of increasing dynamic strain using step section is negated by increase in damping and decrease in forcing function. However, SPEHs show slightly better performance in terms of specific power and thus making them suitable for practical scenarios where the ratio of power to system mass is critical.

Kirigami auxetic structure for high efficiency power harvesting in self-powered and wireless structural health monitoring systems

Kirigami and auxetic topologies are combined to design an innovative metamaterial-based substrate (MetaSub) for piezoelectric energy harvesters. The proposed MetaSub piezoelectric energy harvester (MPEH) contains both advantageous metamaterial properties of negative Poisson’s ratio capability and enhanced planar stretchability. A computational parametric analysis is conducted to develop the optimum design for the MPEH to trap the maximum elastic energy. A finite element analysis (FEA) is employed to analytically and numerically validate the simulation model of the MPEH. Accordingly, two experimental results of conventional and auxetic strain energy harvesters are used to evaluate the power enhancement of the MPEH. The FEA results demonstrate the average power gained by the MPEH at a low level of frequency and strain excitation (10 Hz and 150 peak-to-peak) is 165 W which easily satisfies the minimum electric power amount required as a sensor node for self-powered wireless sensor networks. The harvested power output of the MPEH is 19.2 times more than power output produced by an equivalent conventional harvester with a plain substrate (8.6 W). The performance of the MPEH is investigated at different combinations of both low and high excitation frequencies. The creative design of the MetaSub can significantly improve the productivity of strain-induced devices whose efficiency is dependent on their deformation performance such as vibration energy harvesters, wearable sensors, flexible actuators, and micro electromechanical applications.

Tapered nonlinear vibration energy harvester for powering Internet of Things

The lack of a sustainable power source to substitute batteries for long-term applications limits the widespread deployment of wireless sensor nodes in this era of the Internet of Things. Conventional linear Vibration Energy Harvesters are inefficient in converting ambient mechanical energy into usable electrical energy owing to their narrow frequency bandwidth when harnessing mechanical energy that is spread over a wide range of frequencies. In this work, we design, develop and demonstrate high power density nonlinear wideband energy harvesters using novel tapered spring architectures in an autonomous wireless sensor node system. These spring structures exhibit a nonlinear restoring force arising from the atypical stress distribution that can be additionally tuned by changing the taper-ratio in the structure. We investigate different tapering designs in order to achieve optimal spring hardening nonlinearities. This nonlinearity aids in widening the operable bandwidth, making the harvesters suitable for scavenging energy from real-world broadband vibrations. We obtain power densities of the order of 2660 μW/cm3g2 in the nonlinear energy harvester, outpacing most contemporary energy scavengers. We present a modified Perturb and Observe algorithm that allows tracing of the maximum power point in the context of non-stationary vibration conditions. We use the fabricated nonlinear device to power a wireless sensor node that reports on vital physical parameters (humidity, temperature), thereby enabling a resilient remote data acquisition system. This demonstrates the potential of our design to provide a sustainable energy source for platforms within the Internet of Things.

Long-term operation of bio-catalyzed cathodes within continuous flow membrane-less microbial fuel cells

Microorganisms were observed to facilitate cathodic oxygen reduction and enhance cathode performance of microbial fuel cells (MFCs). However, the long-term activity and stability of bio-catalyzed cathode needs to be explored. This study evaluated the long-term performance of bio-catalyzed cathode and iron(II) phthalocyanine (FePc)-catalyzed cathode MFCs through effluent water quality, electricity production and electrochemical impedance spectroscopy (EIS) analysis under different scenarios, including conventional wastewater treatment and energy harvesting using a power management system (PMS). During the continuous operation, both systems demonstrated high chemical oxygen demand and ammonium removal, but bio-catalyzed cathode MFCs could achieve significantly better total nitrogen removal than FePc-catalyzed cathode MFCs. The FePc-coated cathode showed constant cathode potential during the entire operation period, but the biocathode showed varied but step-wise increased cathode potential to achieve more than 500 mV versus the standard hydrogen electrode, likely due to the gradual enrichment of biocathode biofilm. EIS analysis revealed that biocathode had higher ohmic resistance than bare carbon felt cathode but the microbial biofilm could largely decrease polarization resistance of cathode material. Microbial community analysis has shown the presence of nitrifying and denitrifying bacteria in the bio-catalyzed cathode biofilm. When connecting PMS, both bio-catalyzed cathode and FePc-catalyzed cathode MFCs successfully charged a capacitor, but the bio-catalyzed cathode MFC voltage significantly dropped to less than 100 mV after charging for 91 h, and gradually recovered when disconnecting PMS. This study has demonstrated the potential application of oxygen reduction bio-catalyzed cathode MFCs for continuous wastewater treatment and energy harvesting for long period of time.

A dual quasi-zero-stiffness sliding-mode triboelectric nanogenerator for harvesting ultralow-low frequency vibration energy

A major purpose of energy harvesting from ambient vibration is to power sensors for structural health monitoring and environment monitoring. However, most types of ambient vibration are in the low-frequency region, which would make conventional energy harvesters inefficient. In this paper, the first attempt to combine a quasi-zero-stiffness (QZS) mechanism and a triboelectric nanogenerator is made, and a QZS triboelectric nanogenerator (QZS-TENG) is devised. In this QZS system, a negative stiffness mechanism (NSM) is constructed by using QZS springs to achieve ultra-low stiffness in a much larger displacement region than that of a traditional QZS device. Based on the geometrical relationship, the exact expression of the restoring force of the QZS-TENG is derived firstly, and then is fitted as a polynomial to obtain its approximate analytical dynamic responses. The electrical properties of the QZS-TENG, including its open circuit voltage, short circuit current, output voltage, output current and output power, are presented in both analytical and numerical results. The numerical results show excellent agreement with the analytical ones, and most importantly, the QZS-TENG exhibits an excellent energy harvesting performance in the ultralow frequency region. This work provides a new application of a QZS mechanism to harvest the ultralow-frequency vibration energy by combining a TENG.

A self-powered analog sensor-data-logging device based on Fowler-Nordheim dynamical systems

Continuous, battery-free operation of sensor nodes requires ultra-low-power sensing and data-logging techniques. Here we report that by directly coupling a sensor/transducer signal into globally asymptotically stable monotonic dynamical systems based on Fowler-Nordheim quantum tunneling, one can achieve self-powered sensing at an energy budget that is currently unachievable using conventional energy harvesting methods. The proposed device uses a differential architecture to compensate for environmental variations and the device can retain sensed information for durations ranging from hours to days. With a theoretical operating energy budget less than 10 attojoules, we demonstrate that when integrated with a miniature piezoelectric transducer the proposed sensor-data-logger can measure cumulative “action” due to ambient mechanical acceleration without any additional external power.

Enhanced electromagnetic wrist-worn energy harvester using repulsive magnetic spring

While wrist-worn electronics have great potential in a variety of areas, their applications are currently constrained by the limited working time of their electrochemical batteries. Harvesting energy from arm swinging motions provides a promising means to address this issue. In this work, we introduce a tiny repulsive magnetic spring to improve the performance of a wrist-worn inertial energy harvester. In contrast to conventional inertial rotational energy harvesters, the proposed device contains a repulsive magnetic spring that consists of two pairs of repulsive magnets. The existence of the magnetic spring lowers the potential energy well depth of the energy harvester by reducing the system’s stiffness, thereby enhancing power generation. An analytical model is built to predict the system performance and investigate the effects of the magnetic spring air gap. To validate this design, a prototype is constructed and tested using a bench-top excitation source that emulates the swinging motion of the human arm. The experiments show that, in the tested excitation frequency (0.7–1.3 Hz) and air gap (2.2–3.6 mm) ranges, the average output power is significantly enhanced by the magnetic spring and smaller air gap of magnets results in more improvement, which agrees well with the simulation results. With the requirement of a minimal amount of space, the magnetic spring helps the energy harvester achieve maximum output power of 151 μW with an air gap of 2.6 mm at 1.3 Hz. Additionally, a maximum power improvement of 425% for an air gap of 2.2 mm at 0.7 Hz is achieved compared with the conventional wrist-worn inertial energy harvester.

Performance enhancement for a magnetic-coupled bi-stable flutter-based energy harvester

This paper aims at presenting a novel magnetic-coupled bi-stable flutter-based energy harvester (MBFEH) for the purpose of enhancing power generation in low speed air flow. The MBFEH comprises of a piezoelectric beam with a magnet on its tip, a hinged rigid flat airfoil, and an external magnet. The magneto-electro-aeroelastic system is theoretically modeled, numerically investigated, and experimentally validated. The influences of the separation distance between the magnets on flutter characteristics and performance of power generation are studied. The numerical and experimental results show that the supercritical flutter will be transformed into the subcritical flutter which realizes a significant reduction of cut-in air speed for energy harvesting. Compared with the conventional flutter-based energy harvester, the cut-in air speed of the MBFEH is reduced by more than 50% when the separation distance is set as 15 mm. The most preferred distance among the tested configurations is 12 mm which broadens the usable air speed by 1.8 m s−1, and leads to a 102% improvement of the energy harvesting performance throughout the air speed region from 2 m s−1 to 6.6 m s−1. The study shows that the proposed MBFEH is an effective design approach for enhancing energy harvesting capability in low air speed range.

Design and optimization of MEMS piezoelectric energy harvester for low frequency applications

Piezoelectric vibrational energy harvester (PVEH) suits best for harvesting vibrational energy from the environment due to the simplicity in design, operation, and compatibility with the micro electro mechanical system (MEMS) technology. In this work, the effect of geometrical parameters on the performance of an Aluminium Nitride (AlN) based MEMS PVEH is analyzed in detail and optimized for lower resonant frequency and higher output power. Electromechanical modeling and validation are carried out for an energy harvester with various proof mass shapes. The optimized PVEH is having a trapezoidal beam and a triangular-shaped proof mass. The effect of the amount of proof mass coverage on the performance parameters is also analyzed. The least resonant frequency is found for the design in which the proof mass coverage is 57 % of the overall length of the harvester and the power peaks when the proof mass coverage becomes 80 %. The proposed structure generated output power of 0.24 $$\mu$$ W at a resonant frequency of 158.8 Hz when an input acceleration of 0.5 g is applied. Then an array using the proposed structure is simulated and compared to an array of conventional rectangular energy harvesters and it is found that array using the proposed structure provides 1.79 times higher power at a lower resonant frequency than the conventional array.

Flow-induced vibration of inherently nonlinear structures with applications in energy harvesting

This paper proposes a novel design for a flow-induced vibration-based energy harvester, consisting of an elastic L-shaped beam, with an inherent nonlinearity in its structural stiffness as an alternative to the classical cantilever beam used in conventional fluidic energy harvester designs. The L-shaped beam supports a prism at its tip and undergoes large-amplitude galloping oscillations. The results from wind tunnel experiments show that by replacing a conventional linear structure that supports the prism with a nonlinear one, the high frequency flow components, shed from the tip prism, were capable of exciting the oscillations of the structure at higher harmonics of the main resonance, thus enhancing the power density of the energy harvester. As a result of improved power density values, the proposed harvester design holds great potential to be used as advanced space-efficient energy harvesters.

Piezoelectric Performance of a Symmetrical Ring-Shaped Piezoelectric Energy Harvester Using PZT-5H under a Temperature Gradient.

With the rapid development of microelectronics technology, low-power electronic sensors have been widely applied in many fields, such as Internet of Things, aerospace, and so on. In this paper, a symmetrical ring-shaped piezoelectric energy harvester (SR-PEH) is designed to provide energy for the sensor to detect the ambient temperature. The finite element method is used by utilizing software COMSOL 5.4, and the electromechanical coupling model of the piezoelectric cantilever is established. The output performance equations are proposed; the microelectromechanical system (MEMS) integration process of the SR-PEH, circuit, and sensor is stated; and the changing trend of the output power density is explained from an energy perspective. In the logarithmic coordinate system, the results indicate that the output voltage and output power are approximately linear with the temperature when the resistance is constant. In addition, the growth rate of the output voltage and output power decreases with an increase of resistance under the condition of constant temperature. In addition, with an increase of temperature, the growth rate of the output power is faster than that of the output voltage. Furthermore, resistance has a more dramatic effect on the output voltage, whereas temperature has a more significant effect on the output power. More importantly, the comparison with the conventional cantilever-shaped piezoelectric energy harvester (CC-PEH) shows that the SR-PEH can improve the output performance and broaden the frequency band.

Improving Current Transformer-Based Energy Extraction From AC Power Lines by Manipulating Magnetic Field

This article presents a novel method to improve energy scavenging from ac power lines under magnetic saturation conditions. The extracted power level of a conventional magnetic energy harvester is limited by the maximum flux density of the magnetic core. When a magnetic core is clamped on ac power lines, the flux density in the core is proportional to the magnetic field strength around the power line. Choosing a high-permeability core has the advantage of harvesting more energy for a given primary current. The flux density in such a core could reach its maximum value when the magnetic field increases. In this scenario, very little energy can be harvested since flux density variation in the core is small. Here we introduce an artificial magnetic field by adding an additional control coil to manipulate the magnetic field of power lines. A power management circuit is employed to store the energy harvested by the control coil and feed it back to the harvester to generate a counter magnetic field. As a result, the core will not be easily driven into the saturation region; hence, more energy can be harvested. Experimental results show that the proposed energy harvester can harvest an average power of 283 mW on a 50 Hz 10 Arms power line (2.34 mW/cm3/Arms), which is increased by 45% compared with the device without the control coil. This new method could provide a promising solution for smart grid monitoring and other industrial sensing applications.

Enhancement of low-speed piezoelectric wind energy harvesting by bluff body shapes: Spindle-like and butterfly-like cross-sections

Fluid-structure interaction can be utilized to harvest the low-speed wind energy for sustaining the low-power sensors for structural health monitoring. To enhance the low-speed wind energy harvesting, this study proposes the novel spindle-like and butterfly-like bluff bodies by coupling both the vortex-induced vibration (VIV) and galloping phenomena. Comprehensive wind tunnel experiments are conducted to investigate the advantages of the two bluff bodies in terms of the bluff body cross-sections and installment directions. The experimental results demonstrate that for both the spindle-like and butterfly-like bluff bodies, the vertical installment and small width ratio are beneficial to the performance in a broad range of wind speeds. Compared to a conventional galloping-based energy harvester, owing to the coupling between the VIV and galloping, the vertical spindle-like bluff body with the smallest width ratio can reduce the threshold wind speed of activating the energy harvesting function by over 13%, and improve the maximum voltage output by over 160%. Finally, taking the spindle-like bluff body as an example, the computational fluid dynamics (CFD) studies are conducted by using XFlow software to interpret the physical insight of performance enhancement. The CFD results show that the vertical installment direction and a small width ratio play an important role. The two designs can lead to a stronger aerodynamic force due to the fast vortex shedding, which improves the energy conversion efficiency from the flow-induced vibrations.