Conventional Energy Harvester Research Articles

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.

High output power density of a shear-mode piezoelectric energy harvester based on Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

Wireless sensing is widely adopted in internet of things (IoT) systems, but battery replacement is a critical issue for these devices. Triboelectricity, solar, heat, and vibration can be potential energy sources. Piezoelectric energy harvesters that can obtain energy from ambient vibrations are thought to be a promising approach to this problem. However, state-of-the-art energy harvesters made from cantilever-structured piezoelectric ceramics exhibit low output power densities. In this paper, we propose a bridge-type shear-mode piezoelectric energy harvester based on Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals. Owing to the large figure-of-merit d15×g15 (1.296 ×10−10C V m N−2) of the crystal and the higher electromechanical transfer efficiency of the flex-tensional structure when compared to a ceramic cantilever structure, the newly designed shear-mode energy harvester exhibits a power density of up to 1.378×104 W m−3. This is much higher than the power densities provided by conventional cantilever energy harvesters based on piezoelectric ceramics (~102 W m−3). The output voltage and maximum output current are 21.6 Vpp and 6×10−4 App, respectively under an inertial force of 0.25 N. This output current and power density are 5.5 times and 3.0 times, respectively, higher than those of the same structured energy harvester made from soft piezoelectric ceramics. A sample wireless sensing and data transmission system is successfully powered by the newly designed energy harvester. This work may help to address the issue of sustainable energy supplies for IoT systems.

Gathering energy from ultra-low-frequency human walking using a double-frequency up-conversion harvester in public squares

Conventional human walking energy harvesters suffer from low-frequency problems. A double-frequency up-conversion magnetostrictive energy harvester was proposed, analyzed, fabricated, and tested. The harvester is mainly composed of a gear rack and a multi-leaf cam. The rack acts as the first frequency up-conversion mechanism for low-frequency walking. The multi-leaf cam carries out the second frequency up-conversion operation. After the two steps, the low walking frequency is increased. A theoretical analysis of the energy harvester was conducted to find factors that influence its performance. A standard concrete block was proposed, which made the application of the energy harvester easy and fast. The energy harvester was fabricated and experiments were carried out. The ratio of the frequency up-conversion mechanism was 8.13. The maximum output voltage and output power of the harvester were 10.06 V (peak-to-peak) and 31.3 mW, respectively. The harvested energy could light up 100 light-emitting diodes (LEDs) at the same time. It could also power an electronic clock normally for more than 90 min. The proposed energy harvester can be applied for gathering low-frequency human walking energy in public squares.

Energy harvester for safety shoes using parallel piezoelectric links

Energy-harvesting devices in shoes have attracted much attention from the fields of elderly support, sports science, and disaster mitigation. In this study, we developed an energy harvester with a parallel link structure and six multi-layered piezoelectric transducers. By using this structure, we realized an effective energy conversion compared with conventional energy harvesters in terms of maximum power, comfort, durability, and availability of inputs with six degrees of freedom. A prototype of the parallel-link piezoelectric energy harvester generated 1.29 mW with human body weight. As a trial use, this energy harvester was installed in safety shoes for powering LEDs in the shoes. The assembly produced a brightness of 0.5 cd on average over a duration of 0.5 s, which is enough to show the wearer his or her position in a dark place.

An asymmetric bending-torsional piezoelectric energy harvester at low wind speed

This paper presents a detailed investigation on a novel asymmetric vortex-induced piezoelectric harvester for capturing wind energy at low wind speed. The asymmetric energy harvester undergoes both bending and torsional vibration caused by vortex-induced vibration. A comprehensive nonlinear distributed model of compound bending-torsion piezoelectric energy harvester is derived using the energy method based on the Euler-Bernoulli beam assumption. The theoretical results show that the asymmetric energy harvester has a lower natural frequency and a smaller electromechanical coefficient than the conventional vortex-induced piezoelectric energy harvester. The asymmetric configuration contributes to a lower corresponding optimal wind speed and is prone to vibrate compared with the symmetric configuration. Experiments were carried out and the experimental results were in good agreement with the numerical results. The asymmetric energy harvester has the advantage of generating more power at low wind speed compared with conventional energy harvester. The results show with the increasing of length of cylinder and eccentric distance, the natural frequency and optimal wind velocity drops, and there exists an optimal length of cylinder for maximum output power. This study provides a simple and feasible method to reduce the working wind speed for vortex-induced piezoelectric energy harvester.

Tunable, multi-modal, and multi-directional vibration energy harvester based on three-dimensional architected metastructures

Conventional vibration energy harvesters based on two-dimensional planar layouts have limited harvesting capacities due to narrow frequency bandwidth and because their vibratory motion is mainly restricted to one plane. Three-dimensional architected structures and advanced materials with multifunctional properties are being developed in a broad range of technological fields. Structural topologies exploiting compressive buckling deformation mechanisms however provide a versatile route to transform planar structures into sophisticated three-dimensional architectures and functional devices. Designed geometries and Kirigami cut patterns defined on planar precursors contribute to the controlled formation of diverse three-dimensional forms. In this work, we propose an energy harvesting system with tunable dynamic properties, where piezoelectric materials are integrated and strategically designed into three-dimensional compliant architected metastructures. This concept enables energy scavenging from vibrations not only in multiple directions but also across a broad frequency bandwidth, thus increasing the energy harvesting efficiency. The proposed system comprises a buckled ribbon with optional Kirigami cuts. This platform enables the induction of vibration modes across a wide range of resonance frequencies and in arbitrary directions, mechanically coupling with four cantilever piezoelectric beams to capture vibrations. The multi-modal and multi-directional harvesting performance of the proposed configurations has been demonstrated in comparison with planar systems. The results suggest this is a facile strategy for the realization of compliant and high-performance energy harvesting and advanced electronics systems based on mechanically assembled platforms.

An Adhesive Surface Enables High-Performance Mechanical Energy Harvesting with Unique Frequency-Insensitive and Pressure-Enhanced Output Characteristics.

Viscoelastic polymer adhesives (VPAs) are common materials broadly used in adhesive tapes for bonding objects tightly in daily life. This work presents a conceptually new strategy of using contact electrification (rather than strong adhesion) of VPAs to directly convert mechanical energy to electric energy, generally showing 202-419% of the electric energy generated by conventional mechanical energy harvesters under the same triggering conditions. More notably, the VPA-based generators (VPAGs) possess unique frequency-insensitive and pressure-enhanced output characteristics. The output power of a VPAG not only does not show regular degradation of performance with the decrease of triggering frequency, but also can be further enhanced by simple introduction of a second VPA layer with a smaller area to increase the applied pressure without the requirement of rising applied force. The average output power density of a VPAG with a second layer of 0.5 cm × 0.5 cm can reach 216.7 µW cm-2 , which is ≈150% larger than that of a VPAG without a second VPA layer. This research is of significance to harvesting the random, irregular, and low-frequency (bio-)mechanical energy that widely exists but is wasted in the environment for both stable electric energy generation and electronic device operation.

Performance Analysis of an Electromagnetically Coupled Piezoelectric Energy Scavenger

The deliberate introduction of nonlinearities is widely used as an effective technique for the bandwidth broadening of conventional linear energy harvesting devices. This approach not only results in a more uniform behavior of the output power within a wider frequency band through bending the resonance response, but also contributes to energy harvesting from low-frequency excitations by activation of superharmonic resonances. This article investigates the nonlinear dynamics of a monostable piezoelectric harvester under a self-powered electromagnetic actuation. To this end, the governing nonlinear partial differential equations of the proposed harvester are order-reduced and solved by means of the perturbation method of multiple scales. The results indicate that, according to the excitation amplitude and load resistance, different responses can be distinguished at the primary resonance. The system behavior may involve the traditional bending of response curves, Hopf bifurcations, and instability regions. Furthermore, an order-two superharmonic resonance is observed, which is activated at lower excitations in comparison to order-three conventional resonances of the Duffing-type resonator. This secondary resonance makes it possible to extract considerable amounts of power at fractions of natural frequency, which is very beneficial in micro-electro-mechanical systems (MEMS)-based harvesters with generally high resonance frequencies. The extracted power in both primary and superharmonic resonances are analytically calculated, then verified by a numerical solution where a good agreement is observed between the results.

Electro-vibration modeling and response of 3D skeletal frame configuration for energy harvesters

3D skeletal frame configuration is introduced as a means for overcoming deficiencies encountered by conventional 1D beam energy harvesters (EHs). A composite finite element model based on 3D beam kinematics is further developed and tailor-made for this purpose. A comprehensive electro-vibration analysis is conducted using a MATLAB code for the 3D skeletal frame EH as an enhanced application of the theory and compared to the corresponding 1D beam harvester. The results obtained by the theory is then validated against numerical responses based on active solid elements. It is shown that the novel 3D skeletal frame configuration offers substantial benefits over the conventional 1D beam including higher strain areas, multi-directionality, and effectively higher extracted power levels. These are actually among the most significant deficiencies by 1D beam topologies. The internal volume of the novel EH along with the surfaces of the tip mass can be utilized for electronic components and circuit boards.

Design and analysis of a vortex-induced bi-directional piezoelectric energy harvester

Vortex-induced vibrations (VIVs) in wind flows have been considered as a promising energy source for piezoelectric energy harvesting. However, a conventional VIV-based piezoelectric energy harvester can only scavenge wind energy from one direction. In this study, we propose a vortex-induced bi-directional piezoelectric energy harvester that can collect wind energy in two orthogonal directions, namely the horizontal and vertical directions. The proposed bi-directional harvester is composed of a U-shaped beam, a pair of piezoelectric patches, and a foam cylinder attached to the center of the beam. The theoretical model of the proposed harvester is established based on Euler-Bernoulli beam theory. Rayleigh oscillators are adopted to model the wake oscillation of the harvester. The proposed harvester is firstly examined under base excitations of two orthogonal directions to validate its resonant frequencies. Subsequently, the dynamic responses of the proposed harvester in vortex-induced vibrations are simulated and the corresponding experiments are carried out. The proposed harvester demonstrates the capability of harvesting wind energy from two directions of wind flow. Parametric analysis is conducted to evaluate the influence of the lengths of the side beam and main beam on the performance of the proposed harvester. The results demonstrate that shortening the side beam significantly increases the lock-in wind speed of the horizontal mode but has little impact to that of the vertical mode. On the other hand, changing the length of the main beam affects the vertical mode more than the horizontal mode. Overall, this study demonstrates that the proposed harvester can scavenge wind energy from two directions of wind flow. The geometry of the U-shaped structure can be adjusted to adapt the harvester to the wind speed in the environment.

A Wideband, Quasi-Isotropic, Kilometer-Range FM Energy Harvester for Perpetual IoT

Unlike conventional energy harvesters that are tuned to individual frequencies and are directional, the proposed wideband (23% fractional bandwidth), omnidirectional system harvests from all FM towers in vicinity. Hence, it does not require each sensor node to be carefully aligned to any one source and makes itself suited for mass-deployment applications such as precision agriculture and structural health monitoring. It harvests as much as 923 $\mu \text{W}$ on a rooftop at 1.54 km from an FM tower while retaining omnidirectionality partly thanks to the proposed antenna, which has a wider bandwidth and a higher measured gain (2.0 dBi) than the commercial reference wideband antenna. It achieves competitive efficiency (56%) and sensitivity (−17 dBm) while retaining wideband operation rather than being specifically optimized to individual frequencies. The system (fabricated on low-cost FR4) harvested outside ambient FM energy indoors at the same 1.54-km location to power a wireless sensor node without needing to shut down periodically.

Performance Analysis of SWIPT in Multi-hop Wireless Sensor Networks

Abstract This paper investigates the performance of simultaneous wireless information and power transfer (SWIPT) in multi-hop amplify-and-forward (AF) and decode-and-forward (DF) wireless sensor networks (WSNs). For SWIPT, conventional energy harvesting (EH) protocols: time switching based relaying (TSR) and power splitting based relaying (PSR) are used. Relays harvest energy from the source using TSR/PSR protocol to assist information transmission to the destination. We have considered both uniform and optimal EH ratios at the relays in each protocol. Using the convex optimization method - Lagrange multiplier and Karush-Kuhn-Tucker (KKT) conditions, we have optimized the EH ratios of a 3-hop network. The mathematical expressions for destination throughput are derived for the aforementioned protocols. Results show that the SWIPT-DF network has higher throughput than the SWIPT-AF network, PSR outdoes TSR at high signal-to-noise ratio (SNR) and optimal EH ratios will result in better network throughput.

Development of an electrostatic induction energy harvester embedded in a mouthguard

Energy harvesting from human motion is expected to the energy source for wearable devices. Although the energy density of human motion is high, the frequency of it is a few Hz, which does not match the conventional energy harvester. Due to this, the size of harvester tends to become large in order to get high output. This paper presents an electrostatic induction energy harvester which can generate high power at low frequency in order to power the mouthguard type sensor. To embed into the mouthguard type sensor, the total thickness of the harvester should be less than 0.2 mm to reduce the discomfort. Furthermore, the final goal of power generated of the harvester was set to a few tens of μW. The proposed harvester consists of electrets that can hold a quasipermanent charge on its surface, dielectric elastomers and electrodes. The mechanical energy applied by the biting force is converted to electrical energy by electrostatic induction. The parametric study of the harvester based on the equivalent circuit model was conducted to maximize the power generated. According to the calculation results, the harvester can achieve 22.7 μW with a load resistance of 570 MΩ, which met the requirements for the mouthguard type sensors. The fabrication and evaluation of the harvester based on the calculation results will be conducted in the future work.

Investigation on various beam geometries for piezoelectric energy harvester with two serially mounted piezoelectric materials

This paper presents the performance (frequency response, open-circuit voltage, optimum load, voltage and power under optimum load) of various designs of cantilever-based piezoelectric energy harvester with multiple piezoelectric materials, which is excited at the fixed end using the source of mechanical vibration and to compare the performance with single piezoelectric-mounted energy harvester. The performance of the energy harvester was determined using experimental and numerical methods. COMSOL Multiphysics 5.3a was used to obtain the numerical results of energy harvester. The results show that inverted taper in thick and width, inverted taper in thick and inverted taper in width piezoelectric energy harvesters produce 46.15%, 13.13% and 37.70% more power than the conventional rectangular piezoelectric energy harvester. The resonant frequency of inverted taper in thick and width, inverted taper in thick and inverted taper in width energy harvesters is 52.05%, 45.5% and 11.08% lower than the conventional rectangular energy harvester. It is observed that the different beam geometries with two piezoelectric material produce more power than the beams with single piezoelectric material.