Conventional Piezoelectric Energy Harvester Research Articles

Modeling and Experimental Study of Vibration Energy Harvester with Triple-Frequency-Up Voltage Output by Vibration Mode Switching.

Conventional wireless sensors rely on chemical batteries. Replacing or charging their batteries is tedious and costly in some situations. As usable kinetic energy exists in the environment, harvesting vibration energy and converting it into electrical energy has become a hotspot. However, the power output capability of a conventional piezoelectric energy harvester (PEH) is limited by its low operational frequency. This paper presents a new mechanism for achieving continuous triple-frequency-up voltage output in a PEH. The proposed system consists of a slender piezoelectric cantilever with two short cantilever-based stoppers. The piezoelectric cantilever undergoes a pure bending mode without contacting the stoppers. In addition, the beam switches into a new vibration mode by contacting the stoppers. The vibration modes switching yields reverses the signs of voltage outputs, inducing triple-frequency-up voltage output. Analytical and experimental investigations are presented, and it is shown that a significant triple-frequency up-conversion of the voltage output can be obtained over a wide frequency range. A peak power output of 3.03 mW was obtained. The proposed energy harvester can support a wireless sensor node.

Fractal-inspired multifrequency piezoelectric energy harvesters

In this Letter, we propose fractal-based piezoelectric energy harvesters (PEHs) for broadband energy scavenging. The introduction of fractal topology into transducers significantly alleviates the inherent limitation of a narrow working bandwidth in commonly used cantilever PEHs. We conduct a finite element analysis and experiments to exploit the performance of fractal cantilever PEHs with different iteration times. Our findings reveal that the higher-order fractal structures generate an increased number of eigenfrequencies as well as modal patterns within a certain range of working bandwidth (i.e., <50 Hz). Experimental results indicate that the efficient energy harvesting bandwidth of the fractal PEHs of iterative levels 1 and 2 is 2.05 and 2.15 times, respectively, larger than the conventional PEHs (i.e., level 0). In addition, the harvested voltage and power of fractal PEHs can be enhanced by attaching a proof mass to compensate for the energy loss in producing iterations. This method exhibits superiority over capturing energy in low-frequency vibration environments, such as wave energy and human movement energy.

A novel wake-excited magnetically coupled underwater piezoelectric energy harvester

This paper proposes a wake-excited magnetically coupled piezoelectric energy harvester (WMPEH) to realize the self-powered function of microelectronic devices in a fluid environment. The WMPEH consists of a fixed column, a vibrating column, magnets, and a piezoelectric composite beam. A series of water tunnel experiments are conducted to prove the usefulness of wake excitation and magnetic coupling, and how it positively or negatively affects the harvester's efficacy. Different fixed and vibrating column diameters and the distance between the two columns affect the performance of the WMPEH. The influence of the wake excitation force generated by the fixed columns with diameters of 5 mm, 10 mm and 15 mm on the vibrating column is analyzed respectively in the experiment. The vibrating column diameter is D, and four different distances are considered, namely 2D, 3D, 4D, and 5D. The results show that the maximum output voltage of WMPEH is increased by 1.96 and 1.34 times, respectively, compared with that of magnetically coupled piezoelectric energy harvester (MPEH) and conventional piezoelectric energy harvester (PEH). Furthermore, increasing the fixed column diameter leads to a decrease in the output voltage of WMPEH in the case of the same vibrating column diameter. Increasing the diameter and mass of the vibrating column for a specific fixed column diameter can enhance the harvester's performance. The maximum output voltage density of the WMPEH is 75.56 V/cm3 when the vibrating column diameter, the fixed column diameter and the distance between the two columns are 20 mm, 5 mm, and 2D, respectively. This proposed design can provide the groundwork to promote the performance of the conventional PEH, further enabling the realization of underwater self-powered systems.

A mosquito-inspired self-adaptive energy harvester for multi-directional vibrations

In this paper, a new concept of direction self-adaptive energy harvesting is put forward for multi-directional vibrations, and a novel direction self-adaptive piezoelectric energy harvester (DSPEH) is explored by introducing a self-adaptive rotation mechanism into the cantilever beam inspired by mosquito wings to validate the new concept. Different from the conventional piezoelectric energy harvester (PEH), the proposed DSPEH has an additional rotation degree of freedom obtained by the rotation unit to realize self-adaptive rotation passively without any manual intervention or power supply. Working principle and theoretical analysis of the proposed DSPEH are conducted and a prototype is fabricated to demonstrate the concept. The energy harvesting performance of the proposed DSPEH is investigated under sweeping frequency and harmonic excitation, and the key parameters affecting the energy harvesting efficiency, such as damping parameters and mass eccentricity coefficient, are analyzed in detail. Simulation and experimental results are in good agreement. Owning to the characteristic of self-adaptive rotation, the most attractive feature of the proposed DSPEH is not simply the ability to realize multi-directional vibration energy harvesting, but the capability of achieving stable and high voltage output levels in multi directions, which is fundamentally distinct from the conventional PEH and other multi-directional energy harvesters. The average output voltage is 30% higher than that of the conventional PEH. Compared with other multi-directional energy harvesters, the proposed DSPEH also has higher energy harvesting efficiency.

A hybrid piezoelectric-electromagnetic energy harvester from vortex-induced vibrations in fluid-flow; the influence of boundary condition in tuning the harvester

In this paper, a hybrid piezoelectric-electromagnetic energy harvester is proposed to harvest energy from fluid flow around a bluff-body using vortex-induced vibration (VIV). The hybrid piezoelectric-electromagnetic harvester combines the two electromechanical transduction mechanisms through the bluff body excited by VIV: piezoelectric macro-fiber composite and an electromagnetic system. The piezoelectric composite is glued to a substrate beam to convert mechanical strain into electricity. A novel implementation of an internal electromagnetic harvester where the change in magnetic flux inside a coiled holder transduces change in magnetic flux to electricity. An analytical model is used to investigate the narrowband synchronization properties in VIV for different submerged conditions that can be tuned for vibration-based energy harvesting. Under synchronization, the structural natural frequency is the same as the vortex shedding frequency, which leads to the generation of a higher output voltage during frequency matching. Therefore, the effects of added mass and boundary conditions are validated experimentally in water flow to tune the submerged energy harvester with the new hydrodynamic properties to increase the harvesting performance. The results show that fully submerging the energy harvester increases the overall added mass, whilst confining it inside a submerged pipe adds stiffness and damping. This means the overall energy harvesting performance decreases with submerging depth and proximity to the boundary. The maximum voltage output occurs within the synchronization region, with piezoelectric output performing best when partially submerged while the electromagnetic oscillator performs best when fully submerged. Implementing a hybrid piezoelectric-electromagnetic energy harvesting system increased the voltage output by up to 23% compared to a conventional piezoelectric energy harvester.

Numerical analysis and experiments of an underwater magnetic nonlinear energy harvester based on vortex-induced vibration

This paper designs an underwater magnetic nonlinear piezoelectric energy harvester (PEH) based on the principle of vortex-induced vibration (VIV). The equivalent stiffness of the magnetic nonlinear PEH is significantly changed by varying the relative position of the magnet. It is observed that the proposed PEH displays hardening behavior and softening behavior due to the impact of magnetic forces, which greatly increase the performance of the magnetic nonlinear PEH. The analysis of the results shows that the open-circuit voltage (VRMS) of the hard stiffness system is increased from 9.43 V to 10.31 V, the frequency band is widened by 36.8%, and the efficiency is higher at high flow rates. The initial vibration velocity of the soft stiffness system is reduced. When the water velocity is 0.2 m/s, its VRMS is 10 times that of the classical configuration. Both numerical simulations and experiments prove that the soft stiffness system is more suitable for applications in low-speed water environments. This proposed design can provide the groundwork to promote the performance of the conventional PEH, further enabling to realize self-powered systems.

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.

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.

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.

Asymmetric SECE Piezoelectric Energy Harvester Under Weak Excitation

Piezoelectric energy harvesters (PEHs) are widely used to convert energy from a piezoelectric transducer into a stable DC form, which enables low-power IoT devices to have an unlimited operating life without using batteries. Under weak excitation conditions, however, the power-extraction efficiency of conventional PEHs is too low to provide power even to low-power IoT devices that requires low operation voltages less than 2 V. This paper proposes an asymmetric synchronous electric charge extraction (ASECE) scheme that improves the extraction efficiency of PEHs at low output voltages under weak excitation. The proposed ASECE is implemented using 0.18 μm CMOS technology. The figure-of-merits (FOMs) of the proposed ASECE while operating under 2 V of output voltage are 7.14 and 6.24 at weak and strong excitations, respectively. The maximum FOM for various different excitation levels is observed to be as high as 7.7. The proposed ASECE is superior to prior art with respect to FOM, by at least 1.15×, 1.63×, and 2.21× under 2 V, 1 V, and 0.5 V outputs, respectively, under strong excitation.

Performance enhancement of MEMS-guided four beam piezoelectric transducers for energy harvesting and acceleration sensing

In the present paper, guided four beam (G4B) piezoelectric transducers with enhanced sensitivities have been designed. Based on the suggested G4B structures, piezoelectric energy harvesters (PEHs) and acceleration transducers with higher voltages than their previously reported counterparts and with lower displacements than the single-cantilever PEHs (SC-PEHs) have been proposed. We have shown that it is possible to arrive at much more output voltages in comparison with the conventional PEHs by redesigning the structure of the cantilever beams. In 1 g acceleration, the maximum output voltage obtained from the proposed PEHs has been 13.49 V whereas the output voltage for the conventional G4B-PEH is 2.87 V. This paper for the first time proposes G4B-PEHs with smaller displacements and larger voltages compared to a SC-PEH. The same G4B framework has been studied as a piezoelectric acceleration transducer. The effect of piezoelectric length on the extracted voltage in both unimorph and bimorph cantilevers has been discussed and the optimized length has been calculated. An analytical method is developed to compute the resonance frequencies of different beam shapes whose results are in a good agreement with numerical simulations.

Improving efficiency of piezoelectric based energy harvesting from human motions using double pendulum system

Harvesting electrical energy from various human motions using piezoelectric energy harvesters (PEH) is gaining research attention in recent years. The energy harvested could potentially power hand held electronic devices and medical devices without the need of external power source for recharging batteries. In this study, an attempt is made to improve the efficiency of PEH to harvest energy from human motions by adopting a double pendulum system coupled with magnetic force interactions. For the purpose of comparison, three configurations of PEH which includes the conventional PEH with cantilever beam (PEHCB), the PEH with single pendulum system (PEHSP) and the PEH with double pendulum system (PEHDP) are experimentally studied. Excitations by both mechanical shaker and major human body parts during walking and jogging motions are investigated. The performance of each configuration, in terms of voltage and power produced as well as the idle time between each cycle, are analysed, compared and discussed. ANSYS© software is used to analyse the proposed model and MATLAB© software is used to calculate the output power. The results demonstrate that, with the use of the proposed double pendulum system, multiple impacts in each motion cycle is generated, thus producing higher voltage and power as compared to the conventional PEHCB. The idle time between each motion cycle is also effectively reduced. The efficiency of the PEH is thus significantly increased.

Multi-branch sandwich piezoelectric energy harvester: mathematical modeling and validation

Energy harvesting from ambient environment has attracted intensive attention over the years for powering low-power autonomous electronic devices. A conventional piezoelectric energy harvester (CPEH) can hardly meet the requirements of effective energy harvesting from wideband, low frequency and low amplitude vibration sources due to its simple substrate and single resonant peak response. Using sandwich structure comprised of a soft-core layer and two thin skins can drastically reduce the natural frequency and increase voltage output of the harvester. The stiffness of sandwich harvester and consequently its resonant frequency can be tuned more flexibly than the CPEH by choosing different materials and adjusting the geometric dimensions of the core and skins. In this paper, a novel multi-branch sandwich piezoelectric energy harvester (MSPEH) is proposed to harvest energy from wideband, low frequency and low amplitude vibration sources. The proposed harvester comprises of a main sandwich beam as substrate with a patch of piezoelectric layer bonded over it. Multiple inner single branches with tip masses are connected to the main substrate to generate multiple resonant peaks and tune the range of the interested frequency. Firstly, a mathematical model of the proposed harvester is presented, and the electromechanical coupling equations are obtained. Subsequently, a prototype of MSPEH with two inner single branches is fabricated and tested under harmonic base excitation to study its performance. When tested at a low harmonic excitation of 0.02 g, the harvester generates 2.48 V, 6.21 V and 1.55 V at three resonant frequencies of 18.18 Hz, 24.74 Hz and 28.12 Hz, respectively. Finally, the accuracy of derived mathematical model is verified by comparing with the predictions from finite element simulation and experimental results. The novel MSPEH offers excellent design flexibility to adjust resonant frequencies by choosing inner single branches and tip masses and thus it has potential to generate sufficient power output from wideband, low frequency and low amplitude vibration sources.

A broadband E-shaped piezoelectric energy harvester based on vortex-shedding induced vibration from low velocity liquid flow

This letter presents an E-shaped piezoelectric energy harvester (PEH) based on vortex-shedding induced vibration (VSIV) for achieving broadband and enhanced energy capture from the liquid flow with low velocities. The PEH is realized by introducing two symmetrical vice piezoelectric beams to a traditional structure consisting of a drive sheet and a main piezoelectric beam. By changing the mass blocks on the sheet and vice beams, the first two order resonance frequencies can be tuned to be close enough to obtain a wide bidirectional tunable operating bandwidth. Experimental results demonstrate that the proposed harvester can adapt to a wider fluid velocity spectrum and bring out higher output performances than the conventional PEH. Under the excitation of vortexes from the liquid flow with low velocities (0.15m/s–0.7m/s), the maximum increase in power, efficiency and velocity spectrum over 20μW can be 70%, 326% and 60%, respectively, compared to its conventional counterpart. The total size of the E-shaped harvester is L×W×H = 90 mm×70 mm×5 mm.

Sandwich piezoelectric energy harvester: Analytical modeling and experimental validation

Piezoelectric energy harvesting from ambient vibration sources has great potential for powering microelectronic devices and wireless sensors. Almost all the conventional piezoelectric energy harvesters (CPEHs) in the literature have been designed with a single metallic layer as substrate along with the piezoelectric material bonded over it. In this work, a novel sandwich structure is used as substrate for designing harvester. The substrate structure comprises of a soft-core material sandwiched between metallic layers. The proposed sandwich piezoelectric energy harvester (SPEH) has lower resonant frequency and generates higher voltage output than the CPEH with the same geometrical dimension. Furthermore, the SPEH offers high design flexibility in terms of tuning the resonant frequency through selection of materials and geometric parameters for the core and metal layers. The mathematical formulation of a generalized electromechanical model of the SPEH is developed using the Lagrange approach. The natural frequencies, displacement and voltage frequency response functions of the harvester are obtained analytically. A single-degree-of-freedom model for the SPEH is also derived. Subsequently, the analytical modeling is validated by finite element simulations and experimental results. When excited at 0.1 g, the SPEH generates 18.8% more voltage output at resonance as compared with a CPEH with the same geometrical dimension and tip mass accompanied by 24% reduction in resonant frequency. At 30 Hz resonance frequency, CPEH generates open-circuit voltage 17.6 V using 15 g of tip mass whereas SPEH uses only 8.2 g of tip mass to generate 16.6 V. SPEH generates 130.8 μW, 426.6 μW and 1158.0 μW at base accelerations 0.05 g, 0.1 g and 0.2 g with optimal resistance, respectively. Finally, the influence of geometric and material properties of core and metallic layers on the performance of SPEH are analyzed comprehensively. The proposed novel SPEH together with its analytical modeling is intended to serve as a basis for future sandwich harvester designs.

An electromechanical finite element model for new CNTs-reinforced harvesters subjected to harmonic and random base excitations

Conventional piezoelectric energy harvesters are cantilever beams made of homogenous substructure and piezoelectric layers that produce alternating voltage due to their vibrations. Recently, a class of new emerging composite materials, the carbon nanotubes (CNTs)-reinforced composite, has been proposed making use of CNTs as the reinforcements in a functionally graded (FG) pattern. Harvesters made of functionally graded CNTs-reinforced substructure materials have not been studied in the energy harvesting literature, yet. Thus, in this study, functionally graded piezoelectric CNTs-reinforced harvesters as new energy harvesters subjected to harmonic and random vibrations are analyzed. The harvester is assumed to be comprised of piezoelectric and FG-CNTs-reinforced substructure layers. Five types of CNTs distributions through the substructure thickness direction are considered. The generalized Hamilton’s principle for electromechanical materials based on Euler–Bernoulli beam assumption is adopted in the derivation of governing equations. The finite element formulation of the equations is also presented. Time and frequency domain analyses of the finite element equations are performed. The output power from the CNTs-reinforced harvesters subjected to random and harmonic base excitations is calculated. The harvested energy of the CNTs-reinforced harvesters is compared, and it is concluded that the CNTs distribution has a significant effect on the deflection, produced voltage and harvested power.

A U-shaped multi-modal bi-directional piezoelectric energy harvester

A conventional piezoelectric energy harvester suffers from narrow bandwidth and uni-directional harvesting. This paper presents a U-shaped multi-modal bi-directional piezoelectric energy harvester to overcome the above issues. The U-shaped structure, composed of a main beam and two identical side beams, can be fabricated by bending a beam into a U shape with both ends clamped. The theoretical model of the U-shaped piezoelectric energy harvester is developed and validated with experimental results. This U-shaped piezoelectric energy harvester demonstrates the capability of harvesting vibration energy in both the vertical and horizontal directions, which are the transverse direction of the main beam and that of the side beams, respectively. Parametric studies are conducted to investigate the influence of the aspect ratio of the U-shaped structure on the modal frequencies and voltage output. It is shown that the first two horizontal modal frequencies can be tuned close to each other by shortening the side beams or extending the main beam. The ratio between the horizontal and vertical modal frequencies can also be adjusted to fit the vibration sources by altering the side beams or the main beam.

Nonlinear Piezoelectric Energy Harvester with Ball Tip Mass

In this study, a nonlinear piezoelectric energy harvester (PEH) with a ball tip mass was designed and fabricated for broadband energy harvesting. The proposed nonlinear PEH exhibits two resonant frequencies (5 and 15 Hz) and can harvest a considerable amount of electrical energy, whereas a conventional PEH with a rigid tip mass only exhibits one (15 Hz). The minimum acceleration that can induce nonlinearity in the proposed PEH was determined to be 3 m s–2. In order to maximize the electrical output of the proposed PEH, 0.1 mm was selected as the optimal vibration amplitude of the ball among three options (0.1, 0.5, and 1.0 mm). The maximum output power of the proposed PEH was measured as 13.5 mW at 15 Hz and at a load resistance of 30 kΩ, which is the matching load resistance calculated and verified with the experimental result. The output power of the proposed PEH was measured to be 1.8 mW at 5 Hz and 45 kΩ, whereas that of the conventional PEH at 5 Hz was 0.03 mW, implying that the proposed PEH possesses one additional resonant frequency over the conventional PEH. In addition, the proposed PEH performs significantly better than the conventional PEH in terms of broadband energy harvesting. At a power level of 100 μW, the proposed PEH at 3 m s–2 provides a bandwidth of 20 Hz, which is more than 133% wider than the 15 Hz provided by the conventional PEH. By utilizing the nonlinearity with a ball tip mass, the PEH vibration is capable of harvesting considerable electrical energy from more than two resonant frequencies.

Scavenging energy from ultra-low frequency mechanical excitations through a bi-directional hybrid energy harvester

A bi-directional hybrid energy harvester (HEH) is presented in this paper to scavenge energy from ultra-low frequency mechanical excitations. The proposed HEH consists of two piezoelectric cantilever beams, a suspended magnet, and a set of coil. Specifically, the two piezoelectric beams work as a conventional piezoelectric energy harvester (PEH), whereas the suspended magnet and the coil constitute an electromagnetic energy harvester (EMEH). The two energy-harvesting units (PEH and EMEH), which are sensitive to excitations coming from different directions, are coupled by the suspended magnet, through which the PEH and EMEH are coherently integrated. The suspended magnet not only induces the coil to generate electricity but also actuates the PEH to work, achieving the simultaneous energy extraction from one excitation through two conversion mechanisms. The dynamic model of the HEH is established. Theoretical simulations and experimental measurements under the sinusoidal excitation indicate that the nonlinear interaction between the PEH and EMEH actuates the two energy-harvesting units to oscillate either chaotically or periodically with large amplitudes, which can improve both the PEH and the EMEH power outputs at ultra-low frequencies, not only expanding the HEH working bandwidth but also making the HEH suitable for ultra-low frequency energy harvesting. Moreover, the hand-shaking test shows that the HEH has a better charging performance than an individual energy-harvesting unit for charging a capacitor. Under the hand-shaking induced excitation, the fabricated HEH prototype can also light up tens of light-emitting diodes (LEDs), demonstrating its potential application for powering some portable electronics.

Electromechanical modeling and power performance analysis of a piezoelectric energy harvester having an attached mass and a segmented piezoelectric layer

Conventional vibration-based piezoelectric energy harvesters (PEHs) have advantages including the ubiquity of their energy source and their ease of manufacturing. However, they have a critical disadvantage as well: they can produce a reasonable amount of power only if the excitation frequency is concentrated near a natural frequency of the PEH. Because the excitation frequency is often spread and/or variable, it is very difficult to successfully design a conventional PEH. In this paper, we propose a new cantilevered PEH whose design includes an attached mass and a segmented piezoelectric layer. By choosing a proper size and location for the attached mass, the gap between the first and second natural frequencies of the PEH can be decreased in order to broaden the effective excitation frequency range and thus to allow reasonable power generation. Especially, the output power performance improves significantly around the second natural frequency of the PEH since the voltage cancellation effect can be made very weak by segmenting the piezoelectric layer at an appropriate location. To investigate the power performance of the new PEH, herein a reduced-order electromechanical analysis model is proposed and the accuracy of this model is validated experimentally. The effects of variable load resistance and piezoelectric layer segmentation location upon the power performance of the new PEH are investigated by means of the reduced-order analysis model.