Cantilever-type Energy Harvester Research Articles

Improving Energy Harvesting from Cantilever-like Structures Based on Beam Geometry

Abstract Purpose Power gain from piezoelectric harvesters depends on several parameters and one of them is to design the substructure as to increase the mechanical strain occurred in the piezoelectric material. In this study, the effect of geometrical modification of the beam on the harvested power was investigated and new geometries were offered for increased power response from cantilever type energy harvesters. Method First, the effectiveness of auxetic structures on harvested power was investigated to see the effect of the negative Poisson’s ratio on harvested power. These structures are very popular in recent years on energy harvesting applications; however, their performances were generally compared to plain structures which is not a fair comparison. Rather, in this study, their performances were compared to non-auxetic nonlinear structures as well as plain geometry. Then, three new shapes inspired by re-entrant auxetic structure were presented for increased power response, and harvested power from these structures were evaluated under different conditions. Results It was shown that the power gain from auxetic structures is very high compared to plain structures; however, this increase in power could also be achieved using a non-auxetic simple rectangular structure in some cases. On the other hand, new geometries offered in this study performed better than the auxetic and non-auxetic geometries in most cases.

Reliability Analysis of Coating Material on Polyvinylidene Fluoride Layers Used in Piezoelectric Vibration Energy Harvesting Device

Piezoelectric energy harvesters operate by converting mechanical vibrations or strains into electrical energy. From recent research, it is understood that the choice of coating material for piezoelectric energy harvesters is a critical consideration that impacts the device’s performance, durability, and compatibility with the intended application. Selecting the right coating material involves balancing the electrical, mechanical, and environmental requirements to optimize energy conversion and reliability. There are methods like the thermocycling process that can provide an accelerated ageing of the energy harvester in order to conduct a reliability assessment. The thermocycling process was carried out for 450 h on six samples of piezoelectric cantilever-type energy harvesters made of copper–nickel- and aluminum-coated PVDF (Polyvinylidene fluoride) piezoelectric material. The effect of aluminum and copper–nickel coating on PVDF piezoelectric material before and after the aging process was studied. The numerical results of the generated output voltage, surface resistance, and capacitance values measured before and after the accelerated aging process are presented in this study. This work also discusses the structure of the developed energy harvester, thermocycling experiment setup, and methodology of conducting the ageing process. It aims to provide a conclusion on the suitability of the PVDF metal coating material, the type of conductive adhesive to be used in order to seal the PVDF material to the harvester core, improvements in the structural design and selection of materials to reduce mechanical fatigue and ensure even stress distribution, and minimizing points of stress concentration, to help mitigate piezoelectric material delamination risks.

Modeling and efficiency maximization of magnetostrictive energy harvester under free vibration

Vibration energy harvesting is becoming increasingly attractive in line with the development of wireless sensor technologies. Magnetostrictive materials inherently exhibit high mechanical strength and are thus suitable for various applications and mass manufacturing of energy harvesting devices. Many studies have been conducted to increase the output power of harvesters, and some utilized analytical methods. However, the optimization methods often take into account only the resonant frequency of the system under forced vibration. These models can produce correct predictions only when steady-state harmonic excitation inputs are considered.In this study, we propose the modeling and optimization method for a cantilever-type magnetostrictive harvester under free vibration. The cantilever has a double-beam structure composed of two parallel Fe-Ga beams with pickup coils. In the modeling, the shape function of the cantilever-type magnetostrictive energy harvester was derived based on the continuity of the internal force and magnetic flux. Hamilton’s principle for an electromagnetic-mechanically coupled system was derived from the virtual work principle. The equation of motion, magnetic circuit equation, and electric circuit equation of the system were respectively derived from the corresponding Euler–Lagrange equations. The harvestable energy of the magnetostrictive energy harvester was calculated by using the symmetric property of eigenvalues. In the efficiency maximization of the harvestable energy, we found that the optimal solution differs depending on the type of given energy. The optimal parameters to maximize the energy efficiency to potential energy and kinetic energy are respectively derived in the form of algebraic solutions. Experimental validation was conducted by measuring the energy harvesting efficiency at different loads.

Constrained Parameter-Splitting Multiple-Scales Method for the Primary/Sub-Harmonic Resonance of a Cantilever-Type Vibration Energy Harvester

In this paper, the approximate analytical solutions obtained by using the constrained parameter-splitting-multiple-scales (C-PSMS) method to the primary and [Formula: see text] sub-harmonic resonances responses of a cantilever-type energy harvester are presented. The C-PSMS method combines the multiple-scales (MS) method with the harmonic balance (HB) method. Different from the erroneous stability results obtained by using the Floquet theory and the classical HB method, accurate stability results are obtained by using the C-PSMS method. It is found that the correction to the erroneous solution when the HB method and Floquet theory are adopted in the stability analysis of the primary and [Formula: see text] sub-harmonic resonances of a largely deflected cantilever-type energy harvester is necessary. On the contrary, the C-PSMS method gives much improved results compared to those obtained by using Floquet theory and HB method when the numbers of terms in each response expression are the same. The frequency response curves of the primary resonance and the [Formula: see text] sub-harmonic resonance of the harvester obtained by the C-PSMS method are compared to those obtained by the HB method and verified by those obtained by the fourth-order Runge–Kutta method. Moreover, the basin of attraction based on the fourth-order Runge–Kutta method is presented to confirm the inaccurate stability results obtained by using the HB method and Floquet theory. The convergence examinations on the stability analysis carried out by the HB method and Floquet theory show that enough terms in the response assumption are needed to achieve relatively accurate stability results when studying the stability of the primary and sub-harmonic resonances of a cantilever by using the HB method and the Floquet theory. However, the low-order C-PSMS method is able to give an accurate frequency-amplitude response and accurate stability results of the primary and sub-harmonic resonances of a largely deflected cantilever-type energy harvester.

An Electromagnetic Vibration Energy Harvester with a Tunable Mass Moment of Inertia.

This paper presents a vibration-based electromagnetic energy harvester whose resonance frequency can be adjusted to match that of the excitation. Frequency adjustment is attained by controlling a rotatable arm, with tuning masses, at the tip of a cantilever-type energy harvester, thereby changing the effective mass moment of inertia of the system. The rotatable arm is mounted on a servomotor that is autonomously controlled through a microcontroller and a photo sensor to keep the device at resonance for maximum power generation. A mathematical model is developed to predict the system response for different design parameters and to estimate the generated power. The system is investigated analytically by a distributed-parameter model to study the natural frequency variation and dynamic response. The analytical model is verified experimentally where the frequency is tuned from 8 to 10.25 Hz. A parametric study is performed to study the effect of each parameter on the system behavior.

Power Conversion Efficiency of Cantilever-Type Vibration Energy Harvesters Based on Piezoceramic Films

Piezoelectric energy harvesters are very attractive to supply devices for remote sensing applications; however, they suffer from some limitations related to their low-power generation. Recently, piezoceramic flexible patches with high power conversion efficiency have been made commercially available. These film transducers can be suitably used to realize compact low-cost vibration energy harvesters. In this article, the performance of a cantilever-type piezoceramic energy harvester (PCEH) has been thoroughly investigated. Different resonance configurations were obtained by varying the proof mass attached to the free end of the beam. The effects of the excitation features (amplitude and frequency) on generated power and energy conversion efficiency have been evaluated. Furthermore, a rectification and regulation circuit was connected downstream to the PCEH in order to achieve a dc output. In such configuration, the influences of the resonance frequency and the electrical load on the recharging and discharging times were also assessed.

Enhanced mechanical energy harvesting capability in sodium bismuth titanate based lead-free piezoelectric

The demand for high-performance lead-free piezoelectric materials towards mechanical energy harvesting has been driven by the continuous requirements of self-powered applications such as wireless sensor network systems and biomedical devices, etc. Herein, manganese-doped sodium bismuth titanate based lead-free ternary piezoelectric system 0.92(Na0.5Bi0.5)TiO3-0.04(K0.5Bi0.5)TiO3-0.04BaTiO3 (NBT-KBT-BT) was developed and the critical role of manganese on tailoring the microstructure and electrical properties was investigated. The highest piezoelectric coefficient (d33) of 140 pC/N with figure of merit (d33 × g33) of 1790 × 10−15 m2/N has been achieved. Both high open-circuit voltage of ∼12.2 V and power density of ∼0.37 μW/mm3 were obtained based on cantilever-type energy harvester. This work provides a promising paradigm for the development of high-performance mechanical energy harvesting devices by tailoring the composition of lead-free piezoelectric ceramics.

Giant current performance in lead-free piezoelectrics stem from local structural heterogeneity

Piezoelectric materials, which convert mechanical vibration energy into electric energy, are essential for vibration energy harvester. Nevertheless, the piezoelectric energy harvesting also encounters the bottleneck that piezoelectric materials generally produce only micro scale current due to its high impedance. In this work, the developed lead-free (Ba0.85Ca0.15)0.9985Sm0.001(Ti0.9Zr0.1)O3 (BCSm0.001TZ) piezoelectric ceramic possesses both high piezoelectric charge constant and low impedance, boosting its energy harvesting performance: an extremely high short-circuit current (60 µA) and large power density (2.1 µW/mm3) in a cantilever-type energy harvester, which is superior to those of other reported ones. Due to the giant current performance, the related charging speed of BCSm0.001TZ energy harvester possessed ~100% enhancement relative to the non-doped counterpart. Electrical property measurement and nanostructure observation revealed that the outstanding electromechanical properties as well as energy harvesting performances in BCSm0.001TZ ceramic benefits from a complex domain architecture and low concentration of defect, which is closely associated with the local structural heterogeneity induced by the rare-earth Sm doping. This work provides a new important paradigm for developing high-performance viable green energy materials and devices, especially for the fast recharging microelectronic storage devices in wireless sensor network.

Building high transduction coefficient BiScO3–PbTiO3 piezoceramic and its power generation characteristics

Improving the power generation characteristics of piezoelectric energy harvesters requires the construction of piezoelectric ceramics with high transduction coefficient (d33 × g33), which remains a big challenge. In this paper, guided by piezoelectric energy harvester applications, the relationship between the composition, microstructure and transduction coefficient of (1 − x)BiScO3–xPbTiO3 material is systematically studied. The results demonstrated that the sample with a composition of x = 0.64 not only has a high Curie temperature (426 °C) which is beneficial to improve the working stability of the device, but also has a very high d33 × g33 value (15,110 × 10−15 m2/N), which is significantly superior to the commercial PZT system. Excellent electrical performance can be attributed to the fact that the composition of x = 0.64 located near MPB has a very high piezoelectric charge constant (505 pC/N) at the same time with moderate dielectric constant (1907). The cantilever-type energy harvester made of optimized composition generated a high output power density of 2.93 μW/mm3 at room temperature, which charged a commercial 47 μF electrolytic capacitor to 22 V in just 220 s and lighted up 72 LEDs for 0.1~0.2 s. Further, x = 0.64 harvester exhibited a large output voltage of 2.76 V even at 350 °C, suggesting its potential use for powering high temperature wireless sensors.

Characterization of piezoelectric MEMS vibration energy harvesters using random vibration

In this study, we fabricated piezoelectric MEMS cantilever-type vibration energy harvesters employing Pb(Zr,Ti)O3 films, which were designed to exhibit a resonant frequency of around 185 Hz. The output power was investigated under random vibration whose power spectral density (PSD) was constant in the frequency regime between 150 and 220 Hz. The PSD of the output power shows that the cantilever vibrates at the resonant frequency of around 183 Hz, and that the resonant frequency decreases and the full-width at half maximum increases with increasing vibrational acceleration. In comparison with the measurement results under sinusoidal vibration, it was clarified that this phenomenon is caused by the soft spring effect due to the nonlinearity of the cantilever vibration. The power generation under random vibration is proportional to the square of the acceleration not only in the linear region but also in the nonlinear region.

Extreme value estimates using vibration energy harvesting

This paper establishes the possibility of utilizing energy harvesting from mechanical vibrations to estimate extreme value responses of the host structure and demonstrates the calibration of these estimates for excitation spectra typical to natural systems. For illustrative purposes, a cantilever type energy harvester is considered for wind excitation. The extreme value estimates are established through a Generalized Pareto Distribution (GPD). Classically well-known Kaimal and Davenport spectra for wind have been considered in this paper for comparison purposes. The applicability of GPD for processes with short-range dependence is explored in both linear and nonlinear systems. The work also demonstrates how return levels can be mapped using energy harvesting levels and indicates that vibration energy harvesting, in its own right, has the potential to be used for extreme value analysis and estimates. The work has impact on health monitoring and assessment of built infrastructure in various stages of repair or disrepair and exposed to nature throughout their lifetime.

Orientation Dependence of Power Generation on Piezoelectric Energy Harvesting Using Stretched Ferroelectric Polymer Films

The piezoelectric vibration energy harvesters were fabricated by using uniaxially stretched poly (vinylidene difluoride/trifluoroethylene) copolymer (P(VDF/TrFE)) film, and the relationship between piezoelectric power generation and molecular orientation was investigated. The molecular orientation in the stretched P(VDF/TrFE) films was evaluated with polarized Fourier transfer infrared (FT-IR) spectra measurement. In stretched films, the main-chains of P(VDF/TrFE) were aligned along the stretching direction. The piezoelectric properties and the electric power generation of stretched P(VDF/TrFE) films were strongly depended on their molecular orientation, measuring by cantilever-type energy harvesters. The piezoelectric coefficient(e) and output power observed in the energy harvester with the film stretched in the longitudinal direction of cantilever were 16.9 mC/m2 and 222 nW, respectively. These values were approximately 2.1 and 3.5 times these of the unstretched elements.

Low Frequency Piezoelectric Energy Harvesters Based on Pb-Free Thin Films

The successful utilization of Pb-free piezoelectric materials for the most useful cantilever-type energy-harvesters has been a critical interest for better performance. Here, we introduce the piezoelectric energy-harvesting characteristics of Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) thin films. The BNT-based thin films have not been reported so far for the energy-harvesting applications. 0.94BNT-0.06BT thin films, which are in the morphotropic phase boundary, showed the best dielectric and piezoelectric performance. The poling effect on the 0.94BNT-0.06BT thin films was also investigated by varying poling electric field, poling temperature and poling time. The 0.94BNT-0.06BT with poling process showed the improved piezoelectric constant of 3.13 C/m2 in the poling condition of 700 kV/cm, 60 oC and 20 min, compared to that of 3.04 C/m2 for films without poling process. XRD patterns showed the increased intensity of (002) peak indicating the increase in the volume fraction of the c-domain of BNT-BT film by applied external electric field, and thus the figure of merit (FOM) values were improved with increased poling field. As a result, the cantilever type energy harvester showed the output power of 2.22 µW from the vibration source with 42 Hz.

Action of torsion and axial moment in a new nonlinear cantilever-type vibration energy harvester

Action of torsion and axial moment in a new nonlinear cantilever-type vibration energy harvester

Development of a Cantilever-Type Electrostatic Energy Harvester and Its Charging Characteristics on a Highway Viaduct.

We have developed a micro-electro-mechanical systems (MEMS) electrostatic vibratory power generator with over 100 W of (root-mean-square) output electric power under 0.03 G (G: the acceleration of gravity) accelerations. The device is made of a silicon-on-insulator (SOI) wafer and is fabricated by silicon micromachining technology. An electret built-in potential is given to the device by electrothermal polarization in silicon oxide using potassium ions. The force factor, which is defined by a proportional coefficient of the output current with respect to the vibration velocity, is 2.34 × 10 C/m; this large value allows the developed vibration power generator to have a very high power efficiency of 80.7%. We have also demonstrated a charging experiment by using an environmental acceleration waveform with an average amplitude of about 0.03 G taken at a viaduct of a highway, and we obtained 4.8 mJ of electric energy stored in a 44 F capacitor in 90 min.

The structural origin of enhanced energy harvesting performance in piezoelectric perovskite

Energy harvesting, which can translate the wasted vibration energy into electric energy, is now a hot topic in the field of new energy, and the key point is to design high power piezoelectric ceramic according with the requirements of low-frequency vibration energy harvesting. In this study, high quality Co-modified 0.2Pb(Zn1/3Nb2/3)O3–0·8Pb(Zr0·50Ti0·50)O3 (PZN–PZT+Co) ceramics have been prepared by the two-stage method, and the energy harvesting characteristics were investigated. The results showed that the hierarchical nanodomain structure boosts the strong piezoelectric activity, leading to the high energy harvesting performance. The PZN–PZT+Co ceramic sintered at 1000°C exhibits an excellent d33×g33 value of 14080×10−15m2/N, which are much larger than that of commercial PZT-based ceramics. In the mode of the cantilever-type energy harvester, the output voltage and energy density of 33V, 4.4μW/mm3 were obtained at a low resonance frequency of 85Hz and acceleration of 10m/s2, showing potential application in piezoelectric energy harvester.

Design optimization of PVDF-based piezoelectric energy harvesters.

Energy harvesting is a promising technology that powers the electronic devices via scavenging the ambient energy. Piezoelectric energy harvesters have attracted considerable interest for their high conversion efficiency and easy fabrication in minimized sensors and transducers. To improve the output capability of energy harvesters, properties of piezoelectric materials is an influential factor, but the potential of the material is less likely to be fully exploited without an optimized configuration. In this paper, an optimization strategy for PVDF-based cantilever-type energy harvesters is proposed to achieve the highest output power density with the given frequency and acceleration of the vibration source. It is shown that the maximum power output density only depends on the maximum allowable stress of the beam and the working frequency of the device, and these two factors can be obtained by adjusting the geometry of piezoelectric layers. The strategy is validated by coupled finite-element-circuit simulation and a practical device. The fabricated device within a volume of 13.1 mm3 shows an output power of 112.8 μW which is comparable to that of the best-performing piezoceramic-based energy harvesters within the similar volume reported so far.

Fabrication of piezoelectric vibration energy harvester using coatable PolyVinylidene DiFluoride and its characterisation

A cantilever-type vibration energy harvester (VEH) made of PolyVinylidene DiFluoride (PVDF) was fabricated and characterised. PVDF is one of polymer piezoelectric material, which is more flexible than ceramic-based piezoelectric materials such as lead zirconate titanate. Since PVDF dissolves in organic solvent, it is coatable on substrate or parts, making it compatible with micro electro mechanical systems process. The fabrication process of VEH is as follows: a PVDF film (thickness: 30 µm) was coated on a phosphor bronze rectangular plate (length: 35 mm, width: 15 mm, thickness: 0.1 mm) by bar-coating method, followed by polarisation by corona discharge method. Aluminium top electrode (length: 30 mm, width: 10 mm, thickness: 0.3 μm) was deposited on the PVDF film by DC sputtering. One end of the plate was clamped by a fixture to form a cantilever, the length of which is 25 mm. Finally, a proof mass (m = 0.2 g) was attached to the free end of cantilever. Output power P at resonant frequency (= 55 Hz) was measured as a function of load resistance R, in which acceleration was set to 17 m/s2. Maximum output of 4.3 µW was achieved at R = 2.1 MΩ, which is not inferior to those of reported VEHs using ceramic piezoelectric materials.

High power density in a piezoelectric energy harvesting ceramic by optimizing the sintering temperature of nanocrystalline powders

Piezoelectric energy harvesting is the research hotspot in the field of new energy, and its core is to prepare piezoelectric ceramics with high transduction coefficient (d33×g33) and large mechanical quality factor (Qm) as well. In addition, the miniaturization of the piezoelectric energy harvester also requires the material to have a submicron fine grain structure. In this work, submicron-structured ternary system, MnO2-doped Pb(Zn1/3Nb2/3)O3-Pb(Zr0.5Ti0.5)O3 was constructed by pressureless sintering of nanocrystalline powders, which has been synthesized for the first time by high-energy ball milling route thereby evading the calcination stage. The microstructure and the energy harvesting characteristics were tailored through changing the sintering temperature. It was found that 1000°C sintered fine-grained specimen (mean grain size ∼0.95μm) showed the maximum d33×g33 value of 9627×10−15m2/N, meanwhile Qm was as large as 774, which was almost seven times larger than pure counterpart. In the mode of the cantilever-type energy harvester, a high power density of 1.5μW/mm3 were obtained for 1000°C sintered specimen at a low resonance frequency of 90Hz and acceleration of 10m/s2, which were further increased to 29.2μW/mm3 when the acceleration increased to 50m/s2, showing the potential applications as a next generation high power multilayer energy harvester.

Piezoelectric properties of Pb(Zr,Ti)O3-Pb(Ni,Nb)O3 ceramics and their application in energy harvesters

The piezoelectric properties of (1-x-y)PbZrO3-xPbTiO3-yPb(Ni1/3Nb2/3)O3 ceramics were investigated. Specimens with a large Pb(Ni1/3Nb2/3)O3 content, which have compositions close to the triple point, show small g33 and d33×g33 values because of their large εT33/ε0. These values increased with a decrease in y (amount of Pb(Ni1/3Nb2/3)O3) and the specimen with x=0.39 and y=0.29 showed the largest g33 of 43×10−3 V·m/N and d33×g33 of 25.2×10−12m2/N. Cantilever-type energy harvesters were fabricated using specimens with 0.38≤x≤0.41 and y=0.29. The output power densities of the energy harvesters were related to the d31×g31×k312 value of the piezoelectric ceramics. The energy harvester fabricated using a specimen with x=0.39 and y=0.29, which has a maximum d31×g31×k312 value, showed the maximum output power density of 1.01mW/cm3.