New simulation approach for tuneable trapezoidal and rectangular piezoelectric bimorph energy harvesters

Enhancing and optimizing the power and operating frequency range of energy harvesters (EH) are important objectives in designing an energy harvester generator. The application of trapezoidal shaped piezoelectric (PZT) cantilever is one way of increasing the harvested power of energy harvesters. Finite element software was used to simulate a tuneable trapezoidal and a rectangular PZT bimorph cantilevers with similar specifications. From the new simulation approach, an open circuit voltage obtained for different resonance frequencies for both generators. The simulation results are compared with the experimental and found to be in good agreement. The results have showed an increase in power over 19 % for the trapezoidal generator over the rectangular generator for a frequency range of 38–122 Hz. The trapezoidal harvester produced maximum power of 0.272 mW at resonance frequency of 34 Hz and acceleration of 2.5 m/s².

     

An innovative piezoelectric energy harvester using clamped–clamped beam with proof mass for WSN applications

In this paper a miniature piezoelectric energy harvester (PEH) with clamped–clamped beam and mass loading at the center is introduced which has more consistency against off-axis accelerations and more efficiency in comparison to other cantilever PEH’s. The beams consist of different layers of Si, piezoelectric, and insulators based on MEMS technology that vibrates by applying an external force to the fixed frame. Due to beam vibration, variable stress is applied to the AlN piezoelectric and a potential difference is created at the output terminals. AlN is deposited on clamped–clamped beams in such a way that produce more stress points which cause more power to be generated in comparison to other cantilever beam PEH’s with about same dimensions. A partial differential equations (PDE) describing the flexural wave propagating in the multi-morph clamped–clamped beam are solved as theoretical calculations for inherent frequency estimation and is confirmed by simulation results. The obtained inherent frequency is 42 Hz which with 1 g (g = 9.81 m/s²) acceleration produces 4 V and 80 µW maximum electrical peak power that can be used in the node of low-power consumption wireless sensor node for wireless sensor network (WSN) applications.

     

Designing and analyzing of a piezoelectric energy harvester with tunable system natural frequency for WSN and biosensing applications

A new structure for PEH with actuation piezoelectric layer for shifting natural frequency of the system is proposed. Beams are consisted to be Si and AlN piezoelectric which is deposited on fixed–fixed beams that produces high stress points and generates more power in comparison to the other cantilever beam PEHs. This PEH with ability of shifting system natural frequency is designed to the size of 0.25 cm² using optimum available space. Actuation piezoelectric layers added on both sides of the beams provides possibility of continues reducing systems natural frequency to less than 10 Hz. Accomplished simulation also confirms theoretical calculation done by PDE method to estimate natural frequency of the system. The natural frequency of the system without actuation voltage is 58 Hz that with 1 g acceleration generated 4.27 V and 71 µW electrical power which can be used in WSN and biosensing applications.

     

A new S-shaped MEMS PZT cantilever for energy harvesting from low frequency vibrations below 30 Hz

In this paper, a new S-shaped piezoelectric PZT cantilever is microfabricated for scavenging vibration energy at low frequencies (<30 Hz) and low accelerations (<0.4g). The maximum voltage and normalized power are 42 mV and 0.31 μW g ⁻², respectively, at input acceleration of 0.06g. For acceleration above 0.06g, the vibration of PZT cantilever changes from a linear oscillation to a nonlinear impact oscillation due to the displacement constraint introduced by a mechanical stopper. Based on theoretical modeling and experimental results, the frequency broadening effect of the PZT cantilever is studied with varying stop distances and input accelerations. The operation bandwidth of the piezoelectric PZT cantilever is able to extend from 3.4 to 11.1 Hz as the stop distance reduces from 1.7 to 0.7 mm for an acceleration of 0.3g, at the expense of the voltage and normalized power at resonance decreasing from 40 to 16 mV and from 17.8 to 2.8 nW g⁻², respectively.     

Design,fabrication and testing of a piezoelectric energy microgenerator

This article presents the design, fabrication and characterization of a micromachined energy harvester utilizing aluminium nitride (AlN) as a piezoelectric thin film material for energy conversion of random vibrational excitations. The harvester was designed and fabricated using silicon micromachining technology where AlN is sandwiched between two electrodes on top of a silicon cantilever beam which is terminated by a silicon seismic mass. The harvester generates electric power when subjected to mechanical vibrations. The generated electrical response of the device was experimentally evaluated at various acceleration levels. A maximum power of 34.78 μW was obtained for the device with a seismic mass of 5.6 × 5.6 mm² at an acceleration value of 2 g. Various fabricated devices were tested and evaluated in terms of the generated electrical power as well as the resonant frequency.     

Fabrication of aluminium doped zinc oxide piezoelectric thin film on a silicon substrate for piezoelectric MEMS energy harvesters

Thin film piezoelectric materials play an essential role in micro electro mechanical system (MEMS) energy harvesting due to its low power requirement and high available energy densities. Non-ferroelectric piezoelectric materials such as ZnO and AlN are highly silicon compatible making it suitable for MEMS energy harvesters in self-powered microsystems. This work primarily describe the design, simulation and fabrication of aluminium doped zinc oxide (AZO) cantilever beam deposited on <100> silicon substrate. AZO was chosen due its high piezoelectric coupling coefficient, ease of deposition and excellent bonding with silicon substrate. Doping of ZnO with Al has improved the electrical properties, conductivity and thermal stability. The proposed design operates in transversal mode (d ₃₁ mode) which was structured as a parallel plated capacitor using Si/Al/AZO/Al layers. The highlight of this work is the successful design and fabrication of Al/AZO/Al on <100> silicon as the substrate to make the device CMOS compatible for electronic functionality integration. Design and finite element modeling was conducted using COMSOL? software to estimate the resonance frequency. RF Magnetron sputtering was chosen as the deposition method for aluminium and AZO. Material characterization was performed using X-ray diffraction and field emission scanning electron microscopy to evaluate the piezoelectric qualities, surface morphology and the cross section. The fabricated energy harvester generated 1.61?V open circuit output voltage at 7.77?MHz resonance frequency. The experimental results agreed with the simulation results. The measured output voltage is sufficient for low power wireless sensor nodes as an alternative power sources to traditional chemical batteries.     

A design method for low-frequency rotational piezoelectric energy harvesting in micro applications

A rotational piezoelectric energy harvester is an electromechanical device that converts ambient mechanical rotation into electric power. The gravity-based method of using the gravity to excite the cantilever beam to deform in the vertical plane has received great attention. The harvester operates effectively at a narrow frequency band, which must be matched with the excitation frequency. For micro applications, low-frequency harvesters are often very difficult to design due to the specific limitations of the size and weight and the thickness of the piezoelectric material. Moreover, low-frequency harvesters require high precision in production and assembly, and small errors can cause large frequency error deviations. In response to this problem, this paper proposes a scheme for designing low-frequency rotational piezoelectric energy harvester, wherein the tuning is accomplished by changing the distance between the mass and the center of rotation. Furthermore, the paper establishes a theoretical model and presents a relationship for frequency adjustment. The experimental results achieved with a piezoelectric fiber composite fit the theoretical results well. The simulation and experimental results show that the resonance frequency of the harvester could be decreased by 63% when the distance between the mass and the center is five times the length of the harvester.

     

A scrape-through piezoelectric MEMS energy harvester with frequency broadband and up-conversion behaviors

We propose a MEMS piezoelectric energy harvester with a wide operating frequency range by incorporating a high-frequency piezoelectric cantilever and a metal base as the top and bottom stoppers with a low-frequency piezoelectric cantilever. Frequency up-conversion of the piezoelectric energy harvester is realized when the low-frequency piezoelectric cantilever impacts and scrapes through the high-frequency piezoelectric cantilever. For an input acceleration of 0.6?g, with top and bottom stopper distances of 0.75 and 1.1?mm, respectively, the operating frequency ranges from 33 to 43?Hz. The output voltage and power up to 95?mV and 94 nW can be achieved. Experimental results indicate that the frequency up-conversion mechanism significantly improves the effective power.     

Micromachined PZT cantilever based on SOI structure for low frequency vibration energy harvesting

A PZT piezoelectric cantilever with a micromachined Si proof mass is designed and fabricated for a low frequency vibration energy harvesting application. The SiO₂ layer in the SOI wafer promotes accurate control of the silicon thickness that is used as a supporting layer in the cantilever beam structure. The entire effective volume of the fabricated device is about 0.7690 mm³. When excited at 0.75g (g = 9.81 m/s²) acceleration amplitude at its resonant frequency of 183.8 Hz, the AC output measured across a resistive load of 16 kΩ connecting to the device in parallel has an amplitude of 101 mV. The average power and power density determined by the same measurement conditions are, respectively, 0.32 μW and 416 μW/cm³.     

一种宽频的磁式压电振动能量采集器

基于环境能量采集的压电振动能量采集器为无线传感器和微机电系统的长期供能提供了一种有效解决方案.目前研制的压电式振动能量采集器存在工作频率高,且频带窄的问题.给出了一种通过磁力的引入使其在低频下工作的、宽频的压电振动能量采集器,并搭建了测试系统对器件进行分析测试.在压电悬臂梁上放置永磁铁取代传统的质量块,同时在悬臂梁的上...     

A piezoelectric cantilever-beam energy harvester (PCEH) with a rectangular hole in the metal substrate

In order to improve the energy conversion performance of a piezoelectric cantilever-beam energy harvester (PCEH), a novel PCEH is developed and designed according to the typical PCEH. Its middle layer is a metal substrate with a rectangular hole. The mathematical model of the PCEH is analyzed, and the mathematical expressions of the eigenfrequency, the displacement of the proof mass and the output voltage and power are derived. In order to verify the validity of the model, the eigenfrequency and frequency domain are analyzed by using COMSOL and Matlab, and the influence of frequency, load resistance and acceleration on voltage and power is studied. Finally, the experimental verification was carried out to further confirm. The results show that the first-order eigenfrequency of the novel PCEH is 43.7 Hz, the optimal output power is 10.69 mW. Therefore, the novel PCEH has a lower frequency, a wider frequency band, and higher output voltage and power, and improves energy conversion performance.

     

Design and experimental study of broadband hybrid energy harvester with frequency-up conversion and nonlinear magnetic force

In this paper, a novel broadband hybrid piezoelectric and electromagnetic energy harvester using in the low frequency vibration environment is proposed, which combines nonlinear magnet force and frequency-up conversion mechanism simultaneously. Performances are studied by theoretical analysis and experimental test. Electromechanical governed equations of harvester are established, and analytical solutions of vibration response, output voltage and power are derived. Then, effects of nonlinear force, spacing between low frequency vibration beam and piezoelectric beam, load resistance and input excitation on harvester performances are investigated by experimental test. It can be concluded that the harvester can be used to work at the low-frequency environment efficiently, and the resonant frequency and harvesting bandwidth can be tuned by the nonlinear force between the magnets and the spacing between beams. Moreover, the larger the nonlinear magnetic force and the smaller the distance between two beams, the lower working frequency and the larger bandwidth. Compared with the corresponding linear apartment, output power and bandwidth of proposed harvester are improved 90% and 125% respectively.

     

微型之字形压电式能量收集器输出电压的建模和仿真

为了有效解决无线传感器网络节点的供电难题,提出之字形结构的微型压电式能量收集器。相比于传统的直悬臂梁,此结构等效加大了压电梁的长度,降低了系统的固有振动频率。建立了之字形压电梁的本构方程和受迫振动方程,推导得到其输出电压的频域表达式。基于之字形压电梁的结构,利用ANSYS软件对其进行了谐响应分析。仿真结果表明,压电梁的输出电压在各阶固有振动频率处存在极值,符合理论分析的结果;输出电压大小随压电梁长度增加而降低,随压电梁宽度增加而升高,但均为非线性关系;压电梁末端质量块的长度和厚度、基体层厚度减小时,会导致输出电压的增大。在论文中所提出的结构尺寸下,10根直梁构成的之字形结构压电梁,在其一阶固有振动频率处,输出电压可达10 V以上,符合无线传感器网络节点的实际供电需求,证明了之字形压电梁结构的有效性。     

A micro electromagnetic low level vibration energy harvester based on MEMS technology

This paper presents a micro electromagnetic energy harvester which can convert low level vibration energy to electrical power. It mainly consists of an electroplated copper planar spring, a permanent magnet and a copper planar coil with high aspect ratio. Mechanical simulation shows that the natural frequency of the magnet-spring system is 94.5 Hz. The resonant vibration amplitude of the magnet is 259.1 μm when the input vibration amplitude is 14 μm and the magnet-spring system is at resonance. Electromagnetic simulation shows that the linewidth and the turns of the coil influence the induced voltage greatly. The optimized electromagnetic vibration energy harvester can generate 0.7 μW of maximal output power with peak–peak voltage of 42.6 mV in an input vibration frequency of 94.5 Hz and input acceleration of 4.94 m/s² (this vibration is a kind of low level ambient vibration). A prototype (not optimized) has been fabricated using MEMS micromachining technology. The testing results show that the prototype can generate induced voltage (peak–peak) of 18 mV and output power of 0.61 μW for 14.9 m/s² external acceleration at its resonant frequency of 55 Hz (this vibration is not in a low ambient vibration level).     

Design, simulation and fabrication of piezoelectric micro generators for aero acoustic applications

Energy harvesters based on acoustic vibration sources can generate electrical power through piezoelectric transduction. Significant miniaturization of electro mechanical devices using MEMS fabrication technology has encouraged the creation of portable, miniature energy harvesters. A niche application is aero acoustics, where wasted, high dB and high frequency sound generated by aircrafts are transformed into useful energy. Having self-powered, miniature acoustic sensors allows noise detection monitoring systems to be self-sustaining. This paper illustrates an Aluminium doped Zinc Oxide (AZO) cantilever beam on stainless steel substrate with a top copper electrode. Design and finite element modelling of the design was conducted using Coventorware™. The AZO piezoelectric thin film was RF-sputtered on the stainless steel substrate. Characterizations were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to evaluate the piezoelectric qualities and surface morphology, respectively. Experimental measurements indicate approximately 345.4 mV AC output voltage (open circuit voltage) is produced at vibration frequencies of 30 kHz. This is in accordance with the Coventorware™ simulation results. This measured power level is sufficient to power a miniature wireless acoustic sensor nodes to monitor noise generated by aircrafts.     

A parasitic type piezoelectric actuator with an asymmetrical flexure hinge mechanism

A parasitic type actuator with an asymmetrical flexure hinge mechanism has been proposed in this study to achieve linear motion with a large working stroke. The principal output direction of the piezoelectric stack is vertical to the motion direction of the mover to obtain a large output load. The composition of the parasitic type actuator and working process are introduced and parasitic motion is explained. Finite element method has been applied to analyze the parasitic motion of the proposed asymmetrical flexure hinge mechanism. Moreover, an experiment system of the parasitic type actuator is set up, and experiments show that the positioning resolution of the actuator is around 0.1 μm; the maximum motion speed could achieve to 2850 μm/s when the input frequency f = 500 Hz and the input voltage U_e = 100 V; the maximum output force F_g is up to 750 g when the input frequency f = 1 Hz and the input voltage U_e = 100 V. This study indicates that the asymmetrical flexure hinge mechanism could achieve parasitic motion for the design and application of piezoelectric actuators with a large working stroke.

     

A resonant microstructure tunability analysis for an out-of-plane capacitive detection MEMS magnetometer

In this paper, the method of tuning the resonant frequency of a micro-resonant clamped–clamped beam has been successfully applied to a MEMS capacitive magnetometer. The resonant structure frequency, which presents the vital component of the sensor, was tuned by applying a bias voltage between the interdigitated capacitive comb-fingers in order to control its spring constant. It has been proved that an applied DC voltage increases the structure stiffness and as a result the resonance frequency to higher values, especially for low motion magnitude. The shifting causes were described through an accurate analytic analysis using the generated electrostatic force between movable and fixed combs, and thereafter have been proved by characterization. The measured resonance frequency of the clamped–clamped beam structure was changed by up to 38 % from the original value (around 18.2 kHz) when a bias voltage of 52 V was applied. Tuning the resonant frequency of the resonating structure has many advantages for the magnetometer since it can serve as a feedback mechanism for error compensation.

     

Comparative study of conventional and magnetically coupled piezoelectric energy harvester to optimize output voltage and bandwidth

Energy harvesting has experienced significant attention from researchers globally. This is due to the quest to power remote sensors and portable devices with power requirements of tens to hundreds of μW. Hence, ambient vibration energy has the potential to provide such power demands. Thus, cantilever beams with piezoelectric materials have been utilized to transduce mechanical energy in vibrating bodies to electrical energy. However, the challenge is to develop energy harvesters that can harvest sufficient amount of energy needed to power wireless sensor nodes at wide frequency bandwidth. In this article, piezoelectric energy harvester (PEH) beams with coupled magnets are proposed to address this issue. With macro fiber composite as the piezoelectric transducer, mathematical models of different system configurations having magnetic couplings are derived based on the continuum based model. Simulations of the system dynamics are done using numerical integration technique in MATLAB software to study the influence of magnetic interactions in generating power and frequency bandwidth due to base excitations at low frequency range. Experimental results comparing conventional system and the proposed piezoelectric beam configurations with coupled magnets are also presented. Finally, the optimal beam separation distance between the magnetic oscillator and PEH is presented in this work.

     

Design and fabrication of PZT microcantilevers with freestanding structure

For developing freestanding piezoelectric microcantilevers with low resonant frequency, some critical mechanical considerations, especially cantilever bending, were given in this study. Two strategies, using piezoelectric thick films and adding a stress compensation layer, were calculationally analyzed for mitigating the cantilever bending, and then was applied for the fabrication of PZT freestanding microcantilevers. (100) oriented PZT thick films with the thickness of 6.93 μm were grown on the Pt/SiO₂/Si substrate by chemical solution deposition (CSD), and the SiO₂ layer with the thickness of 1.0 μm was kept under the PZT layer as a stress compensation layer of the freestanding microcantilevers. The freestanding microcantilevers fabricated with the micromachining process possessed the resonant frequency of 466.1 Hz, and demonstrated no obvious cantilever bending.     

双晶压电悬臂梁俘能器的建模与仿真

针对双晶片悬臂梁式压电俘能器的优化问题,考虑悬臂梁末端位移与质量块质心位移的差异,对Roundy数学模型进行了修正.通过ANSYS有限元软件对俘能器建模并进行模态分析和谐响应分析,当质量块长度逐渐变大时,修正后数学模型对俘能器一阶固有频率和输出电压有更好的预测精度.研究了质量块形状和负载对俘能器输出特性的影响规律,发现在质量块质量不变时,提高质量块的质心高度能提高俘能器的发电能力,对俘能器的结构优化具有借鉴意义.