碰撞式微型压电风能采集器实验研究_英文_贺学锋

第11卷第3期2013年5月纳米技术与精密工程Nanotechnology and Precision Engineering Vol．11No．3May 2013Experiment Studies on Impact-Based Piezoelectric Wind Energy HarvesterHe Xuefeng 1，2，Gao Jun 1，2，Xia Huilu 1（1．Key Laboratory of Optoelectronic Technology and Systems of Ministry of Education ，Chongqing University ，Chongqing 400044，China ；2．Microsystem Research Center ，Chongqing University ，Chongqing 400044，China ）Abstract ：To improve the output performances of wind energy harvesters under low speed wind ，a piezoe-lectric wind energy harvester based on impact was proposed．The harvester consists of a cylindrical bluff body ，a hinged-splitter plate ，a piezoelectric composite cantilever beam and a fixture．By utilizing the im-pact between the splitter plate hinged on the cylindrical bluff body and the piezoelectric cantilever ，the working wind speed is effectively decreased．The prototype of the wind energy harvester was assembled and measured to evaluate the performances．Experimental results showed that the initial distance between the splitter plate and the cantilever beam significantly affected the working wind speed and the output power of the harvester．The proof mass on the piezoelectric cantilever can increase the output power．The measured maximum output power of the wind energy harvester was 64μW for a matched resistor of 200k Ωwhen wind speed was 15m /s．Keywords ：wind-induced-vibration ；impact ；piezoelectricity ；wind energy harvester碰撞式微型压电风能采集器实验研究贺学锋1，2，高军1，2，夏辉露1（1．重庆大学光电技术及系统教育部重点实验室，重庆400044；2．重庆大学微系统研究中心，重庆400044）收稿日期：2013-03-04．基金项目：国家自然科学基金资助项目（61076106）；高等学校科技创新工程重大项目培育资金资助项目（708072）．作者简介：贺学锋（1970—），男，教授，博士，hexuefeng@cqu．edu．cn．通讯作者：高军，jungao@cqu．edu．cn．摘要：为提高基于风致振动机理的微型风能采集器在低风速下的输出功率，设计了一种新型的碰撞式微型压电风能采集器．采集器主要由圆柱形钝体、铰接分隔板、压电悬臂梁和支架组成．通过铰接分隔板和压电悬臂梁的碰撞有效降低了采集器的工作风速．加工制作了采集器的原理样机并在小型风洞内进行了实验测量．通过实验发现分隔板与压电片横向间距对采集器的工作风速和输出功率有很大的影响．压电悬臂梁自由端添加质量块可以提高输出功率．风速15m /s 、外接200k Ω优化负载时，采集器最大输出功率为64μW．关键词：风致振动；碰撞；压电；风能采集器中图分类号：TM387文献标志码：A文章编号：1672-6030（2013）03-0191-05With the development of MEMS technology and ul-tra-low power consumption integration circuits （ICs ），self-powered sensor nodes of wireless sensor networks （WSNs ）attract more and more attention ［1］．Energy har-vesters which convert the ambient physical energy into electrical energy have been studied extensively．Due to the ubiquitous wind energy in natural environment ，wind energy harvesters have broad application prospects．Com-·192·纳米技术与精密工程第11卷第3期pared with traditional electromagnetic wind harvesters，piezoelectric wind energy harvesters，which are of high energy density，simple structure and easy to be miniatur-ized，are more capable of producing higher power output with the same volume［1-8］．To apply wind energy harvesters to power wireless sensing nodes，the working wind speed need to be de-creased and the output power need to be improved．Akaydin et al［9］placed a flexible polyvinylidene fluoride （PVDF）beam directly in the wake of a cylindrical bluff body，and only acquired4μW maximum output power when wind speed was6.8m/s．Pobering et al［10］fixed piezoelectric cantilever beams directly behind the bluff bodies，and the power output was54μW under wind speed of45m/s．This paper proposed a wind energy harvester based on impact，which was inspired by researches on inhibiting wind-induced-vibration of a cylinder by a hinged-splitter plate［11-12］．By utilizing the impacts between a hinged-splitter plate and a piezoelectric composite beam，the har-vester effectively increased the output power under low speed wind．A prototype of the harvester was fabricated and experimentally studied．1Impact-based wind energy harvesterBluff bodies with a hinged-splitter plate were exten-sively studied for inhibiting fluid induced vibration．Shukla et al［11］studied the performances of a hinged-splitter plate in the wake of a circular cylinder in a water tunnel，and found a periodic oscillation of the plate when the ratio of plate length to cylinder diameter is not more than3．Sudhakar and Vengadesan［12］analyzed this prob-lem by CFD simulation，used immersed boundary method to solve the Navier-Stokes equations，and presented three kinds of vortex shedding patterns，which were caused by the interaction of the wake shedding from the cylinder and the plate．Gu et al［13］tested several hinged plate with dif-ferent lengths in a wind tunnel and studied the pressure distribution，fluctuating force and frequency characteris-tics．A periodic oscillation was also observed in their ex-periment．To harvest the broadband and low frequency vibra-tion energy，impact-based vibration energy harvesters with different structures were proposed．Umeda et al［14］studied an impact-based piezoelectric energy harvester，using a ball to impact a copper plate with bonded piezoe-lectric sheet．They studied the conversion efficiency of mechanical energy to electrical energy and proposed that the conversion efficiency would be improved if the ball and the plate did not separate from each other after the collision．Renaud et al［15］proposed a harvester，which was composed of a channel with a sliding object and two cantilevers fixed on each side of the channel，to harvest the energy from the motion of human limbs．Gu［16］de-signed a harvester which can harvest low-frequency vibra-tion energy by utlizing the impacts between a low frequen-cy beam and a high frequency beam．In this paper，an impact-based wind energy harvest-er shown in Fig．1is proposed．It mainly consists of four parts：a cylindrical bluff body，a hinged-splitter plate，a piezoelectric cantilever beam and a fixture．The bluff body is fixed on the fixture．The splitter plate is hinged on the bluff body and it can swing around the hinge point．When the air passes through，the splitter plate vi-brates periodically and there will be collisions when the vibration amplitude exceeds the gap between the plate and the cantilever．The collision changes the stress in the pie-zoelectric layer of the cantilever，and the stress gives rise to potential difference between the top and bottom elec-trodes of the piezoelectriclayer．Fig．1Schematic of an impact-based wind en-ergy harvesterThe above harvester has two states depending on the wind speed．Firstly，the vibration amplitude of the plate is small and there is no impact under low speed wind load．The deformation of the piezoelectric beam is very small and the output voltage is very low in this case．Sec-ondly，as the speed becomes higher，the vibration ampli-tude of the plate is large enough to exceed the gap be-tween the splitter plate and the beam．At that moment，the cantilever beam is impacted by the splitter plate and produces large deformation，which generates a voltage be-2013年5月贺学锋等：碰撞式微型压电风能采集器实验研究（英文）·193·tween the top electrode and bottom electrode of the piezo-electric layer．The plate and the beam are separated from each other after the impact．After that ，the cantilever beam vibrates freely and performs a free vibration until a next impact occurs．2Prototype assembly and experimental setupTo study the performances of the harvester ，a proto-type （shown in Fig．2）was assembled with a cylindrical polycarbonate （PC ）as bluff body （with the diameter of 20mm ）and an iron plate as splitter plate （40mm ˑ30mm ˑ0.35mm ）．They were stuck together by a plastic sheet which acted as a hinge．The hinge length was 1mm．A T215-H4-203X piezoelectric bimorph from piezo systems was used as the cantilever．The piezoelectric bi-morph included a 102μm-thick metal shim sandwichedbetween two layers of 139μm-thick PZT-5H ，and the di-mensions were 31.8mm ˑ6.4mm ˑ0.38mm．The can-tilever was clamped by printed circuit board （PCB ）which was wired for electric power output．The experi-mental setup is shown in Fig．3．There are mainly four parts ：wind tunnel ，speed controller ，oscilloscope （Wave-Surf 422，LeCroy Corporation ）and mounted harvester．The wind speed was measured by an anemometer （CTV100，KIMO Instruments ）．The root mean square （RMS ）open circuit voltage was measured by the oscillo-scope．Fig．2Prototype of wind energyharvesterFig．3Experimental setup3Experimental results and discussionThe prototype of the impact-based wind energy har-vester was fixed and tested in the wind tunnel．Fig．4is the open circuit voltage waveforms of the harvester at wind speed of 12m /s．Fig．4（a ）is the waveform of the harvester without a proof mass at the free end of the pie-zoelectric cantilever beam．It can be seen that there was a large voltage pulse in each cycle．The pulse came from the large deformation caused by the impact between split-ter plate and the cantilever beam．In Fig．4（b ）when there was a proof mass at the free end of the piezoelectric cantilever beam ，the output voltage at the same wind speed was quite different．The peak-peak open circuit voltage decreased ，but the RMS open circuit voltage in-creased．The influence of proof mass and other parame-ters on the performance of the harvester will be discussed in detail asbelow．Fig．4Open circuit voltage with wind speed of 12m /sFirstly ，the influence of the initial distance between the splitter plate and cantilever beam on the performances of the harvester was studied．The initial distance was set as 0mm ，5mm and 10mm ，respectively．Another proto-type without splitter plate was also tested．The measuredRMS open circuit voltages are shown in Fig．5．When·194·纳米技术与精密工程第11卷第3期wind speed was larger than 7m /s ，compared with the one without splitter plate ，the other three produced much lar-ger output voltages．The output voltage of the prototype with the initial distance of 0mm was higher than the other three under wind speed of 3—7m /s．But when wind speed was larger than 7m /s ，the output voltage of the prototype with 0mm initial distance is lower than those of the other two prototypes with the initial distances of 5mm and 10mm ，respectively．Fig．5Influence of initial distance According to Umeda et al ［14］，the proof masses have significant influence on the conversion efficiency of vibra-tion energy harvesters．To further improve the output power of the impact-based wind energy harvester ，a tung-sten proof mass with dimension of 8mm ˑ6mm ˑ4mm was attached to the free end of the cantilever．Exper-imental results are given in Fig．6．According to Fig．6，the proof mass at the free end of the cantilever beam can significantly increase the outputpower．Fig．6Influence of proof massTo obtain the maximum output power of the harvest-ers under a specified wind speed ，the RMS voltages on different resistors with the resistances from 10k Ωto 1M Ωwere measured．The output power delivered to the load was calculated by P =U 2/R ，where U is the RMSvoltage on the resistor．The output power on different re-sistors under 15m /s was shown in Fig．7．The matched resistance where the output power reached the maximum value was about 200k Ω．The output power on thematched resistance was 64μW for the harvester with a proof mass at the free end of the cantilever ，while the power on the same electrical load was 54μW for that without a proof mass．The proof mass at the free end of the cantilever can increase the outputpower．Fig．7Output power of harvester4ConclusionA wind energy harvester utilizing the impacts be-tween a splitter plate and a piezoelectric composite canti-lever to improve the output power under low speed wind was proposed．Wind tunnel experiments were carried out to analyze the influence of different parameters on output characteristics of the impact-based wind energy harvester．The output power of 64μW was obtained for a matched resistance of 200k Ωwhen wind speed was 15m /s．Ac-cording to the experimental results ，the initial distance between the cantilever beam and the splitter plate has sig-nificant influence on the performances of the harvester．The proof mass at the free end of the cantilever can in-crease output power of the harvester．AcknowledgementThis work was supported by the National Natural Sci-ence Foundation of China （No．61076106）and the Cul-tivation Fund of the Key Scientific and Technical Innova-tion Project of Ministry of 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