周期性热激励下PZT陶瓷的输出功率特性分析

前期实验主要分析了PZT热释电陶瓷在周期性热激励下其温度、输出电压和电流的变化特性。在此基础上,实验研究了PZT热释电陶瓷在周期性热激励下其输出功率的变化特性,主要讨论了PZT热释电陶瓷热电转换装置在接入不同负载时其输出功率的变化情况,并通过阻抗优化,获得最大的输出功率。实验结果表明,在0.1Hz调频频率下,当不接负载时,装置输出功率可达72.1μW,输出功率密度1.47mW/cm₃;当接入负载时,使负载阻值在0~20MΩ内变化,实验得出当负载阻值为7MΩ时装置产生的功率最大(实验所用的PZT热释电陶瓷的阻抗为7.96MΩ),达到了66.7μW,输出功率密度601.9μW/cm₃。     

一种小型热释电能量转换装置的特性分析

设计了一种小型热释电能量转换装置,基于热释电效应对该装置进行了理论分析,推导出了该装置的输出电流与电压的表达式。通过理论分析与实验的方法对简谐热激励下该装置的能量转换特性进行了研究,结果表明:当对装置进行调频处理时,热释电单元表面的温度将发生周期性的变化,并且在其正负极之间产生周期性变化的电压;调频频率、热源功率、装置散热情况及热释电陶瓷表面吸热率对该装置的输出电压会产生一定的影响;该装置产生的电能能量密度可达7.4mJ/cm3,可满足某些特殊场合的能量需求。     

压电陶瓷激励影响燃气燃烧器性能的实验研究

应用热线风速仪和TESTO360烟气分析仪分别对压电陶瓷激励下燃气燃烧器冷、热态情况进行了测量,主要考察了压电陶瓷激励频率、幅值对掺混区域速度场、燃烧器出口NOx生成量和温度分布的影响。实验结果表明,各种频率的压电陶瓷激励对助燃风流动及其与天然气的掺混都有一定效果,但千赫兹量级的激励频率的激励效果更为明显一些,且激励造成的时均速度变化程度要弱于湍流度变化。压电陶瓷激励下,燃烧器NOx生成量和燃烧温度均有所提高,表明燃烧更趋完全。     

PZT与TeBi半导体材料热电转换特性的对比分析

选取PZT热释电陶瓷和TeBi半导体作为实验材料,对二者的热电转换特性进行了对比研究。采用恒热流和调频热流两种加热方式对热释电陶瓷和半导体发电片进行加热,使其进行热电直接转换。实验结果表明,PZT热释电陶瓷在调频热流作用下热电转换效果较好,其最优转换频率在0.1Hz左右,热释电陶瓷所发出的电能为交流电,且表现出大电压、小电流的特点;TeBi半导体在恒热流作用下热电转换效果较好,其所发出的电能为直流电,表现出小电压、大电流的特点。     

悬臂梁压电发电机输出特性及其影响因素分析

为研究悬臂梁压电发电机的输出特性及其影响因素,设计搭建了悬臂梁物理实验模型。通过空载、负载和短路实验测试了振动频率、振动位移和负载大小对其输出电压的影响,对比了不同尺寸压电陶瓷的发电能力,为压电式发电技术的发展和改进提供详细的数据基础和实验依据。研究表明:当振动频率接近压电振子的谐振频率时,发电机有较高电压输出,而随着振动位移的增大,输出电压会线性增加,二者相比,振动位移对输出电压的影响更显著。发电机直接带负载的能力较弱,当外界负载与发电机内阻匹配时才能保持稳定的电压输出。对于不同尺寸的压电陶瓷来说,其长宽比越接近1,发电能力越强。     

冷凝器不锈钢波纹管导波检测技术的研究

为了实现对冷凝器不锈钢波纹管的主动健康监测,采用附着在结构上的压电陶瓷晶片以及套在结构表面的电磁声换能器激励接收导波模态,优化各种参数以用于缺陷的识别和评估。试验选取经Hanning窗调制的正弦脉冲信号在波纹管中激励中心频率240kHz的纵向超声导波L(0,2)模态,用于波纹管中人工缺陷的检测,并分析了L(0,2)模态对不同类型缺陷的敏感程度。试验结果表明,利用压电陶瓷晶片和电磁声传感器激励接收频率为240kHz的L(0,2)模态可以识别波纹管中的裂纹缺陷。     

冷、热端温度对半导体热电堆发电性能影响的初步研究

对半导体热电堆的发电性能进行了实验研究,得出这种半导体热电堆在冷端温度不变的情况下,其发电性能与热端温度的关系,以及半导体热电堆在热端温度的情况下,冷端温度对其发电性能的影响,发现半导体热电堆作为电源时,其内阻对它的性能指标有很大的影响,而且内阻随着温度的升高而增大,采用间化的方法从理论上计算了热电堆的特性,得到了计算与实验结果基本吻合。     

过充、过热及其共同作用下车用三元锂离子电池热失控特性北大核心CSCD

锂离子电池作为目前电动汽车的主要能源电池,其在外界滥用条件下的热失控问题受到广泛关注,研究不同滥用下尤其是多种滥用共同作用下的电池热失控特性可有效提高电池使用安全性。本工作以车用50 Ah方型动力三元锂离子电池单体作为研究对象,利用大功率充放电循环仪和电加热装置,进行了1 C倍率过充、150 W局部过热及其共同作用下的电池热失控实验。对不同工况下热失控实验现象、质量损失、温度变化、升温速率变化、升温部位和电压变化等实验结果进行对比分析,结果表明:过充过热共同作用下电池热失控具有更大危险性,电池热失控时间比单一滥用减少约35%,热失控时电池SOC比过充减小约35%,电池电压会出现“持续上升—突降至零”现象。本研究可为车用三元锂离子电池热管理系统安全设计提供参考。     

具有PCM的汽车尾气温差发电器的变工况模拟

以内燃机为动力的汽车尾气余热具有高度瞬变特性,而温差发电器(termoelectric generator,TEG)往往对温度的变化较为敏感,针对这一矛盾,在尾气管道和热电模块之间添加相变材料层以减缓尾气温度波动对热电模块性能的影响。通过模拟计算的方法,比较了变工况条件下,相变材料层的添加对热电模块热端平均温度、输出电压等因素的影响。结果表明,相变材料(phase change materia,PCM)的添加对热电模块热端温度波动起到了良好的缓冲作用,大大提高了TEG输出电压的稳定性。     

热声堆材料对制冷效果的影响

为了提高热声效率转换,在黄铜和不锈钢这类传统热声堆材料的基础上,创造性地引入了毛细玻璃管和PVC塑料材质的热声堆。基于搭建以氩气为工质的扬声器驱动型热声制冷机,进行热声堆两端温差对制冷效果影响的实验研究。研究表明:当激励电流不变时,随着声场频率的升高,热声堆两端温差升高,制冷效果得到改善;当声场频率与激励电流相同时,毛细玻璃管材质输出的温差最大,制冷效果最佳。     

Pyroelectric energy converter using co-polymer P(VDF-TrFE) and Olsen cycle for waste heat energy harvesting

This study was concerned with designing, building, and testing a pyroelectric energy converter to directly convert waste heat into electricity. The pyroelectric effect refers to the flow of charges to or from the surface of a material upon heating or cooling. The device consisted of a teflon cylindrical chamber with a piston oscillating vertically and driving a working fluid back and forth between a heat source and a cold heat exchanger. The Olsen cycle was performed on co-polymer 60/40 poly(vinylidene fluoride–trifluoroethylene) [P(VDF-TrFE)] thin films sandwiched between metallic electrodes. Their temperature oscillation, charge, voltage and the overall heat input and output were measured experimentally. Then, the electrical power generated and the energy efficiency were computed. The effects of channel width, frequency, and stroke length on temperature swing, heat input, as well as energy and power densities were investigated. Reducing the channel width and increasing the stroke length had the largest effect on device performance. A maximum energy density of 130 J/l was achieved at 0.061 Hz frequency with temperature oscillating between 69.3 and 87.6 °C. Furthermore, a maximum power density of 10.7 W/l was obtained at 0.12 Hz between 70.5 and 85.3 °C. In both cases, the low and high electric fields in the Olsen cycle were 202 and 739 kV/cm. To the best of our knowledge, this is the largest energy density achieved by any pyroelectric energy converter using P(VDF-TrFE). It also matches performances reported in the literature for more expensive lead zirconate stannate titanate (PZST) ceramic films operated at higher temperatures.     

Three-Dimensional Pyroelectric Analysis of a Functionally Graded Piezoelectric Hollow Sphere

A three-dimensional analytical piezothermoelastic solution is presented for a functionally graded piezoelectric spherical shell subjected to various thermal boundary conditions applied on the inner and outer surfaces. Material properties are assumed to vary along the radius, r, obeying a power law. Both the thermal field and the pyroelectric responses are resolved using the state space method. On introducing three displacement and two stress functions, two independent kinds of state equations are derived from the basic equations of piezoelectricity. It is interesting that the first kind is a homogeneous equation only related to the purely elastic behavior of the sphere, yet the second has an inhomogeneous term associated with the thermal effect to determine the pyroelectric responses. The state equations are solved by expanding the field variables into series of spherical harmonic functions. Numerical examples are performed to investigate the influence of material inhomogeneity on the pyroelectric responses of the spherical shell.     

A vibration-based electromagnetic and piezoelectric hybrid energy harvester

This work presents the fabrication and testing of a vibration-based single energy hybrid harvester (VSEHH). Electromagnetic and piezoelectric transduction mechanisms are utilized for energy extraction in the developed harvester. Electromagnetic portion of the device composed of a permanent magnet, planar coil and wound coil, however, for piezoelectric portion polyvinylidene difluoride (PVDF) membrane is used. In the harvester the PVDF membrane having the magnet is kept loose in order to exploit the spring softening nonlinearity. At lower base excitation levels (less than 0.5g) the response of the VSEHH is linear, however, from 0.5 to 2.5g the harvester exhibits spring softening nonlinearity and at acceleration levels greater than 2.5g, the spring hardening nonlinearity is invoked. Because of nonlinear behavior of the harvester, the shift of resonant frequency, the sudden jump-up and jump-down phenomena result in the enhancement of the harvester's frequency bandwidth. Under sinusoidal excitation and at 123 Hz frequency and 4g acceleration, the electromagnetic portion of the harvester produced 40.6 mV load voltage and 212.7 μW with planar coil and 73.5 mV load voltage and 319.1 μW power with wound coil. Moreover, under the same vibrations condition a load voltage of 2930 mV and power of 57.6 μW is generated by the piezoelectric portion of the harvester. Collectively, the harvester is capable of producing a power of 589.4 μW and a power density of 334.13 μW/cm³. Furthermore, when subjected to broadband random vibrations, two central frequency peaks are produced, one is due to spring softening and the other corresponds to the spring hardening of the membrane.     

高转移效率的压电电源研究

基于压电材料的性能,设计了并联多层的压电电源结构,试验验证了压电材料产生电能的性能,并进行了稳压电路设计。结果表明,采用并联多层方式设计的压电电源结合桥式整流电路对存贮电容进行二次充电,可降低压电材料产生的电压,提高压电材料产生的电流及其能量转移效率,进而提升存贮电容电压,稳压后可作为某些电路的电源使用。     

多传感器数据融合技术在气门动态特性试验中的应用

压电式加速度传感器的漂移问题在气门动态特性试验中难以避免。气门加速度信号的微小漂移,将导致积分的速度信号严重失真。试验采用压电式加速度传感器和电涡流位移传感器测量气门动态特性,并将多传感器数据融合技术应用于气门动态试验数据处理中。由加速度信号积分和位移信号微分获得速度信号,分析两种传感器不同的频响特性,采用小波分解、融合并重构,提取相对准确的气门速度信号。     

DEFORMATION OF A PIEZOTHERMOELECTRIC COMPOSITE PLATE CONSIDERING THE COUPLING EFFECT

The response of a thin piezothermoelastic composite plate subjected to stationary thermal and electric fields is investigated. Solutions are based on the classical lamination theory, and both the direct piezoelectric effect and the pyroelectric effect in the constitutive relations of piezothermoelasticity are considered. Numerical results show that these coupled effects have a significant influence on the response of the deflection, and the middle surface deflection with these coupled effects is larger than that without them. The laminate configuration and the number of layers have an influence of the response of the deflection     

High Power Density Pyroelectric Energy Conversion in Nanometer-Thick BaTiO3 Films

Solid-state pyroelectric nanomaterials can be used for thermal-to-electrical energy conversion in the presence of temperature fluctuations. This article reports investigation of energy conversion in a 200 nm thick BaTiO₃ film using the pyroelectric Ericsson cycle at cycle frequencies up to 3 kHz. The high cycle frequencies were achieved due to the low thermal mass of the nanometer-scale film, unlike previous studies in which the electrical power output was limited by the rate of heat transfer through the pyroelectric material. A microfabricated platform that allowed precise thermal and electrical cycling enabled us to study the effect of electric field range, temperature oscillation amplitude, and cycle frequency on the electrical power output from pyroelectric Ericsson cycles. We measured a maximum power density of 30 W/cm³ for a temperature range 20–120°C and electric field range 100–125 kV/cm, which represents a significant improvement over past work on pyroelectric cycles. The approach presented in this article could lead to high-power waste heat harvesting in systems with high-frequency temperature oscillations.     

THERMOELASTIC LAMB WAVES IN ELECTRICALLY SHORTED TRANSVERSELY ISOTROPIC PIEZOELECTRIC PLATE

The propagation of Lamb waves in a homogeneous, transversely isotropic, piezothermoelastic plate, which is stress free, electrically shorted, and thermally insulated (or isothermal), is investigated. Secular equations for the plate in closed form and isolated mathematical conditions for symmetric and antisymmetric wave mode propagation are derived in completely separate terms. It is shown that the motion of the purely transverse shear horizontal (SH) mode gets decoupled from the rest of the motion and remains unaffected due to piezoelectric, pyroelectric, and thermal effects. The secular equations for stress-free piezoelectric, thermoelastic, and elastic plates are deduced as special cases in the current analysis. At short wavelength limits the secular equations for symmetric and skew symmetric modes reduce to Rayleigh surface wave frequency equation, because a finite-thickness plate in such a situation behaves like a semi-infinite medium. The amplitudes of dilatation, electrical potential, and temperature change are also computed during the symmetric and skew symmetric motion of the plate. Finally, numerical solutions of various secular equations and other relevant relations are carried out for cadmium selenide (6 mm class) material. The dispersion curves, attenuation coefficients and amplitudes of dilatation, temperature change, and electrical potential for symmetric and antisymmetric wave modes are presented graphically to illustrate and compare the analytical results. The theory and numerical computations are found to be in close agreement. The coupling between the thermal/electric/elastic fields in piezoelectric materials provides a mechanism for sensing thermomechanical disturbances from measurements of induced electric potentials and for altering structural responses via applied electric fields. Therefore, the analysis will be useful in the design and construction of Lamb wave sensors, temperature sensors, and surface acoustic wave filter devices.     

Improving the efficiency of pyroelectric conversion

Pyroelectric conversion utilizes low‐grade waste heat as a heat source, and thus produces clean energy. Low‐grade heat is abundant in the various industries and it is practically free. It can be converted to high‐voltage electricity by pyroelectric conversion. Our pyroelectric converter uses copolymer of poly‐vinylidene fluoride with trifluoroethylene [60/40% P(VDF–TrFE)]. Previously, we encountered a substantial power loss due to internal leakage at high temperature and voltage. In order to increase the power output, we examined the effect of polymer purification using solvent extraction. We compared the electrical properties of purified copolymer with those of ‘as‐received’ copolymer. Although we removed only 0.4 wt% of the copolymer by solvent extraction, the electrical resistivity of purified copolymer was 35% higher than that of the ‘as‐received’ copolymer. We also observed that thin films produced using purified copolymer were able to withstand 50% higher electric field before they were ruined by the electrical short circuit. Subsequently, we conducted pyroelectric conversion using 25 µ m thick 60–40% P(VF₂–TrFE) copolymer films. Copolymer purification resulted in a three‐fold increase in net power output. Net power output per unit volume of the ‘as‐received’ copolymer was 95 J L^?1 but it increased to 279 J L^?1 for purified copolymer. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2007. Published by John Wiley & Sons, Ltd.