Power output estimation and experimental validation for piezoelectric energy harvesting systems

Many modern devices especially for ubiquitous computing or wireless sensor networks need a long life energy source. Batteries or accumulators are often an insufficient solution. Low frequency vibrations can be found in the most technical facilities or even in the human movements. Even while these vibrations are neither wanted nor used in the most times, they enable us to generate electrical energy. Piezoelectric flexural transducers are a promising choice for utilizing the vibrations for energy harvesting. There are two major influences on the amount of generated energy. First there is the frequency behavior of the piezoelectric transducers, for optimal power output the transducer should be driven in resonance. Second, the energy output is highly dependent on the electrical load of the connected application. Both circumstances, working frequency and electrical load, typically are boundary conditions for the development of the generator. Therefore, it is necessary to handpick the type of piezoelectric elements. To meet the requirements of development engineers, a model based design method for energy harvesting systems is needed. As a first step towards such a method, this work proposes a model for the estimations of the power output of piezoelectric flexural transducers. For the validation of this model an experiment is described in detail. The results of the model and the experiments are compared.     

Energy harvesting using piezoelectric materials: Case of random vibrations

A dramatic consumption reduction of integrated circuits related to the development of mobile electronic devices has been reached over the past years, enabling the use of ambient energy instead of batteries. The focus is here on the transformation of ambient mechanical vibrations into electrical energy. This paper compares the performances of a vibration-powered electrical generator using PZT piezoelectric ceramics associated to two different power conditioning circuits. A new approach of the piezoelectric power conversion based on a nonlinear voltage processing is presented and implemented using a particular circuit. Theoretical predictions and experimental results show that the new technique may increase the power harvested by a factor up to 4 compared to the Standard technique. The power optimization problem is in particular examined in the case of broadband, random vibrations.     

A simple and powerful analytical model for MEMS piezoelectric multimorphs

We have developed an analytical model for use in design and modelling of piezoelectric MEMS devices. The model allows for incorporation of any number of device material layers in a multimorph structure including piezoelectric materials. The resulting lumped circuit model fully incorporates the electro-mechanical coupling effects in the piezoelectric layers as well as electrical or mechanical loading of the device structure. Since the model is analytic, and only requires the specification of well-defined material properties, it allows for fast and interactive modelling of a multitude of MEMS device structures incorporating piezoelectric materials. We will demonstrate the capability of the model by presenting results from fitting the model to impedance measurements performed on cantilever structures. This allows for extraction of device and material parameters that are difficult to obtain by other means, such as the piezoelectric coefficient and the mechanical quality factor.     

Advances in energy harvesting using low profile piezoelectric transducers

The vast reduction in the size and power consumption of sensors and CMOS circuitry has led to a focused research effort on the on-board power sources which can replace the batteries. The concern with batteries has been that they must always be charged before use. Similarly, the sensors and data acquisition components in distributed networks require centralized energy sources for their operation. In some applications such as sensors for structural health monitoring in remote locations, geographically inaccessible temperature or humidity sensors, the battery charging or replacement operations can be tedious and expensive. Logically, the emphasis in such cases has been on developing the on-site generators that can transform any available form of energy at the location into electrical energy. Piezoelectric energy harvesting has emerged as one of the prime methods for transforming mechanical energy into electric energy. This review article provides a comprehensive coverage of the recent developments in the area of piezoelectric energy harvesting using low profile transducers and provides the results for various energy harvesting prototype devices. A brief discussion is also presented on the selection of the piezoelectric materials for on and off resonance applications. Analytical models reported in literature to describe the efficiency and power magnitude of the energy harvesting process are analyzed.

基于压电材料的变压器振动能量收集装置研究

变压器振动信号在线监测是检测变压器运行状态的重要手段,振动传感器的供能方式制约了振动检测方法的应用。为了实现振动传感器取能,文中设计了一种基于压电材料的变压器振动能量收集装置,利用收集的振动能量为振动传感器供电。首先,根据变压器振动特性,采用多模态取能方式,建立三悬臂式压电取能结构的输出电压与输出功率模型。其次,通过Comsol Multiphysics仿真分析能量收集装置输出功率和外加激励频率的关系。最后,搭建变压器振动能量收集实验平台,测得压电式能量收集装置的实际输出功率为11.547 μW。利用振动能量收集装置为振动传感器供电,可以保障在线监测设备的供电,减少外接电源对设备安全稳定运行的影响。     

MEMS薄膜磁通门传感器的制作与特性

首先论述了微型平面磁通门传感器的原理和结构,在此基础上,详细介绍了基于微机电机械加工技术(MEMS)的集成磁通门传感器探头的制作过程(包括溅射、电镀、光刻、反应离子刻蚀(RIE)等)。分别采用高磁导率、低矫顽力的Co基非晶合金带材以及坡莫合金作为磁心制成磁通门探头。测试结果表明,在40kHz激励频率下,带材磁心探头的工作范围为±75μT,而坡莫合金磁心探头为±60μT,灵敏度分别为31.07V/T和23.76V/T。结果基本可以满足地磁场±60μT的测量要求。     

Performance of printable supercapacitors in an RF energy harvesting circuit

We report the fabrication of a supercapacitor on a plastic substrate with mass-production-compatible methods and its characterisation using galvanostatic and voltammetric methods. The supercapacitor is prepared in ambient conditions using activated carbon and an aqueous, non-acidic electrolyte. The obtained capacitances are 0.45 F and 0.21 F for device sizes of 4 cm² and 2 cm², respectively. Additionally, we demonstrate the utilisation of the supercapacitor in an autonomous energy harvesting and storage system. The RF energy harvester comprises a printed loop antenna and a half-wave organic diode rectifier operating at 13.56 MHz frequency. The harvested energy is stored in two supercapacitors connected in series to increase the maximum operating voltage. In order to power a device such as a sensor or a small indicator display, voltage regulation is needed. A voltage regulator, implemented as an application specific integrated circuit (ASIC), was designed for this purpose, and fabricated commercially. We demonstrate the ability of the harvester storage unit to power the regulator for hours with a constant regulator output voltage and power. The effect of supercapacitor charging time on the actual supercapacitor charging state is also discussed, as a slower charging rate is found to have a significant effect on the output of the supercapacitor.     

A study of flexible piezoelectric generators by sputtering ZnO thin film on PET substrate

Abstract

Flexible technology has recently received much attention in the field of flexible sensors, wearable electronic devices, flexible transparent displays, and energy harvesters. Zinc oxide (ZnO) thin film is the preferred material for use in flexible devices due to its environmental friendliness, high electrical performance and low synthesis temperature. In addition, ZnO possesses a non-centrosymmetric crystal structure, causing a piezoelectric effect in the material. This work presents the fabrication of flexible piezoelectric generators using the deposition of ZnO on a PET substrate using sputtering techniques. The fabricated flexible generators are capable of generating an output power of 14 µW through an optimal resistive load of 750 kΩ. An output voltage of 2.00 Vp and a current of 150 μA measured across a 750 kΩ resistor were subsequently obtained.     

A shoe-equipped piezoelectric transducer system based on PVDF film

Many piezoelectric transducers mounted in shoes have been conducted to harvest energy from walking. However, the energy harvested is influenced by some factors, such as the structure of piezoelectric transducer, piezoelectric material and so forth. Taking into account these factors, a wide-band energy harvester-shoe equipped piezoelectric transducer with cantilever beam structure based on polyvinylidene fluoride (PVDF) piezoelectric film is designed and examined in this paper. The piezoelectric transducer makes little difference in the sensation with the device mounted in the shoes when walking. The harvester can provide a maximum output power of 0.48 mW at the load resistance of 300 kΩ. This study demonstrates that it is feasible to scavenge energy from human motion by piezoelectric harvester to power wearable sensors, such as pedometer, respiration and pulse monitoring system and so on.     

基于MEMS技术的汽车传感器研究进展

随着汽车传感器的迅速发展和对MEMS(微机电系统)技术研究的深入,基于MEMS技术的汽车传感器具有广阔的应用前景。本文就MEMS汽车传感器的研究应用现状、MEMS汽车传感器的分类、制作加工技术和工艺等进行了简述,并详细介绍了几种典型的MEMS汽车传感器,最后对MEMS汽车传感器今后的发展进行了探讨。     

Mechanisms of Pb(zr0.53Ti0.47)O3 thin film etching with ECR/RF reactor

Abstract

Ferroelectric capacitive devices for memory and MEMS applications require patterned ferroelectric thin films with high anisotropic etched features. In this paper, physical and chemical parameters during etching of Pb(Zr_0.53Ti_0.47)O₃ (PZT) by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask were investigated as a function of gas chemistry (Ar, halogen gases), substrate bias RF power and working pressure (from 5 × 10^?4 Pa to 1Pa). The etch processes were characterized in terms of etch rate, selectivity and mask stability. High etching rate processes (up to 70 nm/min with removable photoresist mask) were obtained and micron scale patterns were demonstrated. The impact of the etch process on the PZT surface layer modification was characterized by AFM, SEM, TEM and XPS. A strong influence of process chemistry and RF bias power on etching selectivity and surface topography (roughness, involatile residues) was observed. No surface damage layer was detected by Transmission Electron Microscopy. However, XPS revealed fluorine (up to 34%) and chlorine radicals (below 10%) in a 10nm thick surface layer.     

QMEMS晶振的MEMS器件真空度测量方法研究

QMEMS晶振是一种采用MEMS(micro-electro-mechanical system)加工技术充分发挥石英(Quartz)晶体材质特性制造出的高性能、高集成度的新型石英晶振。利用QMEMS晶振体积小、性能稳定的特点,提出将QMEMS晶振作为传感器内置于MEMS器件管壳内部,对MEMS器件腔体内部真空度进行实时监测的方法。在对石英晶振测量真空原理进行分析的基础上,研究了QMEMS晶振的结构和管壳开口方法,设计了一套基于QMEMS晶振气压传感器的真空度测量系统,实现了对真空度的测量,并对系统进行了标定。试验表明,该真空计可实现1~30kPa压强范围的测量,测量精度约为5%,能满足MEMS器件实时真空度测量要求。     

Large area deposition of Pb(Zr,Ti)O<Subscript>3</Subscript> thin films for piezoelectric MEMS devices

Pb(Zr,Ti)O₃ (PZT) thin films deposited on insulating ZrO₂ buffered silicon wafer are intended to be employed for in-plane polarized piezoelectric MEMS devices. Multi-target reactive sputtering system for large area deposition of in-situ crystallized PZT thin films and the ZrO₂ buffer layer has been employed. The interface analysis of multilayer structures by high resolution transmission microscope, X-ray diffraction, optical refraction, and absorption spectra studies has been presented. At a substrate temperature of 520°C and excess lead deposition condition, the formation of a PZT superstructure has been revealed. The substrate temperature of 580°C leads to the crystallization of PZT directly into a single phase perovskite crystal structure. A pronounced Urbach behavior in our PZT thin films has been observed by optical absorption studies. The surface roughness of PZT films deposited on a ZrO₂ buffer layer is much higher than that on conducting platinized silicon wafer.     

Correlation between the sawyer-tower measured charge/area of a thin film PZT ferroelectric and the thickness mode piezoelectric coupling coefficient

Abstract

We have observed a 40% increase in the piezoelectrical coupling of a PZT layer upon application of a 10 μs pulse of 17 × 10⁴ V/cm, which generated a polarization of 2.2 μc/cm². A qualitative analysis of this data is given.     

基于MEMS传感器技术的微型化、数字式倾角仪的研究

本文介绍了一种新型的数字倾角仪。把微机电系统(MEMS)技术的高精度倾角传感器和微处理器有机结合,借助智能算法,设计了一种高性能的倾角测量仪,缩小了仪器体积,提高了仪器精度和抗震性;研究结果表明:该数字倾角仪测量范围可达±15°,分辨力达到0.01°,可广泛应用于建筑、石油、煤矿和地质勘探等各种需要测量倾角的场合。     

基于MEMS/GPS/地磁组合的弹体姿态解算

MEMS惯性器件由于具有自主性、连续性和隐蔽性等优点被广泛运用于载体的姿态解算中,但由于MEMS惯性器件的制作精度和误差积累等问题使得解算出的姿态信息并不准确.同时由于地磁传感器可以实现高精度的姿态测量,但不能独立解算出姿态信息.因此为了提高惯导姿态解算的精度,所以采用GPS、地磁辅助惯导进行姿态解算.设计的方案是在传统惯导姿态解算误差状态方程的基础上,将地磁和GPS解算的滚转、偏航和俯仰角与惯导解算出来的相应角的差值添加到传统惯导姿态解算误差状态方程中,以速度误差和滚转、偏航和俯仰角误差为量测值,估计出组合系统的姿态误差,并与惯导解算出的姿态误差进行对比,从而验证所提出的方法的可行性.     

基于IMU旋转的MEMS器件误差调制技术研究

MEMS惯性器件低信噪比和漂移大成为影响其应用范围的主要因素,提出基于惯性测量单元(IMU)转动的MEMS器件误差旋转自补偿方法。将MEMS输出信息利用小波降噪技术进行预处理,以此消除旋转调制方案不能自补偿的随机噪声信号并提高器件输出信噪比,分析IMU转动方案下的误差调制原理并探讨旋转调制的工程可实现性。搭建MEMS转动实验环境并开展降噪与IMU静止和转动条件下的导航实验,结果表明,采用旋转状态下的MEMS惯导系统可有效地提高系统自身测姿和定位精度。     

Extensive electromechanical characterization of PZT thin films for MEMS applications by electrical and mechanical excitation signals

In this work we present a unique measurement method to estimate the effective transverse piezocoefficient e _31,f of piezoelectric thin films which is often used in micro electromechanical systems (MEMS). This method utilizes basically a 4-point bending setup specially adapted to be used with thin film samples. It allows the application of very homogeneous well defined mechanical stresses to the device. Stress and corresponding strain distribution are verified by Finite Element simulations. Measurements are shown to demonstrate the capability and repeatability of the setup on sol-gel processed PZT thin film samples. In conjunction with additional measurement results it is possible to fully determine the electromechanical characteristics.     

Studies on piezo coefficients of PLD and sol-gel grown PZT thin film for devices

Abstract

The effect of electrical (DC) contact poling processes on the ferroelectric and piezoelectric properties of sol–gel and pulsed laser-deposited PZT thin films has been investigated as a function of the poling field, temperature and time. The remnant polarization and piezoelectric coefficient are found to increase with and saturate at dc-poling field of 100- 300?kV/cm, temperature of 100–120?°C and poling time of 10–20?min. as compared with un-poled PZT thin films. The P-E hysteresis loops of poled PLD grown PZT films shows sharper switching behaviour as compared to imbalanced loop in sol-gel grown films. An improvement of piezoelectric and ferroelectric properties of sol–gel PZT thin films is found, as compared to those deposited using pulsed laser deposition (PLD), indicating that a poling process is required for sol–gel PZT thin films.