A broadband bistable piezoelectric cantilever-based vibration energy harvester with nonlinear high power extraction

This work presents a nonlinear vibration energy harvester, which combines a nonlinear bistable broadband piezoelectric cantilever used to transduce ambient vibration energy, with synchronized capture for efficient harvesting over broadband sources. An accurate model of the bistable transducer, that augments the Butterworth van Dyke piezoelectric model to capture the external magnetic force added as a bias to the external vibrations, is presented. Its validity has been demonstrated through physical implementation and experimental validation against simulation of the mathematical model. For efficient extraction of the transduced energy, nonlinear extraction circuits, namely synchronous charge extraction (SCE) and parallel synchronized switch harvesting on inductor (SSHI), are employed. The switching in these circuits is implemented using a fully self-propelled, low-power electronic breaker circuit, capable of detecting extrema in the waveform to perform switching. Both simulated and experimental power outputs from the bistable harvester have been presented, with the SCE and parallel-SSHI providing average outputs with more than one-hundred (100) fold increase over the harvested power reported in literature for the same input, and further, even more significant gains are observed for broadband excitations. For the above mentioned harvester, bistability is introduced through the use of two repelling magnets, one mounted on the cantilever tip and the other at a fixed location opposite it. Excitations that can overcome the repulsive magnetic force cause the cantilever to snap between its two equilibrium states, increasing amplitude and velocity of vibration, resulting in higher power outputs. This improved performance is observed whenever the cantilever operates in the bistable mode. Lower-amplitude excitations are unable to overcome the repulsive force, causing the cantilever to vibrate around one of its equilibrium states, and with smaller amplitudes in the presence of the opposing repulsion. To circumvent this issue, the second part of the work presents a completely mechanical way of increasing the range of excitation amplitudes over which the system remains bistable, by spring-loading the previously fixed-positioned magnet, and restricting its motion in the horizontal direction, towards and away from the cantilever. Then, whenever the cantilever moves towards the spring-loaded magnet, the latter is pushed away due to the repulsive force, increasing the distance between the magnets, thereby reducing the repulsive force required to be overcome for bistable operation. The opposite occurs when the cantilever moves away. Thus, the role of spring-loading is to introduce a type of negative feedback, through the self-adjustment of the distance between the magnets, favoring bistable operation over a larger range of excitations, and this is accomplished without an added energy cost. A 90% gain in power output levels over the fixed magnet system was observed

Toward Small-Scale Wind Energy Harvesting: Design, Enhancement, Performance Comparison, and Applicability

© 2017 Liya Zhao and Yaowen Yang. The concept of harvesting ambient energy as an alternative power supply for electronic systems like remote sensors to avoid replacement of depleted batteries has been enthusiastically investigated over the past few years. Wind energy is a potential power source which is ubiquitous in both indoor and outdoor environments. The increasing research interests have resulted in numerous techniques on small-scale wind energy harvesting, and a rigorous and quantitative comparison is necessary to provide the academic community a guideline. This paper reviews the recent advances on various wind power harvesting techniques ranging between cm-scaled wind turbines and windmills, harvesters based on aeroelasticities, and those based on turbulence and other types of working principles, mainly from a quantitative perspective. The merits, weaknesses, and applicability of different prototypes are discussed in detail. Also, efficiency enhancing methods are summarized from two aspects, that is, structural modification aspect and interface circuit improvement aspect. Studies on integrating wind energy harvesters with wireless sensors for potential practical uses are also reviewed. The purpose of this paper is to provide useful guidance to researchers from various disciplines interested in small-scale wind energy harvesting and help them build a quantitative understanding of this technique

Energy harvesting technologies and devices from vehicular transit and natural sources on roads for a sustainable transport: state-of-the-art analysis and commercial solutions

The roads we travel daily are exposed to several energy sources (mechanical load, solar radiation, heat, air movement, etc.), which can be exploited to make common systems and apparatus for roadways (i.e., lighting, video surveillance, and traffic monitoring systems) energetically autonomous. For decades, research groups have developed many technologies able to scavenge energy from the said sources related to roadways: electromagnetism, piezoelectric and triboelectric harvesters for the cars’ stress and vibrations, photovoltaic modules for sunlight, thermoelectric solutions and pyroelectric materials for heat and wind turbines optimized for low-speed winds, such as the ones produced by moving vehicles. Thus, this paper explores the existing technologies for scavenging energy from sources available on roadways, both natural and related to vehicular transit. At first, to contextualize them within the application scenario, the available energy sources and transduction mechanisms were identified and described, arguing the main requirements that must be considered for developing harvesters applicable on roadways. Afterward, an overview of energy harvesting solutions presented in the scientific literature to recover energy from roadways is introduced, classifying them according to the transduction method (i.e., piezoelectric, triboelectric, electromagnetic, photovoltaic, etc.) and proposed system architecture. Later, a survey of commercial systems available on the market for scavenging energy from roadways is introduced, focusing on their architecture, performance, and installation methods. Lastly, comparative analyses are offered for each device category (i.e., scientific works and commercial products), providing insights to identify the most promising solutions and technologies for developing future self-sustainable smart roads

Design and optimization of piezoelectric MEMS vibration energy harvesters

Low-power electronic applications are normally powered by batteries, which have to deal with stringent lifetime and size constraints. To enhance operational autonomy, energy harvesting from ambient vibration by micro-electromechanical systems (MEMS) has been identified as a promising solution to this universal problem. In this thesis, multiple configurations for MEMS-based piezoelectric energy harvesters are studied. To enhance their performances, automated design and optimization methodologies with minimum human efforts are proposed. Firstly, the analytic equations to estimate resonant frequency and amplitude of the harvested voltage for two different configurations of unimorph MEMS piezoelectric harvesters (i.e., with and without integration of a proof mass) are presented with their accuracy validated by using finite element method (FEM) simulation and prototype measurement. Thanks to their high accuracy, we use these analytic equations as fitness functions of genetic algorithm (GA), an evolutionary computation method for optimization problems by mimicking biological evolution. By leveraging the micro-fabrication process, we demonstrate that the GA can optimize the mechanical geometry of the prototyped harvester effectively and efficiently, whose peak harvested voltage increases from 310 mV to 1900 mV at the reduced resonant frequency from 886 Hz to 425 Hz with the highest normalized voltage density of 163.88 among the alternatives. With an intention of promoting uniform stress distribution along the piezoelectric cantilever and providing larger area for placing proof masses, in this thesis a T-shaped cantilever structure with two degrees-of-freedom (DOF) is proposed. Thanks to this special configuration, a considerable amount of stress/strain can be obtained from the tip part of the structure during the vibration, in addition to the anchor region. An analytic model for computing the frequency response of the proposed structure is derived, and the harvester performance is studied analytically, numerically and experimentally. The conventional MEMS energy harvesters can only generate voltage disadvantageously in a narrow bandwidth at higher frequencies. Therefore, in this thesis we further propose a piezoelectric MEMS harvester with the capability of vibrating in multiple DOF, whose operational bandwidth is enhanced by taking advantage of both multimodal and nonlinear mechanisms. The proposed harvester has a symmetric structure with a doubly-clamped configuration enclosing three proof masses in distinct locations. Thanks to the uniform mass distribution, the energy harvesting efficiency can be considerably enhanced. To determine the optimum geometry for the preferred nonlinear behavior, we have also used optimization methodology based on GA. The prototype measurements demonstrate that our proposed piezoelectric MEMS harvester is able to generate voltage at 227 Hz (the first mode), 261.8 Hz (the second mode), and 286 Hz (the third mode). When the device operates at its second mode frequency, nonlinear behavior can be obtained with extremely small magnitude of base excitation (i.e., 0.2 m/s²). Its normalized power density (NPD) of 595.12 (μW·cm⁻³·m⁻²·s⁴) is found to be superior to any previously reported piezoelectric MEMS harvesters in the literature. In this dissertation, we also propose a piezoelectric MEMS vibration energy harvester with the capability of oscillating at ultralow (i.e., less than 200 Hz) resonant frequency. The mechanical structure of the proposed harvester is comprised of a doubly clamped cantilever with a serpentine pattern associated with several discrete masses. In order to obtain the optimal physical aspects of the harvester and speed up the design process, we have utilized a deep neural network, as an artificial intelligence (AI) method. Firstly, the deep neural network was trained, and then this trained network was integrated with the GA to optimize the harvester geometry to enhance its performance in terms of both resonant frequency and generated voltage. Our numerical results confirm that the accuracy of the network in prediction is above 90%. As a result, by taking advantage of this efficient AI-based performance estimator, the GA is able to reduce the device resonant frequency from 169Hz to 110.5Hz and increase its efficiency on harvested voltage from 2.5V to 3.4V under 0.25g excitation. To improve both durability and energy conversion efficiency of the piezoelectric MEMS harvesters, we further propose a curve-shaped anchoring scheme in this thesis. A doubly clamped curve beam with a mass at its center is considered as an anchor, while a straight beam with proof mass is integrated to the center of this anchor. To assess the fatigue damage, which is actually critical to the micro-sized silicon-based piezoelectric harvesters, we have utilized the Coffin-Manson method and FEM to study the fatigue lifetime of the proposed geometry comprehensively. Our proposed piezoelectric harvester has been fabricated and its capability in harnessing the vibration energy has been examined numerically and experimentally. It is found that the harvested energy can be enlarged by a factor of 2.66, while this improvement is gained by the resonant frequency reduction and failure force magnitude enlargement, in comparison with the conventional geometry of the piezoelectric MEMS harvesters

Modélisation et optimisation mécanique d'un récupérateur piézoélectrique d'énergie vibratoire

Dans la dernière décennie, plusieurs chercheurs ont démontré un intérêt concernant la possibilité de récupérer de l'énergie mécanique provenant de structures vibrantes. Une façon commune de procéder consiste à utiliser l'effet piézoélectrique direct à partir d'une poutre en porte-à-faux ayant des céramiques piézoélectriques intégrées. Les études portant sur la modélisation du phénomène se sont jusqu'ici limitées à des geometries simples de récupérateur tandis que peu d'études se sont intéressées à la modélisation d'une forme optimale de récupérateur. Les travaux de recherche de ce mémoire étudient donc le phénomène de récupération d'énergie vibratoire afin d'élaborer un design optimal de récupérateur piézoélectrique. Le phénomène piézoélectrique est d'abord décrit théoriquement afin que le volume piézoélectrique soit intégré adéquatement à une structure vibrante. Une analyse détaillée de modèles est ensuite réalisée pour faire ressortir les bases de la récupération d'énergie vibratoire. À la lumière de cette analyse, une modélisation semi-analytique est développée à partir des approximations de Rayleigh-Ritz et intégrée à un modèle électromécanique. Une fois validée, des études numériques sont réalisées avec ce modèle permettant ainsi de poser le problème d'optimisation de la géométrie du récupérateur. Un algorithme génétique est finalement utilisé pour maximiser la puissance récupérée. La géométrie optimale permet de récupérer une puissance de 62.8 mW lorsque le récupérateur est soumis à une source vibratoire ayant une amplitude d'accélération de 9.81 m.s⁻² et une fréquence d'excitation de 100 Hz, ce qui constitue une densité énergétique de 0.38 mW.g⁻¹

Magneto-inductive wireless underground sensor networks: novel longevity model, communication concepts and workarounds to key theoretical issues using analogical thinking

This research has attempted to devise novel workarounds to key theoretical issues in magneto-inductive wireless underground sensor networks (WUSNs), founded on analogical thinking (Gassmann & Zeschky 2008). The problem statement for this research can be summarized as follows. There has been a substantial output of research publications in the past 5 years, devoted to theoretically analysing and resolving the issues pertaining to deployment of MI based WUSNs. However, no alternate solution approaches to such theoretical analyses have been considered. The goal of this research was to explore such alternate solution approaches. This research has used the principle of analogical thinking in devising such alternate solution approaches. This research has made several key contributions to the existing body of work. First, this research is the first of its kind to demonstrate by means of review of state-of-the-art research on MI based WUSNs, the largely theoretical genus of the research to the exclusion of alternate solution approaches to circumvent key theoretical issues. Second, this research is the first of its kind to introduce the notion of analogical thinking as a solution approach in finding viable workarounds to theoretical impediments in MI based WUSNs, and validate such solution approach by means of simulations. Third, this research is the first of its kind to explore novel communication concepts in the realm of MI based WUSNs, based on analogical thinking. Fourth, this research is the first of its kind to explore a novel longevity model in the realm of MI based WUSNs, based on analogical thinking. Fifth, this research is also the first to extend the notion of analogical thinking to futuristic directions in MI based WUSNs research, by means of providing possible indicators drawn from various other areas of contemporary research. In essence, the author believes that the findings of this research mark a paradigm shift in the research on MI based WUSNs