A Flexible Doubly Clamped Beam Energy Harvester with a Standard Rectifier Electric Circuit

While wearable electronics are rapidly developing nowadays, it is greatly limited by the power solutions. Flexible piezoelectric energy harvester presents advantages of high energy density, compact architecture, and easy integration with MEMS, which provides an attractive prospect to power these next generation electronics. Since the flexible devices are usually devised with wavy, island-bridge, and precisely controlled buckling structures, the doubly clamped beam structure for energy harvesting application is analytically studied in this paper. Combine with Euler-Bernoulli beam theory and separation variable method, the analytical expression for output voltage is derived. By conducting the analytical simulation, it is found that the output power is related with the geometry dimensions, external excitation and load resistances. For further validation, experiment is systematically studied. By connecting the standard rectifier electric circuit with the energy harvesting device, it is found that a 0.1uF capacitor can be fully charged in 0.15 s, and the charged output voltage is about 2.5 V, which are successfully used for powering LEDs

Analytical Modeling of a Doubly Clamped Flexible Piezoelectric Energy Harvester with Axial Excitation and Its Experimental Characterization

With the rapid development of wearable electronics, novel power solutions are required to adapt to flexible surfaces for widespread applications, thus flexible energy harvesters have been extensively studied for their flexibility and stretchability. However, poor power output and insufficient sensitivity to environmental changes limit its widespread application in engineering practice. A doubly clamped flexible piezoelectric energy harvester (FPEH) with axial excitation is therefore proposed for higher power output in a low-frequency vibration environment. Combining the Euler–Bernoulli beam theory and the D’Alembert principle, the differential dynamic equation of the doubly clamped energy harvester is derived, in which the excitation mode of axial load with pre-deformation is considered. A numerical solution of voltage amplitude and average power is obtained using the Rayleigh–Ritz method. Output power of 22.5 μW at 27.1 Hz, with the optimal load resistance being 1 MΩ, is determined by the frequency sweeping analysis. In order to power electronic devices, the converted alternating electric energy should be rectified into direct current energy. By connecting to the MDA2500 standard rectified electric bridge, a rectified DC output voltage across the 1 MΩ load resistor is characterized to be 2.39 V. For further validation of the mechanical-electrical dynamical model of the doubly clamped flexible piezoelectric energy harvester, its output performances, including both its frequency response and resistance load matching performances, are experimentally characterized. From the experimental results, the maximum output power is 1.38 μW, with a load resistance of 5.7 MΩ at 27 Hz, and the rectified DC output voltage reaches 1.84 V, which shows coincidence with simulation results and is proved to be sufficient for powering LED electronics

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

A unified electromechanical finite element dynamic analysis of multiple segmented smart plate energy harvesters: circuit connection patterns

This paper presents the techniques for formulating the multiple segmented smart plate structures with different circuit connection patterns using the electromechanical finite element dynamic analysis. There are three major contributions in the proposed numerical studies. First, the electromechanical discretization has been developed for generalizing the coupled system of Kirchhoff’s smart plate structures with circuit connection patterns. Such constitutive numerical models reduced from the extended Lagrange equations can be used for the physical systems including, but not restricted to, the multiple piezoelectric and electrode segments. Second, the multiple piezoelectric or electrode segments can be arranged electrically in parallel, series, and mixed series–parallel connections with the on–off switching techniques where the electrical outputs of each connection are further connected with the standard AC–DC circuit interfaces. Third, the coupling transformation technique (CTT) has been introduced by modifying the orthonormalized global element matrices into the scalar form equations. As a result, the multimode frequency response function and time-waveform signal response equations are distinctly formulated for each circuit connection. Further parametric numerical case studies are also discussed in this paper. The benefit of using the circuit connection patterns with the on–off switching techniques is that the studies can be used for an adaptive vibration power harveste

Bi-stable buckled energy harvesters actuated via torque arms.

Vibrational energy harvesters (VEH) are one way to generate electricity. Though the energy quantities are not enough to run desktop computers, they can power remote devices such as temperature, pressure, and accelerometer sensors or power biological implants. New versions of the Bluetooth protocol can even be used with VEH technology to send wireless data. An important aspect of VEH devices is the power output, operating frequency, and bandwidth. This dissertation investigates a novel method of actuating the primary buckled energy harvesting structure using torque arms as a force amplification mechanism. Buckled structures can exhibit snap-through and has the potential to broaden the operating frequency for the VEH. Macro and MEMS size prototypes are fabricated and evaluated via a custom made shaker table. The effect of compliance arms, which pin the center beam with piezoelectric strips, are also evaluated along with damping ratios. ANSYS models evaluating generated power are created for use in future optimization studies. Lastly, high energy orbitals (HEO) are observed in the devices. Results show that buckling lowers and broadens the output power of the new devices. Reverse sweeps drastically increase the operating frequency during snap-through. Rectangular compliance arms made of poly-lactic acid (PLA) generated the most power of all compliance arms tested. HEO performance can be induced by perturbing the system while maintaining the same input force which increases power output

A Novel Micro Piezoelectric Energy Harvesting System

(Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2007(PhD) -- İstanbul Technical University, Institute of Science and Technology, 2007Bu tezde yeni bir titreşim temelli mikro enerji harmanlayıcı sistemi önerilmiştir. Titreşimler ve ani hareketler, mekanik yapının sadece eğilmesine değil aynı zamanda gerilmesine yol açar, bu sayede sistem doğrusal olmayan bölgede çalışır. İnce piezoelektrik film tabakası mekanik stresi elektrik enerjisine çevirir. Mikrowatt mertebesinde güç seviyeleri mm3’lük aletlerle elde edilebilir, bu da güneş panellerinde elde edilen güç yoğunlukları kadar yüksektir. Algılayıcı kabiliyeti sayesinde bilgi depolayabilen, kum tanesi büyüklüğünde olan ve üretiminde kullanılan temel malzeme silikon olan bu aletler “zeki kum” olarak isimlendirilmiştir. Mekanik yapının modellenmesi ve tasarımı geliştirilmiş ve üretim sonuçları da ayrıca verilmiştir. Sistemin bilgi gönderebilmesi ve alabilmesi amacıyla iyi bilinen RFID teknolojisi tabanlı bir kablosuz haberleşme yöntemi önerilmiştir. Bu bağlamda, paket taşımacılığında sürekli ivme denetleme, sınır güvenliği için kendinden beslemeli algılayıcılar, çabuk bozulan yiyeceklerin taşımacılığında sıcaklık denetleme ve pilsiz kalp atışı algılayıcı gibi birçok uygulama önerilmiştir.In this thesis, a novel, vibration based micro energy harvester system is proposed. Vibrations or sudden movements cause the mechanical structure does not only bend but also stretch, thus working in non-linear regime. The piezoelectric thin film layer converts the mechanical stress into the electrical energy. Microwatts of power can be achieved with a mm3 device which yields a high power density levels on the order of the solar panels. This device is named “smart sand”, because it has also sensor capabilities that can store information, its size is almost a sand grain and the main material used for the fabrication is silicon. The modeling and design of the mechanical structure has been developed and fabrication results have also been given in the thesis. In order for the system to send and receive the information, a wireless communication scheme is proposed which is based on the well-known RFID technology. In this concept, several applications are proposed such as continuous acceleration monitoring in package delivery, self-powered sensors for homeland security, temperature monitoring of the perishable food item delivery and a batteryless heart rate sensor.DoktoraPh

Geometric Nonlinear Finite Element and Genetic Algorithm Based Vibration Energy Harvesting from Functionally Graded Nonprismatic Piezolaminated Beams

Energy harvesting technology has the ability to create autonomous, self-powered systems which do not rely on the conventional battery for their operation. The term energy harvesting is the process of converting the ambient energy surrounding a system into some useful electrical energy using certain materials. Among several energy conversion techniques, the conversion of ambient vibration energy to electrical energy using piezoelectric materials has great deal of importance which encompasses electromechanical coupling between mechanical and electrical domains. The energy harvesting systems are designed by incorporating the piezoelectric materials in the host structure located in vibration rich environment. The work presented in this dissertation focuses on upgrading the concept of energy harvesting in order to engender more power than conventional energy harvesting designs. The present work deals with first the finite element (FE) formulation for coupled thermo-electro-mechanical analysis of vibration energy harvesting from an axially functionally graded (FG) non-prismatic piezolaminated cantilever beam. A two noded beam element with two degrees of freedom (DOF) at each node has been used in the FE formulation. The FG material (i.e. non-homogeneity) in the axial direction has been considered which varies (continuously decreasing from root to tip of such cantilever beam) using a proposed power law formula. The various cross section profiles (such as linear, parabolic and cubic) have been modelled using the Euler-Bernoulli beam theory and Hamilton‘s principle is used to solve the governing equation of motion. The simultaneous variation of tapers (both width and height in length directions) is incorporated in the mathematical formulation. The FE formulation developed in the present work has been compared with the analytical solutions subjected to mechanical, electrical, thermal and thermo-electro-mechanical loading. Results obtained from the present work shows that the axially FG nonprismatic beam generates more output power than the conventional energy harvesting systems. Further, the work has been focussed towards the nonlinear vibration energy harvesting from an axially FG non-prismatic piezolaminated cantilever beam. Geometric nonlinear based FE formulation using Newmark method in conjunction with Newton-Raphson method has been formulated to solve the obtained governing equation. Moreover, a real code GA based constrained optimization technique has also been proposed to determine the best possible design variables for optimal power harvesting within the allowable limits of ultimate stress of the beam and voltage of the PZT sensor. It is observed that more output power can be obtained based on the present optimization formulation within the allowable limits of stress and voltage than that of selection of design variables by trial and error in FE modelling

Graphene/P(VDF-TrFE) Heterojunction Based Wearable Sensors with Integrated Piezoelectric Energy Harvester

Graphene, with its outstanding material properties, including high carrier mobility, atomically thin nature, and ability to tolerate mechanical deformation related strain up to 20% before breaking, make it very attractive for developing highly sensitive and conformable strain/pressure sensor for wearable electronics. Unfortunately, graphene by itself is not piezoresistive, so developing a strain sensor utilizing just graphene is challenging. Fortunately, graphene synthesized on Cu foil can be transferred to arbitrary substrates (preserving its high quality), including flexible polymer substrates, which will allow the overall flexibility and conformability of the sensing element, to be maintained. Furthermore, a graphene/polymer based sensor devices can be easily patterned into an array over dimensions reaching several feet, taking advantage of large area synthesis of graphene, which will make the ultimate sensor very inexpensive. If a piezo-electric polymer, such as P(VDF-TrFE), is chosen to form a heterojunction with graphene, it will strongly affect the carrier density in graphene, due to the fixed charge developing on its surface under strain or pressure. Taking advantage of the high carrier mobility in graphene, such a charge change can result in very high sensitivity to pressure and strain. Hence, these features, coupled with the flexible nature of the device and ease of fabrication, make it a very attractive candidate for use in the growing wearable technology market, especially biomedical applications and smart health monitoring system as well as virtual reality sensors. In this dissertation, various unique properties of graphene and P(VDF-TrFE), and their current applications and trends are discussed in chapter 1. Additionally, synthesis of graphene and P(VDF-TrFE) and their characterizations by various techniques are investigated in chapter 2. Based on piezoelectric property of P(VDF-TrFE), a highly flexible energy harvesters on PDMS as well as PET substrates have been developed and demonstrated their performances in chapter 3. As follow-up research, graphene/P(VDF-TrFE) heterojunction based wearable sensors with integrated piezoelectric energy harvester on flexible substrates have also been fabricated and demonstrated for practical wearable application in chapter 4. Finally, major findings and future directions of the project are discussed in chapter 5

Micro-générateurs piézoélectriques pour des applications de récupération d'énergie

This PhD thesis focuses on the thermal energy harvesting at microscale to propose an alternative to thermoelectric materials. The aim is to conceive, fabricate and characterize a microscopic harvester to take profit of the increase of thermal exchanges and oscillation frequencies with the downscaling. It is based on a double-step transduction: thermo-mecanical one thanks to the thermal buckling of a bilayer plate initially curved, and piezoelectric.Rectangular structures of different sizes composed of AlN and Al have been fabricated and characterized. The transverse curvature of the rectangular plate being to high, optimized structures having a butterfly shape have also been fabricated and characterized.Le sujet de ce travail de thèse s'inscrit dans la récupération d'énergie thermique à l'échelle microscopique pour proposer une alternative aux matériaux thermoélectriques. L'objectif est de concevoir, fabriquer et caractériser un récupérateur microscopique pour tirer profit de l'augmentation des échanges thermiques et des fréquences d'oscillations avec la réduction d'échelle. Il est basé sur une double transduction, thermo-mécanique grâce au flambage d'une poutre bi-couche initialement courbe, et piézoélectrique.Des structures rectangulaires de différents tailles à base d'AlN et d'Al ont été fabriquées et caractérisées. La courbure transverse des plaques rectangulaires étant trop importante, des structures optimisées en forme de papillons ont par ailleurs été fabriquées et caractérisées