Showing papers on "Energy harvesting published in 2011"

Energy Harvesting Sensor Nodes: Survey and Implications

Abstract: Sensor networks with battery-powered nodes can seldom simultaneously meet the design goals of lifetime, cost, sensing reliability and sensing and transmission coverage. Energy-harvesting, converting ambient energy to electrical energy, has emerged as an alternative to power sensor nodes. By exploiting recharge opportunities and tuning performance parameters based on current and expected energy levels, energy harvesting sensor nodes have the potential to address the conflicting design goals of lifetime and performance. This paper surveys various aspects of energy harvesting sensor systems- architecture, energy sources and storage technologies and examples of harvesting-based nodes and applications. The study also discusses the implications of recharge opportunities on sensor node operation and design of sensor network solutions.

Piezoelectric Energy Harvesting

Abstract: About the Authors. Preface. 1. Introduction to Piezoelectric Energy Harvesting. 1.1 Vibration-Based Energy Harvesting Using Piezoelectric Transduction. 1.2 An Examples of a Piezoelectric Energy Harvesting System. 1.3 Mathematical Modeling of Piezoelectric Energy Harvesters. 1.4 Summary of the Theory of Linear Piezoelectricity. 1.5 Outline of the Book. 2. Base Excitation Problem for Cantilevered Structures and Correction of the Lumped-Parameter Electromechanical Model. 2.1 Base Excitation Problem for the Transverse Vibrations. 2.2 Correction of the Lumped-Parameter Base Excitation Model for Transverse Vibrations. 2.3 Experimental Case Studies for Validation of the Correction Factor. 2.4 Base Excitation Problem for Longitudinal Vibrations and Correction of its Lumped-Parameter Model. 2.5 Correction Factor in the Electromechanically Coupled Lumped-Parameter Equations and a Theoretical Case Study. 2.6 Summary. 2.7 Chapter Notes. 3. Analytical Distributed-Parameter Electromechanical Modeling of Cantilevered Piezoelectric Energy Harvesters. 3.1 Fundamentals of the Electromechanically Coupled Distributed-Parameter Model. 3.2 Series Connection of the Piezoceramic Layers. 3.3 Parallel Connection of Piezoceramic Layers. 3.4 Equivalent Representation of the Series and the Parallel Connection Cases. 3.5 Single-Mode Electromechanical Equations for Modal Excitations. 3.6 Multi-mode and Single-Mode Electromechanical FRFs. 3.7 Theoretical Case Study. 3.8 Summary. 3.9 Chapter Notes. 4. Experimental Validation of the Analytical Solution for Bimorph Configurations. 4.1 PZT-5H Bimorph Cantilever without a Tip Mass. 4.2 PZT-5H Bimorph Cantilever with a Tip Mass. 4.3 PZT-5A Bimorph Cantilever. 4.4 Summary. 4.5 Chapter Notes. 5. Dimensionless Equations, Asymptotic Analyses, and Closed-Form Relations for Parameter Identification and Optimization. 5.1 Dimensionless Representation of the Single-Mode Electromechanical FRFs. 5.2 Asymptotic Analyses and Resonance Frequencies. 5.3 Identification of Mechanical Damping. 5.4 Identification of the Optimum Electrical Load for Resonance Excitation. 5.5 Intersection of the Voltage Asymptotes and a Simple Technique for the Experimental Identification of the Optimum Load Resistance. 5.6 Vibration Attenuation Amplification from the Short-Circuit to Open-Circuit Conditions. 5.7 Experimental Validation for a PZT-5H Bimorph Cantilever. 5.8 Summary. 5.9 Chapter Notes. 6. Approximate Analytical Distributed-Parameter Electromechanical Modeling of Cantilevered Piezoelectric Energy Harvesters. 6.1 Unimorph Piezoelectric Energy Harvester Configuration. 6.2 Electromechanical Euler-Bernoulli Model with Axial Deformations. 6.3 Electromechanical Rayleigh Model with Axial Deformations. 6.4 Electromechanical Timoshenko Model with Axial Deformations. 6.5 Modeling of Symmetric Configurations. 6.6 Presence of a Tip Mass in the Euler-Bernoulli, Rayleigh, and Timoshenko Models. 6.7 Comments on the Kinematically Admissible Trial Functions. 6.8 Experimental Validation of the Assumed-Modes Solution for a Bimorph Cantilever. 6.9 Experimental Validation for a Two-Segment Cantilever. 6.10 Summary. 6.11 Chapter Notes. 7. Modeling of Piezoelectric Energy Harvesting for Various Forms of Dynamic Loading. 7.1 Governing Electromechanical Equations. 7.2 Periodic Excitation. 7.3 White Noise Excitation. 7.4 Excitation Due to Moving Loads. 7.5 Local Strain Fluctuations on Large Structures. 7.6 Numerical Solution for General Transient Excitation. 7.7 Case Studies. 7.8 Summary. 7.9 Chapter Notes. 8. Modeling and Exploiting Mechanical Nonlinearities in Piezoelectric Energy Harvesting. 8.1 Perturbation Solution of the Piezoelectric Energy Harvesting Problem: the Method of Multiple Scales. 8.2 Monostable Duffing Oscillator with Piezoelectric Coupling. 8.3 Bistable Duffing Oscillator with Piezoelectric Coupling: the Piezomagnetoelastic Energy Harvester. 8.4 Experimental Performance Results of the Bistable Peizomagnetoelastic Energy Harvester. 8.5 A Bistable Plate for Piezoelectric Energy Harvesting. 8.6 Summary. 8.7 Chapter Notes. 9. Piezoelectric Energy Harvesting from Aeroelastic Vibrations. 9.1 A Lumped-Parameter Piezoaeroelastic Energy Harvester Model for Harmonic Response. 9.2 Experimental Validations of the Lumped-Parameter Model at the Flutter Boundary. 9.3 Utilization of System Nonlinearities in Piezoaeroelastic Energy Harvesting. 9.4 A Distributed-Parameter Piezoaeroelastic Model for Harmonic Response: Assumed-Modes Formulation. 9.5 Time-Domain and Frequency-Domain Piezoaeroelastic Formulations with Finite-Element Modeling. 9.6 Theoretical Case Study for Airflow Excitation of a Cantilevered Plate. 9.7 Summary. 9.8 Chapter Notes. 10. Effects of Material Constants and Mechanical Damping on Power Generation. 10.1 Effective Parameters of Various Soft Ceramics and Single Crystals. 10.2 Theoretical Case Study for Performance Comparison of Soft Ceramics and Single Crystals. 10.3 Effective Parameters of Typical Soft and Hard Ceramics and Single Crystals. 10.4 Theoretical Case Study for Performance Comparison of Soft and Hard Ceramics and Single Crystals. 10.5 Experimental Demonstration for PZT-5A and PZT-5H Cantilevers. 10.6 Summary. 10.7 Chapter Notes. 11. A Brief Review of the Literature of Piezoelectric Energy Harvesting Circuits. 11.1 AC-DC Rectification and Analysis of the Rectified Output. 11.2 Two-Stage Energy Harvesting Circuits: DC-DC Conversion for Impedance Matching. 11.3 Synchronized Switching on Inductor for Piezoelectric Energy Harvesting. 11.4 Summary. 11.5 Chapter Notes. Appendix A. Piezoelectric Constitutive Equations. Appendix B. Modeling of the Excitation Force in Support Motion Problems of Beams and Bars. Appendix C. Modal Analysis of a Uniform Cantilever with a Tip Mass. Appendix D. Strain Nodes of a Uniform Thin Beam for Cantilevered and Other Boundary Conditions. Appendix E. Numerical Data for PZT-5A and PZT-5H Piezoceramics. Appendix F. Constitutive Equations for an Isotropic Substructure. Appendix G. Essential Boundary Conditions for Cantilevered Beams. Appendix H. Electromechanical Lagrange Equations Based on the Extended Hamilton s Principle. Index.

A Review of Piezoelectric Energy Harvesting Based on Vibration

Abstract: This paper reviews energy harvesting technology from mechanical vibration. Recent advances on ultralow power portable electronic devices and wireless sensor network require limitless battery life for better performance. People searched for permanent portable power sources for advanced electronic devices. Energy is everywhere around us and the most important part in energy harvesting is energy transducer. Piezoelectric materials have high energy conversion ability from mechanical vibration. A great amount of researches have been conducted to develop simple and efficient energy harvesting devices from vibration by using piezoelectric materials. Representative piezoelectric materials can be categorized into piezoceramics and piezopolymers. This paper reviews key ideas and performances of the reported piezoelectric energy harvesting from vibration. Various types of vibration devices, piezoelectric materials and mathematical modeling of vibrational energy harvestings are reviewed.

Optimal Energy Allocation for Wireless Communications with Energy Harvesting Constraints

Abstract: We consider the use of energy harvesters, in place of conventional batteries with fixed energy storage, for point-to-point wireless communications. In addition to the challenge of transmitting in a channel with time selective fading, energy harvesters provide a perpetual but unreliable energy source. In this paper, we consider the problem of energy allocation over a finite horizon, taking into account channel conditions and energy sources that are time varying, so as to maximize the throughput. Two types of side information (SI) on the channel conditions and harvested energy are assumed to be available: causal SI (of the past and present slots) or full SI (of the past, present and future slots). We obtain structural results for the optimal energy allocation, via the use of dynamic programming and convex optimization techniques. In particular, if unlimited energy can be stored in the battery with harvested energy and the full SI is available, we prove the optimality of a water-filling energy allocation solution where the so-called water levels follow a staircase function.

Reverse electrowetting as a new approach to high-power energy harvesting

Abstract: High-power mechanical energy harvesting could be an alternative to batteries, but efficient energy conversion technology has been missing. Here, a novel mechanical-to-electrical energy conversion method is described that is based on reverse electrowetting and is uniquely suited for high-power energy harvesting.

Platform architecture for solar, thermal and vibration energy combining with MPPT and single inductor

Abstract: A 0.35µm CMOS energy processor with multiple inputs from solar, thermal and vibration energy sources is presented. Dual-path architecture for energy harvesting is proposed that has up to 13% higher conversion efficiency compared to the conventional two stage storage-regulation architecture. To minimize the cost and form factor, a single inductor has been time shared for all converters. A novel low power maximum power point tracking (MPPT) scheme with 95% tracking efficiency is also introduced.

Energy Harvesting From Hybrid Indoor Ambient Light and Thermal Energy Sources for Enhanced Performance of Wireless Sensor Nodes

Abstract: In this paper, a hybrid of indoor ambient light and thermal energy harvesting scheme that uses only one power management circuit to condition the combined output power harvested from both energy sources is proposed to extend the lifetime of the wireless sensor node. By avoiding the use of individual power management circuits for multiple energy sources, the number of components used in the hybrid energy harvesting (HEH) system is reduced and the system form factor, cost and power losses are thus reduced. An efficient microcontroller-based ultra low power management circuit with fixed voltage reference based maximum power point tracking is implemented with closed-loop voltage feedback control to ensure near maximum power transfer from the two energy sources to its connected electronic load over a wide range of operating conditions. From the experimental test results obtained, an average electrical power of 621 μW is harvested by the optimized HEH system at an average indoor solar irradiance of 1010 lux and a thermal gradient of 10 K, which is almost triple of that can be obtained with conventional single-source thermal energy harvesting method.

Recent progress in MEMS electret generator for energy harvesting

Abstract: Energy harvesting is a method by which energy naturally present in the environment is captured and then converted into electricity for use in low-power electronics. Among the various energy sources, structural vibration is believed to be useful for powering wireless sensors in various applications such as sensor network and structural health monitoring. In the present paper, after a brief introduction to electret materials and charging technologies, recent progress in microelectromechanical systems (MEMS) electret generators is reviewed. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Piezoelectric MEMS Energy Harvester for Low-Frequency Vibrations With Wideband Operation Range and Steadily Increased Output Power

Abstract: A piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvesting cantilever consists of a silicon beam integrated with piezoelectric thin film (PZT) elements parallel-arranged on top and a silicon proof mass resulting in a low resonant frequency of 36 Hz. The whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency up-sweep. Load voltage and power generation for different numbers of PZT elements in series and in parallel connections were compared and discussed based on experimental and simulation results. Moreover, the EH device has a wideband and steadily increased power generation from 19.4 nW to 51.3 nW within the operation frequency bandwidth ranging from 30 Hz to 47 Hz at 1.0 g. Based on theoretical estimation, a potential output power of 0.53 μW could be harvested from low and irregular frequency vibrations by adjusting the PZT pattern and spacer thickness to achieve an optimal design.

Investigation of Rectenna Array Configurations for Enhanced RF Power Harvesting

Abstract: RF power harvesting enables controllable and simultaneous wireless power delivery to many RF devices. Devices built with this unique technology can be sealed, embedded within structures, or made mobile, thus eliminating additional service for a battery. A key component of this technology is the "rectenna," which is composed of antennas and rectifying circuitry to convert RF energy into dc power. Typically, multiple rectenna elements are used to generate the dc power for reliable device operation. This letter compares two different rectenna architectures for maximum RF-to-dc power conversion efficiency. A simple rectenna design ex ample containing a 2 × 2 planar antenna array will be presented to demonstrate such RF power harvesting technology. The parameter, Rectenna Topology Indicator (RTI), is introduced for performance comparison.

Biomechanical energy harvesting from human motion: theory, state of the art, design guidelines, and future directions

Abstract: Biomechanical energy harvesting from human motion presents a promising clean alternative to electrical power supplied by batteries for portable electronic devices and for computerized and motorized prosthetics. We present the theory of energy harvesting from the human body and describe the amount of energy that can be harvested from body heat and from motions of various parts of the body during walking, such as heel strike; ankle, knee, hip, shoulder, and elbow joint motion; and center of mass vertical motion. We evaluated major motions performed during walking and identified the amount of work the body expends and the portion of recoverable energy. During walking, there are phases of the motion at the joints where muscles act as brakes and energy is lost to the surroundings. During those phases of motion, the required braking force or torque can be replaced by an electrical generator, allowing energy to be harvested at the cost of only minimal additional effort. The amount of energy that can be harvested was estimated experimentally and from literature data. Recommendations for future directions are made on the basis of our results in combination with a review of state-of-the-art biomechanical energy harvesting devices and energy conversion methods. For a device that uses center of mass motion, the maximum amount of energy that can be harvested is approximately 1 W per kilogram of device weight. For a person weighing 80 kg and walking at approximately 4 km/h, the power generation from the heel strike is approximately 2 W. For a joint-mounted device based on generative braking, the joints generating the most power are the knees (34 W) and the ankles (20 W). Our theoretical calculations align well with current device performance data. Our results suggest that the most energy can be harvested from the lower limb joints, but to do so efficiently, an innovative and light-weight mechanical design is needed. We also compared the option of carrying batteries to the metabolic cost of harvesting the energy, and examined the advantages of methods for conversion of mechanical energy into electrical energy.

Impact-driven, frequency up-converting coupled vibration energy harvesting device for low frequency operation

Abstract: This paper presents experiments and models of an energy harvesting device in which a low frequency resonator impacts a high frequency energy harvesting resonator, resulting in energy harvesting predominantly at the system's coupled vibration frequency. Analysis shows that a reduced mechanical damping ratio during coupled vibration enables increased electrical power generation as compared with conventional technology. Experiments demonstrate that the efficiency of electrical power transfer is significantly improved with the coupled vibration approach. An average power output of 0.43 mW is achieved under 0.4g acceleration at 8.2 Hz, corresponding to a power density of 25.5 µW cm − 3. The measured power and power density at the resonant frequency are respectively 4.8 times and 13 times the measured peak values for a conventional harvester created from a low frequency beam alone.

Ultra-wide bandwidth piezoelectric energy harvesting

Abstract: Here, we present an ultra wide-bandwidth energy harvester by exploiting the nonlinear stiffness of a doubly clamped microelectromechanical systems (MEMSs) resonator. The stretching strain in a doubly clamped beam shows a nonlinear stiffness, which provides a passive feedback and results in amplitude-stiffened Duffing mode resonance. This design has been fabricated into a compact MEMS device, which is about the size of a US quarter coin. Based on the open circuit voltage measurement, it is expected to have more than one order of magnitude improvement in both bandwidth (more than 20% of the peak frequency) and power density (up to 2 W/cm3) in comparison to the devices previously reported.

Method and apparatus for harvesting energy

Abstract: An energy harvesting circuit includes one or more broadband or narrow band antennas to detect WIFI (wireless fidelity) or other RF (radio frequency) signals. The signals are rectified and voltage multiplied, and the resultant DC voltage is provided to a power management circuit. The output of the power management circuit charges a lithium battery or other storage device within the energy harvesting circuit. The energy stored in the battery or storage device is provided through a DC/DC converter circuit to a USB output connector to power or recharge the batteries of an external electronic device connected to the USB output connector of the energy harvesting circuit.

Networking low-power energy harvesting devices: Measurements and algorithms

Abstract: Recent advances in energy harvesting materials and ultra-low-power communications will soon enable the realization of networks composed of energy harvesting devices. These devices will operate using very low ambient energy, such as indoor light energy. We focus on characterizing the energy availability in indoor environments and on developing energy allocation algorithms for energy harvesting devices. First, we present results of our long-term indoor radiant energy measurements, which provide important inputs required for algorithm and system design (e.g., determining the required battery sizes). Then, we focus on algorithm development, which requires nontraditional approaches, since energy harvesting shifts the nature of energy-aware protocols from minimizing energy expenditure to optimizing it. Moreover, in many cases, different energy storage types (rechargeable battery and a capacitor) require different algorithms. We develop algorithms for determining time fair energy allocation in systems with predictable energy inputs, as well as in systems where energy inputs are stochastic.

Electromechanical Modeling and Nonlinear Analysis of Axially Loaded Energy Harvesters

Abstract: To maximize the electromechanical transduction of vibratory energy harvesters, the resonance frequency of the harvesting device is usually tuned to the excitation frequency. To achieve this goal, some concepts call for utilizing an axial static preload to soften or stiffen the structure (Leland and Wright, 2006, "Resonance Tuning of Piezoelectric Vibration Energy Scavenging Generators Using Compressive Axial Preload, " Smart Mater. Struct., 15, pp. 1413-1420; Morris et al., 2008, "A Resonant Frequency Tunable, Extensional Mode Piezoelectric Vibration Harvesting Mechanism, " Smart Mater. Struct., 17, p. 065021). For the most part, however, models used to describe the effect of the axial preload on the harvester's response are linear lumped-parameter models that can hide some of the essential features of the dynamics and, sometimes, oppose the experimental trends. To resolve this issue, this study aims to develop a comprehensive understanding of energy harvesting using axially loaded beams. Specifically, using nonlinear Euler-Bernoulli beam theory, an electromechanical model of a clamped-clamped energy harvester subjected to transversal excitations and static axial loading is developed and discretized using a Galerkin expansion. Using the method of multiple scales, the general nonlinear physics of the system is investigated by obtaining analytical expressions for the steady-state response amplitude, the voltage drop across a resistive load, and the output power. These theoretical expressions are then validated against experimental data. It is demonstrated that in addition to the ability of tuning the harvester to the excitation frequency via axial load variations, the axial load aids in (i) increasing the electric damping in the system, thereby enhancing the energy transfer from the beam to the electric load, (ii) amplifying the effect of the external excitation on the structure, and (iii) enhancing the effective nonlinearity of the device. These factors combined can increase the steady-state response amplitude, output power, and bandwidth of the harvester.

A nanogenerator for energy harvesting from a rotating tire and its application as a self-powered pressure/speed sensor.

Abstract: Harvesting unexploited energy in the living environment to power small electronic devices and systems is attracting increasing massive attention. [ 1–7 ] As the size of the devices has shrunk to the nanoor microscale, the power consumption also decreased to a modest level, i.e., the microwatts to milliwatts range. It is entirely possible to drive such a device by directly scavenging energy from its working environment. This self-powered technology makes periodic battery replacement or recharging no longer necessary and it is thus attractive for portable or inaccessible devices. Mechanical energy is a very conventional energy source in our living environment, with sources including the vibration of a bridge, friction in mechanical transmission systems, deformation in the tires of moving automobiles, etc., all of which are normally wasted. This form of energy is particularly important when other sources of energy, such as sun light or thermal gradients, are not available. A nanogenerator (NG) is designed to transfer such energy into electric energy by the piezoelectric effect. [ 8–14 ] The fundamental mechanism of a NG is that, when it is dynamically strained under an extremely small force, a piezoelectric potential is generated in the nanowire and a transient fl ow of electrons is induced in an external load, as driven by the piezopotential to balance the Fermi levels at the two contacts. For bicycles, cars, trucks, and even airplanes, a self-powered monitoring system for measuring the inner tire pressure is not only important for the safe operation of the transportation tool, but also for saving energy. In this work, a NG was integrated onto the inner surface of a bicycle tire, demonstrating the possibility for energy harvesting from the motion of automobiles. A small liquid-crystal display (LCD) screen was lit directly using a NG that scavenges mechanical energy from deformation of the tire during its motion. The effective working area of the nanogenerator was about 1.5 cm × 0.5 cm and the maximum output power density approached 70 μ W cm − 3 . Integration of many nanogenerators is presented for scale-up. Furthermore, the NG showed the potential to work as a self-powered tire-pressure sensor and speed detector. This work provides a simple demonstration of the broad application prospects of NGs in the fi eld of energy harvesting and self-powered systems.

Optimal Packet Scheduling on an Energy Harvesting Broadcast Link

Abstract: The minimization of transmission completion time for a given number of bits per user in an energy harvesting communication system, where energy harvesting instants are known in an offline manner is considered. An achievable rate region with structural properties satisfied by the 2-user AWGN Broadcast Channel capacity region is assumed. It is shown that even though all data are available at the beginning, a non-negative amount of energy from each energy harvest is deferred for later use such that the transmit power starts at its lowest value and rises as time progresses. The optimal scheduler ends the transmission to both users at the same time. Exploiting the special structure in the problem, the iterative offline algorithm, FlowRight, from earlier literature, is adapted and proved to solve this problem. The solution has polynomial complexity in the number of harvests used, and is observed to converge quickly on numerical examples.

Piezoelectric wind energy harvester for low-power sensors

Abstract: There has been increasing interest in wireless sensor networks for a variety of outdoor applications including structural health monitoring and environmental monitoring. Replacement of batteries that power the nodes in these networks is maintenance intensive. A wind energy–harvesting device is proposed as an alternate power source for these wireless sensor nodes. The device is based on the galloping of a bar with triangular cross section attached to a cantilever beam. Piezoelectric sheets bonded to the beam convert the mechanical energy into electrical energy. A prototype device of size approximately 160 × 250 mm was fabricated and tested over a range of operating conditions in a wind tunnel, and the power dissipated across a load resistance was measured. A maximum power output of 53 mW was measured at a wind velocity of 11.6 mph. An analytical model incorporating the coupled electromechanical behavior of the piezoelectric sheets and quasi-steady aerodynamics was developed. The model showed good correlati...

An investigation of energy harvesting from renewable sources with PVDF and PZT

Abstract: Piezoelectric materials have been in use for many years; however, with an increasing concern about global warming, piezoelectricity has gained significant importance in research and development for extracting energy from the environment. In this work the voltage responses of ceramic based piezoelectric fibre composite structures (PFCs) and polymer based piezoelectric strips, PVDF (polyvinylidene fluoride), were evaluated when subjected to various wind speeds and water droplets in order to investigate the possibility of energy generation from these two natural renewable energy sources for utilization in low power electronic devices. The effects of material dimensions, drop mass, releasing height of the drops and wind speed on the voltage output were studied and the power was calculated. This work showed that piezoelectric polymer materials can generate higher voltage/power than ceramic based piezoelectric materials and it was proved that producing energy from renewable sources such as rain drops and wind is possible by using piezoelectric polymer materials.

Recent Progress in Piezoelectric Conversion and Energy Harvesting Using Nonlinear Electronic Interfaces and Issues in Small Scale Implementation

Abstract: This paper aims at providing an up-to-date review of nonlinear electronic interfaces for energy harvesting from mechanical vibrations using piezoelectric coupling. The basic principles and the direct application to energy harvesting of nonlinear treatment of the output voltage of the transducers for conversion enhancement will be recalled, and extensions of this approach presented. Latest advances in this field will be exposed, such as the use of intermediate energy tanks for decoupling or initial energy injection for conversion magnification. A comparative analysis of each of these techniques will be performed, highlighting the advantages and drawbacks of the methods, in terms of efficiency, performance under several excitation conditions, complexity of implementation and so on. Finally, a special focus of their implementation in the case of low voltage output transducers (as in the case of microsystems) will be presented.

Experimental Duffing oscillator for broadband piezoelectric energy harvesting

Abstract: This paper presents an experimental piezoelectric energy harvester exhibiting strong mechanical nonlinear behavior. Vibration energy harvesters are usually resonant mechanical systems working at resonance. The resulting mechanical amplification gives an output power multiplied by the mechanical quality factor Q when compared to non-resonant systems, provided that the electromechanical coupling k2 is high as well as the mechanical quality factor Q. However, increasing the Q value results in a narrowband energy harvester, and the main drawback is the difficulty of matching a given vibration frequency range to the energy harvester's resonance frequency. Mechanical nonlinear stiffness results in a distortion of the resonance peak that may lead to a broadband energy harvesting capability while keeping a large output power as for high Q systems. This paper is devoted to an experimental study of a Duffing oscillator exhibiting piezoelectric electromechanical coupling. A nonlinear electromechanical model is first presented including piezoelectric coupling, a nonlinear stiffness as for a Duffing oscillator, and an additional nonlinear loss term. Under harmonic excitation, it is shown that for a particular excitation range, the power frequency bandwidth is multiplied by a factor of 5.45 whereas the output power is decreased by a factor of 2.4. In addition, when compared to a linear system exhibiting the same power bandwidth as for the nonlinear one (which is here 7.75%), the output power is increased by a factor of 16.5. Harmonic study is, however, partially irrelevant, because Duffing oscillators exhibit a frequency range where two stable harmonic solutions are possible. When excited with sine bursts or colored noise, the oscillator remains most of the time at the lowest solution. In this paper, we present a technique—called fast burst perturbation—which consists of a fast voltage burst applied to the piezoelectric element. It is then shown that the resonator may jump from the low solution to the high solution at a very small energy cost. Time-domain solution of the model is presented to support experimental data.

Energy Scavenging Power Supply

Abstract: An energy scavenging power system and method may include an energy conversion system having at least one transducer configured to harvest energy, an energy management and storage system configured to store harvested energy; and a load regulation system configured to provide stored energy to power one or more low power-consumption loads The energy management and storage system may include a start-up capacitor having a small capacitance to allow for quick charging and fast turn-on, a short term capacitor to provide energy to the load or loads once turned-on, and a long term capacitor having a large capacitance to provide for sustained energy delivery to the loads The system also may include a common charging bus that receives energy from each transducer, conditioned if necessary, and which then determines the capacitor to which the energy should be delivered

The experimental validation of a new energy harvesting system based on the wake galloping phenomenon

Abstract: In this paper, a new energy harvesting system based on wind energy is investigated. To this end, the characteristics and mechanisms of various aerodynamic instability phenomena are first examined and the most appropriate one (i.e. wake galloping) is selected. Then, a wind tunnel test is carried out in order to understand the occurrence conditions of the wake galloping phenomenon more clearly. Based on the test results, a prototype electromagnetic energy harvesting device is designed and manufactured. The effectiveness of the proposed energy harvesting system is extensively examined via a series of wind tunnel tests with the prototype device. Test results show that electricity of about 370 mW can be generated under a wind speed of 4.5 m s − 1 by the proposed energy harvesting device. The generated power can easily be increased by simply increasing the number of electromagnetic parts in a vibrating structure. Also, the possibility of civil engineering applications is discussed. It is concluded from the test results and discussion that the proposed device is an efficient, economic and reliable energy harvesting system and could be applied to civil engineering structures.

Towards an autonomous self-tuning vibration energy harvesting device for wireless sensor network applications

Abstract: Future deployment of wireless sensor networks will ultimately require a self-sustainable local power source for each sensor, and vibration energy harvesting is a promising approach for such applications. A requirement for efficient vibration energy harvesting is to match the device and source frequencies. While techniques to tune the resonance frequency of an energy harvesting device have recently been described, in many applications optimization of such systems will require the energy harvesting device to be able to autonomously tune its resonance frequency. In this work a vibration energy harvesting device with autonomous resonance frequency tunability utilizing a magnetic stiffness technique is presented. Here a piezoelectric cantilever beam array is employed with magnets attached to the free ends of cantilever beams to enable magnetic force resonance frequency tuning. The device is successfully tuned from �27% to +22% of its untuned resonance frequency while outputting a peak power of approximately 1 mW. Since the magnetic force tuning technique is semi-active, energy is only consumed during the tuning process. The developed prototype consumed maximum energies of 3.3 and 3.9 J to tune to the farthest source frequencies with respect to the untuned resonance frequency of the device. The time necessary for this prototype device to harvest the energy expended during its most energy-intensive (largest resonant frequency adjustment) tuning operation is 88 min in a low amplitude 0.1g vibration environment, which could be further optimized using higher efficiency piezoelectric materials and system components. (Some figures in this article are in colour only in the electronic version)