An Impedance Matching Solution to Increase the Harvested Power and Efficiency of Nonlinear Piezoelectric Energy Harvesters

Circuit theory and nonlinear dynamics are instrumental to design efficient energy harvesters for ambient mechanical vibrations. In this work, we show that an impedance matching networks can be designed that maximizes the harvested power, and improves the power efficiency. The proposed matching network achieves impedance matching at a single frequency, that can be chosen at will by the designer, and does not need to coincide with the resonant frequency of the harvester. Moreover, the matching network also increases the harvested power over a wide frequency bandwidth. According to our numerical simulations, the matching network increases the maximum harvested power by a factor greater than 3, and the power harvested over the whole frequency spectrum by a factor of 6. The frequency bandwidth can be further extended considering nonlinear energy harvesters. Even using the matching network designed for the linear case, performance is significantly nonetheless improved for the nonlinear harvester

Mini Wind Harvester and a Low Power Three-Phase AC/DC Converter to Power IoT Devices: Analysis, Simulation, Test and Design

Wind energy harvesting is a widespread mature technology employed to collect energy, but it is also suitable, and not yet fully exploited at small scale, for powering low power electronic systems such as Internet of Things (IoT) systems like structural health monitoring, on-line sensors, predictive maintenance, manufacturing processes and surveillance. The present work introduces a three-phase mini wind energy harvester and an Alternate Current/Direct Current (AC/DC) converter. The research analyzes in depth a wind harvester’s operation principles in order to extract its characteristic parameters. It also proposes an equivalent electromechanical model of the harvester, and its accuracy has been verified with prototype performance results. Moreover, unlike most of the converters which use two steps for AC/DC signal conditioning—a rectifier stage and a DC/DC regulator—this work proposes a single stage converter to increase the system efficiency and, consequently, improve the energy transfer. Moreover, the most suitable AC/DC converter architecture was chosen and optimized for the best performance taking into account: the target power, efficiency, voltage levels, operation frequency, duty cycle and load required to implement the aforementioned converter

Strongly coupled piezoelectric energy harvesters: Finite element modelling and experimental validation

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordPiezoelectric energy harvesters (PEHs) are usually connected to a load resistor matching to the impedance of their internal capacitance to characterise the power generation during transducer design and optimisation. For strongly-coupled PEHs operating near resonance, this simple RC matching method underestimates the power output and fails to characterise the dual power peaks but are still often used in both simulation and experiment. This study analysed the internal impedance network and the power output characteristics of PEHs. Based on the analysis, a novel and efficient finite element model (FEM) for strongly coupled PEHs was developed and applied to a pre-stressed piezoelectric stack energy harvester (PSEH). A stationary analysis was first performed to simulate the pre-stressed state of the PSEH. The FEM then analysed the internal impedance of the pre-stressed PSEH, which was used as the optimal load resistance to simulate the electric power output. The simulated internal impedance and electric power output of the PSEH were validated by the experiment with good agreement. The FEM developed precisely predicted the electric power output, including the two identical power peaks, of the strongly coupled PSEH operating near resonance and outside resonance. In contrast, the FEM with the traditional RC matching showed only one power peak and significantly underestimated the power output near resonance, although it was still valid outside resonance. The developed FEM was also able to predict the effects of the static pre-stress and coupling efficiency figure of merit on the PSEH. The coupling efficiency figure of merit was found to increase the power output.Engineering and Physical Sciences Research Council (EPSRC

Harvesting energy from non-ideal vibrations

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 147-152).Energy harvesting has drawn significant interest for its potential to power autonomous low-power applications. Vibration energy harvesting is particularly well suited to industrial condition sensing, environmental monitoring and household environments where low-level vibrations are commonly found. While significant progress has been made in making vibration harvesters more efficient, most designs are still based on a single constant vibration frequency. However, most vibration sources do not have a constant frequency nor a single harmonic. Therefore, the inability to deal with non-ideal vibration sources has become a major technological obstacle for vibration energy harvesters to be widely applicable. To advance the state of vibration energy harvesting, this thesis presents a design methodology that is capable of dealing with two major non-ideal vibration characteristics: single harmonic frequency shifting and multi-frequency/broadband excitation. This methodology includes a broad-band impedance matching theory and a power electronics architecture to implement that theory. The generalized impedance matching theory extends the well known single frequency impedance matching model to a multi-frequency impedance matching model. By connecting LC tank circuits to the harvester output, additional resonant frequencies are created thereby enabling the energy harvesting system to effectively harvest energy from multi-harmonic vibration sources. However, the required inductors in the LC tank circuits are often too large (>10 H) to be implemented with discrete components. The power electronics proposed here addresses this issue by synthesizing the tank circuits with a power factor correction (PFC) circuit. This circuit mainly consists of an H-bridge, which contains four FETs, and a control loop that turns the FETs on and off at the right time such that the load voltage and current display the characteristics of the multiple tank circuits. By using this proposed power electronics, we demonstrate dual-frequency energy harvesting from a single mechanically resonant harvester. Simulation and experimental results match well and demonstrate that the proposed power electronics is capable of implementing higher order multi-resonant energy harvesting systems. In conclusion, this thesis presents both a theoretical foundation and a power electronics architecture that enables simultaneous effective multi-frequency energy harvesting with a single mechanically resonant harvester. The tunability of the power electronics also provides the possibility of dynamic real-time tuning which is useful to track non-stationary vibration sources.by Samuel C. Chang.Ph.D

Piezoelectric Vibration Energy Harvesting From Coupled Structural-Acoustic Systems

A comprehensive theoretical and experimental study of the fundamentals and the underlying phenomena governing the operation of piezoelectric vibration energy harvesting from coupled structural-acoustic systems is presented. Analytical and finite element models are developed based on variational formulations to describe the energy harvesting from uncoupled structural elements as well as structural elements coupled with acoustic cavities. The models enable the predictions of the structural displacement, output electric voltage, and fluid pressure for various loading conditions on the energy harvesting system. The developed models also include dynamic magnification means to enhance the energy harvesting capabilities and enable harnessing of the vibration energy over a broader operating frequency range. The predictions of all the models are experimentally validated by using structural elements varying from beams to plates. Close agreements are demonstrated between the theoretical predictions and the obtained experimental results. The theoretical and experimental tools developed, in this dissertation, provide invaluable means for designing a wide variety of efficient energy harvesters for harnessing the vibrational energy inside automobiles, helicopters, aircrafts, and other types of structures that interact internally or externally with a fluid medium. With such harnessed energy, a slew of on-board sensors can be powered to enable the continuous monitoring of the condition and health of these structures without the need for external power sources

On the application of circuit theory and nonlinear dynamics to the design of highly efficient energy harvesting systems

Ambient dispersed mechanical vibrations are a viable energy source, that can be converted into usable electric power. Ambient vibrations are random process, that can be modeled by superposition of periodic signals. When most of the energy is concentrated in a narrow frequency band, a single periodic function may be a reasonable approximation. This work shows that circuit theory, complemented with nonlinear dynamics methods, are instrumental in designing efficient energy harvesters for ambient mechanical vibrations. It is also shown that the average extracted power can be maximized by a proper load matching, and that the introduction of nonlinearities results in a larger frequency bandwidth, increasing the efficiency of the harvester at frequencies close to the resonance. Even for the nonlinear harvester, the matched load boosts the performance by a large amount

Impedance-based finite element modelling of a highly-coupled and pre-stressed piezoelectric energy harvester

This work presents an experimentally validated impedance-based finite element model (FEM) of a highly-coupled prestressed piezoelectric energy harvester (PEH) with piezoelectric multilayer stacks (PMSs). The FEM first simulates the status of the PEH as a result of the static pre-stress. It then analyses the internal impedance || of the pre-stressed PEH, which is used as the optimal load resistance for power output generation. The developed FEM is able to precisely predict (1) the maximum power output at each frequency without the tedious load-resistance sweeping approach traditionally used; (2) the dual-power-peaks phenomenon of highly-coupled PEHs, which cannot be observed when using the traditional approach of = 1⁄. This model provides a useful tool for the design and optimization highlycoupled piezoelectric energy harvesters

Acoustic power distribution techniques for wireless sensor networks

Recent advancements in wireless power transfer technologies can solve several residual problems concerning the maintenance of wireless sensor networks. Among these, air-based acoustic systems are still less exploited, with considerable potential for powering sensor nodes. This thesis aims to understand the significant parameters for acoustic power transfer in air, comprehend the losses, and quantify the limitations in terms of distance, alignment, frequency, and power transfer efficiency. This research outlines the basic concepts and equations overlooking sound wave propagation, system losses, and safety regulations to understand the prospects and limitations of acoustic power transfer. First, a theoretical model was established to define the diffraction and attenuation losses in the system. Different off-the-shelf transducers were experimentally investigated, showing that the FUS-40E transducer is most appropriate for this work. Subsequently, different load-matching techniques are analysed to identify the optimum method to deliver power. The analytical results were experimentally validated, and complex impedance matching increased the bandwidth from 1.5 to 4 and the power transfer efficiency from 0.02% to 0.43%. Subsequently, a detailed 3D profiling of the acoustic system in the far-field region was provided, analysing the receiver sensitivity to disturbances in separation distance, receiver orientation and alignment. The measured effects of misalignment between the transducers are provided as a design graph, correlating the output power as a function of separation distance, offset, loading methods and operating frequency. Finally, a two-stage wireless power network is designed, where energy packets are inductively delivered to a cluster of nodes by a recharge vehicle and later acoustically distributed to devices within the cluster. A novel dynamic recharge scheduling algorithm that combines weighted genetic clustering with nearest neighbour search is developed to jointly minimise vehicle travel distance and power transfer losses. The efficacy and performance of the algorithm are evaluated in simulation using experimentally derived traces that presented 90% throughput for large, dense networks.Open Acces

Piezoelectric Energy Harvesting: Enhancing Power Output by Device Optimisation and Circuit Techniques

Energy harvesting; that is, harvesting small amounts of energy from environmental sources such as solar, air flow or vibrations using small-scale (≈1cm 3 ) devices, offers the prospect of powering portable electronic devices such as GPS receivers and mobile phones, and sensing devices used in remote applications: wireless sensor nodes, without the use of batteries. Numerous studies have shown that power densities of energy harvesting devices can be hundreds of µW; however the literature also reveals that power requirements of many electronic devices are in the mW range. Therefore, a key challenge for the successful deployment of energy harvesting technology remains, in many cases, the provision of adequate power. This thesis aims to address this challenge by investigating two methods of enhancing the power output of a piezoelectric-based vibration energy harvesting device. Cont/d