Piezoelectric energy harvesting utilizing metallized poly-vinylidene fluoride (PVDF)

The primary objective of the enclosed thesis was to identify and develop a viable concept for an autonomous sensor system that could be implemented onto the surface of a road. This was achieved by an analysis of combinations of materials, sensing methods, power sources, microsystems, energy storage options, and wireless data transmission systems; the sub-systems required for an autonomous sensor. Comparison of sensing methods for the application of an on-road, autonomous sensor yielded a piezoelectric material as the ideal choice. A 52μm thin film of poly- vinylidene fluoride (PVDF) was chosen and coated with Ag electrodes on both sides.This was due to many constraints imposed by the intended environment including: physical, electrical, thermal, and manufacturing characteristics. One major hurdle in providing an autonomous sensor is the power source for the sensing, encoding, and transmission of data. Research involved determining the option best suited for providing a power source for the combination of sensors and wireless telemetry components. An energy budget of 105μJ was established to determine an estimate of energy needed to wirelessly transmit data with the selected RF transmitter. Based on these results, several candidates for power sources were investigated, and a piezoelectric energy harvesting system was identified to be the most suitable. This is an ideal case as the sensor system was already based on a piezoelectric material as the sensing component. Thus, a harvesting circuit and the sensor can be combined into one unit, using the same material. By combining the two functions into a single component, the complexity, cost and size of the unit are effectively minimized. In order to validate the conclusions drawn during this sensor system analysis and conceptual research, actual miniaturized systems were designed to demonstrate the ability to sense and harvest energy for the applications in mind. This secondary aspect of the research was a proof-of-concept, developing two prototype energy harvesting/sensing systems. The system designed consisted of a PVDF thin film with a footprint of 0.2032 m x 0.1397m x 52μm. This film was connected to an energy-harvesting prototype circuit consisting of a full-wave diode bridge and a storage capacitor. Two prototypes were built and tested, one with a 2.2μF capacitor, the other with a 0.1mF capacitor. The film was first connected to an oscilloscope and impulsed in an open circuit condition to determine the sensor response to a given signal. Secondly, the energy harvesting circuits were tested in conjunction with the film to test the energy supply component of the system. Lastly, the film and both energy-harvesting systems underwent full scale testing on a road using a vehicle as the stimulus. Both systems showed excellent rectification of the double polarity input with an evident rise in voltage across the capacitor, meaning energy was harvested. Typical results from the tests yielded 600-800mV across the 2.2μF capacitor, harvesting only a few μJ of energy. The 0.1mF capacitor system yielded approximately 4V per vehicle axle across the capacitor, harvesting 400-800μJ of energy. This equates to 4-8 times the required energy for wireless data transmission of the measurement data, which was estimated by other research groups to be on the order of 105μJ for the given system, and therefore proves the concept both, for bench-top and full-scale on-road experiments under controlled laboratory conditions

Energy harvesting from human and machine motion for wireless electronic devices

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A Nail-Size Piezoelectric Energy Harvesting System Integrating a MEMS Transducer and a CMOS SSHI Circuit

Piezoelectric vibration energy harvesting has drawn much interest to power distributed wireless sensor nodes for Internet of Things (IoT) applications where ambient kinetic energy is available. For certain applications, the harvesting system should be small and able to generate sufficient output power. Standard rectification topologies such as the full-bridge rectifier are typically inefficient when adapted to power conditioning from miniaturized harvesters. Therefore, active rectification circuits have been researched to improve overall power conversion efficiency, and meet both the output power and miniaturization requirements while employing a MEMS harvester. In this paper, a MEMS piezoelectric energy harvester is designed and cointegrated with an active synchronized switch harvesting on inductor (SSHI) rectification circuit designed in a CMOS process to achieve high output power for system miniaturization. The system is fully integrated on a nail-size board, which is ready to provide a stable DC power for low-power mini sensors. A MEMS energy harvester of 0.005 cm3 size, co-integrated with the CMOS conditioning circuit, outputs a peak rectified DC power of 40.6 µW and achieves a record DC power density of 8.12 mW/cm3 when compared to state-of-the-art harvesters

Doctor of Philosophy

dissertationMicroelectromechanical systems (MEMS) resonators on Si have the potential to replace the discrete passive components in a power converter. The main intention of this dissertation is to present a ring-shaped aluminum nitride (AlN) piezoelectric microreson

Real World Assessment of an Auto-parametric Electromagnetic Vibration Energy Harvester

The convention within the eld of vibration energy harvesting (VEH) has revolved around designing resonators with natural frequencies that match single fixed frequency sinusoidal input. However, real world vibrations can be random, multi-frequency, broadband and time-varying in nature. Building upon previous work on auto-parametric resonance, the fundamentally different approach allows multiple axes vibration and has the potential to achieve higher power density as well as wider operational frequency bandwidth. This paper presents the power response of a packaged auto-parametric VEH prototype (practical operational volume 126 cm^3) towards various real world vibration sources including vibration of a bridge, a compressor motor as well as an automobile. At auto-parametric resonance (driven at 23.5 Hz and 1 grms), the prototype can output a peak of 78.9 mW and 4.5 Hz of -3dB bandwidth. Furthermore, up to ~1 mW of average power output was observed from the harvester on the Forth Road Bridge. The harvested electrical energy from various real world sources were used to power up a power conditioning circuit, a wireless sensor mote, a MEMS (micro-electromechanical system) accelerometer and other low power sensors. This demonstrates the concept of self-sustaining vibration-powered wireless sensor systems in real world scenarios, to potentially realise maintenance-free autonomous structural health and condition monitoring.This work was supported by EPSRC (grant EP/L010917/1) and the Cambridge Centre for Smart Infrastructure and Construction

Electromechanical modeling and experimental analysis of a compression-based piezoelectric vibration energy harvester

Over the past few decades, wireless sensor networks have been widely used in the field of structure health monitoring of civil, mechanical, and aerospace systems. Currently, most wireless sensor networks are battery-powered and it is costly and unsustainable for maintenance because of the requirement for frequent battery replacements. As an attempt to address such issue, this article theoretically and experimentally studies a compression-based piezoelectric energy harvester using a multilayer stack configuration, which is suitable for civil infrastructure system applications where large compressive loads occur, such as heavily vehicular loading acting on pavements. In this article, we firstly present analytical and numerical modeling of the piezoelectric multilayer stack under axial compressive loading, which is based on the linear theory of piezoelectricity. A two-degree-of-freedom electromechanical model, considering both the mechanical and electrical aspects of the proposed harvester, was developed to characterize the harvested electrical power under the external electrical load. Exact closed-form expressions of the electromechanical models have been derived to analyze the mechanical and electrical properties of the proposed harvester. The theoretical analyses are validated through several experiments for a test prototype under harmonic excitations. The test results exhibit very good agreement with the analytical analyses and numerical simulations for a range of resistive loads and input excitation levels. © 2014 The Author(s)

Design and simulation of contour mode MEMS resonator on Si for power converters

pre-printMicroelectromechanical systems (MEMS) resonators on Si have the potential to replace the discrete passive components in a power converter. These devices not only can reduce the size and weight of the converter but also can facilitate the implementation of power converter on a chip. In this paper, a contour mode MEMS resonator has been presented that can achieve resonant frequency in the range of several MHz, and the operating principles of the device have been discussed in detail. This device was simulated in COMSOL Multiphysics, and a resonant converter has been simulated in PSIM to harvest energy from a thermo electric generator. The equivalent electrical model of the MEMS resonator was incorporated into that circuit validating the feasibility of using MEMS resonator in power conversion systems. Detailed fabrication process of the device has been presented and implemented at University of Utah's Nanofab. Initial experimental characteristics of the resonator have been included in the paper

MULTI‐PHYSICAL MODELLING AND PROTOTYPING OF AN ENERGY HARVESTING SYSTEM INTEGRATED IN A RAILWAY PNEUMATIC SUSPENSION

The aim of this PhD thesis is the investigation of an energy harvesting system to be integrated in a railway pneumatic spring to recovery otherwise wasted energy source from suspension vibration. Exploiting the piezoelectric effect to convert the mechanical energy into an electrical one, the final scope consists on the use of this system to power supply one or more sensors that can give useful information for the monitoring and the diagnostics of vehicle or its subsystems. Starting from the analysis of the energy sources, a multi‐physical approach to the study of an energy harvesting system is proposed to take into account all physics involved in the phenomenon, to make the most of the otherwise wasted energy and to develop a suitable and affordable tool for the design. The project of the energy harvesting device embedded in a railway pneumatic spring has been carried out by means of using a finite element technique and multi‐physics modelling activity. The possibility to combine two energy extraction processes was investigated with the purpose of making the most of the characteristics of the system and maximize the energy recovering. Exploiting commercial piezoelectric transducers, an experimental activity was conducted in two steps. A first mock‐up was built and tested on a shaker to develop the device and to tune the numerical model against experimental evidence. In the second step a fullscale prototype of an air spring for metro application with the EH system was realized. In order to test the full‐scale component, the design of a new test bench was carried out. Finally, the Air spring integrated with the EH device was tested and models validated

The Convergence of Parametric Resonance and Vibration Energy Harvesting

Energy harvesting is an emerging technology that derives electricity from the ambient environment in a decentralised and self-contained fashion. Applications include self-powered medical implants, wearable electronics and wireless sensors for structural health monitoring. Amongst the vast options of ambient sources, vibration energy harvesting (VEH) has attracted by far the most research attention. Two of the key persisting issues of VEH are the limited power density compared to conventional power supplies and confined operational frequency bandwidth in light of the random, broadband and fast-varying nature of real vibration. The convention has relied on directly excited resonance to maximise the mechanical-to-electrical energy conversion efficiency. This thesis takes a fundamentally different approach by employing parametric resonance, which, unlike the former, its resonant amplitude growth does not saturate due to linear damping. Therefore, parametric resonance, when activated, has the potential to accumulate much more energy than direct resonance. The vibrational nonlinearities that are almost always associated with parametric resonance can offer a modest frequency widening. Despite its promising theoretical potentials, there is an intrinsic damping dependent initiation threshold amplitude, which must be attained prior to its onset. The relatively low amplitude of real vibration and the unavoidable presence of electrical damping to extract the energy render the onset of parametric resonance practically elusive. Design approaches have been devised to passively minimise this initiation threshold. Simulation and experimental results of various design iterations have demonstrated favourable results for parametric resonance as well as the various threshold-reduction mechanisms. For instance, one of the macro-scale electromagnetic prototypes (∼1800 cm3) when parametrically driven, has demonstrated around 50% increase in half power band and an order of magnitude higher peak power (171.5 mW at 0.57 ms−2) in contrast to the same prototype directly driven at fundamental resonance (27.75 mW at 0.65 ms−2). A MEMS (micro-electromechanical system) prototype with the additional threshold-reduction design needed 1 ms−2 excitation to activate parametric resonance while a comparable device without the threshold-reduction mechanism required in excess of 30 ms−2. One of the macro-scale piezoelectric prototypes operated into auto-parametric resonance has demon-strated notable further reduction to the initiation threshold. A vacuum packaged MEMS prototype demonstrated broadening of the frequency bandwidth along with higher power peak (324 nW and 160 Hz) for the parametric regime compared to when operated in room pressure (166 nW and 80 Hz), unlike the higher but narrower direct resonant peak (60.9 nW and 11 Hz in vacuum and 20.8 nW and 40 Hz in room pressure). The simultaneous incorporation of direct resonance and bi-stability have been investigated to realise multi-regime VEH. The potential to integrate parametric resonance in the electrical domains have also been numerically explored. The ultimate aim is not to replace direct resonance but rather for the various resonant phenomena to complement each other and together harness a larger region of the available power spectrum