Die Weiterentwicklung klassischer, elektronischer Identifikationstechnologien leistet einen wichtigen Beitrag zum technischen Fortschritt in Industrie, Logistik und Gesundheitswesen. Die vorliegende Dissertationsschrift beschreibt die Entwicklung eines Dual-Feed-Antennendesigns für passive UHF-RFID-Transponder auf kritischen Oberflächen. Die zu Grunde liegende Antennenstruktur besteht aus einem Microstrip-Patch unter Verwendung eines verlustarmen Substratmaterials. Dieser erfährt eine Optimierung hinsichtlich seiner Lesereichweite, insbesondere auf kritischen Oberflächen. Ein Zwei-Port-Konzept mit gekoppeltem Feed-Line-Anpassnetzwerk reduziert die Anzahl benötigter, diskreter Komponenten und ermöglicht eine kostengünstige Herstellung mittels klassischer Ätzverfahren. Verschiedene Ansätze zur Modellierung und zur analytischen Berechnung der Antennenparameter werden dargestellt. Des Weiteren erfolgt eine Verifikation der Antennenstruktur anhand eines Konzepts für einen passiven Energy-Harvesting-RFID-Transponder, der zur Temperaturüberwachung in den genannten Branchen eingesetzt werden kann. Dieses Konzept schließt ein effizientes Energiemanagement mittels eines Ultra-Low-Power-Mikrocontrollers sowie Ansätze zur Energiegewinnung und -speicherung mit ein und stellt die Wahl wichtiger Systemparameter und Bauelemente anhand anwendungsspezifischer Abschätzungen dar.

With higher frequencies now being used in RFID systems, antennas are becoming much smaller resulting in more space on tags that can be used for innovative array designs to harvest more wireless energy. This master's thesis outlines and details a new methodology for designing and simulating the staggered pattern charge collector, a technique to improve harvesting wireless energy. Staggered pattern charge collectors enable RFID tag's to produce a higher DC voltage from a charge pump circuit by creatively using multiple arrays to increase the antenna power conversion gain without limiting the half power beamwidth. This thesis discusses the basics of patch antennas and charge pumps as well as an optimization technique for the staggered pattern array by maximizing integrated power conversion gain (IPCG). An example of a staggered pattern charge collector is fully specified from design through simulation, in preparation for fabrication. This methodology allows for the staggered pattern charge collectors to be designed, simulated, and fabricated quickly and effectively.

Structural health monitoring systems provide a promising route to real-time data for analyzing the current state of large structures. In the wake of two high-profile bridge collapses due to an aging highway infrastructure, the interest in implementing such systems into fracture-critical and structurally deficient bridges is greater now than at any point in history. Traditionally, these technologies have not been cost-effective as bridges lack existing wiring architecture and the addition of this is cost prohibitive. Modern wireless sensor networks (WSN) now present a viable alternative to traditional networking; however, these systems must incorporate localized power sources capable of decade-long operation with minimal maintenance. To this end, this thesis explores the development of two energy harvesting systems capable of long-term bridge deployment with minimal maintenance. First, an electromagnetic, linear, vibrational energy harvester is explored that utilizes the excitations from passing traffic to induce motion in a translating permanent magnet mass. This motion is then converted to electrical energy using Faraday’s law of induction. This thesis presents a review of vibrational energy harvesting literature before detailing the process of designing, simulating, prototyping, and testing a selected design. Included is an analysis of the effects of frequency, excitation amplitude, load, and damping on the power production potential of the harvester. Second, a solar energy harvester using photovoltaic (PV) panels is explored for powering the critical gateway component of the WSN responsible for data aggregation. As solar energy harvesting is a more mature technology, this thesis focuses on the methodologies for properly sizing a solar harvesting system and experimentally validating the selected design. Fabrication of the prototype system was completed and field testing was performed in Austin, TX. The results validate the selected system’s ability to power the necessary 14 W DC load with a 0° panel azimuth angle (facing direct south) and 45° tilt. / text

Low-power requirements of contemporary sensing technology attract research on alternate power sources that can replace batteries. Energy harvesters function as power sources for sensors and other low-power devices by transducing the ambient energy into usable electrical form. Energy harvesters absorbing the ambient vibrations that have potential to deliver uninterrupted power to sensing nodes installed in remote and vibration rich environments motivate the research in vibrational energy harvesting. Piezoelectric bimorphs have been demonstrating a pre-eminence in converting the mechanical energy in ambient vibrations into electrical energy. Improving the performance of these harvesters is pivotal as the energy in ambient vibrations is innately low. The present work is organized in three major sections: firstly, audit of the energy available in a vibrating source and design for effective transfer of the energy to harvesters, secondly, design of vibration energy harvesters with a focus to enhance their performance, and lastly, identification of key performance metrics influencing conversion efficiencies and scaling analysis for MEMS harvesters. Typical vibration levels in stationary installations such as surfaces of blowers and ducts, and in mobile platforms such as light and heavy transport vehicles, are determined by measuring the acceleration signal. The frequency content in the signal is determined from the Fast Fourier Transform. A method of determining the energy associated with the vibrating source and the associated power using power spectral density of the signal is proposed. Power requirements of typical sensing nodes are listed with an intent to determine the adequacy of energy harvesting. Effective transfer of energy from a given vibration source is addressed through the concept of dynamic vibration absorption, which is a passive technique for suppressing unintended vibrations. Optimal absorption of energy from a vibration source entails the determination of absorber parameters such as resonant frequency and damping. We propose an iterative method to obtain these parameters for a generic case of large number of identical vibration absorbers resembling harvesters by minimizing the total energy absorbed by the system. The proposed method is verified by analysing the response of a set of cantilever absorber beams placed on a vibrating cantilever plate. We find, using our method, the values of the absorber mass, resonant frequency and damping of the absorber at which significant amount of energy supplied to the system flows into the absorber, a scenario which is favourable for energy harvesting. We emphasize through our work that monitoring energies in the system and optimizing their flow is both rational and vital for designing multiple harvesters that absorb energy from a given vibration source optimally. Enhancing the performance of piezoelectric energy harvesters through a multilayer and, in particular, a multistep configuration is presented. Partial coverage of piezoelectric material in steps along the length of a cantilever beam results in a multistep piezoelectric energy harvester. We find that the power generated by a multistep beam is almost twice of that generated by a multilayer harvester made out of the same volume of polyviny-lidine fluoride (PVDF), further corroborated experimentally. Improvements observed in the power generated prove to be a boon for weakly coupled, low pro le, piezoelectric materials. Thus, in spite of the weak piezoelectric coupling observed in PVDF, its energy harvesting capability can be improved significantly by using it in a multistep piezoelectric beam configuration. Besides, the effect of piezoelectric step length and thickness in a piezoelectric unimorph harvester and performance metrics such as piezoelectric coupling factor and efficiency of conversion are presented. Modeling of a hybrid energy harvester composed of piezoelectric and electromagnetic mechanisms of energy conversion motivated by the need to determine the contribution of each domain to the power generated by the harvester is presented, particularly, when multiple domains exist in a single harvester. Two exclusive schemes of energy transduction are represented using equivalent circuits, which allow modeling any additional transduction scheme employed in the hybrid harvester with relative ease. Furthermore, a method of determining optimal loads in the respective domains using the equivalent circuit of the hybrid harvester is presented. Four different hybrid energy harvesters were fabricated and evaluated for their performance in comparison with that estimated from the proposed models. Additionally, scaling laws for hybrid energy harvesters are presented. The power developed by both piezoelectric and electromagnetic domains is observed to decrease with width and length cubed. Power indices and figures of merit in a hybrid harvester are proposed and are used to estimate the efficiencies of the four fabricated hybrid harvesters. The important design parameters for micro scale harvesting are identified by performing scaling analysis on MEMS piezoelectric harvesters. Performance of energy harvesters is directly related to the harvester attributes, viz., size, material, and end-mass. Depending on the contribution from each attribute, the power developed by MEMS harvesters can vary widely. A novel method of delineating the power developed by a harvester using five exclusive factors representing scaling, composition, inertia, material, and power (SCIMP) factors is presented. Although the proposed method can be extended to bi-morph and multilayer harvesters, in the present work, we elucidate it by applying it to a MEMS unimorph. We also present a unique coupling factor that ensures maximum power factor in a harvester. As any tiny increment in the power generated would considerably improve the power densities of MEMS harvesters, we focus on enhancing the power developed by maximizing each of the five exclusive factors irrespective of material and size. Furthermore, we demonstrate the competence of the proposed method by applying it on nine different MEMS harvesters reported in the literature. Considering the close match between the reported and predicted performance, we emphasize that monitoring the proposed factors is sufficient to attain the best performance from a harvester.

Die wechselhafte Energiebereitstellung für drahtlose Sensorknoten durch Solarzellen stellt das Energiemanagement dieser Systeme vor große Herausforderungen. Bedingt durch saisonale und kurzfristige Effekte treten kontinuierlich Schwankungen in der Eingangsleistung auf, gleichzeitig soll jedoch eine zuverlässige und konstante Systemfunktion realisiert werden. Um dies miteinander zu vereinbaren, wird ein Modell zur Beschreibung der erwarteten Eingangsleistung aufgestellt, mit welchem der planmäßige Energieverlauf bestimmt werden kann. Dieser kann wiederum mit der realen Eingangsleistung verglichen werden, um den tatsächlichen energetischen Zustand des Sensorknotens zu bestimmen. Daraus lassen sich beispielsweise Entscheidungskriterien für die Steuerung der Energieverteilung oder Betriebszustände ableiten. Im Rahmen der Arbeit werden die physikalischen Hintergründe zur Modellierung der eingehenden Sonnenenergie beschrieben, der Stand der Technik zur Modellierung aufgezeigt und ein Modell als Basis für die weiteren Untersuchungen ausgewählt. Dieses wird auf die stark limitierte Hardware von drahtlosen Sensorknoten angepasst. Die Herausforderungen liegen dabei hauptsächlich in der geringen verfügbaren Rechenleistung, wenig Datenspeicher im System und dem Ziel, möglichst wenig Energie für die Berechnung zu verbrauchen. Im Ergebnis zeigt sich, dass ein angepasstes Modell auf drahtlosen Sensorsystemen umgesetzt werden kann und trotz der starken Limitierungen lauffähig ist. Es wird eine deutliche Verbesserung in der Verteilung der Energie über den Tag ermöglicht, wodurch sich trotz wechselhafter Quelle eine konstante Systemfunktion ergibt. Nebenher wird die Zuverlässigkeit und Ausfallsicherheit erhöht und Überdimensionierungen in Energiespeicher und Solarzelle können verringert werden. Das modellbasierte Energiemanagement stellt somit einen wichtigen Baustein für eine gesicherte Energieversorgung drahtloser Sensorsysteme dar. / The volatile energy supply by solar cells for wireless sensor nodes causes vast challenges for the energy management of such systems. Conditioned by seasonal and short time effects, the incoming power continuously varies. Simultaneously a reliable and constant function of the system has to be realized. To reconcile this, a model for the expected incoming solar power has been derived, which enables the estimation of the planned energy curve. This curve can be compared with the real progression of incoming power measured in parallel, to determine the current state of energy of a sensor node. This comparison is used to derive decision criteria for the control of the energy distribution or operating conditions. Within this work, the physical backgrounds for the modelling of the incoming solar energy and the state of the art of modelling solar power are described. A model is chosen as basis for further investigations and adapted to the limited hardware of wireless sensor nodes. The main challenges are the reduced processing power, few data memory in the system and the objective to consume as few energy as possible for the calculation. The results show that an adapted model can be implemented on wireless sensor systems and that it is executable despite the heavy limitations. This enables a distinct improvement of the distribution of energy across the day, which results in a constant systems function, despite the varying incoming power. At the same time the reliability and failure safety are being improved and the oversizing of the solar cell and the storage elements can be reduced. Therefore the model based energy management is an important component for a stable power supply of wireless sensor systems.

Energy harvesting is identified as a promising alternative solution for powering implantable biosensors. It can completely replace the batteries, which are introducing many limitations, and it enables the development of self-powered implantable biosensors. An interface circuit is necessary to correct for differences in the voltage and power levels provided by an energy harvesting device from one side, and required by biosensor circuits from another. This thesis investigates the available energy harvesting sources within the human body, selects the most suitable one and proposes the power management unit (PMU), which serves as an interface between a harvester and biosensor circuits. The PMU targets the efficient power transfer from the selected source to the implantable biosensor circuits. Based on the investigation of potential energy harvesting sources, a thermoelectric energy harvester is selected. It can provide relatively high power density of 100 μW/cm2 at very low temperature difference available in the human body. Additionally, a thermoelectric energy harvester is miniature, biocompatible, and it has an unlimited lifetime. A power management system architecture for thermoelectric energy harvesters is proposed. The input converter, which is the critical block of the PMU, is implemented as a boost converter with an external inductor. A detailed analysis of all potential losses within the boost converter is conducted to estimate their influence on the conversion efficiency. The analysis showed that the inevitable conduction and switching losses can be reduced by the proper sizing of the converter’s switches and that the synchronization losses can be almost completely eliminated by an efficient control circuit. Additionally, usually neglected dead time losses are proved to have a significant impact in implantable applications, in which they can reduce the efficiency with more than 2%. An ultra low power control circuit for the boost converter is proposed. The control is utilizing zero-current switching (ZCS) and zero-voltage switching (ZVS) techniques to eliminate the synchronization losses and enhance the efficiency of the boost converter. The control circuit consumes an average power of only 620 nW. The boost converter driven by the proposed control achieves the peak efficiency higher than 80% and can operate with harvested power below 5 μW. For high voltage conversion ratios, the proposed boost converter/control combination demonstrates significant efficiency improvement compared to state-of-the-art solutions. / <p>QC 20150413</p>

This thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.

Energy harvesting of ambient and aeroelastic vibrations is important for reducing the dependence of wireless sensing and networks on batteries. We develop a configuration for a piezoelectric energy harvester with the capability to wirelessly communicate vibration measurements while using those vibrations to power the sensing and communication devices. Particularly, we perform experiments that aim at identifying challenges to overcome in the development of such a configuration. Towards that objective, we successfully tested a self-powered real-time point-to-point wireless communication system between a vibration sensor and transmission and receiving modules. The sensing device and transmission module are powered by the vibrating object using a piezoelectric energy harvester. The communication is established by using two XBee modules. In the second part of this dissertation, we address the optimization of the output power of piezoelectric energy harvesters of aeroelastic vibrations. Given the complexity of high-fidelity simulations of the coupling between the fluid flow, structural response and piezoelectric transduction, we develop and experimentally validate a phenomelogical reduced-order model for energy harvesting from wake galloping. We also develop a high-fidelity simulation for the same phenomena. The modeling and high-fidelity simulations can be a part of a multi-disciplinary optimization framework to be used in the design and operation of galloping-based energy harvesters. / Doctor of Philosophy / Energy harvesting of ambient or flow-induced vibrations is important for reducing the dependence on batteries in wireless sensing and networks to monitor deterioration conditions, environmental pollution or wildlife conservation. Balancing the benefits and shortcomings of a specific approach, namely piezoelctric transduction, for energy harvesting from vibrations, we address a specific challenge related to the development of a configuration that allows for communicating measured vibrations using their power. Furthermore, given the low levels of output power from piezoelectric transduction, we address the need to optimize power output levels through the development of predictive models that depend on geometry and speed of the fluid flow.

With the threatening of global warming and energy crises, searching for renewable and green energy resources with reduced carbon emissions is one of the most urgent challenges to the sustainable development of human civilization. In the past decades, increasing research efforts have been committed to seek for clean and renewable energy sources as well as to develop renewable energy technologies. Mechanical motion ubiquitously exists in ambient environment and people’s daily life. In recent years, it becomes an attractive target for energy harvesting as a promising supplement to traditional fuel sources and a potentially alternative power source to battery-operated electronics. Until recently, the mechanisms of mechanical energy harvesting are limited to transductions based on piezoelectric effect, electromagnetic effect, electrostatic effect and magnetostrictive effect. Widespread usage of these techniques is likely to be shadowed by possible limitations, such as structure complexity, low power output, fabrication of high-quality materials, reliance on external power sources and little adaptability on structural design for different applications. In 2012, triboelectric nanogenerator (TENG), a creative invention for harvesting ambient mechanical energy based on the coupling between triboelectric effect and electrostatic effect has been launched as a new and renewable energy technology. The concept and design presented in this thesis research can greatly promote the development of TENG as both sustainable power sources and self-powered active sensors. And it will greatly help to define the TENG as a fundamentally new green energy technology, featured as being simple, reliable, cost-effective as well as high efficiency.

The main objectives of this dissertation is to investigate the prospects of embedded thermoelectric devices integrated in a chip package and to develop a design methodology aimed at taking advantage of the on-chip on-demand cooling capabilities of the thermoelectric devices. First a simulation framework is established and validated against experimental results, which helps to study the cooling capabilities of embedded thermoelectric coolers (TEC) in both a transient and steady state. The potential for up to 15°C of total cooling has been shown. The thermal simulation framework allows for rapid assessment of TEC and system level thermal performance. Next, the thesis develops a co-simulation environment that is capable of simulating the thermal and electrical domain and couples them to design intelligent TEC controllers. These controllers are implemented on chip and can leverage the transient cooling capability of the device. The controllers are simulated within the co-simulation environment and their potential to control high power chip events are thoroughly investigated. The system level overheads are considered and discussions on implementation techniques are presented. The co-simulation framework is also extended to allow for simulation of real predictive technology microprocessor cores and their workloads. Finally the thesis implements a fully on-chip autonomous energy system that takes advantage of the TEC in its reverse energy harvesting mode and uses the same device to harvest energy and use the energy to power the on-chip cooling circuit. This increases the overall energy efficiency of the cooler and verifies the TEC control methods.