Pyroelectric energy scavenging is the process of converting wasted energy from a system to power another one, based on the pyroelectric effect of piezoelectric materials. Pyroelectrically generated power is a function of the surface of material, the pyroelectric coefficient, and the temporal temperature gradient. In the current project, a simple model is developed to predict the power generation based on the temporal change in temperature of material. In addition, a model is validated with experimental measurements from several piezoelectric materials. It is shown that energy generation can be enhanced by using piezoelectric materials with significantly higher pyroelectric coefficients such as pre-stressed piezoelectric materials or thin films. Meanwhile, a method of continuously harvesting energy from pyroelectric materials is demonstrated using an innovative cyclic heating scheme. Besides, simple analytic expressions are developed for ideal voltage, power and power densities as a function of pyroelectric constant, permittivity, surface area, thickness, temperature variation.

In recent years, there has been recent increase in the deployment of wireless sensor networks. These sensors are typically powered by a battery which has limited life span. This problem can be overcomed by using energy scavenging or power harvesting which is the process of converting ambient energy from the environment into usable electrical energy. It can be used in applications such as remote patient monitoring, implantable sensors, machinery/equipment monitoring and so on. The thesis presents the RF scavenging system and mainly focuses on the study of the rectifier architectures which is one of the key components in the RF scavenging system. The thesis also provides the design challenges while implementing the different rectifier structures, which are PMOS bridge rectifier, CMOS differential rectifier and charge pump. The functionality of the rectifier structures are studied by simulation using RF signal of 900 MHz and implemented in 0.35μm and 65 nm technologies to compare the results. The simulation results shows that there is a tradeoff between high output DC voltage and high power efficiency. Maximum DC output voltage of 1 V is obtained from input amplitude level of 0.16 V using 7-stage charge pump rectifier. In the other hand maximum power efficiency of 23 % is obtained using CMOS differential rectifier.

With ample radio transmitters scattered throughout urban landscape, RF energy scavenging emerges as a promising approach to extract energy from propagating radio waves in the ambient environment to continuously charge low power electronics. With the ability of generating power from RF energy, the need for batteries could be eliminated. The effective distance of a RF energy scavenging system is highly dependent on its conversion efficiency. This results in significant limitations on the mobility and space requirement of conventional RF energy scavenging systems as they operate only in presence of physically large antennas and conversion circuits to achieve acceptable efficiency. This thesis presents a number of novel design strategies in the antenna and rectifier designs for miniaturized RF energy scavenging system. In the first stage, different energy scavenging systems including solar energy scavenging system, thermoelectric energy scavenging system, wind energy scavenging system, kinetic energy scavenging system, radio frequency energy scavenging system and hybrid energy scavenging system are investigated with regard to their principle and performance. Compared with the other systems, RF energy scavenging system has its advantages on system size and power density with relatively stable energy source. For a typical RF energy scavenging system, antenna and rectifier (AC-DC convertor) are the two essential components to extract RF energy and convert to usable electricity. As the antenna occupies most of the area in the RF energy scavenging system, reduction in antenna size is necessary in order to design a miniaturized system. Several antennas with different characteristics are proposed in the second stage. Firstly, ultra-wideband microstrip antennas printed on a thin substrate with a thickness of 0.2 mm are designed for both half-wave and full-wave wideband RF energy scavenging. Ambient RF power is distributed over a wide range of frequency bands. A wideband RF energy scavenging system can extract power from different frequencies to maximize the input power, hence, generating sufficient output power for charging devices. Wideband operation with 4 GHz bandwidth is obtained by the proposed microstrip antenna. Secondly, multi-band planar inverted-F antennas with low profile are proposed for frequency bands of GSM 900, DCS 1800 and Wi-Fi 2.4 GHz, which are the three most promising frequency bands for RF energy scavenging. Compared with previous designs, the triple band antenna has smaller dimensions with higher antenna gain. Thirdly, a novel miniature inverted-F antenna without empty space covering Wi-Fi 2.4 GHz frequency band is presented dedicated for indoor RF energy scavenging. The antenna has dimensions of only 10 × 5 × 3.5 mm3 with appreciable efficiency across the operating frequency range. In the final stage, a passive CMOS charge pump rectifier in 0.35 μm CMOS technology is proposed for AC to DC conversion. Bootstrapping capacitors are employed to reduce the effective threshold voltage drop of the selected MOS transistors. Transistor sizes are optimized to be 200/0.5 μm. The proposed rectifier achieves improvements in both power conversion efficiency and voltage conversion efficiency compared with conventional designs. The design strategies proposed in this thesis contribute towards the realization of miniaturized RF energy scavenging systems.

The purpose of this thesis is the development and analysis of applications for ionic polymers as energy harvesting devices. The specific need is a self-contained energy harvester to supply renewable power harvested from ambient vibrations to a wireless sensor. Ionic polymers were investigated as mechanical to electrical energy transducers. An ionic polymer device was designed to harvest energy from vibrations and supply power for a wireless structural health monitoring sensor.The ionic polymer energy harvester is tested to ascertain whether the idea is feasible. Transfer functions are constructed for both the open-circuit voltage and the closed-circuit current. The impedance of the device is also quantified. Using the voltage transfer function and the current transfer function it is possible to calculate the power being produced by the device.Power generation is not the only energy harvesting application of ionic polymers, energy storage is another possibility. The ionic polymer device is tested to characterize its charge and discharge capabilities. It is charged with both DC and AC currents. An energy storage comparison is performed between the ionic polymers and capacitors. While the polymers performed well, the electrolytic capacitors are able to store more energy. However, the ionic polymers show potential as capacitors and have the possibility of improved performance as energy storage devices. Current is measured across resistive loads and the supplied power is calculated. Although the power is small, the ionic polymers are able to discharge energy across a load proving that they are capable of supplying power. / Master of Science

As the world faces an energy crisis with depleting fossil fuel reserves, alternate energy sources are being researched ever more seriously. In addition to renewable energy sources, energy recycling and energy scavenging technologies are also gaining importance. Technologies are being developed to scavenge energy from ambient sources such as vibration, radio frequency and low grade waste heat, etc. Waste heat is the most common form of wasted energy and is the greatest potential source of energy scavenging. Pyroelectricity is the property of some materials to change the surface charge distribution with the change in temperature. These materials produce current as temperature varies in them and can be utilized to convert thermal energy to electrical energy. In this work a novel approach to vary temperature in pyroelectric material to convert energy has been investigated. Microelectromechanical Systems or MEMS is the new technology trend that takes advantage of unique physical properties at micro scale to create mechanical systems with electrical interface using available microelectronic fabrication techniques. MEMS can accomplish functionalities that are otherwise impossible or inefficient with macroscale technologies. The energy harvesting device modeled and developed for this work takes full benefit of MEMS technology to cycle temperature in an embedded pyroelectric material to convert thermal energy from low grade waste heat to electrical energy. Use of MEMS enables improved performance and efficiency and overcomes problems plaguing previous attempts at pyroelectric energy conversion. A Numerical model provides accurate prediction of MEMS performance and sets design criteria, while physics based analytical model simplifies design steps. A SPICE model of the MEMS device incorporates electrical conversion and enables electrical interfacing for current extraction and energy storage. Experimental results provide practical implementation steps towards of the modeled device. Under ideal condition the proposed device promises to generate energy density of 400 W/L.

A conversão de vibração em energia elétrica tem sido investigada por diversos grupos de pesquisa na última década. A principal motivação é a prospecção de fontes alternativas de energia elétrica para sistemas eletroeletrônicos remotamente operados e com fontes limitadas de energia. Diferentes mecanismos de transdução são investigados na literatura para a coleta de energia, entretanto, o piezelétrico tem se destacado devido à densidade de energia que proporciona e também facilidade de uso. Uma alternativa promissora que começa a ser estudada por alguns grupos de pesquisas é a conversão de energia de oscilações aeroelásticas em energia elétrica. Apesar da natureza destrutiva da maioria dos fenômenos aeroelásticos, eles apresentam um grande potencial para o estudo de novos mecanismos e sistemas para coleta de energia. A conversão piezelétrica de energia a partir de oscilações aeroelásticas lineares tem sido investigada. Entretanto, a geração piezoaeroelástica de energia pode se tornar mais atrativa e prática se realizada a partir sistemas aeroelásticos não lineares. A conversão se daria a partir de oscilações persistentes e com amplitude limitada (oscilações em ciclo limite – LCO) ocorrendo em um amplo intervalo de velocidades de escoamento. Define-se o objetivo deste projeto como a investigação numérica da conversão piezelétrica de energia a partir de oscilações aeroelásticas não lineares. Um modelo por elementos finitos para placa plana com piezocerâmicas é desenvolvido, respeitando-se as hipóteses de uma placa de von Kàrmàn. O carregamento aerodinâmico não estacionário é determinado a partir do método de malha de dipolos e uma aproximação do domínio do tempo obtida a partir da formulação apresentada por Roger. Os resultados eletroaeroelásticos são apresentados para asas com diferentes razões de aspecto investigadas em uma ampla faixa de velocidades e considerando-se diversos valores de resistores no domínio elétrico. / The converting of vibration into usable electrical energy has been investigated by several researches groups in the last decade. The main motivation is the possibility of obtaining alternatives electrical energy sources to power electronic system remotely operated and with limited energy sources. Different transduction mechanism has been presented in the energy harvesting literature. However the piezoelectric has been gained more attention because not only of its power density but also its ease of use. A promissory alternative that is becoming studied is the converting of aeroelastic oscillation into electrical energy. Despite of the destructive nature of unstable aeroelastic phenomena (such as, flutter), they present a great potential to the study of innovative mechanism to harvest energy. Although the piezoelectric energy conversion using linear aeroelastic has been investigated in the literature, the use of non linear aeroelastic system can be more practical and attractive. The non linear aeorelastic harvesting occurs by persistent oscillation and with limited amplitudes (Limited Cycle Oscillation – LCO) and can be performed by considerable velocity interval greater than the linear flutter speed. The objective of this work is to investigate the energy harvesting by non linear aeroelastic oscillation. A finite element model of a thin plate (with piezoceramics) is developed), using the non linear hypothesis of von Karman. The unstable aerodynamic loading is obtained by a doublet-lattice method (DLM) and with its time domain conversion using the Roger approximation. The eletroaeroelastic results are presented for several wings with different aspect ratios, and with different resistance values in the electrical domain. The eletroaeroelastic results of the generator wing are investigated for several airspeed greater than its linear flutter speed.

A conversão de vibração em energia elétrica tem sido investigada por diversos grupos de pesquisa na última década. A principal motivação é a prospecção de fontes alternativas de energia elétrica para sistemas eletroeletrônicos remotamente operados e com fontes limitadas de energia. Diferentes mecanismos de transdução são investigados na literatura para a coleta de energia, entretanto, o piezelétrico tem se destacado devido à densidade de energia que proporciona e também facilidade de uso. Uma alternativa promissora que começa a ser estudada por alguns grupos de pesquisas é a conversão de energia de oscilações aeroelásticas em energia elétrica. Apesar da natureza destrutiva da maioria dos fenômenos aeroelásticos, eles apresentam um grande potencial para o estudo de novos mecanismos e sistemas para coleta de energia. A conversão piezelétrica de energia a partir de oscilações aeroelásticas lineares tem sido investigada. Entretanto, a geração piezoaeroelástica de energia pode se tornar mais atrativa e prática se realizada a partir sistemas aeroelásticos não lineares. A conversão se daria a partir de oscilações persistentes e com amplitude limitada (oscilações em ciclo limite – LCO) ocorrendo em um amplo intervalo de velocidades de escoamento. Define-se o objetivo deste projeto como a investigação numérica da conversão piezelétrica de energia a partir de oscilações aeroelásticas não lineares. Um modelo por elementos finitos para placa plana com piezocerâmicas é desenvolvido, respeitando-se as hipóteses de uma placa de von Kàrmàn. O carregamento aerodinâmico não estacionário é determinado a partir do método de malha de dipolos e uma aproximação do domínio do tempo obtida a partir da formulação apresentada por Roger. Os resultados eletroaeroelásticos são apresentados para asas com diferentes razões de aspecto investigadas em uma ampla faixa de velocidades e considerando-se diversos valores de resistores no domínio elétrico. / The converting of vibration into usable electrical energy has been investigated by several researches groups in the last decade. The main motivation is the possibility of obtaining alternatives electrical energy sources to power electronic system remotely operated and with limited energy sources. Different transduction mechanism has been presented in the energy harvesting literature. However the piezoelectric has been gained more attention because not only of its power density but also its ease of use. A promissory alternative that is becoming studied is the converting of aeroelastic oscillation into electrical energy. Despite of the destructive nature of unstable aeroelastic phenomena (such as, flutter), they present a great potential to the study of innovative mechanism to harvest energy. Although the piezoelectric energy conversion using linear aeroelastic has been investigated in the literature, the use of non linear aeroelastic system can be more practical and attractive. The non linear aeorelastic harvesting occurs by persistent oscillation and with limited amplitudes (Limited Cycle Oscillation – LCO) and can be performed by considerable velocity interval greater than the linear flutter speed. The objective of this work is to investigate the energy harvesting by non linear aeroelastic oscillation. A finite element model of a thin plate (with piezoceramics) is developed), using the non linear hypothesis of von Karman. The unstable aerodynamic loading is obtained by a doublet-lattice method (DLM) and with its time domain conversion using the Roger approximation. The eletroaeroelastic results are presented for several wings with different aspect ratios, and with different resistance values in the electrical domain. The eletroaeroelastic results of the generator wing are investigated for several airspeed greater than its linear flutter speed.

Récupérer l'énergie mécanique ambiante est une alternative prometteuse afin d'assurer l'autonomie énergétique d'appareils nomades. Le développement des générateurs électrostatiques souples reste toutefois à ce jour anecdotique du fait des hautes tensions de polarisation employées, de la nécessité de grandes déformations mécaniques mais aussi de l'utilisation de matériaux peu conventionnels et mal caractérisés. Le but de cette thèse est d'apporter des avancées scientifiques et des solutions aux verrous technologiques précités. Tout d'abord, une caractérisation rigoureuse des propriétés électriques et mécaniques de deux matériaux communément utilisés pour ces applications (acrylate VHB 4910 et silicone Polypower) nous a donné accès aux propriétés physiques dans un fonctionnement réel de ces polymères : influence de la précontrainte, de la nature des électrodes... Ces données ont permis d'élaborer des lois analytiques fiables que nous avons ensuite insérées dans un modèle thermodynamique permettant de définir avec précision les puissances et densités d'énergie récupérables pour ces générateurs. Des pistes d'amélioration des matériaux utilisés dans les applications générateurs peuvent être dégagées de notre modèle. Le second verrou à lever concerne la source haute tension de polarisation nécessaire à ces générateurs électrostatiques. Pour cela, nous avons proposé une solution innovante couplant l'élastomère diélectrique à un électret. Différentes configurations de générateurs hybrides dans des géométries 2D et 3D ont été évaluées. Enfin, nous avons réalisé un prototype qui a délivré une puissance de l'ordre de 35µW sachant qu'une optimisation de ce prototype est réalisable et que des puissances récupérées de plusieurs centaines de µW sont tout à fait réalistes. / Scavenging mechanical ambient energy is a promising solution to ensure the autonomy of wearable transducers. Nevertheless, the development of soft electrostatic generator (DEG) is up to now slow down due to the use of high bias voltage, high strain and innovative mischaracterized materials. The aim of this Ph-D thesis is to propose innovative solutions to these technological barriers. Firstly, a complete characterization of the electrical and mechanical properties of two commonly used dielectric polymer (acrylate VHB 4910 and silicone Polypower) has revealed the true physical properties of these polymers and especially the influence of the pre-stress and the nature of the electrode used. Thanks to these data, reliable analytic laws have been proposed and inserted into our thermodynamic model in order to predict the output power and scavenged energy density for the DEG. Moreover, our model allow us to propose improvements for the materials used in these applications. The second challenge is to propose an alternative to the high bias voltage needed for these soft generators. We have proposed an innovative solution combining an electret and a dielectric elastomer. Various configurations of hybrid generators in 2D or 3D geometry have been modelled and evaluated. Finally, a prototype has been designed allowing scavenging 35µW. With an appropriate optimization of our prototype, hundreds of µW can be scavenged.

Improvements in embedded electronics which have effectively reduced power consumption requirements as well as advancements in IC technology allowing utilization of low power inputs have made Energy Harvesting a popular power solution for low power applications such as WSNs. In many implementation areas, we can see solar, thermal, and vibration energy harvesting techniques have taken the role of batteries as power source. Now that Energy Harvesting is a popular and considerably mature technology, with proper design and installation, any object exposing energy has the ability to be promoted as a power source. We are currently living in Internet age where we connect to the world through network packets. Ethernet, by far, is the most popular LAN technology which allows us to plug and play. Therefore, on an Ethernet link, billions of packets where our data are encapsulated in are traversing every hour. We assume each of these packets exposes some level of energy on an Ethernet link. The challenge here is harvesting the energy available from Ethernet packets and transforming it into useful energy so that it can be used to power devices such as WSNs. In this thesis work, we have revealed how much energy is available from Ethernet packets, and how much of it can be made usable. We have also designed a system where a WSN is generating all of its operating power solely from Ethernet packets and consuming this energy in communication with a base station.

Στην εργασία αυτή μελετήθηκαν αρχιτεκτονικές χρονοπρογραμματισμού διεργασιών σε κόμβο ασύρματου δικτύου αισθητήρων, ο οποίος έχει πηγή περιορισμένης και μεταβλητής ισχύος. Τα ασύρματα δίκτυα αισθητήρων αποτελούνται από κόμβους που επικοινωνούν και ανταλλάσουν δεδομένα μεταξύ τους. Κάθε κόμβος πρέπει να έχει μεγάλη αυτονομία λειτουργίας και μικρή κατανάλωση ενέργειας. Στην εργασία αυτή προσομοιώθηκε ένα μοντέλο ενός κόμβου με πηγή ενέργειας την ηλιακή ισχύ, καθώς και ένα σύνολο διεργασιών με συγκεκριμένα χαρακτηριστικά και προθεσμίες εκτέλεσης. Εξετάστηκε η βέλτιστη διαχείριση της ενέργειας για την επιτυχή εκτέλεση των διεργασιών. Αρχικά μελετήθηκαν διάφοροι αλγόριθμοι χρονοπρογραμματισμού των διεργασιών του κόμβου (task scheduling), προσομοιώθηκε ένας βέλτιστος αλγόριθμος πραγματικού χρόνου (Lazy Scheduling Algorithm), μελετήθηκε και συγκρίθηκε η συμπεριφορά του. Στο επόμενο στάδιο, σχεδιάσθηκε μία αρχιτεκτονική για τον αλγόριθμο αυτό και υλοποιήθηκε με τη γλώσσα VHDL. Το υλικό, που προέκυψε με διαδικασία σύνθεσης της περιγραφής VHDL, προσομοιώθηκε και διαπιστώθηκε η αποτελεσματικότητα και η χαμηλή κατανάλωση ενέργειας του. Στο τελικό στάδιο βελτιώθηκε η αρχιτεκτονική του υλικού και μειώθηκε ακόμη περισσότερο η κατανάλωση ενέργειας. / -