An Integrated AC-DC Rectifier Converter for Low Voltage Piezoelectric Energy Harvesting and Constant-Voltage Lithium-Ion Cell Charging Application

Energy harvesting is probably one the most sought after solutions that is being given attention to and has become of great importance for last few years. Due to advances in microelectronics and growing demand of autonomous devices, researchers have been working on harvesting energy from ambient sources such as solar, thermal, wind and kinetic energy. Also, growth of rechargeable battery technology has resulted in research in ambient energy harvesting for charging purposes. In this field, piezoelectric effect has been identified as a viable solution to address both low power applications and battery charging applications. Piezoelectric effect is described as the phenomenon of generating a voltage from a mechanical stress and vice-versa. Piezoelectric elements have been seen to offer outstanding performance in scavenging energy because of their high power density, which make them suitable for integrated micro-generators. Many vibration-based harvesting technology use piezoelectric transducers as AC power source. This work emphasizes on vibration based piezoelectric energy harvesting from a very low input voltage source. The main objective of the thesis is to design a power converter that can successfully rectify and boost piezoelectric AC voltages from a few hundred millivolts to a stable usable DC voltage without the use of a bridge diode rectifier circuit. The thesis begins with the introduction to the concept of energy harvesting and piezoelectricity, followed by investigation of a 13x25 mm, 28µm thick, laminated piezoelectric thin film made of Polyvinylidene Fluoride (PVDF) acting as the transducer. The transducer was subjected to a repeated vibration impulse and its resultant voltage response was determined. The thesis then moves towards presenting an integrated AC-DC rectifier converter which eliminates the use of full bridge diode rectifiers that have been known for being inefficient for low power energy harvesting. The stages of operation of the power converter is presented along with the simulation results. The work has also been extended to show the charging application of a Lithium-Ion thin film cell under constant voltage charging scheme using a MATLAB/SIMULINK battery model. A prototype of the converter was also built in the laboratory and presented to show the performance of the integrated AC-DC rectifier converter. A dSPACE controller board was employed to implement the open loop control and the converter switching scheme. Experimental results were presented and assessed before finally moving onto the conclusion and suggested future works

Inductively Coupled CMOS Power Receiver For Embedded Microsensors

Inductively coupled power transfer can extend the lifetime of embedded microsensors that save costs, energy, and lives. To expand the microsensors' functionality, the transferred power needs to be maximized. Plus, the power receiver needs to handle wide coupling variations in real applications. Therefore, the objective of this research is to design a power receiver that outputs the highest power for the widest coupling range. This research proposes a switched resonant half-bridge power stage that adjusts both energy transfer frequency and duration so the output power is maximally high. A maximum power point (MPP) theory is also developed to predict the optimal settings of the power stage with 98.6% accuracy. Finally, this research addresses the system integration challenges such as synchronization and over-voltage protection. The fabricated self-synchronized prototype outputs up to 89% of the available power across 0.067%~7.9% coupling range. The output power (in percentage of available power) and coupling range are 1.3× and 13× higher than the comparable state of the arts.Ph.D

A Single Inductor, Multiple Input Piezoelectric Interface Circuit Capable of Harvesting Energy from Asynchronously Vibrating Sources

The energy harvesting industry has seen steady growth in recent years. This growth has been driven by the increasing demand for remote sensing, implantable technologies, and increased battery life in mobile and hand held devices. Due to the limited amount of energy available from ambient sources, any system that attempts to harness energy from them should necessarily be highly efficient to make the net output power useful. A lot of work has been done on minimizing losses in piezoelectric energy harvesters. Most of this has however been limited to harvesters with single vibration sources or multiple sources vibrating synchronously. This work presents a multiple input piezoelectric energy harvester capable of harvesting from multiple piezoelectric energy sources vibrating asynchronously (at different frequencies, or at the same frequency but in different phases) using a single inductor. The use of a single inductor eliminates the extra quiescent power consumption, component count, printed circuit board real estate that would have been incurred by using a one inductor per input device. The inductor is time shared between three input devices using a digital control circuit which regulate access to the inductor while avoiding any destructive interaction between the input devices. The chip was designed in a 0.18µm technology and achieves a conversion efficiency of 60%. Testing with three asynchronously vibrating sources shows that the chip extracts maximum power from all inputs simultaneously, independent of vibration frequency or phase

Circuits and Systems for Energy Harvesting and Internet of Things Applications

The Internet of Things (IoT) continues its growing trend, while new “smart” objects are con-stantly being developed and commercialized in the market. Under this paradigm, every common object will be soon connected to the Internet: mobile and wearable devices, electric appliances, home electronics and even cars will have Internet connectivity. Not only that, but a variety of wireless sensors are being proposed for different consumer and industrial applications. With the possibility of having hundreds of billions of IoT objects deployed all around us in the coming years, the social implications and the economic impact of IoT technology needs to be seriously considered. There are still many challenges, however, awaiting a solution in order to realize this future vision of a connected world. A very important bottleneck is the limited lifetime of battery powered wireless devices. Fully depleted batteries need to be replaced, which in perspective would generate costly maintenance requirements and environmental pollution. However, a very plausible solution to this dilemma can be found in harvesting energy from the ambient. This dissertation focuses in the design of circuits and system for energy harvesting and Internet of Things applications. The first part of this dissertation introduces the research motivation and fundamentals of energy harvesting and power management units (PMUs). The architecture of IoT sensor nodes and PMUs is examined to observe the limitations of modern energy harvesting systems. Moreover, several architectures for multisource harvesting are reviewed, providing a background for the research presented here. Then, a new fully integrated system architecture for multisource energy harvesting is presented. The design methodology, implementation, trade-offs and measurement results of the proposed system are described. The second part of this dissertation focus on the design and implementation of low-power wireless sensor nodes for precision agriculture. First, a sensor node incorporating solar energy harvesting and a dynamic power management strategy is presented. The operation of a wireless sensor network for soil parameter estimation, consisting of four nodes is demonstrated. After that, a solar thermoelectric generator (STEG) prototype for powering a wireless sensor node is proposed. The implemented solar thermoelectric generator demonstrates to be an alternative way to harvest ambient energy, opening the possibility for its use in agricultural and environmental applications. The open problems in energy harvesting for IoT devices are discussed at the end, to delineate the possible future work to improve the performance of EH systems. For all the presented works, proof-of-concept prototypes were fabricated and tested. The measured results are used to verify their correct operation and performance

Energy harvesting technologies and devices from vehicular transit and natural sources on roads for a sustainable transport: state-of-the-art analysis and commercial solutions

The roads we travel daily are exposed to several energy sources (mechanical load, solar radiation, heat, air movement, etc.), which can be exploited to make common systems and apparatus for roadways (i.e., lighting, video surveillance, and traffic monitoring systems) energetically autonomous. For decades, research groups have developed many technologies able to scavenge energy from the said sources related to roadways: electromagnetism, piezoelectric and triboelectric harvesters for the cars’ stress and vibrations, photovoltaic modules for sunlight, thermoelectric solutions and pyroelectric materials for heat and wind turbines optimized for low-speed winds, such as the ones produced by moving vehicles. Thus, this paper explores the existing technologies for scavenging energy from sources available on roadways, both natural and related to vehicular transit. At first, to contextualize them within the application scenario, the available energy sources and transduction mechanisms were identified and described, arguing the main requirements that must be considered for developing harvesters applicable on roadways. Afterward, an overview of energy harvesting solutions presented in the scientific literature to recover energy from roadways is introduced, classifying them according to the transduction method (i.e., piezoelectric, triboelectric, electromagnetic, photovoltaic, etc.) and proposed system architecture. Later, a survey of commercial systems available on the market for scavenging energy from roadways is introduced, focusing on their architecture, performance, and installation methods. Lastly, comparative analyses are offered for each device category (i.e., scientific works and commercial products), providing insights to identify the most promising solutions and technologies for developing future self-sustainable smart roads

A Three – tier bio-implantable sensor monitoring and communications platform

One major hindrance to the advent of novel bio-implantable sensor technologies is the need for a reliable power source and data communications platform capable of continuously, remotely, and wirelessly monitoring deeply implantable biomedical devices. This research proposes the feasibility and potential of combining well established, ‘human-friendly' inductive and ultrasonic technologies to produce a proof-of-concept, generic, multi-tier power transfer and data communication platform suitable for low-power, periodically-activated implantable analogue bio-sensors. In the inductive sub-system presented, 5 W of power is transferred across a 10 mm gap between a single pair of 39 mm (primary) and 33 mm (secondary) circular printed spiral coils (PSCs). These are printed using an 8000 dpi resolution photoplotter and fabricated on PCB by wet-etching, to the maximum permissible density. Our ultrasonic sub-system, consisting of a single pair of Pz21 (transmitter) and Pz26 (receiver) piezoelectric PZT ceramic discs driven by low-frequency, radial/planar excitation (-31 mode), without acoustic matching layers, is also reported here for the first time. The discs are characterised by propagation tank test and directly driven by the inductively coupled power to deliver 29 μW to a receiver (implant) employing a low voltage start-up IC positioned 70 mm deep within a homogeneous liquid phantom. No batteries are used. The deep implant is thus intermittently powered every 800 ms to charge a capacitor which enables its microcontroller, operating with a 500 kHz clock, to transmit a single nibble (4 bits) of digitized sensed data over a period of ~18 ms from deep within the phantom, to the outside world. A power transfer efficiency of 83% using our prototype CMOS logic-gate IC driver is reported for the inductively coupled part of the system. Overall prototype system power consumption is 2.3 W with a total power transfer efficiency of 1% achieved across the tiers

RF Power Transfer, Energy Harvesting, and Power Management Strategies

Energy harvesting is the way to capture green energy. This can be thought of as a recycling process where energy is converted from one form (here, non-electrical) to another (here, electrical). This is done on the large energy scale as well as low energy scale. The former can enable sustainable operation of facilities, while the latter can have a significant impact on the problems of energy constrained portable applications. Different energy sources can be complementary to one another and combining multiple-source is of great importance. In particular, RF energy harvesting is a natural choice for the portable applications. There are many advantages, such as cordless operation and light-weight. Moreover, the needed infra-structure can possibly be incorporated with wearable and portable devices. RF energy harvesting is an enabling key player for Internet of Things technology. The RF energy harvesting systems consist of external antennas, LC matching networks, RF rectifiers for ac to dc conversion, and sometimes power management. Moreover, combining different energy harvesting sources is essential for robustness and sustainability. Wireless power transfer has recently been applied for battery charging of portable devices. This charging process impacts the daily experience of every human who uses electronic applications. Instead of having many types of cumbersome cords and many different standards while the users are responsible to connect periodically to ac outlets, the new approach is to have the transmitters ready in the near region and can transfer power wirelessly to the devices whenever needed. Wireless power transfer consists of a dc to ac conversion transmitter, coupled inductors between transmitter and receiver, and an ac to dc conversion receiver. Alternative far field operation is still tested for health issues. So, the focus in this study is on near field. The goals of this study are to investigate the possibilities of RF energy harvesting from various sources in the far field, dc energy combining, wireless power transfer in the near field, the underlying power management strategies, and the integration on silicon. This integration is the ultimate goal for cheap solutions to enable the technology for broader use. All systems were designed, implemented and tested to demonstrate proof-of concept prototypes

Ultra-Low Power Transmitter and Power Management for Internet-of-Things Devices

Two of the most critical components in an Internet-of-Things (IoT) sensing and transmitting node are the power management unit (PMU) and the wireless transmitter (Tx). The desire for longer intervals between battery replacements or a completely self-contained, battery-less operation via energy harvesting transducers and circuits in IoT nodes demands highly efficient integrated circuits. This dissertation addresses the challenge of designing and implementing power management and Tx circuits with ultra-low power consumption to enable such efficient operation. The first part of the dissertation focuses on the study and design of power management circuits for IoT nodes. This opening portion elaborates on two different areas of the power management field: Firstly, a low-complexity, SPICE-based model for general low dropout (LDO) regulators is demonstrated. The model aims to reduce the stress and computation times in the final stages of simulation and verification of Systems-on-Chip (SoC), including IoT nodes, that employ large numbers of LDOs. Secondly, the implementation of an efficient PMU for an energy harvesting system based on a thermoelectric generator transducer is discussed. The PMU includes a first-in-its-class LDO with programmable supply noise rejection for localized improvement in the suppression. The second part of the dissertation addresses the challenge of designing an ultra- low power wireless FSK Tx in the 900 MHz ISM band. To reduce the power consumption and boost the Tx energy efficiency, a novel delay cell exploiting current reuse is used in a ring-oscillator employed as the local oscillator generator scheme. In combination with an edge-combiner PA, the Tx showed a measured energy efficiency of 0.2 nJ/bit and a normalized energy efficiency of 3.1 nJ/(bit∙mW) when operating at output power levels up to -10 dBm and data rates of 3 Mbps. To close this dissertation, the implementation of a supply-noise tolerant BiCMOS ring-oscillator is discussed. The combination of a passive, high-pass feedforward path from the supply to critical nodes in the selected delay cell and a low cost LDO allow the oscillator to exhibit power supply noise rejection levels better than –33 dB in experimental results

High-Efficiency Low-Voltage Rectifiers for Power Scavenging Systems

Abstract Rectifiers are commonly used in electrical energy conversion chains to transform the energy obtained from an AC signal source to a DC level. Conventional bridge and gate cross-coupled rectifier topologies are not sufficiently power efficient, particularly when input amplitudes are low. Depending on their rectifying element, their power efficiency is constrained by either the forward-bias voltage drop of a diode or the threshold voltage of a diode-connected MOS transistor. Advanced passive rectifiers use threshold cancellation techniques to effectively reduce the threshold voltage of MOS diodes. Active rectifiers use active circuits to control the conduction angle of low-loss MOS switches. In this thesis, an active rectifier with a gate cross-coupled topology is proposed, which replaces the diode-connected MOS transistors of a conventional rectifier with low-loss MOS switches. Using the inherent characteristics of MOS transistors as comparators, dynamic biasing of the bulks of main switches and small pull-up transistors, the proposed self-supplied active rectifier exhibits smaller voltage drop across the main switches leading to a higher power efficiency compared to conventional rectifier structures for a wide range of operating frequencies in the MHz range. Delivery of high load currents is another feature of the proposed rectifier. Using the bootstrapping technique, single- and double-reservoir based rectifiers are proposed. They present higher power and voltage conversion efficiencies compared to conventional rectifier structures. With a source amplitude of 3.3 V, when compared to the gate cross-coupled topology, the proposed active rectifier offers power and voltage conversion efficiencies improved by up to 10% and 16% respectively. The proposed rectifier using the bootstrap technique, including double- and single-reservoir schemes, are well suited for very low input amplitudes. They present power and voltage conversion efficiencies of 75% and 76% at input amplitude of 1.0 V and maintain their high efficiencies over input amplitudes greater than 1.0V. Single-reservoir bootstrap rectifier also reduces die area by 70% compared to its double-reservoir counterpart.---------Résumé Les redresseurs sont couramment utilisés dans de nombreux systèmes afin de transformer l'énergie électrique obtenue à partir d'une source alternative en une alimentation continue. Les topologies traditionnelles telles que les ponts de diodes et les redresseurs se servant de transistors à grilles croisées-couplées ne sont pas suffisamment efficaces en terme d’énergie, en particulier pour des signaux à faibles amplitudes. Dépendamment de leur élément de redressement, leur efficacité en termes de consommation d’énergie est limitée soit par la chute de tension de polarisation directe d'une diode, soit par la tension de seuil du transistor MOS. Les redresseurs passifs avancés utilisent une technique de conception pour réduire la tension de seuil des diodes MOS. Les redresseurs actifs utilisent des circuits actifs pour contrôler l'angle de conduction des commutateurs MOS à faible perte. Dans cette thèse, nous avons proposé un redresseur actif avec une topologie en grille croisée-couplée. Elle utilise des commutateurs MOS à faible perte à la place des transistors MOS connectés en diode comme redresseurs. Le circuit proposé utilise: des caractéristiques intrinsèques des transistors MOS pour les montages comparateurs et une polarisation dynamique des substrats des commutateurs principaux supportés par de petits transistors de rappel. Le redresseur proposé présente des faibles chutes de tension à travers le commutateur principal menant à une efficacité de puissance plus élevée par rapport aux structures d’un redresseur conventionnel pour une large gamme de fréquences de fonctionnement de l’ordre des MHz. La conduction des courants de charge élevée est une autre caractéristique du redresseur proposé. En utilisant la méthode de bootstrap, des redresseurs à simple et à double réservoir sont proposés. Ils présentent une efficacité de puissance et un rapport de conversion de tension élevés en comparaison avec les structures des redresseurs conventionnels. Avec une amplitude de source de 3,3 V, le redresseur proposé offre des efficacités de puissance et de conversion de tension améliorées par rapport au circuit à transistors croisés couplés. Ces améliorations atteignent 10% et 16% respectivement. Les redresseurs proposés utilisent la technique de bootstrap. Ils sont bien adaptés pour des amplitudes d'entrée très basses. À une amplitude d'entrée de 1,0 V, ces derniers redresseurs présentent des rendements de conversion de puissance et de tension de 75% et 76%. Le redresseur à simple réservoir réduit également l’aire de silicium requise de 70% par rapport à la version à double-réservoir