On-chip adaptive power management for WPT-Enabled IoT

Internet of Things (IoT), as broadband network connecting every physical objects, is becoming more widely available in various industrial, medical, home and automotive applications. In such network, the physical devices, vehicles, medical assistance, and home appliances among others are supposed to be embedded by sensors, actuators, radio frequency (RF) antennas, memory, and microprocessors, such that these devices are able to exchange data and connect with other devices in the network. Among other IoT’s pillars, wireless sensor network (WSN) is one of the main parts comprising massive clusters of spatially distributed sensor nodes dedicated for sensing and monitoring environmental conditions. The lifetime of a WSN is greatly dependent on the lifetime of the small sensor nodes, which, in turn, is primarily dependent on energy availability within every sensor node. Predominantly, the main energy source for a sensor node is supplied by a small battery attached to it. In a large WSN with massive number of deployed sensor nodes, it becomes a challenge to replace the batteries of every single sensor node especially for sensor nodes deployed in harsh environments. Consequently, powering the sensor nodes becomes a key limiting issue, which poses important challenges for their practicality and cost. Therefore, in this thesis we propose enabling WSN, as the main pillar of IoT, by means of resonant inductive coupling (RIC) wireless power transfer (WPT). In order to enable efficient energy delivery at higher range, high quality factor RIC-WPT system is required in order to boost the magnetic flux generated at the transmitting coil. However, an adaptive front-end is essential for self-tuning the resonant tank against any mismatch in the components values, distance variation, and interference from close metallic objects. Consequently, the purpose of the thesis is to develop and design an adaptive efficient switch-mode front-end for self-tuning in WPT receivers in multiple receiver system. The thesis start by giving background about the IoT system and the technical bottleneck followed by the problem statement and thesis scope. Then, Chapter 2 provides detailed backgrounds about the RIC-WPT system. Specifically, Chapter 2 analyzes the characteristics of different compensation topologies in RIC-WPT followed by the implications of mistuning on efficiency and power transfer capability. Chapter 3 discusses the concept of switch-mode gyrators as a potential candidate for generic variable reactive element synthesis while different potential applications and design cases are provided. Chapter 4 proposes two different self-tuning control for WPT receivers that utilize switch-mode gyrators as variable reactive element synthesis. The performance aspects of control approaches are discussed and evaluated as well in Chapter 4. The development and exploration of more compact front-end for self-tuned WPT receiver is investigated in Chapter 5 by proposing a phase-controlled switched inductor converter. The operation and design details of different switch-mode phase-controlled topologies are given and evaluated in the same chapter. Finally, Chapter 6 provides the conclusions and highlight the contribution of the thesis, in addition to suggesting the related future research topics.Internet de las cosas (IoT), como red de banda ancha que interconecta cualquier cosa, se está estableciendo como una tecnología valiosa en varias aplicaciones industriales, médicas, domóticas y en el sector del automóvil. En dicha red, los dispositivos físicos, los vehículos, los sistemas de asistencia médica y los electrodomésticos, entre otros, incluyen sensores, actuadores, subsistemas de comunicación, memoria y microprocesadores, de modo que son capaces de intercambiar datos e interconectarse con otros elementos de la red. Entre otros pilares que posibilitan IoT, la red de sensores inalámbricos (WSN), que es una de las partes cruciales del sistema, está formada por un conjunto masivo de nodos de sensado distribuidos espacialmente, y dedicados a sensar y monitorizar las condiciones del contexto de las cosas interconectadas. El tiempo de vida útil de una red WSN depende estrechamente del tiempo de vida de los pequeños nodos sensores, los cuales, a su vez, dependen primordialmente de la disponibilidad de energía en cada nodo sensor. La fuente principal de energía para un nodo sensor suele ser una pequeña batería integrada en él. En una red WSN con muchos nodos y con una alta densidad, es un desafío el reemplazar las baterías de cada nodo sensor, especialmente en entornos hostiles, como puedan ser en escenarios de Industria 4.0. En consecuencia, la alimentación de los nodos sensores constituye uno de los cuellos de botella que limitan un despliegue masivo práctico y de bajo coste. A tenor de estas circunstancias, en esta tesis doctoral se propone habilitar las redes WSN, como pilar principal de sistemas IoT, mediante sistemas de transferencia inalámbrica de energía (WPT) basados en acoplamiento inductivo resonante (RIC). Con objeto de posibilitar el suministro eficiente de energía a mayores distancias, deben aumentarse los factores de calidad de los elementos inductivos resonantes del sistema RIC-WPT, especialmente con el propósito de aumentar el flujo magnético generado por el inductor transmisor de energía y su acoplamiento resonante en recepción. Sin embargo, dotar al cabezal electrónico que gestiona y condicionada el flujo de energía de capacidad adaptativa es esencial para conseguir la autosintonía automática del sistema acoplado y resonante RIC-WPT, que es muy propenso a la desintonía ante desajustes en los parámetros nominales de los componentes, variaciones de distancia entre transmisor y receptores, así como debido a la interferencia de objetos metálicos. Es por tanto el objetivo central de esta tesis doctoral el concebir, proponer, diseñar y validar un sistema de WPT para múltiples receptores que incluya funciones adaptativas de autosintonía mediante circuitos conmutados de alto rendimiento energético, y susceptible de ser integrado en un chip para el condicionamiento de energía en cada receptor de forma miniaturizada y desplegable de forma masiva. La tesis empieza proporcionando una revisión del estado del arte en sistemas de IoT destacando el reto tecnológico de la alimentación energética de los nodos sensores distribuidos y planteando así el foco de la tesis doctoral. El capítulo 2 sigue con una revisión crítica del statu quo de los sistemas de transferencia inalámbrica de energía RIC-WPT. Específicamente, el capítulo 2 analiza las características de diferentes estructuras circuitales de compensación en RIC-WPT seguido de una descripción crítica de las implicaciones de la desintonía en la eficiencia y la capacidad de transferencia energética del sistema. El capítulo 3 propone y explora el concepto de utilizar circuitos conmutados con función de girador como potenciales candidatos para la síntesis de propósito general de elementos reactivos variables sintonizables electrónicamente, incluyendo varias aplicaciones y casos de uso. El capítulo 4 propone dos alternativas para métodos y circuitos de control para la autosintonía de receptores de energíaPostprint (published version

Magnetostriktiivinen energian louhinta teräksestä

Energy harvesting is defined as electronic devices acquiring the energy they need to operate from their environment. Potential energy sources in the environment include light, temperature gradients, electromagnetic radiation and kinetic energy. The development of energy harvesting technologies together with a drop in the energy consumption of electronic devices may in the near future make many devices energy independent, which means a drop in the maintenance need of the devices, greater reliability and a reduction in the amount of battery waste. The main aim of the experimental part of this thesis was to present and further develop a new kinetic energy harvesting method, which can harvest energy from elastic waves propagating in steel structures, and to develop harvesting electronics that can be used with the new method. This new method is based on the magnetoelastic effect, which is a natural phenomenon that causes the magnetization of a ferromagnetic material to change when the dimensions of the material are changed. This phenomenon is also known as the inverse magnetostrictive effect. A change in the magnetization of a material will also cause a change in the magnetic flux passing through the material. Since a change in the magnetic flux of a coil will induce and electromotive force in the coil, the magnetoelastic effect can be utilized in energy harvesting. The basic idea behind the new method is harvesting energy from an impact loaded steel bar with a coil wound around the bar. Impact loading a steel bar will cause an elastic wave to propagate along the bar, which will cause alternating compressive and tensile stresses in the steel bar. Since steels are ferromagnetic materials, the strains will alter the magnetization of the bar inducing an electromotive force in a coil around the bar. Thus a part of the kinetic energy carried by the elastic is transduced to electrical energy. In the experimental part a test setup, an experimental harvesting generator and electronic harvesting circuits, to be used with the method, were implemented. The mean power that can be achieved with the experimental method depends on the magnitude and frequency of the impact loading, but during testing mean output power of the harvesting generator was between 1-5 mW, when an elastic wave was propagating in the bar. This is a sufficient mean power for a low power wireless sensor. The thesis also includes a literature survey, which aims to give the reader basic knowledge of existing kinetic energy harvesting methods and magnetostrictive phenomena

Microelectronic Design with Integrated Magnetic and Piezoelectric Structures

This thesis investigates the possibility of integrating the standard CMOS design process with additional microstructures enhancing circuit functionalities. More specifically, the thesis faces the problem of miniaturization of magnetic and piezoelectric devices mostly focused on the application field of EH (Energy Harvesting) systems and ultra-low power and ultra-low voltage systems. It shows all the most critical aspects which have to be taken into account during the design process of miniaturized inductors for PwrSoC (Power System on Chip) or transformers. Furthermore it shows that it is possible to optimize the inductance value and also performances by means of a proper choice of the size of the planar core or choosing a different layout shape such as a serpentine shape in place of the classic toroidal one. A new formula for the correct evaluation of the MPL (Magnetic Path Length) was also introduced. Concerning the piezoelectric counterpart, it is focused on the design and simulation of various MEMS PTs based on a SOI (Silicon on Insulator) structure with AlN (Alluminum Nitride) as active piezoelectric element, in perspective of having a SoC with embedded MEMS devices and circuitry. Furthermore it demonstrates for the first time the use of a PT (Piezoelectric Transformer) for ultra-low voltage EH applications. A new boost oscillator based on a discrete PZT (Lead Zirconate Titanate) PT instead of a MT (Magnetic Transformer) has been modelled and tested on a circuit made up by discrete devices, showing performances comparable to commercial solutions like the LTC3108 from Linear. Furthermore this novel boost oscillator has been designed in a 0.35μm technology by ST Microelectronics, showing better performances as intuitively expected by the developed mathematical model of the entire system

Amélioration du contrôle vibratoire autonome de smart structures par échange modal d’énergie

In a context of embedded structures, the next challenge is to develop an efficient, energetically autonomous vibration control technique. Synchronized Switch Damping techniques (SSD) have been demonstrated interesting properties in vibration control with a low power consumption. For compliant or soft smart structures, modal control is a promising way as specific modes can be targetted. This Ph-D work examines a novel energy transfer concept and design of simultaneous energy harvesting and vibration control on the same host structure. The basic idea is that the structure is able to extract modal energy from the chosen modes, and utilize this harvested energy to suppress the target modes via modal control method. We propose here a new technique to enhance the classic SSD circuit due to energy harvesting and energy transfer. Our architecture called Modal Synchronized Switching Damping and Harvesting (Modal SSDH) is composed of a harvesting circuit (Synchronized Switch Harvesting on Inductor SSHI), a Buck-Boost converter and a vibration modal control circuit (SSD). Various alternatives of our SSDH techniques were proposed and simulated. A real smart structure is modeled and used as specific case to test the efficiency of our concept. Piezoelectric sensors and actuators are taken as active transducers, as they develop the direct and inverse effects useful for the energy harvesting and the vibration damping. Optimization are running out and the basic design factors are discussed in terms of energy transfer. Simulations, carried out under bi-harmonic and noise excitation, underline that our new SSDH concept is efficient and robust. Our technique improve the damping effect of semi-active method compared to classic SSD method thanks to the use of harvested modal energy.Le travail de cette thèse propose une nouvelle méthode de contrôle appelée SSDH (Synchronized Switch Damping and Harvesting) basée sur l’idée de redistribution de l’énergie récupérée pour réduire l’énergie vibratoire d’une structure. De nombreuses recherches ont concerné le contrôle de vibration des structures souples. L’utilisation de l’approche modale pour ce genre de structure présente de nombreux intérêts. Dans le cadre de cette thèse l’idée est de récupérer l’énergie des modes qui ne sont pas contrôlés de façon à améliorer l’effet d’amortissement des modes ciblés par le contrôle sur une même structure. Pour cela, sur la base de la technique semi-active de contrôle, un circuit de contrôle modal a été conçu pour être compatible, via un convertisseur, avec des techniques semi-active de récupération d’énergie qui ont elles même été adaptées en modal. Plusieurs variantes de la méthode SSDH ont été testées en simulation. De façon à estimer l’efficacité du concept, une application sur un modèle expérimental d’une smart structure simple est proposée. Actionneurs et capteurs utilisent des matériaux piézoélectriques qui présentent les effets directs et inverses utiles pour la récupération d’énergie et le contrôle vibratoire. Après optimisation des différents paramètres électromécaniques et électriques, les résultats des simulations menées sous excitations bisinusoidale ou en bruit blanc, montrent que la nouvelle méthode de contrôle autoalimentée SSDH est efficace et robuste. Elle améliore sensiblement l’amortissement produit par les techniques semi-actives modales de base (SSDI) grâce à l’utilisation de l’énergie modale récupérée

Miniaturized Power Electronic Interfaces for Ultra-compact Electromechanical Systems

Advanced and ultra-compact electromechanical (EM) systems, such as kinetic energy harvesting and microrobotic systems are deemed as enabling solutions to provide efficient energy conversion. One of the most critical challenges in such systems is to develop tiny power electronic interfaces (PEIs) capable of addressing power conditioning between EM devices and energy storage units. This dissertation presents technologies and topological solutions toward fabricating miniaturized PEIs to efficiently regulate erratic power/voltage for kinetic energy harvesting and drive high-voltage actuators for microrobotic systems. High-frequency resonant-switching topologies are introduced as power stages of PEIs that allow small footprint of the circuit without suffering from switching losses. Two types of bridgeless resonant ac-dc converters are first introduced and developed to efficiently convert arbitrary input voltages into a regulated dc output voltage. The proposed topologies provide direct ac-dc power conversion with less number of components, in comparison to other resonant topologies. A 5-mm×6-mm, 100-mg, 2-MHz and 650-mW prototype is fabricated for validation of capability of converting very-low ac voltages into a relatively higher voltage. A resonant gate drive circuit is designed and utilized to further reduce gating losses under high-frequency switching and light-load condition. The closed-loop efficiency reaches higher than 70% across wide range of input voltages and output powers. In a multi-channel energy harvesting system, a multi-input bridgeless resonant ac-dc converter is developed to achieve ac-dc conversion, step up voltage and match optimal impedance. Alternating voltage of each energy harvesting channel is stepped up through the switching LC network and then rectified by a freewheeling diode. The optimal electrical impedance can be adjusted through resonance impedance matching and pulse-frequency-modulation (PFM) control. In addition, a six-input standalone prototype is fabricated to address power conditioning for a six-channel wind panel. Furthermore, the concepts of miniaturization are incorporated in the context of microrobots. In a mobile microrobotic system, conventional bulky power supplies and electronics used to drive electroactive polymer (EAP) actuators are not practical as on-board energy sources for microrobots. A bidirectional single-stage resonant dc-dc step-up converter is introduced and developed to efficiently drive high-voltage EAP actuators. The converter utilizes resonant capacitors and a coupled-inductor as a soft-switched LC network to step up low input voltages. The circuit is capable of generating explicit high-voltage actuation signals, with capability of recovering unused energy from EAP actuators. A 4-mm × 8-mm, 100-mg and 600-mW prototype has been designed and fabricated to drive an in-plane gap-closing electrostatic inchworm motor. Experimental validations have been carried out to verify the circuit’s ability to step up voltage from 2 V to 100 V and generate two 1-kHz, 100-V driving voltages at 2-nF capacitive loads

A POWER DISTRIBUTION SYSTEM BUILT FOR A VARIETY OF UNATTENDED ELECTRONICS

A power distribution system (PDS) delivers electrical power to a load safely and effectively in a pre-determined format. Here format refers to necessary voltages, current levels and time variation of either as required by the empowered system. This formatting is usually referred as "conditioning". The research reported in this dissertation presents a complete system focusing on low power energy harvesting, conditioning, storage and regulation. Energy harvesting is a process by which ambient energy present in the environment is captured and converted to electrical energy. In recent years, it has become a prominent research area in multiple disciplines. Several energy harvesting schemes have been exploited in the literature, including solar energy, mechanic energy, radio frequency (RF) energy, thermal energy, electromagnetic energy, biochemical energy, radioactive energy and so on. Different from the large scale energy generation, energy harvesting typically operates in milli-watts or even micro-watts power levels. Almost all energy harvesting schemes require stages of power conditioning and intermediate storage - batteries or capacitors that reservoir energy harvested from the environment. Most of the ambient energy fluctuates and is usually weak. The purpose of power conditioning is to adjust the format of the energy to be further used, and intermediate storage smoothes out the impact of the fluctuations on the power delivered to the load. This dissertation reports an end to end power distribution system that integrates different functional blocks including energy harvesting, power conditioning, energy storage, output regulation and system control. We studied and investigated different energy harvesting schemes and the dissertation places emphasis on radio frequency energy harvesting. This approach has proven to be a viable power source for low-power electronics. However, it is still challenging to obtain significant amounts of energy rapidly and efficiently from the ambient. Available RF power is usually very weak, leading to low voltage applied to the electronics. The power delivered to the PDS is hard to utilize or store. This dissertation presents a configuration including a wideband rectenna, a switched capacitor voltage boost converter and a thin film flexible battery cell that can be re-charged at an exceptionally low voltage. We demonstrate that the system is able to harvest energy from a commercially available hand-held communication device at an overall efficiency as high as 7.7 %. Besides the RF energy harvesting block, the whole PDS includes a solar energy harvesting block, a USB recharging block, a customer selection block, two battery arrays, a control block and an output block. The functions of each of the blocks have been tested and verified. The dissertation also studies and investigates several potential applications of this PDS. The applications we exploited include an ultra-low power tunable neural oscillator, wireless sensor networks (WSNs), medical prosthetics and small unmanned aerial vehicles (UAVs). We prove that it is viable to power these potential loads through energy harvesting from multiple sources

Imaging Sensors and Applications

In past decades, various sensor technologies have been used in all areas of our lives, thus improving our quality of life. In particular, imaging sensors have been widely applied in the development of various imaging approaches such as optical imaging, ultrasound imaging, X-ray imaging, and nuclear imaging, and contributed to achieve high sensitivity, miniaturization, and real-time imaging. These advanced image sensing technologies play an important role not only in the medical field but also in the industrial field. This Special Issue covers broad topics on imaging sensors and applications. The scope range of imaging sensors can be extended to novel imaging sensors and diverse imaging systems, including hardware and software advancements. Additionally, biomedical and nondestructive sensing applications are welcome