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

Power Processing for Electrostatic Microgenerators

Microgenerators are electro-mechanical devices which harvest energy from local environmental from such sources as light, heat and vibrations. These devices are used to extend the life-time of wireless sensor network nodes. Vibration-based microgenerators for biomedical applications are investigated in this thesis. In order to optimise the microgenerator system design, a combined electro-mechanical system simulation model of the complete system is required. In this work, a simulation toolkit (known as ICES) has been developed utilising SPICE. The objective is to accurately model end-to-end microgenerator systems. Case-study simulations of electromagnetic and electrostatic microgenerator systems are presented to verify the operation of the toolkit models. Custom semiconductor devices, previously designed for microgenerator use, have also been modelled so that system design and optimisation of complete microgenerator can be accomplished. An analytical framework has been developed to estimate the maximum system effectiveness of an electrostatic microgenerator operating in constant-charge and constant-voltage modes. The calculated system effectiveness values are plotted with respect to microgenerator sizes for different input excitations. Trends in effectiveness are identified and discussed in detail. It was found that when the electrostatic transducer is interfaced with power processing circuit, the parasitic elements of the circuit are reducing the energy generation ability of the transducer by sharing the charge during separation of the capacitor plates. Also, found that in constant-voltage mode the electrostatic microgenerator has a better effectiveness over a large operating range than constant-charge devices. The ICES toolkit was used to perform time-domain simulation of a range of operating points and the simulation results provide verification of the analytical results

Surface micromachined MEMS variable capacitor with two-cavity for energy harvesting

In this research, a novel MEMS variable capacitor with two capacitive cavities for energy harvesting was developed that use the wasted energy associated with undesirable mechanical vibrations to power microelectronic sensors and actuators widely found in structures and systems surrounding us. The harvested power, though very small, can have a profound effect on the usage of microsensors. First, the self-powered sensors will no longer require regular battery maintenance. Second, the self-powered chip is a liberating technology. On a circuit board, it can simplify the connection. On a commercial jet, the sensors can greatly simplify cabling. The design, fabrication, modeling and complete set of characterization of MEMS variable capacitors with two-cavity are presented in details in this thesis. The MEMS variable capacitors are unique in its two-cavity design and use of electroplated nickel as the main structural material. The device consists of 2x2 mm² movable capacitive proof mass plates with a thickness of 30 [mu]m suspended between two fixed electrodes forming two vertical capacitors. When the capacitance increases for one cavity, it decreases for the other. This allows using both up and down directions to generate energy. The suspended movable plates are supported by four serpentine springs with a thickness of 3-5 [mu]m that are attached to the address lines on a silicon substrate only at the anchors' points which is made of electroplated nickel. The serpentine suspension beams are made with a width, thickness and total length (four serpentine turns) of 15 [mu]m, 5 [mu]m and 1485 [mu]m. Five gold stoppers with height of 2-4 [mu]m were electroplated on the fixed plates to prevent snap-down of the movable plates by overwhelming electrostatic force. SiO2 and Si3N4 thin layers were patterned on the fixed plates to insulate the stoppers and enhance the dielectric property of capacitive cavities. The MEMS variable capacitor with two-cavity has been designed and modeled using MEMS CAD tool and COMSOL Multi-PhysIncludes bibliographical references (pages 108-118)

Integration of Bulk Piezoelectric Materials into Microsystems.

Bulk piezoelectric ceramics, compared to deposited piezoelectric thin-films, provide greater electromechanical coupling and charge capacity, which are highly desirable in many MEMS applications. In this thesis, a technology platform is developed for wafer-level integration of bulk piezoelectric substrates on silicon, with a final film thickness of 5-100μm. The characterized processes include reliable low-temperature (200˚C) AuIn diffusion bonding and parylene bonding of bulk-PZT on silicon, wafer-level lapping of bulk-PZT with high-uniformity (±0.5μm), and low-damage micro-machining of PZT films via dicing-saw patterning, laser ablation, and wet-etching. Preservation of ferroelectric and piezoelectric properties is confirmed with hysteresis and piezo-response measurements. The introduced technology offers higher material quality and unique advantages in fabrication flexibility over existing piezoelectric film deposition methods. In order to confirm the preserved bulk properties in the final film, diaphragm and cantilever beam actuators operating in the transverse-mode are designed, fabricated and tested. The diaphragm structure and electrode shapes/sizes are optimized for maximum deflection through finite-element simulations. During tests of fabricated devices, greater than 12μmPP displacement is obtained by actuation of a 1mm2 diaphragm at 111kHz with <7mW power consumption. The close match between test data and simulation results suggests that the piezoelectric properties of bulk-PZT5A are mostly preserved without any necessity of repolarization. Three generations of resonant vibration energy harvesters are designed, simulated and fabricated to demonstrate the competitive performance of the new fabrication process over traditional piezoelectric deposition systems. An unpackaged PZT/Si unimorph harvester with 27mm3 active device volume produces up to 205μW at 1.5g/154Hz. The prototypes have achieved the highest figure-of-merits (normalized-power-density × bandwidth) amongst previously reported inertial energy harvesters. The fabricated energy harvester is utilized to create an autonomous energy generation platform in 0.3cm3 by system-level integration of a 50-80% efficient power management IC, which incorporates a supply-independent bias circuitry, an active diode for low-dropout rectification, a bias-flip system for higher efficiency, and a trickle battery charger. The overall system does not require a pre-charged battery, and has power consumption of <1μW in active-mode (measured) and <5pA in sleep-mode (simulated). Under 1g vibration at 155Hz, a 70mF ultra-capacitor is charged from 0V to 1.85V in 50 minutes.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91479/1/aktakka_3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91479/2/aktakka_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91479/3/aktakka_1.pd

ELECTROMECHANICAL MODELING OF A HONEYCOMB CORE INTEGRATED VIBRATION ENERGY CONVERTER WITH INCREASED SPECIFIC POWER FOR ENERGY HARVESTING APPLICATIONS

Innovation in integrated circuit technology along with improved manufacturing processes has resulted in considerable reduction in power consumption of electromechanical devices. Majority of these devices are currently powered by batteries. However, the issues posed by batteries, including the need for frequent battery recharge/replacement has resulted in a compelling need for alternate energy to achieve self-sufficient device operation or to supplement battery power. Vibration based energy harvesting methods through piezoelectric transduction provides with a promising potential towards replacing or supplementing battery power source. However, current piezoelectric energy harvesters generate low specific power (power-to-weight ratio) when compared to batteries that the harvesters seek to replace or supplement. In this study, the potential of integrating lightweight cellular honeycomb structures with existing piezoelectric device configurations (bimorph) to achieve higher specific power is investigated. It is shown in this study that at low excitation frequency ranges, replacing the solid continuous substrate of a conventional piezoelectric bimorph with honeycomb structures of the same material results in a significant increase in power-to-weight ratio of the piezoelectric harvester. In order to maximize the electrical response of vibration based power harvesters, the natural frequency of these harvesters is designed to match the input driving frequency. The commonly used technique of adding a tip mass is employed to lower the natural frequency (to match driving frequency) of both, solid and honeycomb substrate bimorphs. At higher excitation frequency, the natural frequency of the traditional solid substrate bimorph can only be altered (to match driving frequency) through a change in global geometric design parameters, typically achieved by increasing the thickness of the harvester. As a result, the size of the harvester is increased and can be disadvantageous especially if the application imposes a space/size constraint. Moreover, the bimorph with increased thickness will now require a larger mechanical force to deform the structure which can fall outside the input ambient excitation amplitude range. In contrast, the honeycomb core bimorph offers an advantage in terms of preserving the global geometric dimensions. The natural frequency of the honeycomb core bimorph can be altered by manipulating honeycomb cell design parameters, such as cell angle, cell wall thickness, vertical cell height and inclined cell length. This results in a change in the mass and stiffness properties of the substrate and hence the bimorph, thereby altering the natural frequency of the harvester. Design flexibility of honeycomb core bimorphs is demonstrated by varying honeycomb cell parameters to alter mass and stiffness properties for power harvesting. The influence of honeycomb cell parameters on power generation is examined to evaluate optimum design to attain highest specific power. In addition, the more compliant nature of a honeycomb core bimorph decreases susceptibility towards fatigue and can increase the operating lifetime of the harvester. The second component of this dissertation analyses an uncoupled equivalent circuit model for piezoelectric energy harvesting. Open circuit voltage developed on the piezoelectric materials can be easily computed either through analytical or finite element models. The efficacy of a method to determine power developed across a resistive load, by representing the coupled piezoelectric electromechanical problem with an external load as an open circuit voltage driven equivalent circuit, is evaluated. The lack of backward feedback at finite resistive loads resulting from such an equivalent representation is examined by comparing the equivalent circuit model to the governing equations of a fully coupled circuit model for the electromechanical problem. It is found that the backward feedback is insignificant for weakly coupled systems typically seen in micro electromechanical systems and other energy harvesting device configurations with low coupling. For moderate to high coupling systems, a correction factor based on a calibrated resistance is presented which can be used to evaluate power generation at a specific resistive load

DESIGN AND IMPLEMENTATION OF ENERGY HARVESTING CIRCUITS FOR MEDICAL DEVICES

Technological enhancements in a low-power CMOS process have promoted enhancement of advanced circuit design techniques for sensor related electronic circuits such as wearable and implantable sensor systems as well as wireless sensor nodes (WSNs). In these systems, the powering up the electronic circuits has remained as a major problem because battery technologies are not closely following the technological improvements in semiconductor devices and processes thus limiting the number of sensor electronics modules that can be incorporated in the design of the system. In addition, the traditional batteries can leak which can cause serious health hazards to the patients especially when using implantable sensors. As an alternative solution to prolonging the life of battery or to mitigate serious health problems that can be caused by battery, energy harvesting technique has appeared to be one of the possible solutions to supply power to the sensor electronics. As a result, this technique has been widely studied and researched in recent years. In a conventional sensor system, the accessible space for batteries is limited, which restricts the battery capacity. Therefore, energy harvesting has become an attractive solution for powering the sensor electronics. Power can be scavenged from ambient energy sources such as electromagnetic signal, wind, solar, mechanical vibration, radio frequency (RF), and thermal energy etc. Among these common ambient sources, RF and piezoelectric vibration-based energy scavenging systems have received a great deal of attention because of their ability to be integrated with sensor electronics modules and their moderate available power density. In this research, both RF and piezoelectric vibration-based energy harvesting systems have been studied and implemented in 130 nm standard CMOS process

Mixed-source charger-supply CMOS IC

The proposed research objective is to develop, test, and evaluate a mixer and charger-supply CMOS IC that derives and mixes energy and power from mixed sources to accurately supply a miniaturized system. Since the energy-dense source stores more energy than the power-dense source while the latter supplies more power than the former, the proposed research aims to develop an IC that automatically selects how much and from which source to draw power to maximize lifetime per unit volume. Today, the state of the art lacks the intelligence and capability to select the most appropriate source from which to extract power to supply the time-varying needs of a small system. As such, the underlying objective and benefit of this research is to reduce the size of a complete electronic system so that wireless sensors and biomedical implants, for example, as a whole, perform well, operate for extended periods, and integrate into tiny spaces.Ph.D

Study, optimization and silicon implementation of a smart high-voltage conditioning circuit for electrostatic vibration energy harvesting system

La récupération de l'énergie des vibrations est un concept relativement nouveau qui peut être utilisé dans l'alimentation des dispositifs embarqués de puissance à micro-échelle avec l'énergie des vibrations omniprésentes dans l environnement. Cette thèse contribue à une étude générale des récupérateurs de l'énergie des vibrations (REV) employant des transducteurs électrostatiques. Un REV électrostatique typique se compose d'un transducteur capacitif, de l'électronique de conditionnement et d un élément de stockage. Ce travail se concentre sur l'examen du circuit de conditionnement auto-synchrone proposé en 2006 par le MIT, qui combine la pompe de charge à base de diodes et le convertisseur DC-DC inductif de type de flyback qui est entraîné par le commutateur. Cette architecture est très prometteuse car elle élimine la commande de grille précise des transistors utilisés dans les architectures synchrones, tandis qu'un commutateur unique se met en marche rarement. Cette thèse propose une analyse théorique du circuit de conditionnement. Nous avons développé un algorithme qui par commutation appropriée de flyback implémente la stratégie de conversion d'énergie optimale en tenant compte des pertes liées à la commutation. En ajoutant une fonction de calibration, le système devient adaptatif pour les fluctuations de l'environnement. Cette étude a été validée par la modélisation comportementale.Une autre contribution consiste en la réalisation de l'algorithme proposé au niveau du circuit CMOS. Les difficultés majeures de conception étaient liées à l'exigence de haute tension et à la priorité de la conception faible puissance. Nous avons conçu un contrôleur du commutateur haute tension de faible puissance en utilisant la technologie AMS035HV. Sa consommation varie entre quelques centaines de nanowatts et quelques microwatts, en fonction de nombreux facteurs - paramètres de vibrations externes, niveaux de tension de la pompe de charge, la fréquence de la commutation de commutateur, la fréquence de la fonction de calibration, etc.Nous avons également réalisé en silicium, fabriqué et testé un commutateur à haute tension avec une nouvelle architecture de l'élévateur de tension de faible puissance. En montant sur des composants discrets de la pompe de charge et du circuit de retour et en utilisant l'interrupteur conçu, nous avons caractérisé le fonctionnement large bande haute-tension du prototype de transducteur MEMS fabriqué à côté de cette thèse à l'ESIEE Paris. Lorsque le capteur est excité par des vibrations stochastiques ayant un niveau d'accélération de 0,8 g rms distribué dans la bande 110-170 Hz, jusqu'à 0,75 W de la puissance nette a été récupérée.Vibration energy harvesting is a relatively new concept that can be used in powering micro-scale power embedded devices with the energy of vibrations omnipresent in the surrounding. This thesis contributes to a general study of vibration energy harvesters (VEHs) employing electrostatic transducers. A typical electrostatic VEH consists of a capacitive transducer, conditioning electronics and a storage element. This work is focused on investigations of the reported by MIT in 2006 auto-synchronous conditioning circuit, which combines the diode-based charge pump and the inductive flyback energy return driven by the switch. This architecture is very promising since it eliminates precise gate control of transistors employed in synchronous architectures, while a unique switch turns on rarely. This thesis addresses the theoretical analysis of the conditioning circuit. We developed an algorithm that by proper switching of the flyback allows the optimal energy conversion strategy taking into account the losses associated with the switching. By adding the calibration function, the system became adaptive to the fluctuations in the environment. This study was validated by the behavioral modeling. Another contribution consists in realization of the proposed algorithm on the circuit level. The major design difficulties were related to the high-voltage requirement and the low-power design priority. We designed a high-voltage analog controller of the switch using AMS035HV technology. Its power consumption varies between several hundred nanowatts and a few microwatts, depending on numerous factors - parameters of external vibrations, voltage levels of the charge pump, frequency of the flyback switching, frequency of calibration function, etc. We also implemented on silicon, fabricated and tested a high-voltage switch with a novel low power level-shifting driver. By mounting on discrete components the charge pump and flyback circuit and employing the proposed switch, we characterized the wideband high-voltage operation of the MEMS transducer prototype fabricated alongside this thesis in ESIEE Paris. When excited with stochastic vibrations having an acceleration level of 0.8 g rms distributed in the band 110-170 Hz, up to 0.75 $\mu$W of net electrical power has been harvested.PARIS-JUSSIEU-Bib.électronique (751059901) / SudocSudocFranceF