Energy scavenging system for indoor wireless sensor network

As wireless communication evolves wireless sensors have begun to be integrated into society more and more. As these sensors are used to a greater extent newer and better ways to keep them working optimally have begun to surface. One such method aims to further the sensors energy independence on humans. This technique is known as energy scavenging. The logic behind energy scavenging is to allow the device to have its own reliable source of energy that does not require upkeep, has a long life expectancy, and does not completely rely on an internal power source. The aim of this thesis is to research techniques for indoor energy scavenging for sensor that is used to monitor patients in a hospital. There are numerous techniques to achieve energy scavenging in wireless sensor networks. Multiple scavenging methods are known such as vibration energy, thermoelectric energy, and photovoltaic energy. All of these methods were analyzed and compared to see which would be optimal for the situation the sensor would be put in. Other techniques come into play to help the efficiency of the sensor network. These methods were also examined to help the energy scavenging to be more feasible

Small scale energy harvesting for use with an electronic door strike

Smart or connected devices are becoming more and more prevalent in modern society. These devices typically consist of miniature sensors and actuators to automate and control common daily activities. The spread of these devices comes with the need to supply power to these devices. A first approach is often to include a battery to allow for remote operation. The immediate drawback to this approach is the eventual need to either replace or recharge this battery. A power generation system that both compact and portable is desired. Any such system which can operate by extracting ambient energy from the environment would see applications in many common devices ranging from common calculators, to industrial equipment health monitoring systems. One common device that is experiencing the transition from a purely mechanical to smart device is the standard door lock. Keyless access is gaining prevalence in both office buildings and private residences as it allows for greater convenience and added security measures. These benefits come at the cost of electrical energy consumption, which is presently being primarily supplied through direct wire routing from the building's main grid. An electronic locking mechanism that is fully physically autonomous and energy independent would be advantageous. In this work the application of energy harvesting methods as they relate to an electronic door strike, or E-strike, are investigated. Multiple different common ambient energy sources are identified and their expected power densities quantified. These range from 9 μW to 7W depending on the source. From these sources human action is identified as possessing the highest power density, and also being the most reliably available source. A system to model the energy flow through an E-strike is derived. This model accounts the maximum available energy, harvesting efficiency, required power draw, and storage capabilities. An E-strike prototype is constructed and experiments are conducted to validate the proposed model. The proposed design provides and energy density of 4.25mJ/cm3. The overarching goal is to identify under what operating conditions an E-strike will be able to operate indefinitely, without the need to add physical power lines or replace batteries. A single combined parameter, the Activation-per-input value is defined and identified as the key characteristic that determines which environments will be suitable for an energy harvesting E-strike. Results of these experiments demonstrate that an E-strike can operate indefinitely with an Activation-per-Input ratio of 0.1 or below

Power-efficient current-mode analog circuits for highly integrated ultra low power wireless transceivers

In this thesis, current-mode low-voltage and low-power techniques have been applied to implement novel analog circuits for zero-IF receiver backend design, focusing on amplification, filtering and detection stages. The structure of the thesis follows a bottom-up scheme: basic techniques at device level for low voltage low power operation are proposed in the first place, followed by novel circuit topologies at cell level, and finally the achievement of new designs at system level. At device level the main contribution of this work is the employment of Floating-Gate (FG) and Quasi-Floating-Gate (QFG) transistors in order to reduce the power consumption. New current-mode basic topologies are proposed at cell level: current mirrors and current conveyors. Different topologies for low-power or high performance operation are shown, being these circuits the base for the system level designs. At system level, novel current-mode amplification, filtering and detection stages using the former mentioned basic cells are proposed. The presented current-mode filter makes use of companding techniques to achieve high dynamic range and very low power consumption with for a very wide tuning range. The amplification stage avoids gain bandwidth product achieving a constant bandwidth for different gain configurations using a non-linear active feedback network, which also makes possible to tune the bandwidth. Finally, the proposed current zero-crossing detector represents a very power efficient mixed signal detector for phase modulations. All these designs contribute to the design of very low power compact Zero-IF wireless receivers. The proposed circuits have been fabricated using a 0.5μm double-poly n-well CMOS technology, and the corresponding measurement results are provided and analyzed to validate their operation. On top of that, theoretical analysis has been done to fully explore the potential of the resulting circuits and systems in the scenario of low-power low-voltage applications.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

MRI-Based Communication with Untethered Intelligent Medical Microrobots

RESUME Les champs magnétiques présent dans un système clinique d’Imagerie par Résonance Magnétique (IRM) peuvent être exploités non seulement, afin d’induire une force de déplacement sur des microrobots magnétiques tout en permettant l’asservissement de leur position - une technique connue sous le nom de Navigation par Résonance Magnétique (NRM), mais aussi pour mettre en œuvre un procédé de communication. Pour des microrobots autonomes équipés de senseurs ayant un certain niveau d'intelligence et opérant à l'intérieur du corps humain, la puissance de transmission nécessaire pour communiquer des informations à un ordinateur externe par des méthodes présentement connues est insuffisante. Dans ce travail, une technique est décrite où une telle perte de puissance d'émission en raison de la mise à l'échelle de ces microrobots peut être compensée par le scanner IRM agissant aussi comme un récepteur très sensible. La technique de communication prend la forme d'une modification de la fréquence du courant électrique circulant le long d'une bobine miniature incorporé dans un microrobot. La fréquence du courant électrique peut être réglée à partir d'une entrée de seuil prédéterminée du senseur mis en place sur le microrobot. La fréquence devient alors corrélée à l’information de l’état du senseur recueilli par le microrobot et elle est déterminée en utilisant l'IRM. La méthode proposée est indépendante de la position et l'orientation du microrobot et peut être étendue à un grand nombre de microrobots pour surveiller et cartographier les conditions physiologiques spécifiques dans une région plus vaste à n’importe quelle profondeur à l'intérieur du corps.----------ABSTRACT The magnetic environment provided by a clinical Magnetic Resonance Imaging (MRI) scanner can be exploited to not only induce a displacement force on magnetic microrobots while allowing MR-tracking for serving control purpose or positional assessment - a technique known as Magnetic Resonance Navigation (MRN), but also for implementing a method of communication with intelligent microrobots. For untethered sensory microrobots having some level of intelligence and operating inside the body, the transmission power necessary to communicate information to an external computer via known methods is insufficient. In this work, a technique is described where such loss of transmission power due to the scaling of these microrobots can be compensated by the same MRI scanner acting as a more sensitive receiver. A communication scheme is implemented in the form of a frequency alteration in the electrical current circulating along a miniature coil embedded in a microrobot. The frequency of the electrical current could be regulated from a predetermined sensory threshold input implemented on the microrobot. Such a frequency provides information on the level of sensory information gathered by the microrobot, and it is determined using MR imaging. The proposed method is independent of the microrobot's position and orientation and can be extended to a larger number of microrobots for monitoring and mapping specific physiological conditions inside a larger region at any depths within the body

Sensor to improve detection of line break or earth faults for Victorian answer lines

This project is an investigation into a possible fault detection system for SWER (single wire earth return) electrical distribution networks in Victoria that focuses on types of faults that are undetectable by conventional protection systems and have the ability to ignite fires. The paper considers why a new detection system is required and then how it could be practically implemented in a general sense. More detailed investigations then focus on communications, power harvesting and fault detection considerations. The devices are proposed to be distributed across SWER networks to enact a detection system. The paper focuses on the many conflicting requirements and subsequent compromises that any eventual design will need to overcome. It is found that electric field power harvesting from the Victorian SWER lines’ 12.7kV conductor can produce power outputs within the range required by standalone detection devices given fairly severe design constraints. Summaries and conclusions are drawn to a level where the project develops a clear methodology to go forward

Functional modelling and prototyping of electronic integrated kinetic energy harvesters

The aim of developing infinite-life autonomous wireless electronics, powered by the energy of the surrounding environment, drives the research efforts in the field of Energy Harvesting. Electromagnetic and piezoelectric techniques are deemed to be the most attractive technologies for vibrational devices. In the thesis, both these technologies are investigated taking into account the entire energy conversion chain. In the context of the collaboration with the STMicroelectronics, the project of a self-powered Bluetooth step counter embedded in a training shoe has been carried out. A cylindrical device 27 × 16mm including the transducer, the interface circuit, the step-counter electronics and the protective shell, has been developed. Environmental energy extraction occurs exploiting the vibration of a permanent magnet in response to the impact of the shoe on the ground. A self-powered electrical interface performs maximum power transfer through optimal resistive load emulation and load decoupling. The device provides 360 μJ to the load, the 90% of the maximum recoverable energy. The energy requirement is four time less than the provided and the effectiveness of the proposed device is demonstrated also considering the foot-steps variability and the performance spread due to prototypes manufacturing. In the context of the collaboration with the G2Elab of Grenoble and STMicroelectronics, the project of a piezoelectric energy arvester has been carried out. With the aim of exploiting environmental vibrations, an uni-morph piezoelectric cantilever beam 60×25×0.5mm with a proof mass at the free-end has been designed. Numerical results show that electrical interfaces based on SECE and sSSHI techniques allows increasing performance up to the 125% and the 115% of that in case of STD interface. Due to the better performance in terms of harvested power and in terms of electric load decoupling, a self-powered SECE interface has been prototyped. In response to 2 m/s2 56,2 Hz sinusoidal input, experimental power recovery of 0.56mW is achieved demonstrating that the device is compliant with standard low-power electronics requirements

Vibration modelling and analysis of piezoelectric energy harvesters

The performance of piezoelectric cantilever beam energy harvesters subjected to base excitation is considered in this work. Based on the linear assumption, a theoretical model is developed to predict the mechanical and electrical responses of the harvester and in comparison to other theoretical models, more accurate mode shape functions are used for the structural part of the harvester. The model is validated against experimental measurements and parameter studies are carried out to investigate the maximum power output in different situations. In some applications, like powering tyre pressure monitoring sensors (TPMS), energy harvesters are subjected to large amplitude shocks and high levels of acceleration, which can cause large bending stresses to develop in the beam, leading to mechanical failure. In this work, a bump stop is introduced in the energy harvester design to limit the amplitude of vibration and prevent large amplitude displacement. A theoretical model is developed to simulate the energy harvester impacting a stop, and the model is used to investigate how the electrical output of the harvester is affected by the stop. The work demonstrates how the model can be used as a design tool for analysing the compromise between the electrical output and structural integrity. Nonlinear behaviour of the energy harvester is observed to have a significant effect on the resonance frequencies when the harvester is subjected to large amplitude base accelerations. To correctly predict the behaviour of the harvester, piezoelectric material nonlinearity and geometric nonlinearity are incorporated in the theoretical model. It is found that the nonlinear softening effect is dominated by the material nonlinearity, while the geometric nonlinearity is less significant. The nonlinear energy harvester model is used in conjunction with the bump stop and results obtained using the linear and nonlinear models are compared to experimental measurements to investigate the importance of using a nonlinear model. The inclusion of nonlinear behaviour is shown to improve significantly the accuracy of predictions under some circumstances. The energy harvester models developed in this work are used to simulate the electrical power generated in a TPMS application, where the harvester embedded in the tyre is subjected to large radial accelerations as the tyre rolls along the road. The simulated results are compared to reported experimental work and agreement is found between the results

Vibration modelling and analysis of piezoelectric energy harvesters

The performance of piezoelectric cantilever beam energy harvesters subjected to base excitation is considered in this work. Based on the linear assumption, a theoretical model is developed to predict the mechanical and electrical responses of the harvester and in comparison to other theoretical models, more accurate mode shape functions are used for the structural part of the harvester. The model is validated against experimental measurements and parameter studies are carried out to investigate the maximum power output in different situations. In some applications, like powering tyre pressure monitoring sensors (TPMS), energy harvesters are subjected to large amplitude shocks and high levels of acceleration, which can cause large bending stresses to develop in the beam, leading to mechanical failure. In this work, a bump stop is introduced in the energy harvester design to limit the amplitude of vibration and prevent large amplitude displacement. A theoretical model is developed to simulate the energy harvester impacting a stop, and the model is used to investigate how the electrical output of the harvester is affected by the stop. The work demonstrates how the model can be used as a design tool for analysing the compromise between the electrical output and structural integrity. Nonlinear behaviour of the energy harvester is observed to have a significant effect on the resonance frequencies when the harvester is subjected to large amplitude base accelerations. To correctly predict the behaviour of the harvester, piezoelectric material nonlinearity and geometric nonlinearity are incorporated in the theoretical model. It is found that the nonlinear softening effect is dominated by the material nonlinearity, while the geometric nonlinearity is less significant. The nonlinear energy harvester model is used in conjunction with the bump stop and results obtained using the linear and nonlinear models are compared to experimental measurements to investigate the importance of using a nonlinear model. The inclusion of nonlinear behaviour is shown to improve significantly the accuracy of predictions under some circumstances. The energy harvester models developed in this work are used to simulate the electrical power generated in a TPMS application, where the harvester embedded in the tyre is subjected to large radial accelerations as the tyre rolls along the road. The simulated results are compared to reported experimental work and agreement is found between the results