Improvements in technology result in evolution of smart devices. One of such smart devices is wireless sensor nodes, which consist of a sensing board, a battery supply and a wireless antenna to transfer data. We can collect information from the environment by deploying thousands of these tiny smart devices. These devices can also be used to monitor natural habitats or used in giant machine parts for performance evolution. Energy efficient operation is an important issue for wireless sensor network design and clustering is one of the most widely used approaches for energy efficiency. This thesis study aims to analyze the performance of clustering algorithms for wireless sensor networks. We proposed five clustering algorithms and perform experiments by using real sensor hardware over different topologies to investigate energy efficiency of the clustering algorithms.

Electrical conductivity (or resistivity) of cementitious materials is considered to be a fundamental property and is commonly measured using nondestructive and noninvasive testing techniques. Therefore, electrical measurements are gaining popularity in both research and field applications for structural health monitoring and material characterization of civil engineering infrastructure systems. Based on the results of measurements, the engineer can schedule maintenance more accurately and give an early warning of possible structural failure. Recently, health monitoring systems are capable of significantly increasing the cost efficiency of maintenance and repair by helping engineers improve the safety and maintainability of structures through early damage detection. The research team at the University of Texas at Austin developed a low-cost, passive, wireless conductivity sensor system. Sensors are wirelessly interrogated using external reader during inspection over the service life of the structure to monitor the conductivity variations within concrete. The focus of this work is to assess the condition of cementitious materials by measuring electrical conductivity using passive wireless sensors. By analyzing the measured conductivity data, the condition of the cementitious material, such as extent of hydration, setting and hardening times, and transport phenomena, can be assessed. This document also provides comprehensive information on the design, fabrication, interrogation, and response of conductivity sensor platforms. / text

Detection and monitoring of the damage created by the corrosion of the steel reinforcement in concrete structures is a challenging and multidisciplinary problem. Economical monitoring strategy that is long-term and nondestructive requires low-cost, battery-free, wireless sensors. Our Electronic Structural Surveillance (ESS) platform uses battery-free passive resonant circuit (tag) as a sensor. The tag is magnetically coupled to an external reader coil. It is interrogated/read remotely in a non-contact (wireless) manner and the state of the sensor is determined from a swept frequency impedance measurement. When paired with the correct sensing element (transducer), the tag can be used for a variety of sensing applications for example, chemical & biochemical sensors. A circuit model of the reader and tag for such a universal battery-free wireless sensor platform is developed. The interaction between design and detection limit is examined. The dependence of the measured signal strength and read range on the various reader and tag circuit parameters is analyzed. Since the values of the circuit of the coils are dependent on their geometries, the effect of specific coil geometry is evaluated and design recommendations are made. / text

The ability to localise objects and persons is a useful ability, that is currently used in everyday life in the form of Global Positioning System (GPS) navigation. Localisation is also useful in data networks. The ability to localise nodes in a network paves the way for applications such as location based services, beamforming and geographic routing. The Radio Interferometric Positioning System (RIPS), is a method originally designed for localisation in wireless sensor networks. RIPS is a promising method due to the fact that it is capable of localisation with high accuracy over long ranges. This is something which other existing methods are not capable of. RIPS makes localisation measurements in a different manner from conventional methods. Instead of making pairwise measurements between a transmitter and receiver, RIPS uses sets of four nodes in each of its measurements. Furthermore, RIPS requires multiple measurements to obtain the correct RIPS measurement value. This value is referred to as a q–range. Multiple q–ranges are required in order to localise a node. This creates overhead in terms of co–operation between the nodes participating in a RIPS measurement. The focus of this research is to provide a possible solution to this problem of overhead. In this dissertation an investigation is launched into the considerations and benefits of implementing RIPS on a single node. This is done by creating a conceptual design for a single wireless node capable of implementing RIPS through the use of multiple antennas. In order to test this conceptual device, a simulation model is created. This simulation model is then validated, verified and used in experiments designed to test the effects of certain design considerations and variables on the conceptual device’s localisation accuracy. The analysis of the results from these experiments shows that the conceptual device’s use of multiple antennas makes RIPS sensitive to errors. Increasing the distances separating the conceptual device’s antennas is found to decrease this sensitivity to errors. This is shown to be caused by the distances separating the antennas imposing limits on the range of q–ranges values that are possible, with smaller distances resulting in smaller ranges of possible q–range values. It is also found that the use of higher frequencies in RIPS measurements results in greater accuracy. This is with the assumption that these frequencies can be accurately transmitted. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2012.

The ability to localise objects and persons is a useful ability, that is currently used in everyday life in the form of Global Positioning System (GPS) navigation. Localisation is also useful in data networks. The ability to localise nodes in a network paves the way for applications such as location based services, beamforming and geographic routing. The Radio Interferometric Positioning System (RIPS), is a method originally designed for localisation in wireless sensor networks. RIPS is a promising method due to the fact that it is capable of localisation with high accuracy over long ranges. This is something which other existing methods are not capable of. RIPS makes localisation measurements in a different manner from conventional methods. Instead of making pairwise measurements between a transmitter and receiver, RIPS uses sets of four nodes in each of its measurements. Furthermore, RIPS requires multiple measurements to obtain the correct RIPS measurement value. This value is referred to as a q–range. Multiple q–ranges are required in order to localise a node. This creates overhead in terms of co–operation between the nodes participating in a RIPS measurement. The focus of this research is to provide a possible solution to this problem of overhead. In this dissertation an investigation is launched into the considerations and benefits of implementing RIPS on a single node. This is done by creating a conceptual design for a single wireless node capable of implementing RIPS through the use of multiple antennas. In order to test this conceptual device, a simulation model is created. This simulation model is then validated, verified and used in experiments designed to test the effects of certain design considerations and variables on the conceptual device’s localisation accuracy. The analysis of the results from these experiments shows that the conceptual device’s use of multiple antennas makes RIPS sensitive to errors. Increasing the distances separating the conceptual device’s antennas is found to decrease this sensitivity to errors. This is shown to be caused by the distances separating the antennas imposing limits on the range of q–ranges values that are possible, with smaller distances resulting in smaller ranges of possible q–range values. It is also found that the use of higher frequencies in RIPS measurements results in greater accuracy. This is with the assumption that these frequencies can be accurately transmitted. / Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2012.

Work described in this thesis is concerned with localisation techniques, for determining the position, of wireless sensors whilst these are immersed in confined industrial processes, such as those occurring in the chemical, pharmaceutical and food processing industries. Two different approaches to localisation were investigated. The first approach employed an existing hardware system that used ultra wide band (UWB) signals whist the second approach used a network localisation method based on information from narrow-band received signals. A prototype UWB-based localisation algorithm processed experimental received UWB pulses to detect their leading edges (LE) that were used to derive Time Difference of Arrival (TDoA) data. In turn TDoA data were converted into distances and used to compute the locations of the sensor nodes. Nevertheless, the process of detecting the LEs caused significant errors in the localisation process. To deal with this problem new automated adaptive LE detection methods were derived that succeeded in reducing localisation errors by half, compared to the prototype method, reaching accuracies of ±2cm. Thorough analysis of TDoA profiles revealed that these follow specific trends depending on the positions of the sensor nodes. A number of properties of TDoA profiles are proved mathematically and incorporated into seven localisation algorithms. These algorithms were examined using experimental TDoA data and shown to achieve average localisation errors up to 3cm. Network-based localisation was examined at a later stage of this research since complexities of large scale measurements and difficulties with equipment, delayed acquiring experimental data. The deployed network consisted of a number of nodes whose positions were known (anchors) that were used to estimate the positions of sensor nodes whose positions where considered to be unknown. Localisation was based on received signal strength (RSS) data, at every node to be localised, in anticipation that RSS could provide distance information that could be used in the localisation procedure. Nevertheless, fluctuations in RSS only allowed using localisation algorithms that associated RSS to the positions of anchors. The average localisation error in the network-based localisation algorithms was between 30cm to 100cm.

Various nondestructive testing (NDT) technologies for construction and performance monitoring have been studied for decades. Recently, the rapid evolution of wireless sensor network (WSN) technologies has enabled the development of sensors that can be embedded in concrete to monitor the structural health of infrastructure. Such sensors can be buried inside concrete and they can collect and report valuable volumetric data related to the health of a structure during and/or after construction. Wireless embedded sensors monitoring system is also a promising solution for decreasing the high installation and maintenance cost of the conventional wire based monitoring systems. Wireless monitoring sensors need to operate for long time. However, sensor batteries have finite life-time. Therefore, in order to enable long operational life of wireless sensors, novel wireless powering methods, which can charge the sensors’ rechargeable batteries wirelessly, need to be developed. The optimization of RF wireless powering of sensors embedded in concrete is studied here. First, our analytical results focus on calculating the transmission loss and propagation loss of electromagnetic waves penetrating into plain concrete at different humidity conditions for various frequencies. This analysis specifically leads to the identification of an optimum frequency range within 20-80 MHz that is validated through full-wave electromagnetic simulations. Second, the effects of various reinforced bar configurations on the efficiency of wireless powering are investigated. Specifically, effects of the following factors are studied: rebar types, rebar period, rebar radius, depth inside concrete, and offset placement. This analysis leads to the identification of the 902-928 MHz ISM band as the optimum power transmission frequency range for sensors embedded in reinforced concrete, since antennas working in this band are less sensitive to the effects of varying humidity as well as rebar configurations. Finally, optimized rectennas are designed for receiving and/or harvesting power in order to charge the rechargeable batteries of the embedded sensors. Such optimized wireless powering systems exhibit significantly larger efficiencies than the efficiencies of conventional RF wireless powering systems for sensors embedded in plain or reinforced concrete.

Les réseaux de capteurs sans-fil sont une nouvelle technologie qui permet de déployer des capteurs hétérogènes et de les faire communiquer sans fil et de façon autonome. Cette capacité nouvelle à surveiller ou instrumenter le monde qui nous entoure ouvre la voie à de nouvelles applications innovantes ou à une évolution majeure d’applications déjà existantes.D’une dizaine de nœuds à plusieurs milliers, les réseaux de capteurs sans fil commencent à conquérir le monde industriel et notre vie quotidienne. Leurs besoins en communications, gestion, génération et stockage de l’énergie, miniaturisation et réduction des coûts ne nécessitent pas seulement de perfectionner les technologies actuelles mais bien d’en inventer de nouvelles. Parmi toutes les applications révolutionnaires des réseaux de capteurs sans fil comme dans la santé, l’environnement, l’industrie et le militaire, l’une des applications les plus transformatrices est la surveillance de structure. La surveillance de structure est l’art de surveiller tout ce qui peut s’abimer, s’user ou tomber en panne. Elle est particulièrement importante dans les domaines des transports et du bâtiment, étant donné que la sécurité des personnes est en jeu. En plaçant aux endroits stratégiques des capteurs sans-fil, il sera possible de prévoir et de prévenir la défaillance d’un pont, l’usure d’un avion ou d’un train ou la déformation d’un bâtiment. La surveillance de structure permet de prévenir les pannes et les défaillances, de réduire les coûts de maintenance et d’améliorer les performances. C’est un processus complexe qui implique plusieurs technologies : des capteurs, la transmission de l’information et l’analyse des données. La nature (accéléromètre, gyroscope, jauge de contrainte, température, pression, fuite, givre, etc. . .), la position ainsi que le nombre de capteurs sont dictés et dépendants des besoins de l’analyse de la structure qui doit être effectuée. De ce fait, les contraintes imposées au système de transmission de données sans fil, afin d’offrir une couverture suffisante de la structure de l’appareil avec plusieurs centaines voire plusieurs milliers de capteurs que leur localisation rendra difficile d’accès, nécessitent des nouvelles innovations en matière d’efficacité énergétique et de performance de communication. Ce travail s’intéresse à la conception et l’implémentation d’un système de transmission de données dans un réseau de capteurs sans-fil. Après une présentation des exigences du système de surveillance de structure aéronautique, l’architecture générale du système de surveillance est décrite. Une couche physique spécifique à haute efficacité énergétique basée sur l’Impulse-Radio UltraWide Band a été conçue. Les designs complets de l’émetteur et du récepteur IR-UWB sont présentés ainsi que l'optimisation du codage canal par rapport à la consommation énergétique. Une couche MAC spécifique permettant un nombre important de nœuds et une efficacité énergétique élevée basée sur du TDMA reconfigurable a été conçue. Plusieurs prototypes ont été implémentés pour valider la conception et démontrer les performances. Ces implémentation utilise des techniques avancées d’optimisation de la consommation énergétique et de reconfigurabilité afin de répondre aux exigences des réseaux de capteurs sans-fil. Des simulations ASIC permettent également de prévoir que ce système permettra de supporter des débits applicatifs de plusieurs centaines de mégabits par seconde, tout en permettant à plusieurs dizaines de nœuds de communiquer. Les performances énergétiques de ce système de communication sont aujourd’hui à l’état de l’art. Enfin, cette technologie de communication sans-fil a été intégrée dans un système complet de deux nœuds capteurs et d’un routeur dans un démonstrateur FPGA / Wireless Sensor Networks (WSN) is an emerging technology which allows deploying wireless communicating autonomous heterogenous sensors. This monitoring capability paves the way for new innovative applications or breakthrough evolution of existing ones. WSN have started to change the industry and our daily lives. Their communication, energy, miniaturization and cost requirements cannot be met by evolutions of current technologies but will require new innovations.Among health, environment, industrial and military applications for WSN, one of the most revolutionary is Structural Health Monitoring (SHM). SHM is the art of monitoring anything which can wear, break down or be damaged. It is of utmost importance in safety sensitive domains such as the transport and construction industries.By placing sensors in carefully chosen locations, SHM will allow failure prediction, cost reduction and improved performance of bridges, planes, building or engines.The tens to thousands of sensors and the huge amount of data generated places a strong burden on the wireless communication of the nodes, which cannot be satisfied with today’s technology. This work presents the design and implementation works such a wireless communication system.Following a presentation of the context and requirement of this work, a general description of the SHM system is given. A specific highly energy efficient physical layer based on Impulse-Radio UltraWide Band (IR-UWB) has been designed.The complete IR-UWB transmitter and receiver are detailed, including the energy efficiency optimized channel coding. A specific Medium Access Control (MAC) layer allowing a large number of communicating nodes based on reconfigurableTime Division Multiple Access (TDMA) was designed. Several prototypes of this system have been implemented to prove feasibility and performance. These implementations employ advanced energy consumption reduction and reconfigurability techniques to answer WSN communication challenges. An ASIC implementation simulation has demonstrated hundreds of megabits per second data rate at state of the art energy efficiency

McMaster University in conjunction with an industrial partner has been designing wireless vibrational condition monitoring sensors for implementation on a vibrating screening machine used in mining applications. A limitation with the current sensor design is their dependency on battery power. In order for the sensors to provide real-time continuous streaming of acceleration data, an alternate power supply was required outside of traditional sources such as batteries or wired power. This thesis outlines the research and development of a power system that harvests the kinetic vibrational energy of a mining screen and converts it into electrical energy for use by a wireless sensor node. During development, multiple prototypes were built and evaluated under laboratory conditions. The core concept of the system is an eccentric pendulum mass excited by the external vibrations of the screening machine used to drive a stepper motor generator. The major design obstacle of the project was how to get the system to self initiate. Both a mechanical and an electrical solution were developed to solve this concern. The final prototype design is fully autonomous, able to react to the start up or shut-down of a screening machine, while also providing a continuous power supply to a wireless vibrational analysis sensor as tested in the lab. With minor optimization, this prototype can be turned into a commercial product for industrial implementation and sale. / Thesis / Master of Applied Science (MASc)

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