Condition monitoring of machines and structures is commonly utilized in order to prevent failures before they can occur. For these reasons, data such as temperature, vibrations or displacements are collected and analysed. Sensors collect this information, which is sent to a base station to be examined. Wired sensors have been used since the appearance of condition monitoring maintenance; however, wireless sensors are becoming more popular in this area. The use of wired sensors can be very expensive, due to the cost related to the installation and maintenance of the wiring between the sensors and the base station. In wind turbines, wired sensor networks are starting to be substituted by wireless sensor networks. However, for tidal turbines, such as those developed by Delta Stream, this is still a challenge. The use of batteries to supply energy to sensors is not an optimal solution for turbines that are located in remote areas. Batteries have a limited life and their replacement is costly and complicated. Thus, alternative sources of energy have to be found. The environment found in a tidal turbine provides several sources of profitable energy, such as vibration and temperature differences which can be used to supply energy by means of energy harvesters. The aim of this project is to demonstrate the operation of self-powered short-range wireless sensor nodes for a potential use in a Delta Stream nacelle of tidal turbine. This project focuses on the wireless communication inside the nacelle (where most of the sensors are located) using a land protocol (Zigbee), and the energy harvesting using waste heat by means of thermoelectric devices. In order to prove the operation of the whole system (thermoelectric generator and sensor node), a power management circuit was also constructed and tested.

<div>Wireless sensor networks are highly integrated across numerous industries from industrial</div><div>manufacturing to personal health monitoring. They provide several key benefits over</div><div>traditional wired systems including positioning flexibility, modularity, interconnectivity, and</div><div>robust data routing schemes. However, their adoption into certain sectors such as vacuum</div><div>and aerospace has been slow due to tight regulation, data security concerns, and device</div><div>reliability.</div><div>Lyophilization is a desiccation technique used to stabilize sensitive food and drug products</div><div>using vacuum sublimation. A series of wireless devices based on the Pirani architecture are</div><div>developed to quantify the spatial variations in pressure and temperature throughout this</div><div>process. The data is coupled to computational fluid dynamics simulations to estimate the</div><div>sublimation rate over time. This information is then used to quantify the heat and mass</div><div>transfer characteristics of the product, allowing estimates of product temperature and mass</div><div>flux to be obtained for an arbitrary cycle. This capability is significant, having the ability</div><div>to accelerate process development and reduce manufacturing time.</div><div>Drying performance during lyophilization is highly sensitive to the dynamics of the freezing</div><div>process. This work therefore also develops a wireless network to monitor both gas</div><div>pressure and temperature throughout the controlled ice nucleation process, a technique used</div><div>to improve batch uniformity by inducing simultaneous and widespread ice nucleation via</div><div>adiabatic decompression. The effects of initial charge pressure, ballast composition, and vial</div><div>size are investigated. Experimental data is supported by numerical modeling to describe the</div><div>evolution of the true gas temperature during the discharge event.</div><div>Finally, The mechanisms governing the lyophilization process are directly applied to the</div><div>aerospace industry in the form of a novel milliNewton-class evaporation-based thruster concept.</div><div>The device was tested under vacuum using a torsional balance and demonstrated peak</div><div>thrust magnitudes on the order of 0.5 mN. A state observer model was then implemented</div><div>to decouple the dynamics of the balance with the time-dependent thrust input. With this</div><div>model the true time-dependent thrust output and corresponding thruster performance are</div><div>analyzed.</div>

In a wide range of industries, machine condition monitoring is one of the most cost effective ways to minimise maintenance efforts and machine downtime. To implement such a system, wireless solutions have increasingly become an attractive proposition due to the ease of installation and minimal infrastructure alternation. However, currently most wireless sensors in the world are powered by a finite battery source. The dependence of batteries not only requires frequent maintenance, but also has adverse environmental consequences associated with battery disposal. These reasons render massive deployment of wireless sensors in the industry problematic. With the advances in semiconductors, power consumption of wireless sensors has been continuously decreasing. It is an inevitable trend for self-powered wireless sensors to emerge and become the norm for machine and environmental monitoring. In this research, vibration is chosen to be the energy source to enable self-powered wireless sensors due to its ubiquitousness in machinery and industrial environments. As a result of relying on resonance, the biggest challenge for vibration-based energy harvesters is their narrow bandwidth. Even a small deviation of the vibration frequency can dramatically reduce the power output. The primary goal of this research is to address this problem. In particular, Piezoelectric generators are identified to be the most suitable technology. In this work, extensive theoretical and experimental studies are conducted in single mass and multi-modal harvesters, and in resonance tuning harvesters by modulus and impedance matching as well as by mechanical actuation. Mathematical modelling plays a significant role in energy harvester designs. A dynamic model that generalises the single degree of freedom models and the continuum models is derived and validated by experiments. The model serves as the building block for the whole research, and it is further refined for the investigation of modulus and impedance matching. In the study of multi-modal harvesters, a continuum model for double-mass piezoelectric cantilever beams is derived and experimentally validated. To study the feasibility of resonance tuning by mechanical means, prototypes were built and performance evaluated. This document details the theoretical basis, concepts and experimental results that extend the current knowledge in the field of energy harvesting. This research work, being highly industrially focused, is believed to be a very significant step forward to a commercial energy harvester that works for a wide range of vibration frequencies.

Due to the unprecedented spatial and temporal resolution they offer, wireless sensor networks are considered an enabling technology for the distributed monitoring of industrial, military, and natural environments. As these systems migrate into vastly different and novel applications, new constraints are discovered that affect network reliability and utility. For example, wireless sensors are typically statically deployed and, unlike mobile systems, cannot move to a new location for better radio reception. As a result, the signal fades caused by non-optimal environmental conditions can increase the outage probability of the system, potentially rendering the network unreliable and ineffectual. Stochastic models that quantify link reliability and the effectiveness of diversity methods are often employed to understand the impact of such fading. However, the performance of these models applied to wireless sensor networks is entirely dependent on the appropriateness of the model with respect to the environment. This work first presents an empirical study of the propagation environment for a wingless, rotary aircraft, showing that the wireless environment within exhibits frequency-selective fading much more severe than predicted by current worst-case models (i.e., Rayleigh). An analysis is then given of the effectiveness of several diversity methods operating within such environments (referred to as hyper-Rayleigh). These fade mitigation techniques are simple enough to be employed for use with low-complexity wireless sensor hardware, and include spatial diversity, polar diversity, two-element passive combining, and two-element phased combining. Two-element phased combining is further developed by examining the effect that smaller element spacing has on diversity gain. A demonstration of a wireless

Wireless sensor networks (WSNs) are composed of hundreds of wireless sensors which collaborate to perform a common task. Because of the small size of wireless sensors, they have some serious limitations including very low computation capability and battery reserve. Such resource limitations require that WSN protocols to be extremely efficient. In this thesis, we focus on the Medium Access Control (MAC) layer in WSNs. We propose a MAC scheme, V-MAC, for WSNs that extends that lifetime of the network. We compare V-MAC with other MAC schemes. V-MAC uses a special mechanism to divide sensors in different groups and then all the members of a group go to sleep at the same time. V-MAC protects WSNs against denial of sleep and broadcast attacks. We present the V-MAC scheme in details and evaluate it with simulations. Our simulations show that V-MAC enjoys significantly higher throughput and network lifetime compared to other schemes.

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.