A MEMS piezoresistive pressure sensor provides a low-cost and accurate means of detecting and quantifying small-scale disturbances in underwater environments. A highly sensitive MEMS pressure sensor has been developed that can be packaged in two different ways – one in a cylindrical housing, and the other in a flexible, yet robust, strip configuration – enabling more freedom for the user to choose an option that fits their needs. The sensing element of each consists of four piezoresistive elements in a Wheatstone Bridge configuration arranged on a deformable buried-oxide layer, which is then bonded to a Silicon base layer with a hollow cavity carved using reactive-ion etching. Previous work has shown the survivability of these sensors in an underwater environment and also measurements of low frequency pressure changes due to flow and varying turbulence intensities. The present work is focused on evaluating these pressure sensors and testing the limits of the sensing element in the low, medium, and high frequency regime (<100Hz to >1kHz) to gain further insight into the performance. Five experimental tests were developed and conducted to guide this research objective. The sensor responses under different flow conditions were measured and analyzed with selected filtering and resampling techniques to eliminate background noises. First, the sensors were calibrated to ensure their linearity and to determine their pressure sensitivities. Then, using bench-top testing rigs and a water tunnel, the sensor performance was evaluated in submerged environments when subjected to multiple small-scale flow disturbances across the tested frequency regime. It was found that the present sensors are capable of providing more accurate measurements across a tested frequency regime of 0 to 20,000Hz when compared to other off-the-shelf products. Testing in submerged environment showed that the sensors are capable of detecting small-scale pressure fluctuations as a result of eddies which are evident in a Von Karman vortex street and a turbulent flow. Despite the presence of EMI noise within a water tunnel, the sensors demonstrated a decay of pressure fluctuations that is consistent with previous research in the field. Overall, the present work increases understanding of the sensors' performances across a broad range of frequencies and provides insight into potential uses and future work. / Master of Science / Pressure sensors are an important, if not the most important, measurement device available today. Pressure sensors play an integral role in the everyday lives for everyone around the world; from applications in medicine, aerospace, autonomy and computation, these sensors provide real-time feedback and help gain a deeper understanding of a system. However, with the technological advances in the Modern Age, there has been a growing need for smaller, cheaper, and faster sensors. As a result, engineers continued to improve sensor performance in the past century with new technologies. A micro-electromechanical system (MEMS) pressure sensor offers a low-cost and energy efficient method to quantify pressure fluctuations within a system. This work focuses on evaluating the performance of three MEMS pressure sensors for use in a submerged environment to detect small-scale pressure fluctuations across a broad range of frequencies. Five different tests were conducted to investigate this research objective. The first three were performed in a controlled underwater environment from which direct conclusions could be made. The last two were performed in an uncontrolled underwater environment from which comparisons to literature and known phenomena were used to draw conclusions. A key result showed that the sensor measurements aligned with prior research in the field. Multiple data reduction techniques were also used during post-processing to ensure accurate data was being collected. The studies showed that the developed MEMS pressure sensors provided the same capabilities as other commercially available pressure measurement devices, all the while displaying a higher sensitivity and broader frequency range. Furthermore, the survivability and robustness of the sensor was proven when subjected to large- and small-scale flow disturbances in a water tunnel.

Prolonging the battery lifetime of sensors has been one of the most important issues in wireless sensor networks (WSNs). With the development of Wireless Power Transfer (WPT) technology, sensors can be recharged and possibly have infinite lifetime. One common approach to achieving this is having a wireless charging vehicle (WCV) move in the system coverage area and charge sensors nearby when it stops. The duration that the WCV stays at each charging location, the amount of traffic that each sensor carries, and the transmission power of individual sensors are closely related, and their joint optimization affects not only the data transmissions in the WSN but also energy consumption of the system. This problem is formulated as a mixed integer and nonconvex optimization problem. Different from existing work that either solves similar problems using genetic algorithms or considers charging sensors based on clusters, we consider the optimum charging time for each sensor, and solve the joint communication and charging problem optimally. Numerical results demonstrate that our solution can significantly reduce the average power consumption of the system, compared to the cluster-based charging solution. / Thesis / Master of Applied Science (MASc) / In a wireless sensor network (WSN), sensor nodes monitor the physical environment and forward the collected data to a data sink for further processing. Sensors are battery powered and, therefore, prolonging the lifetime of their batteries is critically important. In a rechargeable WSN (RWSN), prolonging the battery lifetime of sensors is achieved through reducing communication energy and recharging the batteries periodically. Reducing the communication energy consumption is done through choosing the best forwarding sensors (i.e., routing) for data collected by each sensor and deciding the transmission power of each sensor (i.e., power allocation). Recharging the batteries is achieved through harvesting energy from external sources. In this thesis, we consider a RWSN that uses wireless power transfer as the energy harvesting technology and jointly optimizes charging and communications in order to minimize the power consumption of the RWSN.

Laser Raman Spectroscopy (LRS) has received worldwide acknowledgement as a powerful molecular ‘finger print’ technique. The Raman spectrum of sample contains useful information such as molecular identity, composition, constituent’s concentration ratio etc. These information are manifested in the Raman spectrum in band heights, peak wavelength, band areas etc. The basis of quantitative analysis in Raman spectroscopy lies in the measurement of Raman band intensity, which is linearly dependent upon the sample concentration. On the other hand, Raman spectroscopy can also yield the qualitative information of samples by exhibiting bands corresponding to various chemical constituents in the sample mixture. The potentiality of Raman spectroscopy to perform quantitative as well as qualitative analysis of samples has been exploited in the development of Raman sensors in conjugation with the techniques of fiber optics. The main focus of the presented doctoral work is to realize a fiber optic Raman sensor to monitor the quality of liquid oxygen (LO2) in a rocket engine feed line. In this research investigation, I have shown how a bulk experimental configuration can be transformed to miniaturized prototype sensor, which is equally capable to determine the ratio of liquid oxygen and liquid nitrogen in their cryogenic mixture. This research was extended to monitor the concentration of oxygen and nitrogen in their gaseous mixture. Further, I have demonstrated that the Raman spectroscopy has the potentiality to measure the temperature of hydrogen in a laboratory environment by monitoring the variation in Raman rotation-vibrational line of hydrogen gas with temperature. Finally, I have experimentally studied the surface enhanced Raman spectroscopy (SERS) of silver colloidal solution, which is another interesting branch of Raman spectroscopy that has transcended the limitation of very low Raman cross-section to offer more insight to the chemical properties of samples.

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The monitoring of pH and free chlorine concentration in drinking water is important for water safety and public health. However, existing laboratory-based analytical methods are laborious, inefficient, and costly. This thesis focuses on the development of an easy-to-use, sensitive, and low-cost drinking water quality monitoring system for pH and free chlorine. An inkjet printing technology with a two-step thermolysis process in air is developed to deposit palladium/palladium oxide (Pd/PdO) films as potentiometric pH sensing electrodes. The redox reaction between PdO and hydronium ions generates the sensor output voltage. A large PdO percentage in the film provides a high sensitivity of ~60 mV/pH. A defect-free Pd/PdO film with small roughness contributes to a fast response and a high stability. When the Pd ink is thermalized in low vacuum, the deposited Pd/PdO film shows a bilayer structure. The residual oxygen in the low vacuum environment assists the decomposition of organic ligands for Pd to form a thin and continuous layer beneath submicron Pd aggregates. The oxidized bilayer film behaves as a temperature sensor with a sensitivity of 0.19% resistance change per °C, which can be used to compensate the sensed pH signals. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is drawn by hand to form a free chlorine sensor. Free chlorine oxidises PEDOT:PSS, whose resistivity increment indicates the free chlorine concentration in the range of 0.5-500 ppm. Also, we simplified an amperometric free chlorine sensor based on amine-modified pencil leads. The simplified sensor is calibration-free, potentiostat-free, and easy-to-use. The pH, temperature, and free chlorine sensors are fabricated on a common substrate and connected to a field-programmable gate array board for data processing and display. The sensing system is user-friendly, cheap, and can accurately monitor real water samples. / Thesis / Doctor of Philosophy (PhD) / Sensitive, easy-to-use, and low-cost pH and free chlorine monitoring systems are important for drinking water safety and public health. In this thesis, we develop an inkjet printing technology to deposit palladium/palladium oxide films for potentiometric pH sensors and resistive temperature sensors. The different electrical and electrochemical properties of the palladium/palladium oxide films are realized by creating different film morphologies using different ink thermolysis atmospheres. The developed pH and temperature sensors are highly sensitive, fast in response, and stable. For free chlorine sensors, a hand drawing process is used to deposit poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), which is an indicator for the free chlorine concentration over a wide range. We also developed a calibration-free free chlorine sensors based on modified pencil leads. Such a free chlorine sensor is integrated with the pH and temperature sensors, and an electronic readout system for accurate on-site drinking water quality monitoring at low cost is demonstrated.