The objective of this research is to present a new model for predicting the piezoresistive effect in microflexures experiencing bending stresses. A linear model describing piezoresistivity exists for members in pure tension and compression. Extensions of this model to more complex loading conditions do not match experimental results. An accurate model of piezoresistivity in complex loading conditions would expand the design possibilities of piezoresistive devices. A new model to predict piezoresistive effects in tension, compression, and more complex loading conditions is proposed. The focus of this research is to verify a unidirectional form of this proposed model for microflexures in tension and bending. Implementation of the unidirectional form of the model involves geometric design, stress analysis, and electrical analysis. One of the ways to implement the model is with finite-element analysis (FEA). The piezoresistive FEA for flexures (PFF) algorithm is an FEA implementation of the unidirectional form of the model for flexures. A case study is then given in which the resistance curves of two test devices are predicted with the PFF algorithm. Results from the PFF implementation of the unidirectional form of the model show a close comparison between analytical prediction and experimental results. This new model could contribute to optimized sensors, feedback control of microdevices, nanopositioning, and self-sensing microdevices.

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Wireless surface acoustic wave (SAW) sensors offer unique advantages over other sensor technologies because of their inherent ability to operate in harsh environments and completely passive operation, providing a reliable, maintenance-free life cycle. For certain SAW sensor applications the challenge is building a wirelessly interrogatable device with the same lifetime as the SAW substrate. The design of these application intensive sensors is complicated by the degradation of device bond wires, die adhesive, and antenna substrate. In an effort to maximize the benefits of the platform, this dissertation demonstrates wafer-level integrated SAW sensors that directly connect the thin film SAW to a thick film on-wafer antenna. Fully integrated device embodiments are presented that operate over a wide range of temperatures using different fabrication techniques, substrates, and coding principles.

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No / This paper presents a novel method to prepare stretchable conductors and pressure sensors based on the gold/polydimethylsiloxane (PDMS) system. The gold films were sputtered onto structured PDMS surfaces produced with a photolithographic surface treatment with the aim of reducing tensile strains in the gold film. Scanning electron microscopy (SEM) and atomic force microscopy analyses showed that these 3D patterns reduce cracks and delaminations in the gold film. Electrical measurements indicate that the patterns also protect the films against repeated tensile cycling, although the un-patterned samples remained conducting as well after the completion of 120 cycles. The extrapolated resistivity value of the patterned sample (4.5 × 10−5 Ωcm) compares well with previously published data. SEM micrographs indicate that the pattern features deflect the cracks and therefore toughen the gold film. However, x-ray photoelectron spectroscopy and contact angle analyses indicate that the patterning process also slightly modifies the surface chemistry. This patterning method was used to prepare capacitive strain gauges with pressure sensitivity (ΔZ/Z)/P of 0.14 kPa−1 in the sub-kPa regime. Such stretchable and potentially conformal low-pressure sensors have not been produced before and could prove advantageous for many smart fabric applications.

Chlorine is used as a powerful disinfectant in water-related industries and in the food industry to remove bacteria and other harmful contaminants. We present a solution-based fabrication process for a biodegradable electrochemical free chlorine sensor using asparagine that is functionalized onto graphene oxide (GO). An ink solution of the GO functionalized with asparagine was fabricated then deposited onto a screen-printed carbon electrode (SPCE) using a spin-coater. The sensor showed high a sensitivity of 0.30 μA ppm−1 over a linear range of 0 to 8 ppm with a hysteresis-limited resolution of 0.2 ppm, very high selectivity in the presence of commonly interfering ions, and an operating voltage well below the reduction potential of dissolved oxygen. The sensor response time to achieve a steady state was 50 s, and it showed little change in its drift response over 16 h and over a temperature range of 10 to 45 °C. From the development of the free chlorine sensor, over 9000 datapoints were collected and used for training a neural network model to quantify and characterize factors affecting the free chlorine sensor performance. A readout system was designed with a printed circuit board and an android app to simplify free chlorine sensing for an end user. / Thesis / Master of Applied Science (MASc) / Free chlorine is used to disinfectant sources of water, and eliminate pathogens. The World Health Organization (WHO) maintains strict amounts of free chlorine in water due to its widespread usage owed to its low cost and persistence in water systems. Too little, and it will not be an effective disinfectant, and too much and the high consumption of free chlorine increases the risk cancer or the formation of hazardous chemicals. Recently, free chlorine sensors that measure an electrical response proportional to the amount of free chlorine are gaining interest for fast, accurate, and repeatable measurements. This thesis focuses on the design, fabrication, and evaluation of these sensors made using biodegradable materials in a solution-based fabrication processes with the aim of working towards large-scale fabrication of a printable ink. First, we review the results achieved by the sensors within recent literature. Second, we present the design of a sensor that aims to achieve environmentally friendly goals and maintain competitive performance characteristics. The, the sensor is tested under various conditions with its performance quantified under different conditions. Third, the sensor is characterized using a neural network to measure its performance and identify sources of improvement for future designs. Finally, we incorporate the sensor with an android app to measure free chlorine in remote water systems.

The development and implementation of biosensors as an integral and growing part of our modern world has prompted the push for precision health as the next step in medicine. Adapted from aircraft engine monitoring, where an array of sensors is used to build a digital twin to preemptively predict problems, precision health requires an increase in molecular monitoring. Organic thin-film transistors (OTFTs), as sensitive, low-cost, and adaptable devices are well suited to meet this need. Phthalocyanines (Pcs), as an organic semiconducting layer for OTFTs, are easily synthesized and highly tunable small molecules which can be deposited through both solution and physical vapor deposition techniques, enhancing their utility. This work presents Pc-based OTFTs for cannabinoid sensing and chemotyping to meet the quality control needs of a growing Canadian and International cannabis industry, and to broadly demonstrate the sensitivity and selectivity attainable with Pc-based OTFTs incorporating molecular analyte sensors. Spectroelectrochemistry is established as a screening technique for Pc-based OTFT sensors and, in combination with thin-film characterization, is used to propose a mechanism for Pc-cannabinoid interactions and OTFT cannabinoid sensitivity with and without a cannabinoid-sensitive chromophore. Thin-film morphologies and polymorphs, pre- and post-analyte exposure, are demonstrated as key drivers of Pc-based OTFT sensing responses and are further explored through controlled deposition conditions and post deposition annealing techniques. Through material screening and thin-film engineering, part-per-billion cannabinoid sensitivity is achieved with Pc-based OTFTs. This report documents several strategies for sensitizing Pc-based OTFT sensors to organic analytes, and the results herein serve as a basis for continued development of Pc-based OTFT biosensors.

<p> Vibration Analysis (VA) is a key technique used for maintenance and fault detection of vibrating machinery. The purpose of maintenance is to analyze how well the machinery is operating within its target parameters, while fault detection is done to diagnose and locate a fault that might be developing on the machinery.</p> <p> If we consider s(n) to be the true signal from a rotating system and e(n) to be the additive noise corrupting the signal, then the observed signal is x(n) = s(n) + e(n). If s(n) is composed of a main driving frequency sm(n) and summed fault frequencies sf(n), then fault detection is the study of sf(n). In fault detection, we eliminate e(n) as much as possible so that sf(n) can be isolated and studied.</p> <p> This thesis presents a technique based on cross-correlation, utilizing a network of sensors, to eliminate e(n) from the measurements, preserving just the correlated frequency content. This is extended to provide a means of localizing the source of the frequency content, based on the relative strengths of the members of the complete set of cross-correlations between all sensors. This technique has been shown to be able to extract a signal buried by noise, in situations where the traditional FFT fails.</p> <p> To enable this, a new VA system has been developed. This introduces new wireless vibration sensors as well as a data capture unit capable of providing real-time VA data to technicians. The system can simultaneously capture data from eight sensors, so the data can be used not only for traditional VA techniques, but also in conjunction with the cross-correlation technique described above. This system is now commercially available and in use by dozens of technicians around the world. </p> / Thesis / Doctor of Philosophy (PhD)

Distributed optical fiber sensors offer unprecedented advantages, and the most remarkable one is the ability to continuously measure physical or chemical parameters along the entire optical fiber, which is attached to the device, structure and system. As the most recently investigated distributed optical fiber sensors, phase-sensitive optical time domain reflectometry (φ-OTDR), Brillouin optical time domain analysis (BOTDA) and Brillouin dynamic grating-optical time domain reflectometry (BDG-OTDR) techniques have been given tremendous attention on the advantage of quantitative measurements ability over high sensitivity and absolute measurement with long sensing distance, respectively. However, the accompanying limitations in terms of static measurement range, acquisition rate, laser frequency drifting noise, and spatial resolution limitations in these techniques hinder their performance in practical applications. This thesis pays particular attention to the above three distributed sensing techniques to explore the fundamental limitations of the theoretical model and improve the sensing performance. Before presenting the novel sensing scheme with improved sensing performance, an introduction about distributed fiber optical sensing, including three main light scattering mechanisms in optical fiber, the recent advancements in distributed sensing and key parameters of Rayleigh scattering- and Brillouin scattering-based sensing systems. After that, a study on the theoretical analysis of large chirping rate pulse generation and the theoretical model of using chirped pulse as interrogation signal in φ-OTDR, BOTDA and BDG-OTDR systems are given. In the disruptive experimental implementations, the sensing performance has been improved in different aspects. By using a random fiber grating array as the distributed sensor, a high-precision distributed time delay measurement in a CP φ-OTDR system is proposed thanks to the enhanced in-homogeneity and reflectivity. In addition, a simple and effective method that utilizes the reference random fiber grating to monitor the laser frequency drifting noise is demonstrated. Dynamic strain measurement with a standard deviation of 66 nε over the vibration amplitude of 30 με is achieved. To solve the limited static measurement range issue, a multi-frequency database demodulation (MFDD) method is proposed to release the large strain variation induced time domain trace distortion by tuning the laser initial frequency. The maximum measurable strain variation of about 12.5 με represents a factor of 3 improvements. By using the optimized chirped pulse φ-OTDR system, a practical application of monitoring the impact load response in an I-steel beam is demonstrated, in which the static and distributed strain variation is successfully reconstructed. To obtain an enhanced static measurement range without a complicated database acquisition process, a photonic approach for generating low-frequency drifting noise, arbitrary and large frequency chirping rate (FCR) optical pulses based on the Kerr effect in the nonlinear optical fiber is theoretically analyzed and experimentally demonstrated by using both fixed-frequency pump and chirped pump. Due to the Kerr effect-induced sinusoidal phase modulation in the nonlinear fiber, high order Kerr pulse with a large chirping rate is generated. Thus the static measurement range of higher order Kerr pulse is significantly improved. Chirped pulse BOTDA based on non-uniform fiber is also analyzed, showing a high acquisition rate that is only limited by the sensor length and averaging times due to the relative Brillouin frequency shift (BFS) changes are directly extracted through the local time delays between adjacent Brillouin traces from two single-shot measurement without frequency sweep process. BFS measurement resolution of 0.42 MHz with 4.5 m spatial resolution is demonstrated over a 5 km non-uniform fiber. A hybrid simultaneous temperature/strain sensing system is also demonstrated, showing a strain uncertainty of 4.3 με and temperature uncertainty of 0.32 °C in a 5 km non-uniform fiber. Besides, the chirped pulse is also utilized as a probe signal in the Brillouin dynamic grating (BDG) detection along the PM fiber for distributed birefringence variations sensing. The strict phase-matching condition only enables part of the frequency components within the chirped probe pulse to be reflected by BDG, giving an adjustable spatial resolution without photo lifetime limitation. The spatial resolution is determined by the frequency chirping rate of the probe pulse.