Detecting long wave infrared (LWIR) light at room temperature has posed a persistent challenge due to the low energy of photons. The pursuit of an affordable, high-performance LWIR camera capable of room temperature detection has spanned several decades. In the realm of contemporary LWIR detectors, they can be broadly classified into two categories: cooled and uncooled detectors. Cooled detectors, such as MCT detectors, excel in terms of high detectivity and fast response times. However, their reliance on cryogenic cooling significantly escalates their cost and restricts their practical applications. In contrast, uncooled detectors, exemplified by microbolometers, are capable of functioning at room temperature and come at a relatively lower cost. Nonetheless, they exhibit somewhat lower detectivity and slower response times. Within the scope of this work, I will showcase two innovative approaches aimed at advancing the next generation of LWIR detectors. These approaches are designed to offer high detectivity, swift response times, and room temperature operation. The first approach involves harnessing Dirac plasmon and the Seebeck effect in graphene to create a photo-thermoelectric detector. In addition, I will introduce the application of scanning near-field microscopy for revealing the plasmons generated in graphene, employing both imaging and spectroscopy techniques. The second approach entails the use of an oscillating circuit integrated with phase change materials and the modulation of frequency induced by infrared illumination to achieve LWIR detection. Finally, I will present the progress made in integrating graphene-based detectors in this work onto readout circuits to enable the development of dense pixel focal plane array.

Most of existing techniques cannot be used to detect molecular biomarkers (i.e., protein and DNA) contained in complex body fluids due to issues such as enzyme inhibition or signal interference. This thesis describes a nanoparticle-based thermal detection method for the highly sensitive detections of multiple DNA biomarkers or proteins contained in different type of fluids such as buffer solution, cell lysate and milk by using solid-liquid phase change nanoparticles as thermal barcodes. Besides, this method has also been applied for thrombin detection by using RNA aptamer-functionalized phase change nanoparticles as thermal probes. Furthermore, using nanostructured Si surface that have higher specific area can enhance the detection sensitivity by four times compared to use flat aluminum surfaces. The detection is based on the principle that the temperature of solid will not rise above its melting temperature unless all solid is molten, thus nanoparticles will have sharp melting peak during a linear thermal scan process. A one-to-one correspondence can be created between one type of nanoparticles and one type of biomarker, and multiple biomarkers can be detected simultaneously using different type nanoparticles. The melting temperature and the heat flow reflect the type and the concentration of biomarker, respectively. The melting temperatures of nanoparticles are designed to be over 100°C to avoid interference from species contained in fluids. The use of thermal nanoparticles allows detection of multiple low concentration DNAs or proteins in a complex fluid such as cell lysate regardless of the color, salt concentration, and conductivity of the sample.

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A novel design of hybrid thermal energy storage (HTES) using Phase Change Material (PCM) was evaluated using a mathematical model. Both single and multi-tank (cascaded) storage were explored to span small to large-scale applications (200-1600 litres). The storage element was based on the concept of a fully-mixed modular tank which is charged and discharged indirectly using two immersed coil heat exchangers situated at the bottom and top of the tank. A three-node model was developed to simulate different thermal behaviors during the operation of the storage element. Experiments were conducted on full-scale 200-l single-tank sensible heat storage (SHS) and hybrid thermal energy storage (HTES) to provide validation for the mathematical model. The HTES incorporated rectangular PCM modules submerged in the water tank. Satisfactory agreement was found between the numerical results and the experimental results obtained by Mather (2000) on single and multi-tank SHS. In addition, good agreement was noticed with the experiments performed by the author on single-tank SHS and HTES at McMaster University. The developed model was found to provide high levels of accuracy in simulating different operation conditions of the proposed design of storage element as well as computational efficiency. A parametric study was undertaken to investigate the potential benefits of the HTES over the SHS, operating under idealistic conditions. The HTES can perform at least two times better than the SHS with the same volume. The PCM volume fraction, melting temperature and properties were found to have critical impact on the storage gains of the HTES. All the parameters must be adjusted such that: (1) the thermal resistance of the storage element is minimized, and (2) most of the energy exchange with the storage element takes place in the latent heat form. The performance of the single-tank HTES was evaluated numerically while operating in a solar thermal domestic hot water (DHW) system for a single-family residence. The PCM parameters were selected to maximize the solar fraction during the operation on a typical spring day in Toronto. The use of the HTES can reduce the tank volume by 50% compared to the matched size of the SHS tank. However, the HTES was found to underperform the SHS when the system was operated in different days with different solar irradiation intensities. The effect of different draw patterns was also investigated. The results indicated that thermal storage is needed only when the energy demand is out-of-phase with the energy supply. For the same daily hot water demand, different consumption profiles; ex. dominant morning, dominant evening, dominant night and dispersed consumptions, showed slight impact on the performance of the system. The concept of multi-tank (cascaded) HTES storage was explored for medium/large scale solar heating applications such as for restaurants, motels, and multi-family residences. The design was based on the series connection of modular tanks through the bottom and top heat exchangers. Each individual tank had a PCM with different melting temperature. The results showed that the cascaded storage system outperformed the single-tank system with the same total volume as a result of the high levels of sequential or tank-to-tank stratification. The use of the cascaded HTES resulted in slight improvement in the solar fraction of the system. / Thesis / Doctor of Philosophy (PhD)

A growing industry demand for smart pressure sensors that can be quickly calibrated to compensate for sensor drift, nonlinearity effects, and hysteresis without the need for expensive equipment has led to the development of a self-calibrating pressure sensor. Pressure sensor inaccuracies are often resolved with sensor calibration, which typically requires the use of laboratory equipment that can produce a known, standard pressure to actuate the sensor. The developed MEMS-based, self-calibrating pressure sensor is a piezoresistive-type sensor with a sensing element made from a silicon on insulator (SOI) wafer using deep reactive-ion etching to create a hollow reference cavity. Using a micro-heater to heat the small, air-filled reference cavity of the sensing element, a standard pressure is generated to actuate the sensor's pressure-sensitive membrane, creating a self-calibration effect. Previous work focused on modeling and improving the thermal performance of the sensor identified potential solutions to extend the sensor's calibration and operating range without increasing the micro-heater's power consumption. This report focuses on using a water liquid-to-vapor phase change inside the sensor's reference cavity to increase the sensor's effective range and response time without increasing power demands. A combination of Ansys Fluent CFD modeling and benchtop experiments were used to guide the development of the two-phase, self-calibrating pressure sensor. A two-phase benchtop testing rig was built to demonstrate the anticipated effects of a liquid-to-vapor phase change in a closed domain and to provide experimental data to anchor CFD models. Due to the complexity of modeling a phase-change within a closed domain with Ansys Fluent R21.1, the CFD modeling was performed in two stages. First, the two-phase benchtop rig was modeled, and validated using benchtop test data to verify the Volume of Fluid multiphase model setup in Ansys Fluent. Then, a 2D Ansys Fluent model of the self-calibrating pressure sensor's reference cavity using the validated multiphase model was made, demonstrating the potential temperature, pressure, and density gradients inside the reference cavity at steady state. Using the guidance from the benchtop testing and CFD modeling, a prototype two-phase, self-calibrating pressure sensor was fabricated with a water volume fraction of at least 0.1 in the reference cavity. Testing the prototype two-phase sensor showed that the addition of a water liquid-to-vapor phase change inside the sensor's reference cavity can nearly triple the sensor's effective range of operation and self-calibration without increasing the power consumption of the cavity micro-heater. / Master of Science / Highly sensitive pressure sensors are essential to many modern engineering applications. For a pressure sensor to be accurate and functional, it must be properly calibrated with a known, standard pressure range that overlaps with the sensor's intended operating range. Mechanical wear, material aging, and thermal effects all reduce a pressure sensor's accuracy over time, requiring recalibration which often involves expensive equipment and long downtimes. To eliminate the need for additional equipment and the removal of the pressure sensor from its use-site for calibration, the authors have developed a pressure sensor capable of self-calibration. The self-calibrating sensor uses a MEMS sensing element with an integrated micro-actuator in the form of a small heating element to create the standard pressure range necessary for calibration. Previous work focused on modeling the thermal performance of the sensor identified potential solutions to extend the sensor's calibration and operating range without increasing the micro-heater's power consumption. This report focuses on using a water liquid-to-vapor phase change inside the sensor's reference cavity to increase the sensor's effective range and response time without increasing power demands. To help guide the development of the two-phase, self-calibrating sensor, a benchtop testing rig and CFD model were used to examine the effects of heating a liquid inside of a closed domain. A 2D CFD model of the sensor's reference cavity was also used to provide insight into the expected temperature and pressure gradients inside the sensing element after heating with the micro-actuator. Using the guidance from the CFD models, a prototype two-phase, self-calibrating pressure sensor was fabricated. Testing the prototype two-phase sensor showed that the addition of a water liquid-to-vapor phase change inside the sensor's reference cavity can nearly triple the sensor's effective range of operation and self-calibration without increasing the power consumption of the cavity micro-heater.

Interfacial phenomena are prevalent in various natural and engineered systems. A thorough understanding of these phenomena is essential for a complete understanding of processes such as phase transitions and interaction of liquid droplets with different surfaces. The insights gained from understanding interfacial behavior are pivotal in fields such as pharmaceuticals, microfluidics, material sciences, and environmental engineering. This dissertation aims to advance our understanding of interfacial behaviors, thereby facilitating the development of innovative technologies for applications in health, defrosting, and omniphobic surfaces. In Chapters 1 and 2, relevant background information and goals are provided to contextualize the research being presented in this dissertation. Chapter 3 introduces a novel metal-free alternative to conventional antiperspirants (containing aluminum salts and zirconium salts). We leverage the composition of human sweat (97% water and 3% minerals) and employ a hygroscopic substance near the outlet of an artificial sweat duct rig. This leads to complete diffusion and dehydration of sweat, forming a natural mineral plug within the artificial sweat duct that halts the flow. Chapter 4 examines the behavior of room temperature water droplets spreading on a flat icy substrate. The use of flat ice, as opposed to cold substrates, eliminates the nucleation energy barrier, enabling freeze front initiation as soon as the bulk temperature of the spreading drop reaches 0 C. Through scaling analysis, we identify distinct thermo-hydrodynamic regimes with varying Weber numbers. Chapter 5 presents a novel construct for lubricant-impregnated surfaces (LIS). To date, most of the investigations characterizing the wettability of LIS have focused on droplet mobility. We pioneer a lubricant-impregnated fiber (LIF) which exhibits unique droplet dynamics due to simultaneous exploitation of both, high mobility and high adhesion. Chapter 6 proposes an innovative approach for defrosting by exploiting the polarizability and natural thermo-voltage of frost sheets. By placing an actively charged electrode near the frost sheet, we observe that frost dendrites migrate towards the electrode. This technique, termed Electrostatic Defrosting (EDF), effectively removes up to 75% of the frost mass for superhydrophobic surfaces and 50% of the frost mass for untreated surfaces in less than 100 s. / Doctor of Philosophy / Raindrops falling on surfaces, pesticides being sprayed on crops, and frost forming on windshields—these seemingly unrelated phenomena all stem from fundamental water-structure interactions and phase change processes. We encounter these occurrences throughout nature, with some being enchanting, like water dancing on lotus leaves or morning dew sparkling on glass, while others can pose risks, such as condensation impairing visibility while driving. This dissertation aims to enhance our understanding of water-structure interactions by utilizing the phase changes of water (transitioning between vapor and ice). Through this exploration, we seek to develop innovative technologies for health, de-icing, and fog harvesting, highlighting the practical applications of such water-structure interactions. Through four distinct projects, we aim to unlock innovative solutions that enhance everyday life and address pressing environmental challenges. In the first project, we introduce a novel antiperspirant construct that utilizes sweat's own minerals to clog sweat ducts by vaporizing water with a hygroscopic material. The second project investigates droplet dynamics on ice, focusing on how freezing initiates at the contact line when droplets make contact. In the third project, we develop a new design for oil-impregnated surfaces by embedding fibers, characterizing droplet behavior on these curved surfaces. We envision these fibers being utilized in industrial fog harvesting systems, where water can be effectively collected through dropwise condensation. Finally, we present an innovative defrosting method that exploits naturally occurring thermovoltage in frost, using a positively charged electrode to facilitate the removal of frost sheets. Together, these projects illustrate the impact of water-structure interactions on technology and the environment.

The main objective of this research is to provide an efficient and reliable method for using multi-level cell (MLC) phase-change memory (PCM) as a main memory. As DRAM scaling approaches the physical limit, alternative memory technologies are being explored for future computing systems. Among them, PCM is the most mature with announced commercial products for NOR flash replacement. Its fast access latency and scalability have led researchers to investigate PCM as a feasible candidate for DRAM replacement. Moreover, the multi-level potential of PCM cells can enhance the scalability by increasing the number of bits stored in a cell. However, the two major challenges for adopting MLC PCM are the limited write endurance cycle and the resistance drift issue. To alleviate the negative impact of the limited write endurance cycle, this thesis first introduces a secure wear-leveling scheme called Security Refresh. In the study, this thesis argues that a PCM design not only has to consider normal wear-out under normal application behavior, most importantly, it must take the worst-case scenario into account with the presence of malicious exploits and a compromised OS to address the durability and security issues simultaneously. Security Refresh can avoid information leak by constantly migrating their physical locations inside the PCM, obfuscating the actual data placement from users and system software. In addition to the secure wear-leveling scheme, this thesis also proposes SAFER, a hardware-efficient multi-bit stuck-at-fault error recovery scheme which can function in conjunction with existing wear-leveling techniques. The limited write endurance leads to wear-out related permanent failures, and furthermore, technology scaling increases the variation in cell lifetime resulting in early failures of many cells. SAFER exploits the key attribute that a failed cell with a stuck-at value is still readable, making it possible to continue to use the failed cell to store data; thereby reducing the hardware overhead for error recovery. Another approach that this thesis proposes to address the lower write endurance is a hybrid phase-change memory architecture that can dynamically classify, detect, and isolate frequent writes from accessing the phase-change memory. This proposed architecture employs a small SRAM-based Isolation Cache with a detection mechanism based on a multi-dimensional Bloom filter and a binary classifier. The techniques are orthogonal to and can be combined with other wear-out management schemes to obtain a synergistic result. Lastly, this thesis quantitatively studies the current art for MLC PCM in dealing with the resistance drift problem and shows that the previous techniques such as scrubbing or error correction schemes are incapable of providing sufficient level of reliability. Then, this thesis proposes tri-level-cell (3LC) PCM and demonstrates that 3LC PCM can be a viable solution to achieve the soft error rate of DRAM and the performance of single-level-cell PCM.

Chalcogenide based Phase Change Materials are currently of great technological interest in the growing field of optoelectronics. Ge₂Sb₂Te₅ (GST) is the most widely studied phase change material, and it has been commercially used in both optical and electronic data storage applications, due to its ability to switch between two different atomic configurations, at high speed and with low power consumption, as well as its high optical and electrical contrast between amorphous and crystalline states. Despite its well-known optical and electrical properties, the operation in combination of optical and electrical domains has not yet been fully investigated. This work studies the operation of GST nano-devices exposed to a combination of optical and electrical stimuli or mixed mode by asking, is it possible to electrically measure an optically induced phase change, or vice versa? If so, how do the optical and electrical responses relate to each other, and is it possible to operate GST with a combination of optical and electrical signals? What are the technical constraints that need to be considered in order to fabricate GST devices that could be operated either optically or electrically? In order to answer these questions, experiments that characterized the optical and electrical responses of GST based nano-devices were performed. It was found that different crystallization mechanisms may have influence in the response, and that the thermal and optical design characteristics of the device play a key role in its operation. Finally a proof of principle, of an opto-electonic memory device that can be read electrically, reset optically and write electrically, is presented. This opens up possibilities for the development of new opto-eloectronic applications such as non-volatile interfaces between future photonics and electronics, high speed optical communication detectors, high speed cameras, artificial retinas and many more.

abstract: Thermal Energy Storage (TES) is of great significance for many engineering applications as it allows surplus thermal energy to be stored and reused later, bridging the gap between requirement and energy use. Phase change materials (PCMs) are latent heat-based TES which have the ability to store and release heat through phase transition processes over a relatively narrow temperature range. PCMs have a wide range of operating temperatures and therefore can be used in various applications such as stand-alone heat storage in a renewable energy system, thermal storage in buildings, water heating systems, etc. In this dissertation, various PCMs are incorporated and investigated numerically and experimentally with different applications namely a thermochemical metal hydride (MH) storage system and thermal storage in buildings. In the second chapter, a new design consisting of an MH reactor encircled by a cylindrical sandwich bed packed with PCM is proposed. The role of the PCM is to store the heat released by the MH reactor during the hydrogenation process and reuse it later in the subsequent dehydrogenation process. In such a system, the exothermic and endothermic processes of the MH reactor can be utilized effectively by enhancing the thermal exchange between the MH reactor and the PCM bed. Similarly, in the third chapter, a novel design that integrates the MH reactor with cascaded PCM beds is proposed. In this design, two different types of PCMs with different melting temperatures and enthalpies are arranged in series to improve the heat transfer rate and consequently shorten the time duration of the hydrogenation and dehydrogenation processes. The performance of the new designs (in chapters 2 and 3) is investigated numerically and compared with the conventional designs in the literature. The results indicate that the new designs can significantly enhance the time duration of MH reaction (up to 87%). In the fourth chapter, organic coconut oil PCM (co-oil PCM) is explored experimentally and numerically for the first time as a thermal management tool in building applications. The results show that co-oil PCM can be a promising solution to improve the indoor thermal environment in semi-arid regions. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2020