Browsing by Subject "Sensor"

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Constricted current perpendicular to plane (CPP) magnetic sensor via electroplating.
(2011-01) Huang, Xiaobo
Electrochemically deposited magnetic nanowires have gained increasing attention since current perpendicular to the plane giant magnetoresistance (CPP-GMR) was observed in multilayered nanowires. Magnetic nanowires have potential for fundamental studies, including measuring spin diffusion lengths and understanding the mechanisms of the electron spin transfer. They also have great potential technological applications as CPP-GMR sensors, magnetic random access memory (MRAM), and next generation magnetic recording heads. Small diameter nanowires are desired in order to have large current density per device and a high areal density for device arrays, for example, 2 Tb/in2 media. In this research, E-beam lithography, nano-imprinting, and self-assembled nanoporous alumina templates (AAO) were studied to achieve as small diameter nanopores as possible. AAO templates with 10 nm diameter were fabricated using both Al foils and Al thin films. Very small diameter (10 nm) CPP-GMR Co/Cu nanowires were fabricated into AAO templates using electrochemical deposition. The magnetic transport properties of these multilayered and trilayered Co/Cu nanowires were investigated. It was found that nanowire anisotropies parallel and perpendicular to the nanowires were dependent on the thicknesses of Co and Cu layers. GMR of 19% was achieved with 10 nm diameter nanowires at room temperature. The magnetic free layers were as thin as 4.5 nm with GMR of 18%. Spin transfer torque switching current densities were measured to be 106 - 108A/cm2. The measurement of spin transfer torque was conducted numerous times with high repeatability in the critical switching currents from parallel to antiparallel alignment (JP-AP) and slight variations in back (JAP-P). Small resistance area products (RA) of 0.003 ohmµm2 were achieved with trilayers that had 40ohm total resistance. All of results in this study show that nanowires with 10 nm diameters have potential application as next generation CCP-GMR sensors and spin transfer torque MRAM.
Fit for Space: Leveraging a Novel Skin Contact Measurement Technique Toward a More Efficient Liquid Cooled Garment
(2016-08) Compton, Crystal
Comfort, mobility, and performance are all affected by the fit and contour of a garment to the body. Understanding the body-garment relationship allows for improvement of all of these aspects, and thus the garment and experience for the wearer. With current methods, it is possible to measure the body-garment relationship primarily in static positions, but mobile analysis is time- and equipment-intensive. A more direct garment contour and body contact monitoring procedure would benefit the functional clothing design community. Mobile measurement is especially important for functional garments, as the body-garment relationship changes over time during body movements. Here, we describe a new method developed to measure the body-garment relationship, specifically for mobile scenarios. This method detects body-garment contact using an electrical signal within a circuit formed between the garment and the body. The analog electrical connection (expressed as a varying voltage using a voltage-divider circuit) between the body and a conductive patch is processed and recorded by a microcontroller. In this investigation three main variables were evaluated for their influence on the measurement of body-garment contact: 1) patch materials, 2) applied force, and 3) patch sizes were tested within the body/garment interface. Material results showed that all of the tested materials (with the exception of one material, which contained the sparsest surface area of conductive material) facilitated a voltage response in the presence of body contact that could be viable for detecting contact between body and garment. However, preliminary tests revealed that materials with lower resistivity and more rigid structure facilitated a smoother signal with less noise, which correlated more closely with the input signal. Applied force results showed that the amount of force between the sensor and the body affects the response of the system. All patch sizes with the exception of the smallest size tested (0.3175 cm) were effective in measuring body-garment contact. The smallest diameter possible for the conductive patch is of interest, in an attempt to minimize its effect on the body-garment measuring system. A 0.635 cm diameter conductive hook fastener sensor was subsequently used to implement this method in a pilot evaluation of LCG (Liquid Cooling Garment) fit. A grid of six analog sensors (maximum amount for microcontroller used) was integrated into the right torso region of the LCG for testing. Various movements that would be similar to movements that astronauts would be performing in EVA were used to test body-garment contact. Results show distinct differences in body contact for each sensor during each movement.
Graphene Lateral Spin Valves For Computing And Magnetic Field Sensing Applications
(2019-01) Hu, Jiaxi
The current complementary metal–oxide–semiconductor (CMOS) technologies are facing greater-than-ever challenges as the Moore’s law approaches to its physical limits. The search for future electronic devices began decades ago. Spintronics, which utilizes the properties of electron spins, is indeed one of the most promising solutions for the beyond-CMOS era. Over the past years, spintronics has been very successful in Hard-disc drives (HDDs) and has significantly increased the storage areal-density. Recently, because of its built-in non-volatility, spintronics has also demonstrated its potential in memory applications. On the other hand, graphene, which is a monolayer of carbon atoms arranged in hexagonal order, is very attractive as the material for spin transport. For example, graphene has the longest spin diffusion length and spin lifetime at room temperature. Therefore, as the device that combines the unique properties from both sides, the graphene lateral spin valve can be useful in many applications. This dissertation mainly explores the use of graphene lateral spin valves for future computing and magnetic field sensing applications. This thesis firstly discusses the spin-circuit model, which is capable of simulating the dc, ac and transient behavior spintronic devices. Using the spin-circuit model, the scaling and energy consumption of all-spin logic devices is quantitatively studied. As one of the original proposals for spin-based computing, ASL utilizes lateral spin valves to process information in the spin domain. By using the physics-based spin-circuit model, the simulations suggest the effect of output-input isolation may be the fundamental challenges that prevent ASL from competing with CMOS in the scheme of conventional Boolean-computing. Next, this thesis explores the application of graphene lateral spin valves in non-Boolean computing and presents an implementation of spintronic Cellular Neural Networks (CNNs). In the graphene-based spintronic CNNs, weights are programmed as spin currents. Because of the tunable spin diffusion length in graphene, the weights can be controlled as local gate voltages, which can tune the weight values over a wide range. The simulation results show that the graphene-based spintronic CNNs have significantly improved scalability, particularly as the number and accuracy of synapses increases. In the last part of this thesis, the width scaling of graphene spin channels is experimentally studied, which is crucial for both the computing and magnetic field sensing applications. By using the graphene deposited by chemical vapor deposition (CVD) and a dedicated fabrication process, a large number of graphene lateral spin valves with consistent interface properties but different channel aspect ratios are fabricated on a single chip. The experimental results show that, as the channel width is scaled from 10 µm to 0.5 µm, the change in the nonlocal spin resistance matches the theory of contact-induced spin relaxation with the interface spin polarization, P, of 3 – 5 %, and spin diffusion length, λs, of 1.5 – 2.5 µm. Meanwhile, the spin-independent baseline resistance dramatically decreases due to the reduction in charge current spreading. However, we find that a remnant baseline remains due to the thermoelectric effects of graphene. By using the gate-voltage and bias-dependent analyses, we attribute the remnant baseline signal to the Joule-heating induced Seebeck voltage. These results suggest that in lateral spin valve design, to avoid any background signals, both the charge and thermal equilibrium conditions should be satisfied.
Graphene Sensors and Perovskite Solar Cells for Water Detection
(2020-08) Kim, Jungyoon
Water quality test is the first step for cleaning water which is a fundamental element for human health and the environment. The objective of this research is to develop very small, cheap, fast, accurate sensors to detect pollutants including phosphate, nitrate, mercury, and chloride in waters. This is a new testing and analysis technique, which can provide accurate sensing capability to assess the cleanness of waters at a very low cost. The proposed new technology is to manufacture graphene based sensors using the micro-manufacturing. Graphene is a monolayer of carbon atoms with outstanding electrical properties well studied material for a decade by many research groups. Since graphene sensitively responds to molecules in liquids, this property will enable the tiny sensors to detect pollutants in water with very high sensitivity and super short response time to pollutants. Even though graphene responds to the surroundings, it does not have the selectivity to the specific target. In this research, the selective membranes are synthesized and applied to the graphene based sensors to detect the target ions such as nitrate, phosphate, chloride, and mercury. The selective membranes are prepared with two different key materials including molecular imprinted polymer and ionophore. The sensor is characterized by a semiconductor analyzer, and the sensors are tested with several ion solutions to verify their selectivity. The detection limits of the sensor are 0.82, 0.26, 0.87 mg/L and 1.125 µg/L for nitrate, phosphate, chloride and mercury, selectively. In addition, the detection limit of nitrate is enhanced to 0.32 mg/L using the AAO substrate. Here, this research also includes developing perovskite solar cells as the power source of the sensors. Since solar energy is clean and independent, it is one of the important renewable energy resources. Silicon solar cells have already been commercialized and used to generate electricity in various fields because solar cells can directly generate electricity from photons, and they do not cause a problem to our environment as well. Among several types of solar cells, the perovskite solar cells have been studied by many research groups owing to low-cost fabrication, low fabrication temperature and high efficiency. This research includes the preparation of the materials and fabrication of flexible perovskite solar cells. We also characterize the surface morphology of the perovskite to check the grain size by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The efficiency of solar cells is measured by the solar simulator. We study the relationship between the grain size and the CVD process time and successfully demonstrate the performance of devices. The flexible solar cells show the power conversion efficiency of 7.6 % under the AM 1.5 G. As extended research, we have tried to find the proper hole transport layer (HTL) for the device and applied two HTLs, including PEDOT:PSS and PTAA to the devices.
Instrumented Socks with Novel Sensors for Fluid Accumulation Monitoring
(2018-08) Zhang, Song
The overarching goal of this dissertation is to develop wearable sensors that can be integrated onto an instrumented sock for home-based monitoring of lower leg fluid accumulation. Swelling in lower extremities is an early indicator of disease deterioration in cardiac failure, chronic venous insufficiency and lymphedema. At-home wearable monitoring and early detection of fluid accumulation can potentially lead to prompt medical intervention and avoidance of hospitalization. Three types of inexpensive and noninvasive wearable sensors are developed: leg size sensor, tissue elasticity sensor and water content sensor. The innovative leg size sensor developed has unique features of being drift-free, and capable of misalignment-rejection. It has an accuracy of being able to differentiate 1mm changes in diameter, much smaller than any changes that can be detected by the human eye. These features were achieved by using dual magnetic sensors, an inductor for generating alternating magnetic fields, and an unscented Kalman filter estimation algorithm. Elasticity is also an important indicator of fluid accumulation and defines how soft the leg is. The novel elasticity sensor has a simple architecture of two thin-film force transducers and two 3D-printed components, which form a cantilever mechanism. Mathematical models were established for the sensor to estimate tissue elasticity. Lab tests conducted on rubber samples with slightly different softness and human body showed promising results. Several generations of instrumented socks with the leg size sensor and the tissue elasticity sensor were fabricated in the lab. These socks were tested and validated to be accurate and useful in an IRB-approved study on healthy volunteers at Mayo Clinic. The leg size sensor was also integrated into a commercially available pneumatic compression medical device for treating lymphedema. A redesigned and miniaturized leg size sensor was sewed onto a wearable band, which was then attached to the pneumatic pump-based wearable system for monitoring lymphedema treatment progress. Finally, a compact water content sensor was developed. Ultrasound velocity in animal and human tissue has been found to change with water content. A novel integration of magnetic sensing and ultrasonic sensing was utilized to measure ultrasound velocity, and renders the previous bulky device wearable.
Optical properties of Iridium(III) cyclometalates:excited state interaction with small molecules and dynamics of light-harvesting materials.
(2012-08) Schwartz, Kyle Robert
The research presented in this thesis concerns the use and understanding of luminescent Ir(III) cyclometalates. Areas of research involve the design, synthesis, and characterization of novel luminescent Ir(III) cyclometalates, including photophysical investigation of their phosphorescent excited states using steady-state and time resolved absorption/luminescence spectroscopies. This broad research description may be further separated into two subareas: study of excited state interaction with small molecules and excited-state dynamics of metal-organic light harvesting dyads. The first chapter of this thesis examines the interaction of Ir(III) cyclometalates with the small molecule carbon dioxide (CO2). It has been the goal of investigators to develop methods for direct optical detection of CO2. This has been difficult as CO2 is considered chemically inert and there are few luminescent probes directly sensitive to CO2. Most optical detection schemes previously developed for CO2 use indirect detection methods, which rely upon measuring changes in pH brought about by hydrolysis of CO2. Research efforts to design a reliable method for the direct optical detection of CO2 were accomplished through development of a system where hydrazine, a simple amino ligand, when coupled into the coordination sphere of an Ir(III) cyclometalate reacts with CO2. The result of this reaction provides a significant shift in the luminescence λmax of the phosphorescent probe, a previously unobserved optical response for the direct detection of CO2. The second chapter investigates phosphorescent excited states and their ability to function as triplet sensitizers for the generation of singlet oxygen (1O2) and luminescent probes for molecular oxygen (O2) concentration. Interaction of phosphorescent excited states with O2 results in energy transfer from the luminescent probe to O2, quenching the phosphorescent excited state. Energy transfer also generates the reactive oxygen species (ROS) 1O2. We have used this duality to develop an analytical methodology to follow the serendipitously discovered photoreactivity of 1O2 with common organic solvent dimethyl sulfoxide (DMSO) using the luminescence profile of Ir(III) and Ru(II) phosphors. Reaction of the triplet sensitized 1O2 with a photooxygenation substrate results in the consumption of O2 from the system and an increase in the observed luminescence intensity. Detailed kinetic investigations of the luminescence recovery and O2 depletion were preformed on air-saturated closed cell systems. Determinations of the quantum efficiencies for the photooxygenation system were performed and differences in choice of triplet sensitizer discussed. Study of 1O2 reactivity with substrates of biological and environmental relevance using this methodology should provide an additional tool to understand better oxidative damage induced by 1O2 within these systems. In chapter three a detailed study involving the design, synthesis, and characterization of the electrochemical and phototophysical properties of Ir(III) cyclometalates with pendant terthiophenes as secondary organic chromophores is presented. The interplay of the excited states between each chromophore represents an interesting photoredox active system for energy-to-light or light-to-energy devices. Greater knowledge of the primary photophysical events within these complexes will provide a better understanding of how energy moves in these hybrid systems after light absorption, leading to increased device efficiency.
Remote-Controlled Self-Assembly of Three-Dimensional Micro Structures for Ultra-Sensitive Sensors and Three-Dimensional Metamaterials
(2018-10) Liu, Chao
Self-assembly has been widely used to fabricate micro-scale three-dimensional (3D) structures for various applications like sensors, drug delivery systems, and advanced robotics (e.g., micro-actuators, micro-machines). Self-assembly is always driven by external sources (e.g., heat, solvent, pH), which makes the assembly process hard to control and leads to extremely low yield. Direct contact of heat or chemicals is usually required to trigger a self-assembly process, which limits the applications of self-assembly and decreases the manipulative capability of the process. To address the issues of the traditional direct triggered self-assembly, my Ph.D. work involved in developing novel remote-controlled self-assembly techniques with microwave and induction energies, combining the self-assembly technique with advanced metamaterial (MM) designs, and exploring their potential applications as 3D sensors and devices. The goal of the work is to achieve advanced remotely controlled self-assembly to improve the yield and manipulative capability of the assembly process and discover new aspects of the assembly technique (e.g., biocompatible assembly, multiple and sequential assembly) and its applications (e.g., 3D sensors, 3D MM devices). For remotely controlled self-assembly, electromagnetic waves can be remotely applied to the metal thin films within the microstructures. Eddy current can be created inside the thin films and generate heat to melt the polymeric hinges. The molten hinges generate surface tension force to transform the two-dimensional (2D) net into 3D microstructures. Induction heating can trigger self-assembly without harming live organs or tissues, which is suitable for biomedical applications. Remote-controlled self-assembly also allows multiple and sequential self-assembly. The movements of each part of structure can be precisely controlled by adjusting the energy sources in a remote location, increasing manipulative capability of the 3D assembly process. The achievement of sequential self-assembly and multiple folding angles in a single structure is essential for building complex microstructures and micro-actuators. One important application for remote-controlled 3D self-assembled structure is to build 3D MM devices. Split ring resonators (SRRs) and closed ring resonators (CRRs) can be patterned on each face of the self-assembled structures to achieve 3D MMs with fully anisotropic and isotropic behaviors. However, the quality factor (Q-factor) of conventional MMs is low (typically under 10), results in low sensitivity and selectivity. To increase Q-factor of the MMs, we developed novel nanopillar-based MMs driven by displacement current. The nanopillar-based MMs contain thousands of metallic nanopillars with nanoscale dielectric gaps between them. Forming the MMs with nanopillars and nano gaps decreases the Ohmic energy loss in the resonator and increases the energy storage in the dielectric nano gaps, thus an enhanced Q-factor up to 14000 can be achieved. The ultra-high Q nanopillar-based MM can be patterned on each face of the self-assembled 3D structures to realize ultra-high Q 3D MM structures. Novel ultra-sensitive THz MMs and 3D MMs combined with remote-controlled self-assembly opens a new area of creating diverse sensors and devices for 3D optoelectronic, 3D MMs, and ultra-high sensitive biomedical sensors. This thesis will be roughly divided into two parts. We begin with part one by introducing the novel remotely controlled self-assembly using electromagnetic energies that I have developed over my Ph.D. program as well as its unique properties and benefits over traditional self-assemblies. The second part involves my design and theory of ultra-high Q nanopillar-based MM and the 3D MM devices by combining the nanopillar-based MM with self-assembly technique.
Sensor Integration Software
(2014-07-23) Murch, Austin
The utilization of templated porous electrodes in electrochemical applications
(2013-09) Fierke, Melissa Ann
The unifying theme within this work is three-dimensionally ordered macroporous (3DOM) carbon. This material consists of an ordered array of pores surrounded by a skeleton of amorphous carbon with nanometer-scale dimensions. 3DOM carbon offers several advantages that make it ideal for use in electrochemical applications. It has a high surface area, an interconnected pore structure, it is electrically conductive and chemically inert, the surface chemistry can be modified and characterized using slight modifications of well-established techniques, and robust monoliths can be produced. Here, 3DOM carbon was utilized in three distinct electrochemical applications. A three-dimensional interpenetrating lithium ion battery with a 3DOM carbon anode and a mixed vanadia/ruthenia cathode was investigated. Optimization of the synthesis of the polymeric separator layer and the ruthenia component of the cathode were carried out. The synthesis conditions and post-synthesis treatment greatly affect the degree of ruthenia deposition within the porous structure and the extent of hydration of the product. An ion-selective electrode system with 3DOM carbon as the solid contact was developed. 3DOM carbon was covered with an ionophore-based sensing membrane, allowing for selective detection of K+ or Ag+. This system exhibited very low detection limits (4.3 ppt for Ag+), unprecedented electrode stability, and little-to-no response to common interferents (such as carbon dioxide and light). The reasons for this excellent performance were investigated using a variety of characterization methods (with an emphasis on electrochemical techniques). The high surface area and low concentration of surface functional groups on 3DOM carbon are important factors. A receptor-based sensor for explosives detection was also developed. The pore walls of 3DOM carbon were modified with a receptor for 2,4-dinitrotoluene (DNT) using a series of chemical and electrochemical modification steps. Only 3DOM carbon that had been modified with the receptor exhibited a response to the presence of DNT. This selective detection of DNT was also possible in the presence of interfering molecules. However, the high capacitance of the 3DOM carbon led to poor limits when using cyclic voltammetry as the detection method. When square wave voltammetry was used, which eliminates the capacitive currents, much improved detection limits (10 μM) were achieved.

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