Browsing by Subject "Sensing"
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Item Application of optical coherence tomography for improved in-situ flaw detection in nylon 12 selective laser sintering(2019-06-19) Lewis, Adam Dudley; Beaman, Joseph J.; Edgar, Thomas F.; Milner, Thomas; Bonnecaze, Roger T; Lynd, NathanielDespite significant advances made since the inception of selective laser sintering (SLS), many of the same problems identified by early researchers including high part porosity, inadequate surface finish, and part strength uncertainty persist today. Because of these challenges, quality validation and improved process control continue to be identified as critical areas of improvement in industry roadmaps. To address these issues, an optical coherence tomography (OCT) sensor is investigated for feasibility of use in in-situ flaw detection in SLS. Benchtop OCT imaging of nylon in solid, liquid, and resolidified phases revealed subsurface imaging through liquid and resolidified nylon material was possible. Subsequent benchtop imaging showed that multiple-scattering was the cause of an imaging artifact which contributed to the limited imaging depth in nylon powder. Additionally, nylon powder was continuously imaged before, during, and after melting and resolidification. The resulting images showed scattering was consistent with the presence of crystalline spherulites, suggesting the spherulites are a strong source of scattering in the nylon 12. An OCT sensor was subsequently mounted on a production-sized research SLS machine. Design and implementation information is detailed including artifact correction and noise subtraction strategies. The OCT sensor is then used to detect various common defects in the SLS process. Imaging single layer individual scanlines revealed deeper melt depth due to overheating from galvo deceleration near the end of the scan lines. Additionally, surface curl was able to be quantified and visualized for a build. Finally, an SLS build was performed at higher powder bed temperatures. OCT images collected from the build were compared with X-ray computed tomography (CT) images, and many of the pores in the OCT images are shown to agree well with those detected in the CT images. One pore in the dataset was much larger than the others in the part. This caused the author to hypothesize that a different mode was responsible for creating these pores which a subsequent build confirmed. A summary of contributions and future work is also listed.Item Cognitive radios : fundamental limits and applications to cellular and wireless local networks(2012-05) Chung, Goochul; Vishwanath, Sriram; Shakkottai, Sanjay; Andrews, Jeffrey; Caramanis, Constantine; Choi, JihwanAn ever increasing number of wirelessly-enabled applications places a very high demand on stringent spectral resources. Cognitive radios have the potential of enhancing spectral efficiency by improving the usage of channels that are already licensed for a specific purpose. Research on cognitive radios involves answering questions such as: how can a cognitive radio transmit at a high data rate while maintaining the same quality of service for the licensed user? There are multiple forms of cognition studied in literature, and each of these models must be studied in detail to understand its impact on the overall system performance. Specifically, the information-theoretic capacity of such systems is of great interest. Also, the design of cognitive radio is necessary to achieve those capacities in real applications. In this dissertation, we formulate different problems that relate to the performance of such systems and methods to increase their efficiency. This dissertation discusses, firstly, the means of "sensing" in cognitive systems, secondly, the optimal resource allocation algorithms for interweave cognitive radio, and finally, the fundamental limits of partially and overly cognitive overlay systems.Item Detecting single-particle insulating collisions in microfluidics as a function of flow rate(2012-12) Nettleton, Elizabeth Grace; Crooks, Richard M. (Richard McConnell); Bard, Allen JThis work presents the first electrochemical observation of single polystyrene microbead collisions with an electrode within a microchannel. We have observed that detecting single microbead collisions is facile with this system. Additionally, we have shown that by increasing flow within the channel, one can increase both the frequency and magnitude of collision signals. This technique may provide a means of signal amplification in future sensing work.Item On-chip silicon photonic waveguide devices for biochemical sensing and optical interconnects(2017-09-15) Yan, Hai, Ph. D.; Chen, Ray T.; Wang, Zheng; Ben-Yakar, Adela; Yeh, Hsin-Chih; Chakravarty, SwapnajitOn-chip photonic devices based on waveguides receives significant attention for its capability in realizing great performance with high integration density. Two of the most representative area of application are biochemical sensing and optical interconnects. Micro- and nano-scale photonic biosensor has become a fast growing research topic driven by the need of portable bio-detection systems with high sensitivity, high throughput, real-time and label-free detection. Various structures, especially those based on silicon-on-insulator (SOI) substrate, have been demonstrated in research, some of which have been developed into commercially available product. In terms of optical interconnect, extensive research and development is underway to try to break the bottleneck in traditional copper interconnect in modern electronics facilities and devices, from local area network to short-reach data links and even down to on-chip interconnect. Silicon photonics is currently the most promising solution to optical interconnect primarily due to its mature processing technologies. Yet other materials, including electro-optic (EO) polymers, are also widely used in specific applications (e.g. EO modulators) for the benefits of high speed and low energy consumption. In this dissertation, various photonic waveguide devices for biochemical sensing and optical interconnect will be presented. First, biosensors based on photonic crystal (PC) microcavities will be demonstrated. A bandpass filter will be introduced to combine multiple PC microcavity sensors into an array. Array of PC biosensors with different parameters was formed to give a wide dynamic range of detection range. The detection of antibiotics and heavy metals will be covered. Then, a novel structure -- subwavelength grating waveguides (SWG) based biosensors will be introduced and its unique thickness-independent surface sensitivity will be analyzed and demonstrated. Thirdly, I will show a novel one-dimensional PC slot waveguide. It offers a simple, high-efficiency and low-loss phase shifter design for silicon-polymer hybrid EO modulators. Strained silicon waveguide for the generation of mid-infrared wave through difference frequency generation will be covered at last. It will show the potential application of chemical sensing with integrated photonic devices.Item Studies of multicomponent assemblies(2012-12) Long, Samuel Reid; Anslyn, Eric V., 1960-; Iverson, Brent L.This dissertation is divided into three major sections (one on dendrimers, one on tripodal metal ligands and one on a research oriented chemistry curricula) with a primary focus on different types of multicomponent assemblies. In the first chapter, a system is described that used a multicomponent assembly of AT-PAMAM dendrimers and an indicator, carboxyfluorescein, to detect and identify various polyanions at a low micromolar concentration. The system was able to successfully differentiate twelve anions, many of biological interest, including three tricarboxylates. The tricarboxylates were differentiated based primarily on the regiochemistry of the anionic groups. In the second chapter, further studies with AT-PAMAM dendrimers were carried out to provide some understanding of the thermodynamic origins of binding. Utilizing isothermal titration calorimetry, the binding of the dendrimers to large polyanionic dendrons with increasing numbers of charges was studied. Through these studies, the thermodynamic values of the binding events were obtained allowing us to explore the properties of the dendrimers. The cooperativity of the system was measured, and primarily negative cooperativity determined by the entropic contributions was uncovered. As the dendrimers increased in size, the thermodynamic origins of binding were determined to a greater extent by the entropy of binding. In the third chapter, a novel dynamic ligand system for metal binding is described. In the presence of a metal salt, a heterocyclic aldehyde and a secondary amine with two heterocyclic arms reversibly condense to form a hemiaminal with a tripodal metal binding site. This chapter describes studies on the metal binding ability, the variety of metals that will lead to this formation, the effects of anions and the range of aldehydes that can be used are described. Furthermore, the system’s reversibility was explored. Finally, the use of a bistriazole secondary amine was explored. The modular nature of triazole formation could lead to the introduction of additional functionalities. The fourth chapter discusses how the novel ligand system could be used to study the enantiomeric excess (ee) of chiral thiols. Based upon the system’s ability to form a stable hemiaminal thioether, a CD signal could be generated that is proportional to the amount of a particular enantiomer in solution. Using this system, a calibration curve relating CD signal and ee can be generated giving the ee of an unknown solution. In the final chapter, a look at the Freshman Research Initiative will be carried out with a focus on the ability to teach basic skills in an introductory laboratory through research. Four different skills or techniques will be explored through three different FRI streams,x and how they teach the four skills. Finally, analysis of the success of the program, particularly students’ success in the next laboratory course in the sequence, is discussed, and a model for adopting this type of teaching at other universities is given.Item Subwavelength and nonreciprocal optical and electromagnetic systems for sensing and communications(2017-06-07) Williamson, Ian Alexander Durant; Wang, Zheng, Ph. D.; Alù, Andrea; Bank, Seth R; Wang, Yaguo; Yu, Edward TThis dissertation is organized into three parts. First, the design for a radio frequency fiber transmission line built out of a grid of micrometer-scale conductors embedded in an insulating polymer cladding is presented to mitigate the skin and proximity effects. By adopting a checkerboard out-of-phase current phasing scheme, the internal inductance of the line is significantly lower than in two-conductor lines and results in an LC bandwidth of approximately 2 GHz, with flat attenuation and linear phase dispersion. The device performance is characterized in terms of its geometric degrees of freedom and a fabricated prototype is presented. Second, the kinetic inductive and plasmonic response of monolayer graphene in the terahertz spectrum is examined in the context of several important applications. The dispersive responses of two-dimensional graphene and three-dimensional copper transmission lines are compared to map the dispersive signaling performance in terms of transmission line cross-sectional size. This demonstrates a surprisingly broadband LC response with flat attenuation in nano-scale lines. This kinetic inductive response of graphene is demonstrated to miniaturize the photonic band structure of a photonic crystal slab where an in-plane periodicity of 300 nm has its photonic band gap in the terahertz spectrum. The sub-diffraction photonic band structure resembles that of the two-dimensional photonic crystal, supporting a wide photonic band gap in extremely thin slabs. The viability of graphene for cavity optomechanics is analyzed from near infrared to terahertz wavelengths, demonstrating a large optomechanical coupling, on the order of 3D optomechanical materials. Third, a class of nonreciprocal devices is proposed based on coupling to the sideband states, called Floquet resonances, that arise in temporally modulated optical resonators. The degrees of freedom in the modulating waveform tailor the energy exchange and phase of the Floquet resonances to realize unique nonreciprocal spectral responses in compact devices. We examine optical scattering from Floquet resonators coupled to narrowband waveguides using temporal coupled-mode theory. A three-port circulator is built out of a cascade of Floquet resonators to demonstrate broadband forward transmission and ideal isolation for dual-carrier waves. Full-wave numerical simulations in the coupled frequency domain demonstrate the circulator in an on-chip photonic crystal platformItem The development and study of materials for optoelectronic devices and sensors(2018-06-15) Moore, Matthew Darren; Sessler, Jonathan L.; Humphrey, Simon M; Que, Emily; Anslyn, Eric V; Slinker, Jason DLuminescence is a property of materials that allows for the emission of photons when a given amount of energy is applied. The luminescent properties of both polymeric and small molecule materials can generally be controlled through rational design, allowing for the development of materials that can be used in a variety of applications (e.g. sensing, light emissive devices, photovoltaics, photochemistry, etc…). Several families of small molecule emissive materials were designed for use in light emitting electrochemical cells (LEECs). A set of iridium complexes was designed to promote rapid turn-on time in devices, as well as raise the LEEC’s external quantum efficiency (EQE). By systematically substituting mesityl groups onto a base iridium complex, the turn-on times were lowered from minutes to seconds for systems containing the new substituents. Furthermore, the EQE was raised from 0.45% to 1.38% for one material. The study of platinum-based emitters in LEEC devices has not been previously reported, thus it is of interest to determine if this subset of highly efficient emitters may behave in devices similarly to iridium complexes. A family of platinum complexes was synthesized and studies are ongoing to establish device behavior. Moreover, an all organic, ionic set of emissive small molecules was synthesized. Studies are similarly ongoing to determine device behavior. Sensing is also an important capability of some emissive materials. The sensitivity of particular materials to their environment is an attribute that can be utilized to design a sensor. By using a mixed lanthanide metal-organic-framework (MOF), the sensing of trace (<0.5%) water in organics was accomplished. How the systems are able to show such sensitivity was also examined to determine how to further improve upon the MOF’s sensing abilities. This same material was further used in a fingerprinting system that permits the rapid identification of unknown solvents.