Browsing by Author "Cooper, Kristie L."

Now showing 1 - 6 of 6
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    Detection and Position Location of Partial Discharges in Transformers Using Fiber Optic Sensors
    Song, Lijun (Virginia Tech, 2004-12-03)
    Power transformers are one of the most important components in the electrical energy network. Extending transformer life is very economically valuable due to power outage. Therefore the development of instruments to monitor the transformer condition is of great interest. Detection of partial discharges (PDs) in power transformers is an effective diagnostic because it may reveal and quantify an important aging factor and provide information on the condition of the transformer. However, partial discharge diagnostics are still not effectively used for online monitoring of transformers because of the complexity of PD measurements and difficulties of discriminating of PDs and other noise sources. This thesis presents a further study of detection and location of partial discharges in power transformers based on previous work conducted at the Center for Photonics Technology (CPT) at Virginia Tech. The detection and positioning system consists of multiple extrinsic Fabry-Parot interferometric (EFPI) fiber acoustic sensors which can survive the harsh environment of oil-filled transformers. This thesis work is focused on optimal arrangement of multiple sensors to monitor and locate PD activities in a power transformer. This includes the following aspects. First, the sensor design requirements are discussed in order to successfully detect and accurately position the PD sources. In the following sections, Finite Element Method (FEM) is used to model the EFPI sensor fabricated at CPT. Experiments were conducted to measure the angular dependence of the frequency response of the sensor. It is shown that within the range of ±45º incident angles, the sensitivity varies by 3-5dB. Finally, the thesis demonstrates a PD positioning experiment in a 500 gallon water tank (R à H = 74" à 30" cylinder) using a hyperbolic positioning algorithm and time difference of arrival (TDOA). Finally we demonstrated that 100% of the positioning data is bounded by a 22.7à 4.1à 5.3 mm₃ cube, with a sensing range of 810 mm using the leading edge method with FIR filtering.
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    Label-free DNA Sequence Detection Using Oligonucleotide Functionalized Fiber Probe with a Miniature Protrusion
    Wang, Xingwei (Virginia Tech, 2006-08-08)
    DNA is the substance that encodes the genetic information that cells need to replicate and to produce proteins. The detection of DNA sequences is of great importance in a broad range of areas including genetics, pathology, criminology, pharmacogenetics, public health, food safety, civil defense, and environmental monitoring. However, the established techniques suffer from a number of problems such as the bulky size, high equipment costs, and time-consuming algorithms so that they are limited to research laboratories and cannot be applied for in-vivo situations. In our research, we developed a novel sensing scheme for DNA sequence detection, featuring sequence specificity, cost efficiency, speed, and ease of use. Without the need for labels or indicators, it may be ideal for direct in-cell application. The principle is simple. With capture DNA immobilized onto the probe by layer-by-layer selfassembly, the hybridization of a complementary strand of target DNA increases the optical thickness of the probe. Three kinds of sensors were developed. The optical fiber tip sensor has been demonstrated with good specificity and high sensitivity for target DNA quantities as small as 1.7 ng. To demonstrate the potential of this structure for practical applications, tularemia bacteria were tested. Two other micrometric structures were designed with specific advantages for different applications. The micro-fiber Bragg grating interferometer (Micro-FBGI) has the intrinsic temperature compensation capability. The micro-intrinsic Fabry-Perot interferometer (Micro-IFPI)features simple signal processing due to its simple configuration. Successful DNA immobilization and hybridization have been demonstrated onto the 25μm Micro-IFPI. Both structures have great potential for nanometric protrusion, allowing future in-cell DNA direct detection. In addition, its quick response time leads to the potential for express diagnosis. What's more, the idea of nanoscale probe has a broad impact in scanning near-field optical microscopy (SNOM), intracellular surgery in cell sensing, manipulation, and injection.
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    Microgap Structured Optical Sensor for Fast Label-free DNA Detection
    Wang, Yunmiao (Virginia Tech, 2011-05-03)
    DNA detection technology has developed rapidly due to its extensive application in clinical diagnostics, bioengineering, environmental monitoring, and food science areas. Currently developed methods such as surface Plasmon resonance (SPR) methods, fluorescent dye labeled methods and electrochemical methods, usually have the problems of bulky size, high equipment cost and time-consuming algorithms, so limiting their application for in vivo detection. In this work, an intrinsic Fabry-Perot interferometric (IFPI) based DNA sensor is presented with the intrinsic advantages of small size, low cost and corrosion-tolerance. This sensor has experimentally demonstrated its high sensitivity and selectivity. In theory, DNA detection is realized by interrogating the sensor's optical cavity length variation resulting from hybridization event. First, a microgap structure based IFPI sensor is fabricated with simple etching and splicing technology. Subsequently, considering the sugar phosphate backbone of DNA, layer-by-layer electrostatic self-assembly technique is adopted to attach the single strand capture DNA to the sensor endface. When the target DNA strand binds to the single-stranded DNA successfully, the optical cavity length of sensor will be increased. Finally, by demodulating the sensor spectrum, DNA hybridization event can be judged qualitatively. This sensor can realize DNA detection without attached label, which save the experiment expense and time. Also the hybridization detection is finished within a few minutes. This quick response feature makes it more attractive in diagnose application. Since the sensitivity and specificity are the most widely used statistics to describe a diagnostic test, so these characteristics are used to evaluate this biosensor. Experimental results demonstrate that this sensor has a sensitivity of 6nmol/ml and can identify a 2 bp mismatch. Since this sensor is optical fiber based, it has robust structure and small size ( 125μm ). If extra etching process is applied to the sensor, the size can be further reduced. This promises the sensor potential application of in-cell detection. Further investigation can be focused on the nanofabrication of this DNA sensor, and this is very meaningful topic not only for diagnostic test but also in many other applications such as food industry, environment monitoring.
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    Multi-cavity Fabry-Perot interferometric thin-film sensor with built-in temperature compensation
    (United States Patent and Trademark Office, 2009-02-24)
    A fiber optic sensor includes at least two Fabry-Perot (FP cavities) defined by at least three partially reflecting surfaces which individually and together are capable of generating different interference spectra which are affected by temperature. One of the FP cavities is formed at an end of the sensor and includes a surface which is capable of supporting a thin film, the optical thickness of which is to be measured. The other FP cavity between the lead-in fiber and the first FP cavity thus does not include the film and can thus independently provide highly accurate temperature information for calibrating the optical length of the second FP cavity and compensation for temperature effects on measurement of the thin film supported thereon, preferably by subtraction of a calibrated temperature-dependent change in optical length of the second FP cavity from the measurement made.
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    Photonic Biosensor Assays to Detect and Distinguish Subspecies of Francisella tularensis
    Cooper, Kristie L.; Bandara, Aloka B.; Wang, Yunmiao; Wang, Anbo; Inzana, Thomas J. (MDPI, 2011-03-07)
    The application of photonic biosensor assays to diagnose the category-A select agent Francisella tularensis was investigated. Both interferometric and long period fiber grating sensing structures were successfully demonstrated; both these sensors are capable of detecting the optical changes induced by either immunological binding or DNA hybridization. Detection was made possible by the attachment of DNA probes or immunoglobulins (IgG) directly to the fiber surface via layer-by-layer electrostatic self-assembly. An optical fiber biosensor was tested using a standard transmission mode long period fiber grating of length 15 mm and period 260 µm, and coated with the IgG fraction of antiserum to F. tularensis. The IgG was deposited onto the optical fiber surface in a nanostructured film, and the resulting refractive index change was measured using spectroscopic ellipsometry. The presence of F. tularensis was detected from the decrease of peak wavelength caused by binding of specific antigen. Detection and differentiation of F. tularensis subspecies tularensis (type A strain TI0902) and subspecies holarctica (type B strain LVS) was further accomplished using a single-mode multi-cavity fiber Fabry-Perot interferometric sensor. These sensors were prepared by depositing seven polymer bilayers onto the fiber tip followed by attaching one of two DNA probes: (a) a 101-bp probe from the yhhW gene unique to type-A strains, or (b) a 117-bp probe of the lpnA gene, common to both type-A and type-B strains. The yhhW probe was reactive with the type-A, but not the type-B strain. Probe lpnA was reactive with both type-A and type-B strains. Nanogram quantities of the target DNA could be detected, highlighting the sensitivity of this method for DNA detection without the use of PCR. The DNA probe reacted with 100% homologous target DNA, but did not react with sequences containing 2-bp mismatches, indicating the high specificity of the assay. These assays will fill an important void that exists for rapid, culture-free, and field-compatible diagnosis of F. tularensis.
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    Study of Multimode Extrinsic Fabry-Perot Interferometric Fiber Optic Sensor on Biosensing
    Zhao, Xin (Virginia Tech, 2006-08-01)
    The electrostatic self-assembly (ESA) method presents an effective application in the field of biosensing due to the uniform nanoscale structure. In previous research, a single mode fiber (SMF) sensor system had been investigated for the thin-film measurement due to the high fringe visibility. However, compared with a SMF sensor system, a multimode fiber (MMF) sensor system is lower-cost and has larger sensing area (the fiber core), providing the potential for higher sensing efficiency. In this thesis, a multimode fiber-optic sensor has been developed based on extrinsic Fabry-Perot interferometry (EFPI) for the measurement of optical thickness in self-assembled thin film layers as well as for the immunosensing test. The sensor was fabricated by connecting a multimode fiber (MMF) and a silica wafer. A Fabry-Perot cavity was formed by the reflections from the two interfaces of the wafer. The negatively charged silica wafer could be used as the substrate for the thin film immobilization scheme. The sensor is incorporated into the white-light interferometric system. By monitoring the optical cavity length increment, the self-assembled thin film thickness was measured; the immunoreaction between immunoglobulin G (IgG) and anti-IgG was investigated.