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No description available.

This dissertation proposes a miniaturized optical fiber based sensor system for the measurement of 3-dimensional vector magnetic fields. The operation of the sensor system is based on the detection of magnetostrictive dimensional changes in the sensor gage using a modified extrinsic Fabry-Perot Interferometer configuration. Because of the magnetostrictive reflector the gap length depends on the magnetic fields applied to the sensor. Since the diameter of the magnetostrictive sensor gage is 125 micrometer which is the same as that of the input/output fiber, the sensor is simply constructed by inserting the sensor gage and the input/output fiber into a small glass tube. The glass tube serves as both an aligner for the sensor gage and input/out fiber, and a passive temperature compensator. In addition, it also enhances the mechanical strength and compactness of the sensor. This sensor design shows 98 percent suppression of the thermally induced sensor output changes. The linear output of the sensor system is enhanced by transverse field annealing which increases magnetostrictive induction in the ferromagnetic sensor gage material and controls the sensor gage geometry. A 5-times increase in sensor sensitivity is obtained with the transverse field annealing and the use of a new magnetostrictive material. A modified sensor gage endface demonstrates 92 percent of fringe visibility, which further improves the performance of the interferometer. The signal fading in the interferometric sensors at the peak or bottom of a fringe is reduced by using a quadrature signal demodulation method. The system has been shown to have a resolution better than 100 nT over a measurement range from 100 to 40,000 nT. This research is supported financially by the Phillips Laboratory of the U.S. Air Force. / Ph. D.

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. / Master of Science

Optical fiber sensor multiplexing reduces cost per sensor by designing a system that minimizes the expensive system components (sources, spectrometers, etc.) needed for a set number of sensors. The market for multiplexed optical sensors is growing as fiberoptic sensors are finding application in automated factories, mines, offshore platforms, air, sea, land, and space vehicles, energy distribution systems, medical patient surveillance systems, etc. Optical path length multiplexing (OPLM) is a modification to traditional white-light interferometry techniques to multiplex extrinsic Fabry-Perot interferometers and optical path length two-mode sensors. Additionally, OPLM techniques can be used to design an optical fiber sensor to detect pressure/force/acceleration and temperature simultaneously at a single point. While power losses and operating range restrictions limit the broadscale applicability of OPLM, it provides a way to easily double or quadruple the number of sensors by modifying the demodulation algorithm. The exciting aspect of OPLM is that no additional hardware is needed to multiplex a few sensors. In this way OPLM works with conventional technology and algorithms to drastically increase their efficiency. [1] / Master of Science

No description available.

No description available.

No description available.

Due to their compact size, sensitivity, and ability to be multiplexed, intrinsic Fabry-Perot interferometers (IFPIs) are excellent candidates for almost any multi-point temperature or strain application, and it is well-known that using a single-mode lead-in fiber, a multi-mode fiber section as the Fabry-Perot cavity, and an additional single-mode fiber as the tail results in a structure that generates strong interference fringes while remaining robust. Though the basic principles behind these sensors are understood, to the best of the author's knowledge there hasn't been a thorough investigation into the design and fabrication of a chain of multiplexed IFPI sensors for industrial use in an environment where serious issues associated with the size of the test coupon, sensor placement, and mechanical reinforcement of the fiber could arise. This thesis details the preparation and results of this investigation. It turns out that fabricating a sensor chain with appropriate sensor spacing and excellent temperature response characteristics proved a significant challenge, and issues addressed include inter-sensor interference, high-temperature mechanical reinforcement for bare fiber sections, and high bending losses. After overcoming these problems, a final sensor chain was fabricated and characterized. This chain was then subjected to a battery of tests at the National Energy Technology Laboratory (NETL), where four multiplexed sensors were installed on a 2â x2â coupon in a simulated gas turbine environment. Final results are presented and analyzed. The work that went into developing this chain lays the foundation for future efforts in developing quasi-distributed temperature sensors by identifying potential obstacles and fundamental limitations for certain approaches. / Master of Science

Several techniques for measuring humidity are presented. The goal of the study is to use the electrostatic self-assembled monolayer synthesis process to fabricate a Fabry-Parot Cavity based optical fiber humidity sensor. The sensing scheme bases on the refractive index change with relative humidity of the film applied to the end of optical fiber. That is, the change in reflected optical power indicates certain humidity. To achieve this, some chemicals induce on specific coating materials were applied at the end of optical fiber. In this thesis, experimental results are given to prove that the humidity sensor has high sensitive and fast response time. Furthermore, we investigate the potential for the use of human breathing monitoring and air flow rate detection. Results from preliminary tests of each are given. / Master of Science