Browsing by Author "Dong, Bo"
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- Analysis of ultrasonic frequency response of surface attached fiber Bragg gratingLi, Zhuoxuan; Pei, Li; Dong, Bo; Ma, Cheng; Wang, Anbo (Optical Society of America, 2012-07-01)In recent years, fiber Bragg grating (FBG), for the well-known advantages over other fiber optic sensors, has attracted more attention in ultrasonic inspection for structure health monitoring (SHM). Spectrum shift of FBG to ultrasonic wave is caused by the refractive index profile changing along the FBG, which can be attributed to nonuniform perturbation caused by strain-optic and geometric effects of ultrasonic wave. Response of FBG to the above two effects was analyzed firstly by the V-I transmission matrix model, showing high computing efficiency. Based on this model, spectra response of FBG under changing ultrasonic frequencies was simulated and discussed. In experiment, the system was able to detect a wideband ultrasonic wave ranging from 15 to 1380 kHz. These results would provide a guideline for an FBGbased acoustic detection system design in a specific ultrasonic frequency. (C) 2012 Optical Society of America
- Apparatus and method for on-line, real-time analysis of chemical gases dissolved in transformer oil(United States Patent and Trademark Office, 2014-06-03)An inspection probe for directly measuring a transmission spectrum of a solvent oil in a transformer includes a tube having a plurality of apertures spaced along a side of the tube to allow oil to pass therethrough, and first and second optical collimators disposed at opposing ends of the tube. The first and second collimators are aligned by the tube such that incident light is transmitted through the first collimator, the tube, and the second collimator to a spectrometer.
- Fiber Optic Sensors for On-Line, Real Time Power Transformer Health MonitoringDong, Bo (Virginia Tech, 2012-08-09)High voltage power transformer is one of the most important and expensive components in today's power transmission and distribution systems. Any overlooked critical fault generated inside a power transformer may lead to a transformer catastrophic failure which could not only cause a disruption to the power system but also significant equipment damage. Accurate and prompt information on the health state of a transformer is thus the critical prerequisite for an asset manager to make a vital decision on a transformer with suspicious conditions. Partial discharge (PD) is not only a precursor of insulation degradation, but also a primary factor to accelerate the deterioration of the insulation system in a transformer. Monitoring of PD activities and the concentration of PD generated combustible gases dissolved in the transformer oil has been proven to be an effective procedure for transformer health state estimation. However current commercially available sensors can only be installed outside of transformers and offer indirect or delayed information. This research is aimed to investigate and develop several sensor techniques for transformer health monitoring. The first work is an optical fiber extrinsic Fabry-Perot interferometric sensor for PD detection. By filling SF6 into the sensor air cavity of the extrinsic Fabry-Perot interferometer sensor, the last potential obstacle that prevents this kind of sensors from being installed inside transformers has been removed. The proposed acoustic sensor multiplexing system is stable and more economical than the other sensor multiplexing methods that usually require the use of a tunable laser or filters. Two dissolved gas analysis (DGA) methods for dissolved hydrogen or acetylene measurement are also proposed and demonstrated. The dissolved hydrogen detection is based on hydrogen induced fiber loss and the dissolved acetylene detection is by direct oil transmission measurement.
- Test of Light Speed Constancy With Light Age Using an Active Fiber-Based Mach-Zehnder InterferometerDong, Bo (Virginia Tech, 2006-05-10)This thesis investigates the constancy of light speed with respect to the light age using an active fiber-based Mach-Zehnder interferometer (MZI) illuminated by sunlight. The original sunlight in one arm, which has the age of 8.3 minutes since it was emitted from the sun, interferes with the young light generated by stimulated emission from an optical amplifier in the other arm, which is coherent to the sunlight. The speed difference between the sunlight and the newly regenerated light is obtained by measuring the phase variations as the interference signal travels along a span of single-mode fiber. System error is eliminated by the self-calibration which is achieved by alternatively switching other two local amplified spontaneous emission light sources and the sunlight as the input to the MZI, and then comparing the measured phase differences of these three sources. The relative accuracy of light speed measurement is . Consider the 8.3 minutes age of the sunlight, for a possible variation of light speed of c with light age in optical fiber, we obtainĢc/c is less than 1.7