Browsing by Author "Miller, Mark S."
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- Advances in elliptical-core two-mode optical fiber sensorsMiller, Mark S. (Virginia Tech, 1990)Methods designed to improve the practicality of the elliptical-core two-mode optical fiber sensors for use in real-life applications are presented. The improvements include the development of insensitive lead fibers and an optical device which allows fringe counting at the output of the sensor. The insensitive leads eliminate extraneous perturbations and effectively isolate the sensing region. The fringe counting optics are designed to generate quadrature-phase shifted signals, thereby allowing the determination of whether the strain is increasing or decreasing. Work performed to advance the understanding of the effect of sensor placement within a composite specimen is also presented. Optical fiber sensors are embedded between different laminae of a graphite-epoxy composite panel, and the outputs of the sensors are shown to be proportional to the distance of the sensor from the neutral axis.
- Optical fiber-based corrosion sensor systemsMiller, Mark S. (Virginia Tech, 1995)An investigation into optical fiber sensing methods for monitoring metallic corrosion 1s presented. A series of sensing techniques are presented and explored, and two techniques are identified as possible candidates for a corrosion sensing system. The first is a technique based on the phenomenon of surface plasmon resonance, a technology useful in the sensing of changes in the index of refraction of a material in a localized area. The second involves the use of a metal-clad fiber sensing region where the standard core/cladding fiber geometry is modified to have a silica core and a metal cladding. A series of improvements to the current surface plasmon devices lead to the choice of a multimode cylindrical geometry for the sensor fiber. Under the correct conditions, energy in the TM modes in the fiber will transfer to a surface plasmon mode coupled to the surface of a metal film on the fiber. Monitoring the spectral output of the sensor provides information on the change in index of refraction of the surrounding material or the remaining thickness of the metal film applied to the fiber. The metal-clad sensor involves replacing the standard dielectric cladding with a metal in the sensing region. The loss of power through this region is directly related to the thickness of the metal cladding, which decreases with corrosion. A theoretical analysis is performed and compared with experimental results which demonstrate the feasibility of the sensing technique. Both the surface plasmon approach and the metal-clad approach are demonstrated as corrosion presence indicators, that is, they cannot currently resolve the level of corrosion, but just indicate when a certain amount of corrosion has occurred. The metal-clad technique is therefore identified as the most practical technique due to its relatively simple operation and easily understandable output response to corrosion. Future improvements are presented for the metal-clad sensor to help resolve the total amount of corrosion and a method is demonstrated for the repeatable fabrication of the metal-clad sensor.
- Split-Spectrum Intensity-Based Optical Fiber Sensors For Measurement Of Microdisplacement, Strain, And PressureWang, Anbo; Miller, Mark S.; Plante, Angela J.; Gunther, Michael F.; Murphy, Kent A.; Claus, Richard O. (Optical Society of America, 1996-08-01)A self-referencing technique compensating for fiber losses and source fluctuations in reflective air-gap intensity-based optical fiber sensors is described. A dielectric multilayer short-wave-pass filter is fabricated onto or attached to the output end face of the lead-in-lead-out multimode fiber. The incoming broadband light from a white light or a light-emitting diode is partially reflected at the filter. The transmitted light through the filter projects onto a mirror The light returning from the reflecting mirror is recoupled into the lead-in-lead-out fiber. These two reflections from the filter and the reflecting mirror are spectrally separated at the detector end. The power ratio of these two reflections is insensitive to source fluctuations and fiber-bending loss. However, because the second optical signal depends on the air-gap separation between the end face of the lead-in-lead-out fiber and the reflecting mirror, the ratio provides the information on the air-gap length. A resolution of 0.13 mu m has been obtained over a microdisplacement measurement range of 0-254 mu m. The sensor is shown to be insensitive to both fiber-bending losses and variations in source power. Based on this approach, a fiber-strain sensor was fabricated with a multilayer interference filter directly fabricated on the end face of the fiber. A resolution of 13.4 microstrain was obtained over a measurement range of 0-20,000 microstrain with a gauge length of 10 mm. The split-spectrum method is also incorporated into a diaphragm displacement-based pressure sensor with a demonstrated resolution of 450 Pa over a measurement range of 0-0.8 MPa. (C) 1996 Optical-Society of America