Jeffrey D. Muhs

Algorithm for a novel fiber optic weigh-in-motion sensor system

Over the past decade, the demand from both government and private industry for small, lightweight, vehicle weight-in-motion (WIM) systems has grown substantially. During the 1980s, several techniques for weighing vehicles in motion were developed that include piezoelectric cables, capacitive mats, and hydraulic and bending-plate load cells. These different systems have advantages and disadvantages that trade off between accuracy, physical size, and system complexity. The smaller portable systems demonstrate medium to poor accuracy and repeatability while the larger more accurate systems are nonportable. A small, lightweight, and portable WIM system based on a fiber-optic pressure transducer has been developed by Oak Ridge National Laboratory (ORNL) to meet the demands of government and industry. The algorithm for extracting vehicle weight from the time-dependent sensor response is developed and presented in this report, along with data collected by the system for several classes of vehicles. These results show that the ORNL fiber-optic WIM system is a viable alternative to other commercial systems that are currently available.

Tracking Systems Evaluation for the “Hybrid Lighting System”

As part of the design and development effort for the “Hybrid Lighting System,” Oak Ridge National Laboratory (ORNL) scientists have evaluated two potential candidate-tracking systems for the solar collector. The first system, the WattSun Solar Tracker, built by Array Technologies, utilizes a patented, closed loop, optical sun sensor to sense the sun’s position and track it. The second tracking system, SolarTrak Controller, built by Enhancement Electronics, Inc., is a micro controller-based tracking system. The SolarTrak micro controller-based Tracker’s sun position is determined by computing the celestial bearing of the sun with respect to the earth using the local time, date, latitude, longitude and time zone rather than sensing the relative bearing of the sun with optical receptors. This system connects directly to the mechanical system hardware supplied by Array Technologies. Both the WattSun Solar Tracker and the SolarTrak Controller were mounted on the prototype “Hybrid Lighting” mechanical system (array) hardware. A simple switch allowed independent testing of each system. Upon completion of the evaluation of the two systems we found the WattSun Solar Tracker controller to be unacceptable for use with our prototype hybrid lighting system. The SolarTrak Controller has performed well to date and provides suitable tracking accuracy for use with our prototype “Hybrid Lighting System”. After a six-month evaluation period at ORNL, the first prototype “Hybrid Lighting System” was installed at Ohio University as part of an “Enhanced Practical Photosynthetic CO2 Mitigation.” This document will highlight the results of the tracker investigation and outline the remaining issues to be addressed, to provide a suitable tracking system for our “Hybrid Lighting” collector.© 2003 ASME

Evaluating thermographic phosphors in an operating turbine engine

The results of a field test in a commercial turbine engine showed that we can remotely measure the temperature of engine components in operating engines using thermographic phosphors. The remote-measurement method exploits the temperature dependence of the characteristic decay time of the laser-induced fluorescence of thermographic phosphors. This paper summarizes recent work leading up to and including a successful test of the thermographic-phosphor method in an operating turbine engine.Copyright

Spectral Transmission of a Solar Collector and Fiber Optic Distribution Hybrid Lighting System

Increased use of solar energy will reduce requirements for non-renewable energy sources such as fossil fuels and reduce associated greenhouse gas emissions. The benefits of replacing fossil-based energy with solar energy are often dependent on the application and operational or duty cycle for power demand. One particularly efficient use of solar energy is hybrid lighting. In hybrid lighting, solar light is concentrated into optical fibers and then coupled with supplemental electrical lighting to maintain a constant level of illumination. The system is able to offer reliable lighting with less energy consumption from the electrical grid (which is often driven by non-renewable sources). This technique offers energy efficiency benefits since the solar light is used directly and suffers no conversion losses. Furthermore, the solar spectrum provides an illumination that lighting engineers value for it’s quality; office inhabitants appreciate for its comfort; and retailers believe leads to increased sales. When available solar light is low, the hybrid system allows traditional light sources to reliably meet lighting demands. The success of the solar hybrid lighting system is dependent on the collection and transmission efficiency of the system. In this study, the spectral transmission of a hybrid lighting system is characterized. The system is composed of a 200-sun concentration reflective solar collector and a plastic fiber optic distribution network. The ultraviolet (UV), visible, and near-infrared (NIR) spectral transmission was characterized over a spectral range of 200 nm to 2400 nm. The UV and NIR performance of the system is critical since optical fiber damage can be caused by both UV and NIR light; thus, optimal system design maximizes the collection and transmission of visible light while minimizing the transmission of the UV and NIR light. Spectral transmission data for all components in the hybrid system are presented, and performance properties relative to solar applications are discussed.

Repeatable sensitivity of optical-time-domain-reflectometry-based strain measurement

Optical time-domain reflectometry (OTDR) is a simple and rugged technique for measuring quantities such as strain that affect the propagation of light in an optical fiber. For engineering applications of OTDR, it is important to know the repeatable limits of its performance. The authors constructed an OTDR-based, submillimeter resolution, strain measurement system from off-the-shelf components. The system repeatably resolves changes in time of flight to within +/- 2 ps. Using a 1 m, single-mode fiber as a gauge and observing the time of flight between Fresnel reflections, we observed a repeatable sensitivity of 400 microstrains. Using the same fiber to connect the legs of a 3 dB directional coupler to form a loop, we observed a repeatable sensitivity of 200 microstrains. Realizable changes to the system that should improve the repeatable sensitivity to 20 microstrains or less are discussed.

Survivability of optical fiber sensor elements embedded in silicon carbide ceramic matrix composites

Optical fiber sensor elements were embedded in ceramic matrix composite (CMC) specimens fabricated at the Oak Ridge National Laboratory using a rapid chemical vapor infiltration (CVI) process. The silica and sapphire optical fiber sensors were placed between adjacent layers of interwoven NicalonR fibers during the stacking of a preform. This preform was then coated with pyrolytic carbon, used as an interface layer, and then densified with additional silicon carbide through CVI. This paper discusses the survivability of both the silica and sapphire optical fiber sensor elements, and suggests the possibility of using embedded optical fiber sensor elements inside high temperature composites for both fabrication monitoring and subsequent in-service lifetime monitoring at high temperatures.

Overview of silicone-rubber fiber optic sensors and their applications

A novel technique for measuring several physical parameters suing a transparent, silicone- rubber optical fiber is described. A discussion of the physical and optical characteristics of the fiber is provided along with preliminary experimental results on various present and future sensor applications. These applications include fiber-optic sensors for detecting and measuring temperature, humidity/moisture, force, and static and dynamic pressure.

Fiber-optic sensors for composite cure analysis and lifetime nondestructive evaluation

A proposed multiplexed fiber-optic sensor system capable of analyzing a composite material during its curing cycle and over its service lifetime is presented. The sensor is composed of two independent sensing schemes that will ultimately be multiplexed onto a specialized single-mode/multimode optical fiber. The first sensing scheme is a fiber-optic viscosity and temperature sensor used for composite cure analyses. This sensor is based on (1) the laser-induced viscosity-dependent fluorescence phenomena observed in epoxy-based composite materials and (2) the temperature-dependent decay-time fluorescence phenomena observed in thermographic phosphors. The second sensor is based on a low-finesse, single-mode fiber-optic Fabry-Perot interferometer and is used as a strain/vibration sensor for lifetime nondestructive evaluations on composites. Experimental results have determined that these sensor concepts are feasible alternatives to cure-analysis monitors and conventional strain-analysis techniques.A proposed multiplexed fiber-optic sensor system capable of analyzing a composite material during its curing cycle and over its service lifetime is presented. The sensor is composed of two independent sensing schemes that will ultimately be multiplexed onto a specialized single-mode/multimode optical fiber. The first sensing scheme is a fiber-optic viscosity and temperature sensor used for composite cure analyses. This sensor is based on (1) the laser-induced viscosity-dependent fluorescence phenomena observed in epoxy-based composite materials and (2) the temperature-dependent decay-time fluorescence phenomena observed in thermographic phosphors. The second sensor is based on a low-finesse, single-mode fiber-optic Fabry-Perot interferometer and is used as a strain/vibration sensor for lifetime nondestructive evaluations on composites. Experimental results have determined that these sensor concepts are feasible alternatives to cure-analysis monitors and conventional strain-analysis techniques.