Michael P. Buric

Active Fiber Bragg Grating Hydrogen Sensors for All-Temperature Operation

The use of liquid hydrogen as a fuel requires low-cost multipoint sensing of hydrogen gas for leak detection and location well below the 4% explosion limit of hydrogen. Herein is presented a multipoint in-fiber hydrogen sensor capable of hydrogen detection below 0.5% concentration with a response time of less than 10 s. Our solution entails use of a fiber Bragg grating (FBG) coated with a layer of hydrogen-absorbing palladium which, in turn, induces strain in the FBG in the presence of hydrogen. Infrared power laser light is used to induce heating in the palladium coating which dramatically decreases sensor response time and increases the sensors sensitivity at low temperatures. This technology promises an inexpensive fiber solution for a multipoint hydrogen detection array with only one fiber feed-through

Enhanced spontaneous Raman scattering and gas composition analysis using a photonic crystal fiber

Spontaneous gas-phase Raman scattering using a hollow-core photonic bandgap fiber (HC-PBF) for both the gas cell and the Stokes light collector is reported. It was predicted that the HC-PBF configuration would yield several hundred times signal enhancement in Stokes power over a traditional free-space configuration because of increased interaction lengths and large collection angles. Predictions were verified by using nitrogen Stokes signals. The utility of this system was demonstrated by measuring the Raman signals as functions of concentration for major species in natural gas. This allowed photomultiplier-based measurements of natural gas species in relatively short integration times, measurements that were previously difficult with other systems.

Improved sensitivity gas detection by spontaneous Raman scattering

Accurate, real-time measurement of the dilute constituents of a gaseous mixture poses a significant challenge usually relegated to mass spectrometry. Here, spontaneous Raman backscattering is used to detect low pressure molecular gases. Rapid detection of gases in the approximately 100 parts in 10(6) (ppm) range is described. Improved sensitivity is brought about by use of a hollow-core, photonic bandgap fiber gas cell in the backscattering configuration to increase collection efficiency and an image-plane aperture to greatly reduce silica-Raman background noise. Spatial and spectral properties of the silica noise were examined with a two-dimensional CCD detector array.

Multiplexable Low-Temperature Fiber Bragg Grating Hydrogen Sensors

A palladium-coated fiber Bragg grating (FBG) inscribed in high attenuation fiber (HAF) capable of measuring hydrogen concentration at -150 degC, well below the 4% explosion limit, is presented. The low-temperature performance of the sensor was improved by heating the gratings as much as 300 K above the ambient temperature with highly attenuated infrared laser light. The sensitivity and response time of the FBG hydrogen sensor were studied as functions of fiber temperature. Through the selection of length and the loss per meter of the HAF, the self-heating scheme demonstrated here enables numerous FBG hydrogen sensors to be multiplexed in a single fiber for multipoint hydrogen sensing using a single fiber feedthrough.

Energy harvesting from mechanical vibrations using piezoelectric cantilever beams

In this paper, a design methodology for an energy harvesting device will be investigated and results will be presented to validate the design. The energy harvesting device in the study is 31- unimorph piezoelectric cantilever beam which was used to convert small amplitude mechanical vibration from a specific machine application into an electrical energy source that could be used for electronic devices with low power requirements. The primary purpose of the design methodology is to illustrate a method to design a cantilever beam that is optimized for a particular application. The methodology will show how the vibration data (frequency and amplitude) from the machine was analyzed and then how this information was incorporated into the final design of the beam. From the given vibration data a range of frequencies where the energy harvesting device will generate the greatest amount of energy is determined. The device is then designed specifically targeting that frequency range. This approach is presented as part of a more general approach to designing energy harvesters for any application. Also, it will be shown how the thickness and type of materials used for each layer of cantilever beam were chosen, completely independent of the vibration data, without effecting the over all optimization process.

Self-heated fiber Bragg grating sensors

This letter demonstrates an approach for tuning fiber Bragg grating sensors with optical energy carried in the same optical fiber. Optical energy carried in the optical fiber was used to heat in-fiber Bragg gratings in order to alter the grating’s optical response to surrounding media. The functional enhancement of optically heated Bragg gratings as sensor devices is demonstrated by a dual-function Bragg grating temperature and level sensing array for liquid at room and cryogenic temperatures.

Piezo-Electric Energy Harvesting for Wireless Sensor Networks

Numerous industrial and military applications require remote sensing of various machine and equipment operating parameters in locations where traditional power sources may not be available and long periods of unattended operation are required. Quite often, however, some source of vibrating energy may be present in operation of the machine in question. Herein, a piezoelectric source is efficiently utilized to generate power for the operation of a microcontroller and radio transmitter to acquire sampled machine data. Various techniques for the efficient conversion, use, and storage of piezoelectric power are detailed and used in a general energy harvesting data transmitter design.

Fiber Bragg grating vacuum sensors

This letter demonstrates functional enhancements of fiber Bragg grating sensors powered by in-fiber light. High-power laser light transmitted in double-clad optical fiber was extracted from the fiber core to heat an on-fiber metal coating. When the power-laser is turned off, the fiber Bragg grating is used as a passive component for temperature sensing. When the laser is turned on, the thermal response of the optically heated grating was used to monitor ambient air pressure. The sensitivity and dynamic range of optically powered fiber sensors can be actively adjusted by in-fiber light to measure vacuum pressures over four orders of magnitude.

Self-heated all-fiber sensing system for cryogenic environments

We present a new design of an all-fiber sensor system to enhance the low-temperature sensing performance of cryogenic fuel. Fiber Bragg gratings (FBGs) are inscribed in high attenuation fibers (HAFs), which absorb in-fiber light to raise the local sensor temperature in a cryogenic environment. The heated sensor displays improved sensitivity and response time to measure multiple parameters. Two sensing applications are described in this paper. First, a HAF–FBG sensor coated with palladium is used to detect hydrogen concentration well below the 4% explosion limit at 173 K. Second, an array of three aluminum-coated sensors is capable of measuring the liquid level at 77 K. In addition, through the selection of the length and attenuation coefficient of HAF, numerous FBG sensors can be multiplexed on a single fiber for multipoint sensing using a single fiber feedthrough.

Theoretical and experimental investigation of evanescent-wave absorption sensors for extreme temperature applications

Recently, significant developments in evanescent wave absorption sensors have been demonstrated for high temperature sensing applications based upon the optical responses of advanced thin film materials. We will demonstrate how such sensors can be utilized in a mode that allows for chemical or temperature sensing starting from basic theoretical considerations. We will also present experimental high temperature sensing results for fabricated sensors. Potential applications of the sensors to be discussed include a range of high temperature systems relevant for fossil energy and combustion monitoring such as industrial combustors or reaction vessels, solid oxide fuel cells, and gas turbines. In these applications, even a small increase in operating efficiency realized via careful observation of in-process parameters and implementation of real-time process controls can result in dramatic savings across the energy industry, illustrating the necessity of pursuing such techniques. It is hoped that sensors of the type described here will allow for unprecedented measurement-access to processes which present challenging high-temperature and chemically reactive environments.