Pressure measurements at various locations of a gas turbine engine are highly desirable to improve the operational performance and reliability. However, measurement of dynamic pressure (1psi (6.9kPa) variation superimposed on the static bias) in the operating environment of the engine, where temperatures might exceed 600°C and pressures might exceed 100psi (690kPa), is a great challenge to currently available sensors. To meet these requirements, a novel type of fiber optic engine pressure sensor has been developed. This pressure sensor functions as a diaphragm-based extrinsic Fabry-Perot interferometric (EFPI) sensor. The structure of the sensor head, composed entirely of fused silica, allows a much higher operating temperature to be achieved in conjunction with a low temperature dependence. The sensor head and the fiber tail have been packaged in a metal fitting connected to a piece of metal extension tubing, which improves the mechanical strength of the sensor and facilitates easy sensor installation. The sensor exhibited very good performance in an engine field test, demonstrating not only that the sensors' package is robust enough for engine operation, but also that its performance is consistent with that of a commercial Kulite sensor.

In this paper, we present a miniature fiber optic pressure sensor. The sensor is extrinsic Fabry-Perot interferometer (EFPI) based with its FP cavity directly fabricated on the tip of the fiber by fusion splicing and chemical etching. The processes are simple, with no other materials but silica fibers involved. The sensor has the same dimension as the fiber itself, only 125μm in diameter. The length of the FP cavity and the interference pattern will change in response to ambient pressure variation. The signal is demodulated by tracing the spectrum shift. Sensitivity can be adjusted for different applications with low or high pressure range. Prototype sensors were fabricated and tested for static response. Dynamic measurements were performed in a turbine engine. Theoretical and experimental analysis of the sensor response are also presented.

Sapphire (single crystal alumina) has superior optical and mechanical properties. With a very high melting point of about 2050°C, sapphire fiber is an excellent candidate in optical fiber sensing area for high-temperature measurements. This paper presents a new type of sapphire-fiber-based extrinsic Fabry-Perot interferometric (EFPI) temperature sensor. The spectral interference pattern is generated by a sapphire diaphragm placed in front of the sapphire fiber. The sensing element is interrogated by a white-light source. Temperature is demodulated from the spectral change of interference pattern. Prototype sensor is tested at high temperature up to 1545°C. Both theoretical and experimental analysis are presented. Preliminary data shows the sensor is very promising for measuring ultra-high temperature.

This paper describes the effort in developing a sapphire temperature prototype sensor for coal gasifier applications. The sensor is tested in laboratory to 1600 degree C and demonstrated 0.47% accuracy with respect to full measurement range. The efforts on sensor prototype development ranging from sensor probe packaging at each level, sensor electronics, LED modulation to remote data access are addressed.

This paper describes two systems that can monitor up to 64 fiber Bragg grating (FBG) strain gauges simultaneously and their use in structural health monitoring applications. One system directly tracks wavelength shifts and provides ~0.3 me sensitivity with data rates to 360 Hz. The second system uses an unbalanced Mach-Zehnder interferometer to convert wavelength to phase. It has a noise floor of ~5 ne/Hz1/2 and data rates to 10 kHz. The wavelength-based system was used in field tests on an all composite hull surface effects ship in the North Sea and on an Interstate highway bridge in New Mexico. The interferometric system has been used to demonstrate enhanced damage detection sensitivity in a series of laboratory experiments that rely on a novel data analysis approach based in nonlinear dynamics and state space analysis. The sensitivity of three of these novel damage detection methods is described.

In this paper, we present a novel point-wise laser writing method that utilizes a focused ultraviolet (UV) laser beam and metallic masks to write local Fresnel reflectors and intrinsic Fabry-Perot interferometric (IFPI) sensors in photosensitive fibers. These UV-induced IFPI sensors have features of low reflectance and low power loss and have the potential to be densely multiplexed. We also present a sweeping laser based measurement system that measures the interference spectra and estimates the optical path distances (OPD) of IFPI sensors. We also demonstrated IFPI sensors for temperature, strain and pressure measurement. Laboratory test results show that these UV-induced IFPI sensors can have a resolution of 0.1°C for temperature measurement and 0.5 micro-strain for strain measurement, and can be used in a temperature environment as high as 600°C.

Radioactive material of high activity levels has to be handled in a nuclear medicine environment. Until now most of these activities are done manually or by rudimentally automated processes. To increase radiation safety and process quality, smart automation strategies for these processes have to be developed. Especially long-term processes with radioactive materials have to be automated in early stages of development. This leads to a certain flexibility regarding requirements demanding an adjustable automation concept. The application of radiation hardened sensors is expensive but even these sensors will be destroyed by radiation effects. To allow therefore standard sensors to be used in radioactive environments, different strategies have been tested: In general, the sensors must be applied in a way to allow an easy access to sensors for replacement purposes. But this approach might not be sophisticated. An additional solution is the reduction of exposure of sensitive parts such as electronics. This means dividing the sensor in a measuring part which is placed in the radioactive environment and in a sensitive, shielded control part as it is realized by fibre optic sensors. The implementation of these approaches is demonstrated in sensor applications for radium handling systems e. g. contactless control of the needle clearance of a dispensing system via a fibre optic sensor. Further scenarios for sensor integration problems are presented in this paper.

Semiconductor nano-particles, or quantum dots, with their relatively high quantum yields, narrow luminescence spectrum, outstanding photostability and the ability to tune their optical properties, are ideal for biological tagging applications and a very powerful tool for chemical sensors. In this paper an overview of this rapidly expanding area of research is presented. Additionally, some results are shown, in the framework of optical oxygen sensors, which establish quantum dots as suitable temperature and intensity references for application in luminescence based chemical sensors.

A low cost, low complexity fiber optic humidity sensor is very desirable because of the various advantages fiber optic sensors have over conventional electrical sensors. In this paper a simple, low cost plastic optical fiber (POF) sensor based on cobalt chloride (CoCl2) and gelatin coating on the curved sensing point with a humidity sensing range from 60% to 95%RH is presented. An investigation into the effect of bending radii of the fiber at the sensing point as well as fiber core diameter on sensitivity of the humidity sensor is conducted to find the best way to improve sensing performance. The sensing mechanism of the POF humidity sensor is the attenuation of the evanescent wave at the bent portion of the fiber by absorption due to CoCl₂. The sensor has a sensing range from 60%RH to 95%RH. The hysteresis error is negligible and a resolution of 0.01%RH is achieved. The repeatability error can be as low as 1.1% for the whole sensing range. Investigation of the effect of fiber diameter shows that the sensitivity of the sensor improves with larger fiber diameters. The sensitivity of the sensor increases when the sensing portion of the fiber is bent to a small radius.

Pavement life span is often affected by the amount of voids in the base and subgrade soils, especially moisture content in pavement. Most available moisture sensors are based on the capacitive sensing using planar blades. Since the planar sensor blades are fabricated on the same surface to reduce the overall size of the sensor, such structure cannot provide very high accuracy for moisture content measurement. As a consequence, a typical capacitive moisture sensor has an error in the range of 30%. A more accurate measurement is based on the time domain refelctometer (TDR) measurement. However, typical TDR system is fairly expensive equipment, very large in size, and difficult to operate, the moisture content measurement is limited. In this paper, a novel microstrip transmission line based moisture sensor is presented. This sensor uses the phase shift measurement of RF signal going through a transmission line buried in the soil to be measured. Since the amplitude of the transmission measurement is a strong function of the conductivity (loss of the media) and the imaginary part of dielectric constant, and the phase is mainly a strong function of the real part of the dielectric constant, measuring phase shift in transmission mode can directly obtain the soil moisture information. This sensor was designed and implemented. Sensor networking was devised. Both lab and field data show that this sensor is sensitive and accurate.

It is possible to dramatically improve the performance, reliability, and maintainability of vehicles and other similarly complex equipment if improved sensing and diagnostics systems are available. Each year military and commercial maintenance personnel unnecessarily replace, at scheduled intervals, significant amounts of lubricant fluids in vehicles, weapon systems, and supporting equipment. Personnel draw samples of fluids and send them to test labs for analysis to determine if replacement is necessary. Systematic use of either on-board (embedded) lubricant quality analysis capabilities will save millions of dollars each year in avoided fluid changes, saved labor, prevented damage to mechanical components while providing associated environmental benefits. This paper discusses the design, the manufacturing, and the evaluation of robust optical sensors designed to monitor the condition of industrial fluids. The sensors reported are manufactured from bulk fused silica substrates. They incorporate three-dimensional micro fluidic circuitry side-by-side with three-dimensional wave guided optical networks. The manufacturing of the optical waveguides are completed using a direct-write process based on the use of femtosecond laser pulses to locally alter the structure of the glass substrate at the nano-level. The microfluidic circuitry is produced using the same femtosecond laser based process, followed by an anisotropic wet chemical etching step. Data will be presented regarding the use of these sensors to monitor the quality of engine oil and possibly some other vehicle lubricants such as hydraulic oil.

The use of LPG embedded in carbon-fiber composite laminates (ELPG), in a 4-3 configuration, for bending measurement has been demonstrated. With increased bending curvatures on the 4 layers side, the coupling strength of the cladding mode decreases while the resonance wavelength remains relatively constant. A reduction in coupling strength leads to a reduction of the resonance amplitude depth. From the bending test covering the range of curvatures from 0m^-1 to 2m^-1, the ELPG yields a sensitivity of 5.065dB/m^-1 and a repeatability of 98.1%. In another investigation, the ELPG ability to determine direction of bend has also been demonstrated by applying bending at the 3 layers side of the laminate. Despite having a short curvature range between 0m^-1 and ~0.626m^-1, the test demonstrates an increase of the cladding mode coupling strength with an increase in bending curvature, thus showing the ELPG ability to differentiate bending directions. By exploiting the unique characteristics of ELPG, two ELPGs can be exploited for 2-axis measurement of structures. Hence the overall cost and complexity of the bending sensor system can be greatly reduced.

For an embedded LPG bending sensor, in which the its resonance coupling strength changes with bending curvature, cross-talk issues between temperature and bending curvature arises if it is to be deployed in non-controlled environments. A 2 x 2 matrix method was thus employed for simultaneous measurement of bending curvature and temperature for the embedded LPG bending sensor. The matrix is made up of bending and temperature coefficients from 2 different fiber-types LPG; one is H2-loaded and the other is Bo/Ge co-doped. To find out the percentage error, a random test has to be carried out and the matrix was deployed for calculation. From the test results, the percentage error achieved for curvature measurement yields less than 6%. For temperature measurement, the percentage error fluctuates between 1.56% and 5.4%. The use of simultaneous measurement of both bending curvature and temperature enables researchers and engineers to measure bending of structures more accurately.

High resolution tunable optical filters are important in dense wavelength division multiplexing (DWDM) applications as channel spacing in optical communications systems can be as low as 0.4nm. The bandwidth of the filter must be narrow, to prevent filtering neighbouring channels. In this paper, a simple, low cost technique for the tuning of the Bragg wavelength of the FBG filter with high resolution and good repeatability is demonstrated. A FBG was embedded in a triangular carbon fiber composite package and aluminium plates were used to clamp the wider end of the package, leaving the thinner end free, like a cantilever beam. A micrometer was placed under the thinner end of the package and the vertical displacement of the micrometer will bend the carbon composite. This bending will produce compression and tension forces on the FBG depending on which side of the package is used, which will result in a shift of the Bragg wavelength. The total tuning range of the FBG filter is 2nm with a resolution of 1pm. The repeatability error was found to be 0.4% over the whole tuning range. The 3dB bandwidth of the reflected spectra from the FBG is 0.235nm, much less than channel spacing of 0.4nm.

A novel Intrinsic Fabry-Perot fiber-optic sensor is presented in this paper. The sensors were made through two simple steps: wet chemical etch and fusion splice. Micro air-gaps were generated inside the fibers and functioned as reflective mirrors. This procedure not only provides a simple and cost effective technology for fabricating intrinsic Fabry-Perot Interferometric (IFPI) fiber sensors, but also provides two possible IFPI structures. Both of the fiber cavity between the air-gaps or the air-gap and cleaved fiber end can be used as sensing elements. With these two structures, this sensor can be used to measure the temperature, strain, pressure, refractive index of chemicals and the thin film thickness by itself. Multi-point measurements can also be achieved by multiplexing. Furthermore, it also can be multiplexed with other sensors such as Long Period Gratings (LPG) to provide compensations for other perturbation sensing. Theoretical and experimental studies of two sensor structures are described. Experimental results show that high resolution and high sensitivity can be obtained with appropriate signal processing.

We report the design and development of a novel optical fiber Bragg grating based displacement sensor. A fiber Bragg grating is glued at a slant orientation onto the lateral side of a specially designed cantilever beam. It is found that the bandwidth of the FBG-based sensor changes linearly with the variation of displacement at the free end of the beam due to the displacement-induced strain gradient. Displacement sensing is realized by measuring the reflected optical power of the signal from the grating with a photodetector. A linear response of 37.9 mV/mm was obtained within a displacement range of 9.0 mm. This sensor is also cost effective due to the use of a simple demodulation method and is inherently temperature-insensitive; eliminating the need for temperature compensation.

The optics industry widely uses silcones for various fiber optic cable potting applications and light emitting diode protection. Optics manufacturers know traditional silicone elastomers, gels, thixotropic gels, and fluids not only perform extremely well in high temperature applications, but also offer refractive index matching so that silicones can transmit light with admirable efficiency. However, because environmental conditions may affect a material's performance over time, one must also consider the conditions the device operates in to ensure long-term reliability. External environments may include exposure to a combination of UV light and temperature, while other environments may expose devices to hydrocarbon based fuels. This paper will delve into the chemistry of silicones and functional groups that lend themselves to properties such as temperature, fuel, and radiation resistance to show shy silicone is the material of choice for optic applications under normally harmful forms of exposure. Data will be presented to examine silicone's performance in these environment.

Low-cost, reliable, miniaturized gas sensors capable of fast, accurate, and in-situ monitoring of gas compositions in harsh environment are essential in developing high-efficiency, clean energy technologies. These sensors permit intelligent process control and optimization of power plant operations, which improves the energy efficiency and system reliability, reduces emissions, and minimizes the maintenance cost. In the past few decades, significant progress has been made in developing physical sensors for measuring various physical quantities under high temperature and high pressure conditions. However, currently available gas chemical sensors cannot withstand the hostile environment found in fossil fuel energy systems. In this paper, we present our exploratory research on nanomaterial enabled fiber optic gas sensors for in-situ chemical monitoring under high temperatures.