Paul Grems Duncan

Remote optical interrogation of embedded optical fiber sensors

A non-contact optical method has been developed for the remote and high-speed interrogation of optical fiber sensors embedded in a structure. The technique allows the use of passive fiber sensor requiring no local on-board electrical power or local electronics in the structure, thus simplifying the design and manufacturing of the structure, and allowing potential applications in low-cost structures where the addition of on-board power and electronics may be cost- prohibitive. For demonstration, multiple absolute extrinsic Fabry-Perot interferometric (AEFPI) strain sensor elements were embedded in a polymer matrix cross-ply laminate coupon. Coupling of broadband optical power into the embedded sensor elements over a distance of several tens of centimeters was achieved using a compact and lightweight broadband light source. Optical radiation received back from the sensors within the test specimen was optically detected and electronically processed to obtain the AEFPI strain sensor output signals using a computer software-based signal processing unit designed for this application. The ability of the opto-electronic receiver unit to both detect changes in strain dynamically was determined by quasi-satirically increasing the load on the specimen using a small loading fixture. The further ability of the system to monitor strain dynamically during rapid motion was demonstrated by moving the specimen with respect to the input and output optics. The limitations of the system due to the operation of the detection system are detailed.

EFPI sensor manufacturing and applications

The continuing development of the extrinsic Fabry-Perot interferometric sensor (EFPI) has led to a number of improvements to the original design. Manufacturing improvements have enabled the sensor to be employed in many diverse applications. This paper describes newly developed techniques used to manufacture the EFPI sensors and presents their use in advanced aerospace applications.

Multiplexing optical fiber-based pressure sensors for smart wings

A novel, multiplexed optical fiber differential-pressure transducer is described for the real-time pressure measurement of airflow in applications involving actuator- and SMA-controlled airfoils and multi-parameter skin friction measurements. The design of the pressure transducer is based upon extrinsic Fabry-Perot interferometry (EFPI) and uses a micromachined silicon diaphragm to modulate the sensing cavity. The pressure transducer was designed to operate from minus 10 to 10 psig and have a resolution of greater than 0.01 psi. Ten pressure transducers were spatially multiplexed and tested for smart wing applications. Results are also reported for an integrated skin friction balance/optical fiber pressure transducer tested in Virginia Techs Supersonic Tunnel (VTSST).

Thin-silica-diaphragm-based fiber optic acoustic sensors

In this sensor, we demonstrate the developing and testing of fiber optic sensors intended to detect acoustic waves. The sensor is based on a novel design housing a thin silica diaphragm and a single mode fiber in an extrinsic Fabry- Perot interferometric structure. The designed sensor is tested for different applications including the detection of the partial discharges inside a power transformer. The test results indicate that the designed sensor can detect acoustic signals with high sensitivity at frequency as high as 200 kHz.

Miniature high-frequency temperature-insensitive fiber optic pressure sensor for gas turbine engine applications

A newly developed fiber optic pressure sensor for gas turbine applications is described in this paper. The sensor is based on Self-Calibrated Interferometric/Intensity-Based fiber optic sensor technologies. In addition to the generic fiber sensor advantages, the new sensor was also shown to have all the distinct advantages of interferometric and intensity-based sensors while their disadvantages are significantly reduced. The sensor has a frequency response of approximately 100 kHz, and can be operate at temperatures up to 700 degrees C. The sensor was tested in simulated flow conditions similar to that found in a gas turbine engine. Excellent agreement was obtained in the measured pressure comparing the fiber-optic sensor to a conventional high frequency, semiconductor based pressure transducer.

Multifunctional fiber optic sensor for manufacturing of thermoset matrix composite materials

Despite the attractive mechanical properties of polymer matrix composites, which include high specific stiffness and strength, their use has been limited in many cost-sensitive applications due to high manufacturing costs. Since the processing of these materials is a major component of the cost of the finished product, the development of adaptive systems using feedback sensors for control of the composite cure process will accelerate the adoption of composites technology for diverse commercial and industrial applications. We present an embeddable fiber optic sensor for monitoring of the cure of thermoset resins by measuring the rheology of the polymer. By coupling a fiber optic strain sensor to an actuator, it is possible to realize a miniature dynamic mechanical analysis system. If the sensor is immersed in a curing thermoset resin, and a time-varying excitation is applied to the actuator, the sensor can be made to vibrate harmonically. By comparing the phase of the excitation to the phase of the resulting strain as detected by the strain sensor, it is possible to derive the loss tangent of the resin, which can be related to the degree of cure of the resin. After the resin hardens, the embedded sensor may be used as a conventional fiber optic strain gage to measure in-service strains.

OPTICAL FIBER SENSORS FOR MONITORING VISIBILITY

Accurate and reliable detection, discrimination, and quantitative measurement of visibility conditions will be crucial in the implementation of weather advisory schemes for Intelligent Transportation Systems. Increasing the amount of information about inclement weather to the motorist can greatly increase the levels of safety and mobility, reduce congestion, and enhance overall economic productivity. Typically, the number of visibility sensors that are deployed along the highway is limited due to their high-cost. Poor visibility conditions, however, are not uniform along the length of the highway, and it is therefore important that a larger number of low-cost and reliable sensors are deployed. Optical fiber sensors which possess unique advantages as compared to conventional electrical sensors may provide an interesting alternative to this problem.

Multiplexing optical-fiber-based pressure sensors for smart wings

A novel fiber optic differential pressure transducer and multiplexing system is described for real-time pressure measurements of airflow on an actuator- and SMA-controlled airfoil. The design of the pressure transducer is based upon extrinsic Fabry-Perot interferometric technology and incorporates a micromachined silicon diaphragm as the pressure sensitive element. The pressure transducer has a full scale operating range of -10 to 10 psig and a resolution of greater than 0.01 psi. Data is presented demonstrating the reproducible performance of the fiber optic sensor after repeated cycling and also at various temperatures. Finally, various multiplexing techniques and results are described.