Thomas A. Wavering

Interferometric optical fiber microcantilever beam biosensor

With the proliferation of biological weapons, the outbreak of food poisoning occurrences, and the spread of antibiotic resistant strains of pathogenic bacteria, the demand has arisen for portable systems capable of rapid, specific, and quantitative target detection. The ability to detect minute quantities of targets will provide the means to quickly assess a health hazardous situation so that the appropriate response can be orchestrated. Conventional test results generally require hours or even several days to be reported, and there is no change for real-time feedback. An interferometric optical fiber microcantilever beam biosensor has successfully demonstrated real time detection of target molecules. The microcantilever biosensor effectively combines advanced technology from silicon micromachining, optical fiber sensor, and biochemistry to create a novel detection device. This approach utilizes affinity coatings on micromachiend cantilever beams to attract target molecules. The presence of the target molecule causes bending in the cantilever beam, which is monitored using an optical displacement system. Dose-response trials have shown measured responses at nanogram/ml concentrations of target molecules. Sensitivity is expected to extend from the nanogram to the picogram range of total captured mass as the microcantilever sensors are optimized.

High-temperature optical fiber sensors for characterization of advanced composite aerospace materials

Optical fiber sensors have numerous advantages over conventional sensing technologies. One such advantage is that optical fiber sensors can operate in high temperature environments. While most conventional electrical-based sensors do not operate reliably over 300 degrees C, fused silica based optical fiber sensors can survive up to 900 degrees C, and sapphire based optical fiber sensors can survive up to 2000 degrees C. Using both fused silica and sapphire technologies, we present result for high temperature strain, pressure, and temperature sensors using Extrinsic Fabry-Perot INterferometric-based and Bragg grating sensors. High temperature strain and temperature sensors were used to conduct fatigue testing of composite coupons at 600 degrees C. The results from these specific high temperature applications are presented along with future applications and directions for these sensors.

Fiber optic affinity ligand sensor for quantification of petroleum and bioremediation

A novel system incorporating optical fiber long-period grating (LPG)-based sensors for rapid detection of biological targets is presented to address the current need for highly responsive, inexpensive, instrumentation for in-situ subsurface bioremediation technologies. With the appropriate configuration, the LPG sensor is able to measure key environmental parameters. The sensor allows for highly sensitive, real-time, refractive index measurements and by applying affinity coatings to the fiber surface, specific binding of molecules can be accomplished using swellable polymers or ligand-based affinity coatings. Advantages of the sensors have are that they are highly responsive, low profile, and can be serially multiplexed within a single-ended probe-like arrangement. This arrangement can be utilized either locally for site characterization or as a distributed sensor to map contaminant levels at multiple depths over a large area. The performance advantages make optical fiber sensors ideal for detection of environmental targets in drinking water, groundwater, soil, and other complex samples. This paper presents recent long-period grating-based sensor results that demonstrate the potential for bioremediation as well as a variety of other chemical and biological sensing applications.

Development of fiber optic sensors for advanced aircraft testing and control

Optical fiber sensors, because of the small size, low weight, extremely high information carrying capability, immunity to electromagnetic interference, and large operational temperature range, provide numerous advantages over conventional electrically based sensors. This paper presents preliminary results from optical fiber sensor design for monitoring acceleration on aircraft. Flight testing of the final accelerometer design will be conducted on the F-18 Systems Research Aircraft at NASA Dryden Flight Research Center in Edwards, CA.

NDE characterization of advanced composite materials with high temperature optical fiber sensors

Optical fiber sensor have numerous advantages over conventional sensing technologies. One exciting capability of optical fiber sensor is their ability to operate in high temperature environments. While most conventional strain, pressure, etc. sensors do not operate reliably over 300 degrees C, fused silica based optical fiber sensor can survive up to 900 degrees C. High temperature materials such as sapphire and silicon carbide can be used to construct sensors that can survive up to 2000 degrees C. A suite of high temperature strain, pressure, and temperature sensor are being developed using the Extrinsic Fabry-Perot Interferometer technology for NDE characterization of advanced composite materials. These sensors have been demonstrated in several applications. High temperature strain and temperature sensors were used to conduct fatigue testing of composite compounds at 600 degrees C. High temperature pressure senors are being developed as microphones for high temperature acoustic testing. The result from these specific high temperature applications are presented along with future applications and directions for these sensors.

Installation and testing of high-temperature optical fiber sensors

We report test results using optical fiber sensor to measure dynamic strain and temperature on ceramic-matrix composite (CMC) specimens at temperatures up to 600 degrees C. For strain sensing we are employing extrinsic Fabry-Perot interferometric strain gages fabricated with gold-coated optical fibers and attached to the CMC specimens using high- temperature ceramic adhesive. For temperature measurements, specially fabricated Bragg and long-period grating sensors are being employed.

Optical fiber interconnected MEMS sensors and actuators

Microelectromechanical systems or MEMS are miniature devices that have several advantages over conventional sensing and actuating technology. MEMS devices benefit form well developed integrated circuit production methods which ensure high volume, high yield processes that create low-cost sensors and actuators. OPtical fiber interconnected MEMS will provide new functionality in MEMS devices such as multiplexed operation for distributed sensing applications. This paper presents approaches in optical fiber to MEMS interfacing and some preliminary results.

Manufacturing and applications of optical fiber sensors and systems

Optical fiber sensors, because of their small size, low weight, extremely high information carrying capability, immunity to electromagnetic interference, and large operational temperature range, provide numerous advantages over conventional electrically based sensors. Fiber-based sensors have found numerous applications in industry for process control, and more recently for monitoring the health of advanced civil structures. This paper presents preliminary results from optical fiber sensor designs for monitoring acceleration and magnetic field.