This paper describes the first successful fiber optic oxygen detection sensor systems developed for the Boeing Delta IV Launch Vehicle harsh environment of engine section. It illustrates a novel multi-point fiber optic microsensor (optrode) based on dynamic luminescence quenching that was developed for measuring oxygen leak detection for the space applications. The sensor optrodes employ the quenching by oxygen of the fluorescence from a ruthenium complex. These optrodes were fabricated using Ruthenium-based fluorescent indicator immobilized in a porous glass rod placed at the end of multimode fiber. The light from a blue LED is launched into the optrode via a fiber optic bundle and used as the excitation source. The optrode’s fluorescent emission intensity in the range of 0% to 10% oxygen is measured as a function of time. The measuring system is based on high reliability and low cost. The system consists of four units: 1) temperature compensated oxygen optrodes combined with an optical setup, 2) multipoint sensor communication fiber optic network cable, 3) digital/analogue optoelectronic signal processing unit with built-in micro controller for control of data acquisition and processing, and 4) a laptop computer for data display and storage. In testing, the sensor exhibited excellent response time and reversibility. To qualify the sensors, performed detail investigation for thermal, humidity, temperature, vibration and accelerate testing for life expectancy of harsh environmental of engine section. Extensive networking using MatLab were carried out for lab and actual field demonstrations.
A miniature fiber-optic chemical sensor system allowing for simultaneous detection of gas concentrations and physical
parameters is described, fabricated and tested. The design is focused on minimizing influence of the sensor onto the
system under test, therefore employing very thin and pliable fiber probes. Microfabrication of the sensor structure is
described and a suitable interrogation setup is introduced. Measurements of O2 and CO2 concentrations are presented and
discussed. Applications in continuous medical monitoring and necessary design and operating parameters are described.
This paper describes the 1st successful Plastic Optical Fiber (POF) cable and Glass Optical Fiber (GOF)
hydrogen detection sensor systems developed for the Boeing Evolved Expandable Lunch Vehicle (EELV)
Delta IV Launch Vehicle harsh environment of engine section. H2 sensors are necessary to monitor the
possible leak of rocket prior launch to avoid explosion, which can be highly dangerous. Due to harsh
environment of launch vehicle, we developed the first combination of 100 m POF and glass fiber H2
sensors. The hydrogen sensor consisted of optrodes distributed at multiple locations along a fiber optic
cable-based network. These hydrogen sensors were used on the Common Booster Core (CBC) of Delta
IV had to perform in temperatures between -18° C and +60° C. The hydrogen sensor sensitive chemistry
was fully reversible and had demonstrated a response to hydrogen gas in the range of 0% to 10% with a
resolution of 0.1 % and a response time of 5 seconds measured at a gas flow rate of 1 cc/mm. The optical
signature of the optrode in the visible spectrum varied proportionally to the local hydrogen gas
concentration. To qualify the POF and fiber optic cables, performed detail investigation for attenuation
loss, thermal, humidity, temperature, vibration and accelerate testing for life expectancy. Extensive
networking using LabView were carried out for lab and actual field demonstrations.
Lithium-ion batteries have been proven efficient as high power density and low self-discharge rate energy storage
systems, specifically in electrical drive vehicles. An important safety factor associated with these systems is the potential
hazardous release and outgassing of toxic chemical vapors such as hydrogen fluoride (HF) and hydrogen sulfides (H2S),
and relatively elevated levels of carbon dioxide (CO2). The release and accumulation of such gases emphasizes an in-line
monitoring need. Intelligent Optical Systems, Inc. (IOS) has identified a viable approach for the development of an
onboard optical sensor array that can be used to monitor battery outgassing. This paper discusses the potential of
developing a battery outgas sensing approach that will meet sensitivity and response time requirements.
Guided wave ultrasound is well suited for inspection of laminate composite structures. Compared to nearly flat or gently
curved composites, performing accurate NDT on sharply curved structures is more complex with standard ultrasound
test methodologies, such as pulse-echo methods. Ultrasound propagation in curved composite structures is investigated
for sharply curved geometries. Responses are predicted based on dispersion models. Experimental results are presented
on 0.25 inch thick curved carbon fiber reinforced plastic (CFRP) composite geometry of an aircraft structural component
and compared with predicted values.
Cryogenic leak detection is critical to space missions, particularly for avoiding launch delays. The real-time, multi-location,
early leak detection of oxygen and hydrogen down to ppm levels is extremely important for safety, reliability,
and economic reasons. One of the significant challenges in meeting these requirements has been the drift effect that is
caused by the exposure to extreme temperatures. This paper discusses the effect of the development of a sensor
supporting matrix to improve the overall behavior of oxygen and hydrogen optical sensors at cryogenic temperatures.
These achievements offer great advances in the fiber optic leak detection of cryogenic oxygen and hydrogen, specifically
for space applications. Emphasis on operational conditions such as -150 K and vacuum environments, in addition to
performance characteristics such as sensitivity (10 ppm) and response time (~ 3 sec), are addressed in this paper.
The U.S. military has a continued interest in the development of handheld, field-usable sensors and test kits for a variety
of diagnostic applications, such as traumatic brain injury (TBI) and infectious diseases. Field-use presents unique
challenges for biosensor design, both for the readout unit and for the biological assay platform. We have developed
robust biosensor devices that offer ultra-high sensitivity and also meet field-use needs. The systems under development
include a multiplexed quantitative lateral flow test strip for TBI diagnostics, a field test kit for the diagnosis of pathogens
endemic to the Middle East, and a microfluidic assay platform with a label-free reader for performing complex
biological automated assays in the field.
Fiber optic sensors have matured to allow the detection of chemical and physical parameters at multiple points, or in a
distributed fashion, along the length of a single optical fiber strand. The electro-optic readout unit connected to the fiber
needs to be tailored to the specific sensor application to balance the requirements for spatial and frequency resolution,
interrogation intervals, readout time, noise suppression, system size and cost, and other parameters. This paper will
discuss different fiber optic sensor configurations and suitable readout strategies to meet the requirements of the sensing
application.
Non-destructive testing of critical structural components is time consuming, while necessary for maintaining safe
operation. Large aerospace structures, such as the vertical stabilizers of aircraft undergo inspection at regular intervals
for damage diagnostics. However, conventional techniques for damage detection and identification before repair can be
scheduled are conducted off-line and therefore can take weeks. The use of guided ultrasound waves is being investigated
to expedite damage detection in composites. We measure the frequency dependent loss of ultrasonic guided waves for a
structure comprising a boron-nitride composite skin sandwiching an aluminum honeycomb. A wide range of ultrasound
frequencies propagate as measured using PZTs, with the lowest attenuation observed about 200-250 kHz. These
measurements are confirmed using optical fiber Bragg grating arrays used as ultrasound transducers.
A system for interrogation of high-frequency events with an FBG array in the presence of large quasi-static fluctuations
has been developed at Intelligent Optical Systems (IOS). The system allows highly sensitive detection of periodic or
transient events up to the MHz range while automatically compensating for slow changes in the FBG center frequency
using a closed loop tracking system. Both the high frequency signal and the low frequency parts of the sensor spectrum
are available for further processing. The system components, setup, and applications are presented and discussed.
This paper describes the successful test of a multi-point fiber optic oxygen sensor system during the static
firing of an Evolved Expandable Launch Vehicle (EELV)/Delta IV common booster core (CBC) rocket
engine at NASA's Stennis Flight Center. The system consisted of microsensors (optrodes) using an
oxygen gas sensitive indicator incorporated onto an optically transparent porous substrate. The modular
optoelectronics and multiplexing network system was designed and assembled utilizing a multi-channel
opto-electronic sensor readout unit that monitored the oxygen and temperature response of the individual
optrodes in real-time and communicated this information via a serial communication port to a remote
laptop computer. The sensor packaging for oxygen consisted of two optrodes - one doped with an
indicator sensitive to oxygen, and the other doped with an indicator sensitive to temperature. The multichannel
oxygen sensor system is fully reversible. It has demonstrated a dynamic response to oxygen gas
in the range of 0% to 100% with 0.1% resolution and a response time of ≤10 seconds. The sensor
package was attached to a custom fiber optic ribbon cable, which was then connected to a fiber optic
trunk communications cable (standard telecommunications-grade fiber) that connected to the
optoelectronics module. Each board in the expandable module included light sources, photo-detectors,
and associated electronics required for detecting oxygen and temperature. The paper illustrates the sensor
design and performance data under field deployment conditions.
Current underwater protection systems are complex expensive devices consisting of multiple electronic sensing
elements. The detection and identification of divers and small submerged watercraft requires very high image
resolution. The high price of an array of conventional piezoelectric transducers and associated electronic components
makes this solution feasible for localized implementations, but the protection of large stretches of coastline requires a
different approach. We present a novel multichannel sonar design that augments current active sonar transducers with
a passive fiber-optic multichannel acoustic emission sensing array. The system provides continuous monitoring of the
acoustic wave reflections emitted by a single projector, yielding information about the size and shape of approaching
objects. A novel fiber hydrophone enclosure is utilized to dramatically enhance the sensor response to the sonar
frequency, while suppressing out-of-band sound sources and noise.
The ability of a fiber hydrophone to respond to acoustic emissions is based on established fiber Bragg grating sensing
techniques. In this approach, the energy of an acoustic wave is converted into the modulation of the in-fiber optical
transducer's optical properties. The obtained results demonstrate significant response of the designed fiber optic
hydrophone to the incident acoustic wave over the frequency domain from 1-80 kHz. Our approach allows selective
tuning of the sensor to a particular acoustic frequency, as well as potential extension of the spectral response to 300-
400kHz.2
This paper describes the successful test of a multi-point fiber optic hydrogen sensor system during the static firing of an Evolved Expandable Launch Vehicle (EELV)/Delta IV common booster core (CBC) rocket engine at NASA's Stennis Flight Center. The system consisted of microsensors (optrodes) using a hydrogen gas sensitive indicator incorporated onto an optically transparent porous substrate. The modular optoelectronics and multiplexing network system was designed and assembled utilizing a multi-channel opto-electronic sensor readout unit that monitored the hydrogen and temperature response of the individual optrodes in real-time and communicated this information via a serial communication port to a remote laptop computer. The sensor packaging for hydrogen consisted of two optrodes -- one doped with an indicator sensitive to hydrogen, and the other doped with an indicator sensitive to temperature. The multi-channel hydrogen sensor system is fully reversible. It has demonstrated a dynamic response to hydrogen gas in the range of 0% to 4% with 0.1% resolution and a response time of less than or equal to 15 seconds. The sensor package was attached to a custom fiber optic ribbon cable, which was then connected to a fiber optic trunk communications cable (standard telecommunications-grade fiber) that connected to the optoelectronics module. Each board in the expandable module included light sources, photo-detectors, and associated electronics required for detecting hydrogen and temperature. The presentation would discuss the sensor design and performance data under field deployment conditions.
Continuous tone gray scale deep UV photomask technology offers new cost effective opportunities for the mass scale production of MEMS structures, diffractive optical elements (DOEs), computer generated holograms (CGHs), and kinoform optics. A new technology for the low cost fabrication of continuous tone gray scale photomasks for deep UV photolithography applications has been demonstrated. This technology is based on the use of a photosensitive spin-on-glass (SOG) thin film deposited onto a UV transparent substrate such as fused silica. Light exposure, from either a lithography setup or a laser pattern generator, onto the photosensitive SOG film induces a color change from clear (UV transparent) to dark (UV absorbing). The amount of photo induced color attenuation on the film is directly proportional to the energy exposure of the light, hence allowing the formation of fully continuous tone patterns. Once exposed the image pattern, with a resolution of 0.1 micrometers, is permanently fixed by heat treatment without the need of an etching step.
A technology for the low cost production of continuous tone gray scale photomasks for deep UV photolithography applications has been demonstrated. This technology is based on the use of a photosensitive spin-on-glass (SOG) thin film deposited onto a UV transparent substrate such as quartz. Different light exposure energies, from either a lithography setup or a laser pattern generator, onto the photosensitive SOG film changes the UV absorption spectrum at both H and I mercury emission lines. The amount of photo induced attenuation on the film is directly proportional to light exposure energy, hence allowing the formation of fully continuous tone patterns. Once the image pattern is photo-generated with a resolution of 0.1 to 1 micrometer, it is permanently fixed by a thermal treatment step without the need of an etching step. This new continuous tone deep UV photomask technology offers new cost effective opportunities for the production of micro-electro-mechanical systems (MEMS) structures, diffractive optical elements (DOEs), computer generated holograms (CGHs), and kinoform optics.
This paper describes progress in the development of a multi-point fiber optic micro sensor (optrode) based on a hydrogen gas sensitive chemistry immobilized in an optically transparent porous substrate. The hydrogen sensitive chemistry is fully reversible and has demonstrated a response to hydrogen gas in the range of 0% to 10% with a resolution of 0. 1 % and a response time of ?5 seconds measured at a gas flow rate of 1 cc/mm. The optical signature of the optrode in the visible spectrum varies proportionally to the local hydrogen gas concentration. The multi-point hydrogen sensing system uses temperature compensated hydrogen optrodes mounted at the tip of optical fibers. The hydrogen optrodes are distributed at multiple locations along a fiber optic cable-based network. A multi-channel optoelectronic sensor readout unit monitors the hydrogen and temperature response of the individual optrodes in real time and communicates this information via a serial communication port to a remote laptop computer.
This paper describes a novel multi-point fiber optic microsensor (optrode) based on dynamic luminescence quenching that is being developed for measuring oxygen leak detection for space applications. The sensor optrodes employ the quenching by oxygen of the fluorescence from a ruthenium complex. These optrodes were fabricated using Ruthenium-based fluorescent indicator immobilized in a porous glass rod placed at the end of multimode fiber. The light from a blue LED is launched into the optrode via a fiber optic bundle and used as the excitation source. The optrode's fluorescent emission intensity in the range of 0% to 10% oxygen is measured as a function of time. The measuring system is based on high reliability and low cost. The system consists of four units: 1) temperature compensated oxygen optrodes combined with a optical setup, 2) multipoint sensor communication fiber optic network cable, 3) digital/analogue optoelectronic signal processing unit with built-in micro controller for control of data acquisition and processing, and 4) a laptop computer for data display and storage. In testing, the sensor exhibited excellent response time and reversibility.
All immunosensors currently described in literature are irreversible. Intelligent Optical Systems, Inc. has developed a revolutionary method for producing reversible immunosensors. In this method, the antibody and a labeled analog (structurally and functionally similar to the antigen) are coimmobilized on the sensor surface. Under equilibrium conditions, the labeled analog interacts with immobilized antibody to produce a sensor response. However, in the presence of antigen (analyte), the equilibrium is disturbed as the analyte competes for the binding sites of the immobilized antibody. This produces a measurable sensor response. The equilibrium is shifted back by washing the analyte away with a wash buffer, and the bound analog interacts with the immobilized antibody. Polarization and intensity based measurements are used to design the analog. Photoinduced electron transfer is used to create fluorescent analogs that provide enhancements in fluorescence intensity that can be measured. This principle can be extended to the detection of bacteria.
A novel approach for the fabrication of single-mode channel waveguides combined with focusing grating couplers by replication into polymer substrates is proposed and experimentally demonstrated. The concept is based on fabricating a master structure containing tall ridge patterns (about 3 micrometers high) combined with shallow, focusing grating structures (about 10 nm depth). By a micromolding technique using nickel shims, this pattern is hot embossed into a polymer substrate which is then full-area coated with a high-index dielectric waveguiding film. The focusing grating coupler is directly connected to the channel guide via a width-tapered waveguide section. An incident collimated beam can thus be coupled without the need for additional optics to the stripe waveguide formed by the film deposited on top of the ridge pattern. Results of experiments on stripe waveguides in quartz, focusing grating couplers in polycarbonate and combined channel waveguide and focusing structures in polycarbonate are presented and discussed. The feasibilty of the novel concept has been demonstrated by coupling a collimated free-space laser beam into a ridge waveguide on a replicated sample. The technology should find applications in integrated optical sensors and other low-cost integrated optical devices.
A miniature integrated optical refractometer chip based on grating coupling into a gradient effective index waveguide has been demonstrated. The gradient of the effective index resulted from shallow gradients of both the thickness and refractive index of a TiO2 waveguiding film deposited on a structured fused silica substrate. A method suitable for determining these gradients and data for the wavelengths of 633 nm and 785 nm is presented. Experiments have been performed where the test liquid was used as the cover medium of the waveguide, influencing the position of a laterally confined waveguide mode which represents a convenient on-chip measuring variable. Refractive indices determined by the chip are compared with those obtained by a commercial refractometer. The experimental results show a refractive index resolution of about 2 X 10-4 for this chip.
Integrated optical transducers with on-chip measuring variables are shown to be suitable for realizing complete miniature sensor modules. Theoretical expressions are derived and discussed that can readily be used for the design of sensors based on converting the value of a measurand into the position of an on-chip integrated optical light pointer. The emphasis is on configurations based on tapered waveguides and chirped grating couplers. The viability of this approach is demonstrated by reporting first experimental results for a novel miniature refractometer chip.
Design considerations and experimental results are presented for the fabrication and characterization of grating couplers in gradient effective index waveguides used for realizing miniature integrated optical sensor modules. Hard dielectric substrates such as glass and fused silica have been structured by photolithographic techniques, while hot embossing has been used for the grating fabrication in plastic substrates. The gradient effective index waveguides were produced by shadow mask evaporation techniques in one single deposition step in a rotating substrate holder arrangement. Optical diffraction measurements, atomic force microscopy, and a newly developed method based on performing spatially resolved grating coupler resonance angle measurements are shown to be valuable tools for the characterization of the waveguides and the grating couplers. The experimental results indicate that the deposition of high-index waveguiding films such as Ta2O5 and TiO2 on previously structured substrates is a viable technique for the cost-effective fabrication of integrated optical sensor chips.
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