Allen Parker is a systems engineer with expertise in the areas of fiber optics and data acquisition. He is currently part of the team that is developing and flight testing an innovative new fiber optic wing shape sensor system installed on the Ikhana unmanned aircraft system.
NASA Tech Briefs: You’ve been called a fiber optics pioneer by some of your peers and coworkers at Dryden. What first sparked your interest in fiber optics and inspired you to pursue a career in it?
Allen Parker: Well, first off I want to correct that. The quote [published in the NASA Dryden X-Press] does say that I am a “super genius in fiber optics,” but I am definitely not a genius, let alone a pioneer in the area of fiber optics. I am a systems engineer, and we were fortunate about 10 years ago to be made aware of some emerging new technology, technology based on fiber optics used as strain sensors. That sparked an interest in us. Dr. Lance Richards and I decided to travel back to NASA Langley, where this technology had originated, and meet with researchers that were involved in the development of this technology. We met with them for a couple of days, saw the potential, and decided to bring it back and apply it to what we do here at Dryden.
NTB: You’re currently working on a unique fiber optic wing shape sensor system that’s being tested on the Ikhana unmanned aerial vehicle. Please tell us about that project and what it’s designed to do.
Parker: The Ikhana aircraft (General Atomics Predator B) was a great opportunity for us to take this technology to the next logical step, flight test. That’s our vision here at Dryden — to fly what others only imagine. We have been, for years, advancing this technology in our lab, making it applicable for flight by increasing the performance as well as reducing the equipment size needed to implement the interrogation of these fibers. So, when Ikhana came along, we thought that it would be the perfect test bed for us to design a system around. This aircraft presented a great initial test platform with very manageable environmental specifications, adequate space, and power capabilities. We designed a system to actively measure, in real time, strain distribution and shape of the Ikhana’s 60-foot wingspan using this fiber optic sensing technology.
NTB: You’ve been working on developing the fiber optic sensing system that’s being tested, which consists of six 20-foot long fibers, each about the diameter of a human hair, attached to each wing. Please explain how the system works and who came up with that concept.
Parker: The concept was originally thought of by a researcher then at NASA Langley, Dr. Mark Froggatt. But Dryden saw the potential and decided that this is an area that we really needed to get involved with. Just imagine — hundreds of strain measurements using a hair sized fiber that’s 20 feet long, if only we could reduce the size and increase the overall system performance.
The sensor technology is based on the system’s ability to interrogate fiber Bragg gratings as they undergo wavelength shifts as a result of strain or temperature changes. The gratings are serially positioned on a single fiber, spaced every half-inch, up to about a 20-foot long-fiber. With this type of spatial resolution, and using multiple 20-foot fibers like what we have on the Ikhana aircraft, we’re able to measure strain and calculate shape at half-inch intervals on the Ikhana’s leading and trailing edge wings. The system that is currently installed on the aircraft is capable of interrogating four of the six 20-foot-long fibers simultaneously. That’s approximately 2,000 strain measurements that we’re making at a rate of about 24 Hz.
NTB: You also came up with the data processing algorithm for this system, which NASA is in the process of trying to patent. What would you say was the biggest technical challenge you faced in developing this system – the hardware or the software?
Parker: When we first came across the innovation, the processing that was involved to analyze the response signal from these fiber Bragg gratings was very processor intensive, performing time to frequency transformation. So, the initial limitation for us was computational hardware needed to implement the algorithm quickly, using commercially available CPUs. We have implemented the original Langley algorithm on multi-core processors as well as DSPs in an attempt to go beyond our 1-2 samples per second limitation. But it wasn’t until we thought of a new way of looking at the data that we were able to really make advances in the overall sample rates. This new algorithm essentially takes the response signal from the gratings and divides it into much smaller manageable segments. With the development of this new algorithm, as well as implementing it within an FPGA, we were able increase our sample rate 1-2 Hz to now 60Hz.
NTB: The current system can measure, monitor, and display the shape of an aircraft’s wing in flight, which is useful data for designers, but the hope is that this technology will someday provide the ability to alter a wing’s shape in flight, allowing it to adapt to changing conditions. Can you explain how this would work and what you think it will take to turn that concept into a reality?
Parker: I’m no aerodynamicist, so I can’t speak intelligently about how that would work in terms of wing morphing. But our ability to sense the shape of a wing would definitely go very far in the control aspect. In order to change or control the shape of a morphing wing to a new state, we must know what the current shape of that wing is. So this type of shape sensing is absolutely necessary. Although over the years, this technology has seen huge improvements, it still has a little ways to go before it would find itself in the feedback of a critical aircraft control loop.
NTB: Eventually, when active wing shape control systems do come to fruition, what would happen to a pilot’s ability to control the aircraft if the fiber optic sensors themselves were to get damaged or fail?
Parker: Well, one of the beauties of this technology – actually there are a couple – is the size of the fiber, about the thickness of a human hair. Because of its size and very little added weight, we can put redundant fibers on an aircraft wing in case one would fail. So redundancy is a big plus for fiber optics because of the weight savings that the technology offers. For severe damages, not only would the fiber optic sensors fail, but conventional sensors would fail as well.
NTB: How durable are these fibers? I mean, they’re only the width of a human hair, so just how strong are they?
Parker: Actually they’re fairly strong. If you consider trying to take a piece of glass, and stretching that glass along its length, it’s difficult to break. Now, if you can bend it into a tight radius, less than a half inch or so, it could break easily. When you put the fiber down on the surface of a specimen, whether it’s an aircraft wing or a panel, you encapsulate it with some type of epoxy. The epoxy offers some protection for the fiber, just like you would on conventional sensors like a strain gauge or a thermocouple.
NTB: So this system could one day be embedded in an aircraft wing, correct?
Parker: That is correct. We are actually doing research with UCLA on embedment techniques and understanding the measurement of an embedded optical sensor.
NTB: Can you envision any other potential applications for this fiber optic sensor technology you’ve developed outside of the aerospace industry?
Parker: Well, just off the top of my head, there are a couple of other industries that come to mind.
One would be in the medical industry. Since these fibers are so small, you can actually use them as a part of a catheter design. There’s an organization that is interested in making a probe that they could send down a person’s throat to monitor swallowing disorders.
We’ve also been approached by the wind-turbine industry about using our technology to improve the aerodynamic efficiencies of their turbines and help improve overall energy production.
Also the automotive industry has expressed an interest for automotive testing, and vehicle health monitoring. So the potential is there for other industries outside of the aerospace industry.
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