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Fiber Optic Sensors
October 6, 2011

Parker's Algorithm Shatters a Technology Barrier

The metallic panel has both conventional and fiber optic sensors. The white bundle of cables contains 100 conventional strain gages, the single yellow cable about 350.The metallic panel has both conventional and fiber optic sensors. The white bundle of cables contains 100 conventional strain gages, the single yellow cable about 350. Dryden aircraft have been used in validation of fiber optic sensors. Fiber optic sensors may also have applications in a number of different fields. (NASA Photo / Tony Landis) › View Larger Image Dryden researcher Allen Parker recently developed an algorithm that permits information from fiber optic sensors to move exponentially faster. In other words, information from fiber optic sensors can now be viewed in real time.

"Sitting at my workbench, a light came on," said Parker, who works from the NASA Advanced Technology Laboratory located at the Aerospace, Education, Research and Operations, or AERO Institute in Palmdale, Calif. "I saw the problem with a different perspective and, shortly afterward, submitted a New Technology Report, and it took off from there."

A key impediment to widespread use of fiber optic sensor technology was the speed at which information from the sensors travelled to the individual needing the information. With his new mathematical equation, or algorithm, that is no longer a problem.

As a result of the breakthrough, Parker has a patent pending for his algorithm, which is called Method for Reducing Rate of Fiber Bragg Grating Sensors. In addition, with removal of a key stumbling block that was holding the technology back, the commercialization possibilities are growing. Dryden's Innovative Partnerships Office recently announced that a licensing agreement is now in place with Texas-based company 4DSP to commercialize the technology, making it readily available for others to use (see related article).

To put Parker's fiber optic sensing development in perspective, the rate of information transfer from fiber optic sensors in the past was one sample every 30 seconds; Parker's algorithm increases that to 100 sweeps of the laser that reads the sensors per second.

Parker also has worked on miniaturization of fiber optic sensor systems. When he first saw a fiber optic sensing system – one developed at Langley Research Center, Hampton, Va. – it took an entire table to contain a system capable of transferring just onescan every 30 seconds.

"Wow, this is neat, but how realistic is it?" Parker said of his first look at a fiber optic sensing system.

Since seeing the Langley system, Parker has worked to reduce the size of the fiber optic sensing system by more than 75 percent. Parker, who was part of a team with William Ko, Anthony Piazza and Lance Richards, first instrumented a Dryden aircraft in 2008 to prove that the accuracy of the fiber optic sensing system was as good as traditional sensors. Flights on the Ikhana unmanned air system validated that point.

With the combination of smaller size and faster data transfer, the fiber optic sensing system is now ready to go and has been proven so through flights on both the Dryden Ikhana Predator B and AeroVironment's Global Observer.

As so often happens, breaking through one technological barrier has led to a new one, Parker said. Now, the limitation will be the capability of the laser. Parker has ideas for how to eventually resolve that problem, too, but for now the algorithm will be expanded; fiber optic systems that now can gather 100 sample per second as a result of this algorithm can be improved to obtain as many as 250 samples per second, he said.

Though aeronautics, space, medicine and drilling have been mentioned as some of the industries with an interest in fiber optic sensing system technology, Parker said there are no limits to how it can be used.

For example, Parker said he believes a day will come when aircraft are fabricated with fiber optics and have systems that tell maintainers exactly what is wrong, without extensive – and expensive – maintenance down periods.

"One direction is for it to become a large-scale system – instrument an entire large-scale aircraft with a single, relatively small system, putting fibers all over the surface of the vehicle to perform comprehensive vehicle health monitoring," he said. "Like a human nervous system, which has 'sensors' embedded throughout the body from the legs, arms, back and all areas, determines the state of the body then feeds that information to the brain – the same is true for this next-generation aircraft system."

Sensing is not limited to strain; other parameters such as temperature, pressure, shape and loads can be measured with a fiber optic sensing system.

For that reason, the oil and gas industries are interested in using fiber optics in specialized drill heads that can sense shape as well as temperature and pressure. A drill operator needs to know exactly how a drill head is positioned, which can be determined by knowing its shape. Temperature and pressure can also tell the operator about the health of the drill.

Closer to home, fiber optics will be added to the F/A-18 No. 853 for flight experiments that could have implications for aero and space vehicles, as well as for structures in space. Fiber optics can be used to take measurements on wing and other aerodynamic surfaces that could be fed into flight control computers for what researchers call a "fly-by-feel" system. The system would be able to compensate for conditions and would therefore use less fuel.

Another result of using fiber optic sensing systems as part of a control system is managing aircraft structural components anticipated to be made of lighter, more flexible materials, Parker explained.

The fiber optic sensing system on F/A-18 No. 853 will include shape as one of the parameters to be measured, fed back into the flight control system and used to control the shape of its wings.

"We hope to have the fiber optics sensing system on the aircraft and start making measurements by end of the year," Parker said.

Meanwhile, a fiber optic sensing system is in development for the Dryden G-III, for a new type of composite flap. The Air Force Research Laboratory wants NASA to design and build a fiber optic sensing system to monitor the strain distribution and shape of the new flap.

Also of interest is how a fiber optic sensing system could be used in assessing the nation's aging infrastructure. Fiber optics can be used on bridges to sense cracks or assess damages from natural disasters such as earthquakes, he said.

During the next several years, Parker envisions working with components such as lasers and optics to greatly reduce the size and cost of the next-generation system. Originally, researchers saw large-scale systems as being able to fit on a rack mount on an airplane. But Parker said building small, rugged systems with four to eight fibers for small, unmanned aerial systems has become a priority. Particularly in new and smaller craft, involving situations in which a vehicle is performing near its structural limits, a fiber optic sensing system could be critical, he added.

The capability of having thousands of sensors to measure strain, temperature or pressure also represents a paradigm shift. New ways of looking at information – and determining what is important – are becoming a new area of interest. An adaptive "smart sensor" is the answer, he said. The new fiber optic sensor systems will be developed with the capability of focusing on what the researcher wants, or where the action is, he added. In other words, researcher would not have to sort through large amounts of data during post analysis to extract important data features.

Regardless of what the next advancement will be in fiber optic sensing technologies, one common thread is that Allen Parker and Dryden researchers will be looking to lead it.

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