Researchers at NASA's Armstrong Flight Research Center (AFRC) have been developing a fiber optic sensing system (FOSS) that represents a major breakthrough in operational monitoring of myriad structures. FOSS consists of eight 40-foot optical fibers, each containing 2,000 fiber Bragg grating (FBG) sensors along its entire length. These fibers are attached to the surface of, or even embedded within a structure. As the structure experiences stress or pressure, the FBG sensors respond to the strain. FOSS uses this response to calculate a variety of critical parameters, including strain, shape deformation, temperature, liquid level, strength, and operational loads.
AFRC researchers’ newest development for FOSS takes this sensing capability a step further, enabling an unprecedented level of speed and detail. This latest development not only provides high spatial resolution of strain, temperature, deformation, and loads, but also simultaneously captures dynamic structural features at strategic locations along the fiber.
Specifically, this technology combines optical frequency domain reflectometry (OFDR) for high spatial resolution with wavelength division multiplexing (WDM) for high acquisition speed in a single fiber. By combining the two types of technologies in a single fiber, FOSS can now process thousands of high-resolution FBG sensors at 100 Hz as well as up to 35 sensors at 5,000 Hz strategically placed along the sensing fiber.
Before the advent of this revolutionary strain sensing technology, users had to choose between high speed or high spatial density — they could not have both features in a single system. AFRC's technology offers the best of both worlds, enabling sensing of specific targets that is 250 times faster than conventional fiber optic technologies as well as super-dense sensing at 1/4” resolution on a single fiber.
This hybrid approach allows for multimode shape and strain sensing in situations requiring a high sampling rate. This high-speed capability further enhances the already dramatic benefits of the highly accurate, light-weight, flexible, non-intrusive, rugged FOSS system.
This type of real-time dynamic structural health monitoring is valuable for many applications. For example, it is ideal for designing and monitoring the structural integrity of aircraft, spacecraft, trucks, automobiles, and other moving vehicles; tracking the structural health of buildings, bridges, tunnels, and dams; improving the efficiency of turbines, drills, pile driving gear, and other industrial equipment; detecting instabilities within power plants, offshore oil rigs, tankers, and cargo ships; and even guiding medical and surgical procedures involving endoscopes, catheters, vascular detection, biosensing, and biopsy.
A video elaborating on this revolutionary technology is available here .