Adaptive Spatial Resolution Enables Focused Fiber Optic Sensing

How It Works The FOSS technology employs efficient, real-time, data driven algorithms for interpreting strain data. The fiber Bragg grating sensors respond to strain due to stress or pressure on the substrate. The sensors feed these strain measurements into the systems algorithms to determine shape, stress, temperature, pressure, strength, and operational load in real time. Why It Is Better Conventional strain gauges are heavy, bulky, spaced at distant intervals (which leads to lower resolution imaging), and unable to provide real-time measurements. Armstrong's system is virtually weightless, and thousands of sensors can be placed at quarter-inch intervals along an optical fiber the size of a human hair. Because these sensors can be placed at such close intervals and in previously inaccessible regions (for example, within bolted joints, embedded in a composite structure), the high-resolution strain measurements are more precise than ever before. The fiber optic sensors are non-intrusive and easy to install—thousands of sensors can be installed in less time than conventional strain sensors and the system is capable of processing information at the unprecedented rate of 100 samples per second. This critical, real-time monitoring capability enables an immediate and informed response in the event of an emergency and allows for precise, controlled monitoring to help avoid such scenarios. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing

The FOSS technology revolutionizes fiber optic sensing by using its innovative algorithms to calculate a range of useful parameters—any and all of which can be monitored simultaneously and in real time. FOSS also couples these cutting-edge algorithms with a high-speed, low-cost processing platform and interrogator to create a single, robust, stand-alone instrumentation system. The system distributes thousands of sensors in a vast network—much like the human body's nervous system—that provides valuable information. How It Works Fiber Bragg grating (FBG) sensors are embedded in an optical fiber at intervals as small as 0.25 inches, which is then attached to or integrated into the structure. An innovative, low-cost, temperature-tuned distributed feedback (DFB) laser with no moving parts interrogates the FBG sensors as they respond to changes in optical wavelength resulting from stress or pressure on the structure, sending the data to a processing system. Unique algorithms correlate optical response to displacement data, calculating the shape and movement of the optical fiber (and, by extension, the structure) in real time, without affecting the structure's intrinsic properties. The system uses these data to calculate additional parameters, displaying parameters such as 2D and 3D shape/position, temperature, liquid level, stiffness, strength, pressure, stress, and operational loads. Why It Is Better FOSS monitors strain, stresses, structural instabilities, temperature distributions, and a plethora of other engineering measurements in real time with a single instrumentation system weighing less than 10 pounds. FOSS can also discern between liquid and gas states in a tank or other container, providing accurate measurements at 0.25-inch intervals. Adaptive spatial resolution features enable faster signal processing and precision measurement only when and where it is needed, saving time and resources. As a result, FOSS lends itself well to long-term bandwidth-limited monitoring of structures that experience few variations but could be vulnerable as anomalies occur (e.g., a bridge stressed by strong wind gusts or an earthquake). As a single example of the value FOSS can provide, consider oil and gas drilling applications. The FOSS technology could be incorporated into specialized drill heads to sense drill direction as well as temperature and pressure. Because FOSS accurately determines the drill shape, users can position the drill head exactly as needed. Temperature and pressure indicate the health of the drill. This type of strain and temperature monitoring could also be applied to sophisticated industrial bore scope usage in drilling and exploration. For more information about the full portfolio of FOSS technologies, see visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing

This technology was developed to improve Armstrong's multi-patented FOSS system, which has long been used to measure temperature and liquid levels in cryogenic environments. When the sensing system's fibers trapped humidity from the surrounding environment before their submersion into cryogenic liquids, the moisture adversely affected outputs. A new manufacturing process solves this problem, increasing reliability and accuracy not only of NASA's FOSS but also any fiber optic sensing system. How It Works Armstrong has developed a two-step process to assemble the sensors. First, the bare sensor fiber is inserted into an oven to expel all moisture from the fiber coating. Then, the moisture-free fiber is placed inside a humidity-controlled glove box to prevent it from absorbing any new moisture. While inside the glove box, the fiber is inserted into a loose barrier tubing that isolates the fiber yet is still thin enough to provide adequate thermal transfer. The tubing can be further purged with various gases while it is inside the glove box to provide additional moisture isolation. This innovation is particularly useful for fiber optic systems that measure temperature and that identify any temperature stratifications within cryogenic liquids. Why It Is Better This process seals sensor fibers from environmental moisture, enabling fiber optic sensing systems to operate reliably in humid environments. The innovation eliminates erroneous readings that can occur due to moisture collection on the fiber sensors. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing

Armstrong has developed a robust fiber optic–based sensing technology that offers extraordinary accuracy in liquid level measurements. The sensing system uses fiber optic Bragg sensors located along a single fiber optic cable. These sensors actively discern between the liquid and gas states along a continuous fiber and can accurately pinpoint the liquid level. How It Works The technology uses a resistive heater wire bundled with the optical fiber. The heater is pulsed to induce a local temperature change along the fiber, and the fiber Bragg grating data is used to monitor the subsequent cooling of the fiber. The length of fiber in the liquid cools more rapidly than the portion of the fiber in the gas above the liquid. The measurement system accurately establishes the location of this transition to within 1/4-inch. Why It Is Better Armstrong's liquid level sensing technology was originally developed to measure cryogenic liquid levels in rockets, and it represents a significant advancement in the state of the art in this application. Conventional methods for measuring cryogenic liquid levels rely on cryogenic diodes strategically placed along a rod or rack. The diodes are mounted in pre-selected, relatively widely spaced positions along the length of a rod; this configuration provides limited, imprecise data. Furthermore, each diode on the rod has two wires associated with it, which means a single system may require a large number of wires, making installation, connectivity, and instrumentation cumbersome. Armstrong's novel technology provides liquid measurements with much greater precision, achieving measurements at 1/4-inch intervals. Furthermore, the streamlined system uses just two wires, which greatly simplifies installation and instrumentation. Due to its extraordinary accuracy and ease of use, Armstrong's measurement system offers important advantages for a wide range of applications beyond cryogenic liquids. In Addition Researchers have developed a new manufacturing process that improves the ability of fiber optic sensing systems to measure temperature and liquid levels when operating in humid environments. The process involves eliminating moisture from the optical fiber coating, then completing the sensor assembly within humidity-controlled conditions. The resulting sensor hardware provides precise and accurate measurements even when operating in a humid environment. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing

Armstrong's technologies provide a convenient way to calculate distributed deformed orientation angles—that is, roll, pitch, and yaw—as well as determine the deformed shape of an object in 3D space. Developed to facilitate monitoring and control of flexible aircraft designs when used in conjunction with Armstrong's multi-patented FOSS technology, these new tools improve shape-sensing accuracy for highly deformable structures such as bridges, wind turbines, robotic instruments, and much more. These tools also can be integrated into commercial fiber optic sensing systems. How It Works Researchers developed a technology that uses curved displacement transfer functions to determine 3D shape and calculate the operational load of a structure. It works by dividing the structure into multiple small domains, whose junctures match sensing stations, so that data is collected in a piecewise, nonlinear fashion. The innovation calculates structural stiffness (bending and torsion) and operational loads (bending moments, shear loads, and torques) in near real time. The method tracks rotations and orientation by employing quaternion mathematical operations, a faster process than rotation matrices used in previous shape-sensing algorithms. The result is an algorithm that can track multiple angles—displacement, twist, and rotation—at the same time to enable curvilinear shaping sensing. Armstrong researchers have validated the method on the large-scale passive aeroelastic tailored (PAT) wing. Why It Is Better These new technologies advance the ability of fiber optic sensing systems to determine the shape and operational loads of nonlinear flexible surfaces. They can improve the structural integrity of a range of large structures—from buildings and bridges to ocean vessels and aircraft. These innovations reliably provide highly accurate critical information in real time, enabling corrective action to avert disasters. For more information about the full portfolio of FOSS technologies, see DRC-TOPS-37 or visit https://technology-afrc.ndc.nasa.gov/featurestory/fiber-optic-sensing