Strain Sensing for Displacement and Two-Dimensional (2-D) Shape

Strain Sensing for Displacement and Two-Dimensional (2-D) Shape

A gust of wind or aerial maneuvers can cause a large displacement in the wings of a lightweight UAV during flight and is the known cause of at least one UAV crash. Therefore, an Armstrong research team has designed an algorithm model that uses fiber optic structural strain measurements to determine deflection and 2-D shape. When combined with the other elements of FOSS, this approach provides higher accuracy and higher spatial resolution than other shape-sensing systems available. Other methods use cameras to image wing deformation; however, these approaches require high-speed processing systems, add weight to structures, and are less accurate than the FOSS approach. The Armstrong methods can be implemented without affecting performance and without the need for structural modifications.

Work to date: The technology has been used to assess large-scale composite wings, to evaluate the Global Observer UAV, and in Ikhana UAV flight testing, which is believed to be the first flight validation test of fiber Bragg grating strain and wing-shape sensing. In eight tests that logged 36 flight hours, a total of six fibers (~3,000 strain sensors) were installed on Ikhana's left and right wings. The fiber optic and conventional strain gauges showed excellent agreement during multiple flight maneuvers.

Benefits

 High spatial resolution: Enables measurements approximately every 0.5 inches

 Easy application: Small enough to be used on sensitive surfaces without affecting performance

Applications

     Determining aerial wing shapes  Monitoring turbine blade shapes

      Structural health monitoring for bridges, buildings, and ships

 Fiber Optic Sensing

Armstrong's portfolio of Fiber Optic Sensing System (FOSS) technologies offers unparalleled options for high-resolution sensing in applications that require a unique combination of high-powered processing and lightweight, flexible, and robust sensors. The system measures real-time strain, which can be used to determine two-dimensional and three-dimensional shape, temperature, liquid level, pressure, and loads, alone or in combination. Initially developed to monitor aircraft structures in flight, the system's capabilities open up myriad new applications for fiber optics-not just in aerospace but also for civil structures, transportation, oil and gas, medical, and many more industries.

The Armstrong approach employs fiber Bragg grating (FBG) sensors, optical frequency domain reflectometry (OFDR) sensing, and ultra-efficient algo-rithms (100 samples/second). Engineers are continually seeking new ways of looking at information and determining what is important. Armstrong's FOSS technologies focus on critical research needs. Whether it is used to determine shape, stress, temperature, pressure, strength, operational load, or liquid level, this technology offers ultra-fast, reliable measurements.