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What is fiber optic sensing?

Fiber optic sensing technology collects strain and temperature data related to the structure to validate the structure and thermal model, ensure structural integrity, and improve operational efficiency.
Fiber optic sensing and traditional technology

Strain gauges and thermocouples have long been the standards for measuring strain and temperature during the testing process. Although these technologies have existed for decades, they are not always able to effectively test and monitor today’s innovations. The limitations of legacy technologies are not related to accuracy, but mainly to the level of insight provided by the data. Strain gauges and thermocouples only provide information points, while certain types of fiber optic sensors can provide spatially continuous data along the entire length of the fiber optic. เพราะฉะนั้น, engineers can measure the strain field and temperature distribution on the structure to better understand the behavior of components under different conditions. Point sensors only allow engineers to monitor key points, while distributed (spatial continuous data) sensors can measure key points and what happens between them. This insight is very valuable when designing new composite materials. นอกจากนี้, fiber optic sensors can be embedded in materials to better understand the internal behavior of composite components and structures.

Fundamentals of Fiber Optic Sensing

The inherent fiber optic sensing technology, in which the fiber optic cable itself is a sensor. In the division of internal sensors, there are generally three generations of technologies: point fiber Bragg grating (เอฟบีจี) based sensors, scattering, and spatially continuous FBG. Scattering technology adopts fully distributed measurement, while FBG technology can have a small number of sensing points or complete distribution, depending on how the system interprets the signal from the sensing elements.

FBG acts as a tiny mirror and is manufactured into the core of optical fibers. When light propagates along the fiber optic, each grating reflects a portion of the signal back into the system. The system recognizes the changes in the return signal and interprets this information to provide accurate strain and temperature measurements. Most FBG based systems have some sensing points along each fiber. Although this multiplexing function is a major advancement in traditional technology, it still cannot provide the sensor density required for monitoring between critical areas. Some advantages of point FBG sensors include accuracy, the ability to perform dynamic testing, and high-speed data acquisition.

Scattering technology does not use FBG at all, but relies on defects in optical cables to obtain readings. At present, three different types of scattering techniques are used in sensing systems, each with different functions. Generally speaking, scattering based fiber optic sensing systems benefit from distributed data and long sensing lengths. However, they have low data fidelity, very slow data acquisition rates on the order of a few minutes, and are susceptible to vibration limitations when performing static operations.