Incorporating Optical Fiber Sensors into Fabrics
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Incorporating Optical Fiber Sensors into Fabrics A. Dhawan1, T. K. Ghosh2, J. F. Muth1 1 ECE Department, NC State University, Raleigh NC 27695 2 College of Textiles, NC State University, Raleigh NC 27695 Optical fiber sensors have many attractive attributes including high sensitivity, environmental robustness, immunity to electromagnetic interference, and the ability to be remotely interrogated. Furthermore, by incorporating optical fibers into woven and nonwoven fabrics these sensors can be distributed across large areas. In woven optical fibers, microscopic bending is an issue due to the fibers going over and under the yarns. Microscopic and macroscopic bending losses are quantified by placing optical fibers on frames of different radii of curvature and measuring the loss of transmitted light. As an example of the non-woven process, electrospinning was used to overlay a net of sub-micron diameter fibers over the optical fibers. This protects the optical fiber, holds it in place, while still permitting flexibility. To form chemical sensors, standard telecommunications grade optical fibers were tapered such that the evanescent wave extended into the environment. Coating the fibers with a thin layer of gold then permits surface plasmon sensors to be formed. However, the resulting sensors were very fragile and hard to place into fabrics. As a result alternative processes were developed that form fiber structures that are robust enough to withstand textile manufacturing processes yet still allow interaction with the environment. INTRODUCTION Optical fiber sensors have many attractive attributes including high sensitivity, environmental robustness, immunity to electromagnetic interference, and have a wide range of applications. [1-2] Recently there has been interest in placing optical fiber sensors into fabrics for a variety of applications, including health monitoring, while exercising, or while bed ridden with illness, or on the battlefield. Other applications where distributed sensing in large area fabrics might be advantageous are in the structural monitoring of bridges or buildings. However there are three principle challenges that face placing optical fiber sensors into fabrics: • •
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Fibers are subject to macro & micro bending when they are flexed, which unpredictably results in leakage of fundamental core modes into cladding, altering transmission of light through the fiber. It can be hard to get the guided light to interact with the environment since the cladding is designed to prevent environmental interactions. A high level of interaction is important for chemical and environment sensing. The usual approach is to remove the cladding or taper the fiber. The sensor must be robust enough to withstand the textile manufacturing process.
Macrobending and microbending power transmission losses in the context of telecommunications are well understood. Typically these analyses assume a single of bend of relatively large radius, or small local deformations of the fiber. When the radius of curvature is such t
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