Optical Fiber Distributed Sensing - Physical Principles and Applications

Abstract

Obtaining the strain data all along the optical fiber, with adequate spatial resolution and strain accuracy, opens new possibilities for structural tests and for structural health monitoring. Formerly, only point sensors, as strain gages or fiber Bragg grating, were available, and information about the response to loads was restricted only to those points on which the sensors were bonded. Unless a sensor was located near the damage initiation point, details about the failure initiation and growth were lost. With a distributed system, the information is given as an array of data with the position in the optical fiber and the strain or temperature data at this point. In this article, the physical principles underlying the different techniques for distributed sensing are discussed, a classification is done based on the backscattered wavelength; this is important to understand its possibilities and performances. The definition of performance for distributed sensors is more difficult than for traditional point sensors because the performance depends on a combination of related measurement parameters. For example, accuracy depends on the spatial resolution, acquisition time, distance range, or cumulated loss prior to measurement location. The field of applications of this new technology is very wide; results of the structural tests of a 40 m long wind turbine blade, detecting the location and load of onset of buckling, and the results of the delamination detection in a composite plate, are presented as examples.

Keywords

distributed sensing fiber optical sensors optical backscatter reflectometry strain monitoring damage detection.

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References

Childers, B.A. , Froggatt, M.E. , Allison, S.G. et al (2001). Use of 3000 Bragg grating strain sensors distributed on four eight-meter optical fibers during static load tests of a composite structure. In: Smart Structures and Materials 2001, Proceedings of the SPIE Conference, San Diego, CA.

Criado, A. , Riezu, M. , Fernandez, A. and Oizm, A. ( 2009). Evaluation of OBR for strain measurements in blade testing . In: Proceedings of European Wind Energy Conference , Marseille, France.

Li, H. , Li, D. and Song, G. ( 2004). Recent applications of fiber optic sensors to health monitoring in civil engineering. Engineering Structures, 26, 1647-1657.

Leung, C. ( 2001). Fiber optic sensors concrete: the future? NDT&E International, 34, 85-94.

Minakuchi, S. , Okabe, Y. and Takeda, N. ( 2007). Barely visible impact damage detection in sandwich structures using non-uniform strain along optical fiber sensors. In: Proceedings of ICCM-16, Kyoto, Japan.

Fernandez-Lopez, A. and Güemes , A. (2009). Experimental measurements of changes induced by delaminations in the strain field using a distributed sensing technique. In: Proceedings of International Workshop on Structural Health Monitoring 2009 , Stanford, CA.