Distributed strain measurement with polymer optical fibers integrated into multifunctional geotextiles

Sascha Liehr*a, Philipp Lenke a, Katerina Krebber a, Monika Seeger b, Elke Thiele b, Heike Metschies bBerhane Gebreselassie c, Johannes Christian Münich d, Lothar Stempniewski d

Federal Institute for Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany

Saxon Textile Research Institute (STFI), Annaberger Str. 240, D-09125 Chemnitz, Germany

Institute of Geotechnics and Geohydraulics, University of Kassel, Department of Geotechnics, Moenchebergstrasse 7, D-34125 Kassel, Germany

Institute of Concrete Structures and Building Materials, University of Karlsruhe, Gotthard-FranzStr.3 / Am Fasanengarten, D-76128 Karlsruhe, Germany

ABSTRACT

Fiber optic sensors based on polymer optical fibers (POF) have the advantage of being very elastic and robust at the same time. Unlike silica fibers, standard PMMA POF fibers can be strained to more than 40 % while fully maintaining their light guiding properties. We investigated POF as a distributed strain sensor by analysing the backscatter increase at the strained section using the optical time domain reflectometry (OTDR) technique. This sensing ability together with its high robustness and break-down strain makes POF well-suited for integration into technical textiles for structural health monitoring purposes. Within the European research project POLYTECT (Polyfunctional textiles against natural hazards) technical textiles with integrated POF sensors, among others sensors are being developed for online structural health monitoring of geotechnical structures. Mechanical deformation in slopes, dams, dikes, embankments and retrofitted masonry structures is to be detected before critical damage occurs. In this paper we present the POF strain sensor properties, reactions to disturbing influences as temperature and bends as well as the results of the different model tests we conducted within POLYTECT. We further show the potential of perfluorinated graded-index POF for distributed strain sensing with increased spatial resolution and measurement lengths.

Keywords: Fiber optic sensors, OTDR, polymer optical fibers (POF), POF sensors, distributed sensor, strain sensor, geotextiles, structural health monitoring