Fibre Optic Sensors: An Overview

SUMMARY Engineering geodesists have the competence to measure the external deformations of structures using automated surveying techniques such as motorized digital levelling systems, autonomous total stations and GPS arrays. The analytical deformation analysis has been fully developed and appropriate software tools are available. During the past decade, physicists have been developing new sensory capabilities to measure the internal parameters of structures as part of so-called smart civil structures. For civil structures, the primary sensing issues are: (i) measuring the reaction of the structure to external loads, and (ii) determining the internal state-of-health of the structure. For these purposes, small fibre optic sensors (FOS) are embedded and spatially distributed in the structure. FOS have been developed to detect variations in crack formation, strain, temperature and corrosion. A significant advantage of FOS is the ability to multiplex a number of continuous or discrete sensors on one fibre to form a distributed sensor system. This paper serves the purpose to make engineering geodesists aware of these developments. It provides background information of embedded and distributed FOS using light intensity changes caused by attenuation, scattering and reflection, or phase changes caused by optical path length or refractive index variations.