Temperature insensitive smart optical strain sensor
An optical strain gage, employing a hollow polyimide-coated glass capillary tube, is currently under development. The capillary tube serves as a waveguide, in which an optical signal is attenuated in an amount proportional to applied bending strain. The capillary is incorporated into an optical fiber link which acts as both the source of signal and as the return path to a photodiode detector. The inherent compatibility of this optical strain sensor with fiber optic telecommunication systems makes it amenable for incorporation into intelligent systems for the continuous monitoring and damage assessment of bridges, highways, piers, airframes, and buildings. By applying various thin films to the interior and/or exterior surfaces of the waveguide, the strain gage can be optimized for specific strain ranges. This optical strain sensor exhibits advantages in comparison to commercially available metal foil (resistance) strain gages, including gage factors 100 times larger and temperature insensitivity for operating temperatures ranging from -25 °C to +51 °C.