In the following we present a low-cost optical system for cracks evolution monitoring.
The transducer principle is based on the variation of light transmitted between two facing fibers
with their axial distance, exploiting the unique light-collecting capabilities of large-core polymer
optical fibers. The characterization shows that the working range of the transducer is up to 3.5cm,
with a resolution of 10$m and a repeatability of 5$m. With our current custom-developed control
unit, up to four transducers can be arranged to provide a multi-axial displacement sensor or to
simultaneously monitor four points for distributed sensing. A closed-loop light
modulation/detection scheme is implemented to reduce the environmental noise sensitivity. The
control unit is interfaced to a PC via USB port or via GSM/GPRS modem to automatically send
periodical reports of the measurements and to issue warnings in case of displacements above a given
threshold. Extensive tests in an environmental chamber have been carried out in order to extract
calibration curves and to compensate for day-night and summer-winter temperature fluctuations.
Absolute spectral backscatter measurements of large-core multimode PMMA polymer optical fibers