Four-point calibration of PVDF sensor using extrinsic Fabry-Perot interferometric sensors

Abstract

The performance of sensor systems in smart structures is subject to orientation, installation, and environmental effects. The capability for initial and maintenance calibrations can provide added confidence in sensor information and facilitate investigations of long-term sensor behavior. The use of Extrinsic Fabry-Perot Interferometric (EFPI) fiber-optic sensors was examined for calibration of companion strain sensors. The output of the EFPI sensor is periodic with strain and the signal behavior with periodic strain displays well-defined harmonic content. In particular, the strains giving maximums and minimums in the harmonics can be calculated from the excitation wavelength and the EFPI gage length. A Polyvinylidene Fluoride (PVDF) piezoelectric strain sensor was surface mounted on a cantilever beam and its voltage-to-strain ratio was precisely calibrated using the accuracy of a co-located EFPI sensor. The experimental responses of both sensors were obtained for a periodic actuation. The PVDF output was calibrated using a linear-fit of the strains obtained from four points in the harmonic response of the reference EFPI sensor. The selected maximum and minimum points of the EFPI harmonics were directly observed with a spectrum analyzer. This fast, efficient approach was performed under resonant conditions with relatively inexpensive demodulation requirements. The results of the calibration compared well with the expected PVDF response.