Simultaneous strain and temperature measurement using a single fiber Bragg grating embedded in a composite laminate

This paper presents a fiber Bragg gating (FBG) sensor that can be surface mounted for simultaneous strain and temperature measurements. By embedding a conventional FBG sensor in a composite laminate, local birefringence is introduced, which causes the bandwidth of the FBG spectrum to vary with strain as well as temperature. As such, temperature and strain can be simultaneously determined from two FBG spectral parameters, i.e. the spectral bandwidth and the Bragg wavelength. Techniques for improving the spectrum of the FBG-composite sensor and for inversely determining the strain and temperature from the measured FBG spectral parameters are discussed. Thermal-mechanical testing of the FBG-composite sensor was carried out to validate the sensor performance. The measurement errors, within one standard deviation, for the strain and temperature measurements were found to be +/- 62 mu epsilon and +/- 1.94 degrees C, respectively.