Evaluation of a Novel Spectral Pair of a Chirp FBG Embedded in a Cantilever Beam for Simultaneous Temperature and Transverse Forces Measurement

An evaluation of a novel spectrum features combining the distant longer and shorter wavelengths of a single chirped fiber Bragg grating (CFBG) for temperature and transverse forces discrimination is experimentally demonstrated. The shift of the two distant wavelengths' pair is compared with the conventional pair combining the bandwidth modulation and center wavelength shift. The CFBG sensor is simply bonded to a cantilever beam and subjected to transverse loading (four times) and a heating-cooling cycle. The transverse forces calibration results show a repeatability of 3.9 pm and 1.7 pm for the bandwidth's and center wavelength's responses, respectively, while the distant wavelengths' show a repeatability of 2.37 pm and 3.01 pm, respectively. The cantilever CFBG sensor exhibits high correlation coefficients of 0.9 between the two heating and cooling data sets, except for the bandwidth, which only had a lower coefficient of 0.75. The linear model of both pairs for calculating temperature and transverse forces can provide an accurate estimate, with the longer-shorter wavelengths' pair having an advantage over the pair of the bandwidth-centre-wavelength. The study has demonstrated the feasibility of the method proposed by our group in a previous work, by which three physical quantities can be measured with a single custom FBG.