LAUSR

Importance of simultaneous measurement of temperature and strain by fiber Bragg grating (FBG) sensors has led to innovation of several renewing techniques. Most of them are based on two FBGs configurations or one non-uniform FBG implementation. Both temperature and strain changes can result in Bragg wavelength shift in reflected spectrum from a uniform FBG. We propose using full width at half maximum (FWHM) of the reflection spectrum as a cross-sensitivity indicator for simultaneous measurement of temperature and strain using only one FBG. When a non-uniform strain is applied to a sample which a uniform FBG is stuck on it, in addition to the Bragg wavelength, FWHM of the reflection spectrum changes. This FWHM change besides the Bragg wavelength shift is used to obtain simultaneously strain and temperature. When a uniform strain is applied to the sample, we get the help of cantilever beam concept. We place a ramp with an angle of θ, similar to a tilted cantilever beam, on a sample under test and stick a FBG on the ramp. A uniform strain applied to the sample, creates a strain gradient along the cantilever beam and of course along the FBG causing a change in the FWHM of reflection spectrum. This FWHM change besides the Bragg wavelength shift is used to obtain simultaneously strain and temperature. In our simulation results, temperature sensitivity of the FBG is 14.2 pm/℃ for Bragg wavelength with no change in the FWHM and strain sensitivity is 0.453 pm/μe for Bragg wavelength and a nonlinear sensitivity according to a quadratic function for FWHM variation.