Abstract
Many efforts have been devoted to simultaneous measurements of strain and temperature by FBG sensors and several improving techniques have been resulted and implemented on the measurement. Most of them are based on two or more FBGs configurations or a single non-uniform FBG implementation. We propose simultaneous measurement of temperature and strain based on peak power changes and Bragg wavelength shifts using only one uniform fiber Bragg grating (FBG). We placed a ramp with the angle of θ, similar to a tilted cantilever beam, on an assumptive structure and stuck a uniform FBG on it. When a uniform strain applied to a structure, the cantilever beam converts it to a non-uniform strain distribution along with itself and consequently the uniform FBG. By creating this non-uniform strain distribution, the peak power of the reflection spectrum of the FBG will be sensitive to strain changes. In addition, the Bragg wavelength shift will be sensitive to both temperature and strain parameters. According to our simulation, temperature sensitivity of 14.15 pm/°C is obtained for FBG sensor without any changes in the peak power. The strain sensitivity of 0.7837 pm/με, and a nonlinear sensitivity according to a quadratic function for peak power variation are also observed.
Highlights
[17] fiber Bragg grating (FBG) written in single mode fiber (SMF) and twin core fiber (TCF) [18], four-core fiber combined with a FBG [19], a combination of Fabry-Perot interferometer (FPI) and FBG [20], superstructure FBG [21], coated FBG [22], FBG in Polarization Maintaining Fiber (PMF) [23], π-Phase-Shifted FBG [24], chirped FBG [25], and FBG written in PANDA fiber [26] have been proposed to solve the problem
Many methods have been proposed for simultaneous measurement of temperature and strain by FBG sensors, none of them can do this using only a single uniform FBG
Researchers have employed a variety of configurations including two or more FBGs, or one special FBG up to now
Summary
Where λB is Bragg wavelength that depends on effective refractive index of fiber (neff) and period of grating (Ʌ). These diagrams are extracted by the conventional method of transfer matrix in FBGs and with the help of MATLAB software. According to figure (1), sensitivity of a uniform FBG to a uniform temperature change is 0.01415 nm/°C and for uniform strain change can be obtained as 0.0012 nm/με, at the Bragg wavelength of 1547 nm which are consistent with uniform FBG standard sensitivities [32]
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