Modeling of Embedded FBG Sensors in Composite Structures for Force–Temperature Decoupling

Structural health monitoring of composite structures requires reliable separation of temperature and force/strain effects in embedded fiber-optic sensors. This paper proposes a two-channel fiber Bragg grating (FBG) sensing workflow that combines deliberately mismatched sensitivity coefficients with dual-edge ratiometric interrogation to enable robust wavelength tracking and subsequent decoupling of measurands. External thermal and mechanical inputs are first converted to equivalent fiber strain and mapped to Bragg-wavelength shifts for two gratings; the reflected spectrum is then demodulated using complementary edge filters that generate photodetector signals I1(λ) and I2(λ). A power-drift-resistant metric R=(I1−I2)/(I1+I2) is formed, and the wavelength is reconstructed via a calibrated inverse mapping λ=f(R) implemented end-to-end in MATLAB/Simulink, including optical demodulation, ADC/DSP processing, and a matrix-based decoupling solver. Within λ≈1549.2-1550.8 nm, responses are complementary (I1:0→0.30 a.u., I2:0.30→0 a.u.) with a balance near 1550.0 nm at ≈0.15 a.u., yielding maximal central sensitivity. Simulations over t=0–15 min show that approaching calibration limits can cause reconstruction saturation and spectral errors of hundreds of picometers, degrading force estimation, while temperature trends remain comparatively stable. These results confirm feasibility of the two-FBG ratiometric concept and motivate extending the calibration range and strengthening the inversion. Future work will focus on wider-range calibration (e.g., optimized/tunable edge filters), regularized or piecewise inversion of f(R)f, explicit noise/drift modeling, and experimental validation in representative composite specimens.