研究目的
To propose a method for estimating the length of single mode fibre Bragg grating (FBG) sensors accurately, which is independent of the stress field and can be used for characterizing gauge length in structural integrity applications.
研究成果
The length of FBG sensors can be accurately estimated from the maximum oscillation frequency of side-lobes in the reflection spectrum, which is robust against stress fields and variations in refractive index. The method is validated through simulations and experiments, showing errors around 0.2-0.3%, and is applicable to various FBG types including partially apodized and non-uniform gratings.
研究不足
The method may not work well for sensors with fully suppressed side-lobes (e.g., Gaussian apodized sensors) and requires a high dynamic range interrogator. Accuracy depends on the assumption of a fixed effective refractive index, with potential errors up to 1%.
1：Experimental Design and Method Selection:
The method uses the approximated transfer matrix model (ATMM) to analyze FBG reflection spectra under non-uniform stress fields, focusing on the maximum oscillation frequency of side-lobes.
2：Sample Selection and Data Sources:
Computer simulations and experimental measurements on a draw tower grating (DTG) sensor with a nominal length of 10 mm.
3：List of Experimental Equipment and Materials:
PXIe 4844 interrogator from National Instruments, optical microscope, thermal stripper, chemical etching solution (15 wt% NH4F and 16 wt% H2SO4).
4：4). Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: For simulation, design an FBG sensor with non-uniform stress and refractive index fluctuations; for experiment, apply various stress fields to the sensor, interrogate with the PXIe 4844, perform Fourier transform on side-lobes, and use microscopy for validation after etching.
5：Data Analysis Methods:
Fourier transform to determine maximum oscillation frequency, calculation of length using L = fmax / (2 * neff), statistical analysis of results.
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