Abstract
Strain response of FBG sensors are investigated at various temperatures from 298 K to 4.2 K. Numerical modelling is carried out for acrylate coated, substrate-free fiber Bragg grating (FBG) sensors at room temperature of 298 K and cryogenic temperatures of 77 K, 10 K and 4.2 K. A 1550 nm Bragg wavelength (λB) FBG sensor is modelled and simulated for applied strain (ε) ranging from 0 to 800 µm/m. The Bragg wavelength shifts (ΔλB) thus obtained are compared with the experimentally investigated values obtained by subjecting the FBG sensor to axial strain, with its sensing part not being bonded to any surface. The MTS25 tensile machine with a cryostat under vacuum conditions (10-4 mbar pressure) is used for the experiments and the required temperatures are maintained using liquid Nitrogen (LN2) and compressed Helium gas (He). The Bragg wavelength shift (ΔλB) versus induced strain (ε) is regressed with a linear polynomial function and the strain sensitivity obtained in both the cases are discussed.
Highlights
Fiber Bragg gratings (FBG) are considered one of the most reliable sensors to monitor crucial process parameters like pressure, temperature, flowrate, concentration, etc [1,2,3,4], thanks to their miniature size, high sensitivity, electrical and magnetic immunity, and multiplexing capabilities
Results & discussion The respective results from the simulation and experiment are individually discussed first and a comparison is made to describe the reliability of the FBG sensor
Experimental test cum calibration is done at 298 K and 77 K. This is a unique and reliable method of calibration because the sensing part of the FBG sensor is not attached to any structure or surface
Summary
Fiber Bragg gratings (FBG) are considered one of the most reliable sensors to monitor crucial process parameters like pressure, temperature, flowrate, concentration, etc [1,2,3,4], thanks to their miniature size, high sensitivity, electrical and magnetic immunity, and multiplexing capabilities. The strain and temperature sensitivities of the FBG, vary from sensor to sensor, requiring a calibration before any measurement. This paper discusses the numerical and experimental investigation of a substrate-free FBG sensor at various temperatures whose sensing part is not attached to any surface. The given displacement is completely transferred to the FBG sensor, i.e., the change in length of the sensor is equal to the displacement This induces a strain in the FBG sensor (FBG 1), which in turn causes a Bragg wavelength shift in it. The Bragg wavelength shift of FBG 2 (∆λB2) which hangs freely in the cryostat is caused only due to the temperature changes. The values of Bragg wavelength shift, displacement, extensometer voltage and temperature are recorded for each given displacement for both 298 K and 77 K. The Braggmeter has good repeatability of ± 1.0 pm, showing that the error in measurement due to the measuring device is negligible
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