Strain-Independent Temperature Measurements with Surface-Glued Polarization-Maintaining Fiber Bragg Grating Sensor...

Area of Science:

• Optical Fiber Sensors
• Strain and Temperature Measurement
• Material Science

Background:

• Surface-glued fiber Bragg gratings (FBGs) are susceptible to strain and temperature variations.
• Accurate temperature monitoring is crucial in diverse engineering applications, including those with electromagnetic fields, rotating components, or vacuum environments.
• Existing methods struggle to decouple strain effects from temperature readings in glued FBG sensors.

Purpose of the Study:

• To develop a novel technique for strain and temperature decoupling in surface-glued FBGs.
• To achieve strain-independent temperature measurements using a unique FBG sensor configuration.
• To validate the sensor's performance across a wide temperature range and assess its reliability against glue-induced strain.

Main Methods:

• A sensor element comprising two FBGs in identical polarization-maintaining fibers, spliced perpendicular to each other, was fabricated.
• The sensor element was aligned and glued with its optical axes parallel and perpendicular to the specimen.
• The averaged Bragg wavelength shifts of both FBGs were analyzed to eliminate glue-induced transversal forces and temperature-dependent effects.

Main Results:

• The proposed methodology successfully achieved strain-independent temperature measurements within a range of -30 °C to 110 °C.
• Temperature uncertainties were consistently below 4 °C across the entire measurement range.
• The averaged Bragg wavelength shifts demonstrated independence from glue-induced strains and material property changes (aging, creeping).

Conclusions:

• This novel technique enables accurate temperature measurements with surface-attached bare FBGs, independent of arbitrary longitudinal and glue-induced strains.
• The method effectively eliminates the influence of temperature-dependent glue-induced transversal forces.
• This breakthrough is highly valuable for applications requiring fully glued sensor designs in demanding environments like high electromagnetic fields, rotating machinery, and space applications.