State-of-strain evaluation with fiber Bragg grating rosettes: application to discrimination between strain and temperature effects in fiber sensors

Abstract

An optical rosette that incorporates fiber Bragg gratings as strain gauges has been designed, fabricated, and tested. We investigated it by measuring the state of strain of a thin plate as the test structure submitted to an increasing load in a four-point bending configuration and for various angular orientations. This device has also been successfully investigated as a self-temperature-compensated in situ uniaxial strain sensor without any angular dependence and with high accuracy in recovery analysis, leading us to expect many industrial applications. Printed circuit processes or integrated optics on polymers would provide a means for accuracy, reproducibility, and integration in a mass-produced process.

Miniature fiber Bragg grating strain rosette based on lossless tapers

“…Therefore three independent strain measurements in three different directions along the plane are sufficient to determine the principal strain axes, as long as the strain measurements are arranged at convenient angles in order to have at least two linearly independent measurements. Based on the standard equations for strain rosettes [8], the local strain equation for each strain sensor can be written as: where ε X and ε Y are the principal strain axes, α is the deviation angle regarding the principal axis, and β is the relation between the angles for each strain gauge. Figure 4 shows the schematic representation of the general problem.…”

“…Different configurations in optical strain sensors have also been reported in literature [4][5][6][7]. In the scope of performing strain measurements with FBGs, Magne et al [8] demonstrated its application on the implementation of an optical strain rosette. Although, due to high losses in fibre curvature, the effective dimension of the rosette is not negligible as it is required for a precise strain measurement.…”

Method for independent strain and temperature measurement in polymeric tensile test specimen using embedded FBG sensors

“…The parameter is the optical fibre photo-elastic coefficient, ℎ is the thermal expansion coefficients of the host material and is the thermo-optic coefficient [14]. The effect of the optical fibre to the overall specimen stiffness is very small, because the FBG cross section << specimen cross section.…”

Exoskeletal Force-Sensing End-Effectors With Embedded Optical Fiber-Bragg-Grating Sensors

“…Various complicated temperature-compensation methods have been proposed, such as the use of dual-wavelength superimposed FBG sensors [60], saturated chirped FBG sensors [61], and an FBG sensor rosette [35]. We chose a simpler method that involved the use of an isolated, strain-free FBG sensor to measure thermal effects.…”