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Fiber Bragg grating (FBG) sensors were used to measure the torsional strain distribution in a second-generation (rare-earth) Ba 2 Cu 3 O y high-temperature superconducting sample tape (SST) at 77 K. Two SST samples were prepared. A slit was fabricated in each sample to allow an optical fiber to be embedded. In the first sample, a 10-mm-long single grating element was inserted into the slit. In the second sample, three grating elements of 10-mm length each were put into the slit. These grating elements were fabricated along a single-mode fiber and could be addressed individually using the wavelength division multiplexing (WDM) technique. Finally, the samples were recoated with a primary and secondary coating to form an embedded sensing system. When the high-temperature superconducting (HTS) tape is subjected to torsion, there is a strain induced in the FBG sensor, which varies the grating period accordingly. It was interrogated using a tunable laser in a WDM scheme. Based on the wavelength shift and the photoelastic properties of the FBG sensor embedded to the HTS tape, the torsional deformation of the HTS tape can be obtained. In this paper, the design and technology requirements to embed the single and WDM FBG sensors into the coated conductors are presented. Initial experiments to measure the torsional strain distribution at 77 K are reported.

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Articles you may be interested inMeasurement error of surface-mounted fiber Bragg grating temperature sensor Rev. Sci. Instrum. 85, 064905 (2014); 10.1063/1.4885463 High resolution magnetostriction measurements in pulsed magnetic fields using fiber Bragg gratings Rev. Sci. Instrum. 81, 033909 (2010); A multiplexed fiber Bragg grating sensor for simultaneous salinity and temperature measurement J. Appl. Phys. 103, 053107 (2008); 10.1063/1.2890156 Fiber optic sensor for dual measurement of temperature and strain using a combined fluorescence lifetime decay and fiber Bragg grating technique Rev. Sci. Instrum. 72, 3186 (2001); ABSTRACT Study of magnetostrictive effects in the bulk superconductors is very essential and cangive more knowledge about the effects like namely, flux pinning induced strain, pincushion distortions in the magnets and so on. Currently used electro mechanical sensors are magnetic field dependent and can only give the global stress/ strain information but not the local stress/ strains. But the information like radius position dependent strain and characterisation of shape distortion in non cylindrical magnets are interesting. Wavelength encoded multiplexed fiber Bragg Grating sensors inscribed in one fiber gives the possibility to measure magentostrictive effects spatially resolved in low temperature and high magnetic field. This paper specifies the design and technology requirements to adapt FBG sensors for such an application. Also reports the experiments demonstrate the properties of glass FBG at low temperature (4.2K) and the results of strain measurement at 4.2K / 8T. The sensor exhibits a linear wavelength change for the strain change.

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