An opto-chemical in-fibre Bragg grating (FBG) sensor for refractive
index measurement in liquids has been developed using fibre side-polishing
technology. At a polished site where the fibre cladding has partly been
removed, a FBG is exposed to a liquid analyte via evanescent field interaction
of the guided fibre mode. The Bragg wavelength of the FBG is obtained in terms
of its dependence on the refractive index of the analyte. Modal and wavelength
dependences have been investigated both theoretically and experimentally in
order to optimize the structure of the sensor. Using working wavelengths far
above the cut-off wavelength results in an enhancement of the sensitivity of the sensor.
Measurements with different mode configurations lead to the separation of
cross sensitivities. Besides this, a second FBG located in the unpolished part
can be used to compensate for temperature effects. Application examples
for monitoring fuels of varying quality as well as salt concentrations under deep
borehole conditions are presented.
A fibre Bragg grating sensor system has been installed and successfully operated in a horizontal-axis wind turbine since February 2004. We herewith report the requirements, design and construction parameters of the sensor system for continuous on-line monitoring of bending loads of the rotor blades and provide examples of the monitoring results.
We report the fabrication and high-temperature characteristics of Bragg gratings in single-crystal sapphire fibres inscribed by infrared femtosecond laser pulses. For stable read-out of the multimode Bragg reflection signal, the sapphire fibre was illuminated by broadband light from a superluminescent diode applying a long section of a step-index multimode silica fibre. This evenly distributed excitation of many guided modes in the sapphire fibre resulted in the polychromator measurement of stable reflection peak shapes and allowed for multiplexed temperature sensing up to 1745 °C at remote read-out with repeatability better than 1 °C. During the temperature tests an annealing process of the sapphire grating was observed at temperatures above 1400 °C. Possibilities for further improvement of sensors performance are discussed with a view to avoiding instabilities from the lack of a fibre cladding that shields the sapphire waveguide from the environment.
A fibre Bragg grating sensor system has been installed in a horizontal axis wind turbine and was successfully tested for already more than one year. We report the requirements, system design and realisation of the sensor system for continuous on-line load monitoring of the rotor blades, and provide examples of strain measurement results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.