Icing causes substantial problems in the integrity of large-scale wind turbines. In this work, a fiber-optic sensor system for detection of icing with an arrayed waveguide grating is presented. The sensor system detects Fresnel reflections from the ends of the fibers. The transition in Fresnel reflection due to icing gives peculiar intensity variations, which categorizes the ice, the water, and the air medium on the wind turbine blades. From the experimental results, with the proposed sensor system, the formation of icing conditions and thickness of ice were identified successfully in real time.
We propose a fiber-optic sensor structure for simultaneous strain and temperature monitoring in cryogenic conditions. The polymer coated fiber Bragg grating sensor makes it a suitable candidate for cryogenic temperature measurement. FBG have been shown to have an enhanced sensitivity of 48 pm °C<sup>-1</sup> from -185 to 25 °C. The cross-sensitivity problem has been solved by introducing a glass capillary tube to encapsulate the coated FBG. The thermal expansion of capillary material was compensated by cleaving the one end of FBG free and the other end with the temperature resistant epoxy resins. Experiments results validate the proposed method can successfully monitor the strain and temperatures at cryogenic temperatures.
We propose a novel aqueous ethanol fiber-optic sensor which is based on Fresnel reflection. It is functionalized with a thin-layer of an ethanol-sensitive graphene oxide (GO) coating on a single mode optical fiber end. The trace of ethanol concentration was measured by the variations in Fresnel reflection intensity and the optical properties of graphene oxide. The sensor output was obtained successfully in response to aqueous ethanol concentration from 20% to 100%. The fiber end with GO film exhibited real- time and remote measurement of ethanol concentration with high precision.
A fiber-optic multi-stress monitoring system which uses 4 FBG sensors and a fiber-optic mandrel acoustic emission sensor is proposed. FBG sensors and a mandrel sensor measure different types of stresses occurring in electrical power transformer, such as temperature and acoustic signals. The sensor system uses single broadband light source to address the outputs of both sensors using single fiber-optic circuitry. An athermal-packaged FBG is used to supply quasi-coherent light for the Sagnac interferometer demodulation which processes the mandrel sensor output. The proposed sensor system could simplify the optical circuit for the multi-stress measurements and enhance the cost-effectiveness of the sensor system.
In this paper, Fresnel reflection based fiber-optic sensor for the real-time monitoring of cryogenic temperature is presented. The proposed sensor system utilizes a linear thermo-optic coefficient of polymer and Fresnel reflection of the fiber end. Epoxy resin and poly methyl metha acrylate (PMMA) are used as sensor head material. The designed sensor head measures the temperature ranging from -180°C to 25°C with an average sensitivity of 0.039dB/°C for epoxy resin and 0.029dB/°C for PMMA. Experimental results have proven the stability and the effectiveness of the proposed sensor system to measure the applied cryogenic temperatures.
Low thermal sensitivity and cross sensitivity of Fiber Bragg Grating (FBG) towards the applied strain, temperature make FBG implementation complicated in composite materials at cryogenic conditions. In order to alleviate this problem, our work focuses on simultaneous strain and temperature monitoring inside the composite material at cryogenic temperatures. The temperature sensitive polymer coating on an FBG sensor makes it a suitable candidate for cryogenic temperature measurement. The average temperature sensitivity of 48 pm °C<sup>-1</sup> was obtained in -180 ~ 25 °C. In addition, the cross sensitivity problem has been adjusted by introducing a glass capillary tube to encapsulate the FBG. The thermal expansion of capillary material was compensated by cleaving the one end of FBG free and the other end with the temperature resistant epoxy resins. Experiments results validate that the proposed method can successfully monitor the strain and temperature factors that can be applied to composite material at cryogenic temperatures.
A fiber-optic epoxy cure monitoring technique for efficient wind turbine blade manufacturing and monitoring is presented. To optimize manufacturing cycle, fiber-optic sensors are embedded in composite materials of wind turbine blades. The reflection spectra of the sensors indicate the onset of gelification and the completion of epoxy curing. After manufacturing process, the same sensors are utilized for in-field condition monitoring. Because of residual stresses and strain gradients from the curing process, the embedded sensors may experience distortions in reflection spectra, resulting in measurement errors. We applied a Gaussian curve-fitting algorithm to the distorted spectra, which substantially improved the measurement accuracy.
A hybrid fiber-optic sensor system which combines fiber Bragg grating (FBG) sensors and a Michelson interferometer is suggested for condition monitoring uses of large scale wind turbine blades. The system uses single broadband light source to address both sensors, which simplifies the optical setup and enhances the cost-effectiveness of condition monitoring system. An athermal-packaged FBG is used to supply quasi-coherent light for the Michelson interferometer demodulation. For the feasibility test, different profiles of test strain, temperature and vibration have been applied to test structures, and successfully reconstructed with the proposed sensor system.
An epoxy cure monitoring system has been constructed by combining fiber grating sensors and Fresnel reflection monitoring. The sensors measure strain and refractive index variations during the curing process, indicating the onset of gelification, the progress, and the end of curing. We used a wavelength-swept laser source to address both types of sensors. The signals from different sensors could be easily separated, resulting in simple optical setup and increased efficiency. The fiber grating sensors are demodulated by a spectrometer. The output fluctuation in the Fresnel reflection was compensated by referencing it with the tapped output of light source.