Composites have added new dimensions to the design and fabrication of various structures. These structures are usually used to withstand hefty loads, so their integrity must be guaranteed. Due to optical sensors' advantages and FBGs' unique position among optical fibre sensors, we propose in this paper the integration of FBG sensors for the monitorisation of the curing temperature and strain of multidirectional carbon-reinforced polymer cured by microwave radiation heating method and for strain monitoring of a fibre reinforced polymer pultrusion beam.
Shape sensing has become an area of great interest for many medical applications, such as epidural administration, colonoscopy, biopsies, and cardiac procedures, where real-time data of a dynamic object is required and visual contact is absent. Fiber Optic Shape Sensors (FOSS) consist of optical multi-fiber cables or Multicore Fibers (MCF) with embedded strain sensors, which can reconstruct the sensor shape from its multidimensional bending. Regrettably, the accuracy of three-dimensional shape sensing is remarkably restricted because of twisting, which makes impossible to correctly detect the bending direction. This paper reports an experimental study aimed at investigating the accuracy of optical shape sensors based on spun multicore fibers in sensing twisting, employing one of the most used multicore fiber geometry for sensing applications, the seven-core fiber. Firstly, a theoretical approach to model the mechanical behavior of multicore fiber was developed. Secondly, a pre-twisted fiber optic shape sensor was fabricated in the Institute for Telecommunications and Multimedia Applications (iTEAM), by inscribing four Fiber Bragg Gratings (FBG) in a Spun Multicore Fiber (diameter of 125.1 μm) with a pre-twisting of 64.9 rotation/meter, manufactured and provided by FIBERCORE. To conclude, a series of experiments were performed to corroborate the theoretical approach and evaluate the sensor performance. The proposed Spun-MCF-based Shape Sensor was able to sense twisting with a sensitivity of 0.23 pm/° and accuracy of 4.81° within a wide dynamic range of ± 270°, maintaining a perfectly elastic behavior at high level of twisting deformation
Fiber Bragg gratings (FBGs) in a poled silicate fiber are used to detect external voltage applied to the fiber’s internal electrodes. This work shows a basic proof-of-concept of a single-ended, fiber-based voltage sensor that can be used to measure periodic high-voltage signals. The setup can be extended to a multiplexed e-field interrogation system and used in the electric power industry for remote sensing of transmission lines and power plants.
An interrogation technique based on phase modulation to intensity modulation conversion due to FBG filtering is presented. A 10 GHz tone is used to phase modulate an optical carrier located at the Bragg wavelength of a given FBG. The modulation index is set to a small value to keep Bessel identities close to 0 in order to avoid higher harmonics. Changes of the Bragg wavelength cause a power change in the photodetected 10 GHz tone. A remarkable linear sensitivity of 1 dB/pm for a shift up to 10 pm of the Bragg wavelength is demonstrated through experimental measurements. The range with linear sensitivity can be enlarged sweeping the source wavelength. This proves that the presented interrogation technique is able to interrogate FBGs with a resolution far below 1 pm and no need of extra postprocessing.
An interrogation technique of cascaded FBGs sensors based on a Microwave Photonics filtering technique under coherent regime is presented. The sensing information of a 5m fiber coil with 500 weak FBGs with a similar central wavelength is retrieved. The principle of operation is based on the calculation of the impulsive response by recording the electrical frequency response of the system. Hot spot detection and temperature measurement are demonstrated through experimental measurements with a temperature sensitivity of 0.6dB/ºC. The resolution in the measurement is related to the bandwidth of the electrical measurement and we have obtained a resolution of 20 cm for an electrical bandwidth of 1 GHz and a SNR bigger than 16dB.
Multicore optical fiber can be used to implement multidimensional optical fiber sensors including curvature sensors. In this paper, a selective core inscription technique is used in order to inscribe a single long period grating in each of the outer cores of the optical fiber. A set of three different long period gratings is inscribed for implementing the curvature sensor. The ability of the sensor for measuring the magnitude and the direction of curvature is demonstrated. The optical fiber sensor is characterized experimentally for curvature magnitudes from 0 m-1 to 1.77 m-1 and curvature directions from 0° to 360°.The maximum curvature sensitivity of the developed sensor is -4.85 nm/m-1.
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