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A 9.5-m continuous chirped fiber Bragg grating (CFBG) interrogated with an optical frequency domain reflectometer is used for strain and temperature measurements. The spatial resolution is 4 mm and the noise level is 0.1 K corresponding to 1 μstrain. The strain profile is also derived from the optical reflection spectrum alone, and the results are in good agreement with the profile obtained from the...
Fuel assembly vibrations in nuclear reactor cores should not be excessive as these can compromise the lifetime of the assembly and lead to safety hazards. This issue is particularly relevant to new reactor designs that use liquid metal coolants. We therefore demonstrate accurate measurements of the vibrations of a fuel assembly in a lead-bismuth eutectic cooled installation with fibre Bragg grating...
A precise measurement technique of long period of fiber grating sensor (LPG) is demonstrated by employing a cascaded chirp LPG (C-CLPG) as a sensing device and by adopting a Fourier transform method for an interrogation technique. In this approach, transmittance of the C-CLPG exhibits periodic channeled spectrum and its strain- and/or temperature-dependent wavelength shift is analyzed by obtaining...
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...
In this paper the behaviour of fibre Bragg grating (FBG) sensors under non-uniform strain distributions was analysed. Using the fundamental matrix approach, the length of the FBG sensor was discretised, with each segment undergoing different strain values. FBG sensors that are embedded inside composites, also undergo such non-uniform strain distributions, when located in the vicinity of failures such...
A well-known structural health monitoring method used to detect and locate damage in civil engineering structures is vibration-based damage identification. It typically monitors the civil structure over time to spot slow or sudden changes in its natural frequencies, damping factors or modal displacements. This approach can prove very powerful, but the sensitivity of those properties to local damage...
Composite materials are increasingly used in aerospace applications, owing to their high strength-to-mass ratio. Such materials are nevertheless vulnerable to impact damage. It is therefore important to investigate the effects of impacts on composites. Here we embed specialty microstructured optical fiber Bragg grating based sensors inside a carbon fiber reinforced polymer, providing access to the...
We propose a high speed strain measurement method using an active mode locking (AML) fiber Bragg grating (FBG) laser sensor with a chirped FBG cavity. The mode-locked frequency of the AML laser depends on both the position and Bragg wavelength of the FBG. Thus, the mode-locked frequency of cascaded FBGs can be detected independently along the cavity length of cascaded FBGs. The strain across FBGs...
New approach in simultaneous measurement of dynamic strain and temperature has been done by using a high birefringence PANDA fiber Bragg grating sensor. By this technique, we have succeeded in discriminating dynamic strain and temperature distribution at the sampling rate of 800 Hz and the spatial resolution of 1 mm. The dynamic distribution of strain and temperature were measured with the deviation...
FBG inscribed on splice joint is proposed to be used as a sensor. It could realize temperature and strain measurement simultaneously because of the different strain responses of the different parts of the FBG inscribed on splice joint, while the temperature responses are same. The strain responses of four overlap values are discussed, which is used to optimize the discrimination capability of the...
We propose a system for precise measurement of multi-point displacement and strain using fiber Bragg grating (FBG) sensors along with intensity-modulated light and two-photon absorption process in a Si-avalanche photodiode (Si-APD). This method sweeps both the optical wavelength and the phase difference between the two modulation signals. The FBGs' reflection spectra and their change due to strain...
A novel Mach-Zehnder interferometer (MZl) based on a pair of long period fiber gratings (LPGs) in an embedded-core hollow optical fiber (ECOF) are proposed and demonstrated experimentally. Two similar LPGs with peak attenuation of approximately 3dB are fabricated in an ECOF by using high-frequency CO2 laser to form an in-fiber MZI. The dependences of the resonant peak on the temperature and the axial...
A 3D-FEM model has been developed to improve the understanding of multi-parameter sensing with Bragg gratings in attached or embedded polarization maintaining fibers. The material properties of the fiber, especially Young's modulus and Poisson's ratio of the fiber's stress applying parts, are crucial for accurate simulations, but are usually not provided by the manufacturers. A methodology is presented...
Dynamic fibre-optic curvature sensing is demonstrated by interrogating chains of fibre segments, separated by broadband Bragg grating reflectors, using range-resolved interferometry (RRI). Four fibre strings, containing four fibre segments each of gauge length 20 cm, are attached to the opposing sides of a support structure and the resulting differential strain measurements allow inference of lateral...
The surface-bonding method of the fiber Bragg grating(FBG) sensor is easier to handle than embedding method. However surface bonded FBG sensors have the limitation of the signal characteristics being affected by the bonding layer. In this study, the effects of the bonding length on the surface installed FBG sensor signal characteristics under various load types were empirically investigated. To evaluate...
Heavy ice coating of overhead transmission lines created the serious threat on the safe operation of power grid. The measurement of conductor icing had been an effective and reliable methods to prevent potential risks, such as conductor breakage, insulator flashover and tower collapse. Because of the advantages of immunity to electromagnetic interference and no demand for power supply in site, the...
We report on the development of an angle sensor which can measure at high bending curvature. Unlike the other sensors, the novel angle sensor can be durable and flexible. The sensors consist of one fiber Bragg grating (FBG) fiber which is located in the middle of each sensor, and are fabricated in varying thickness to confirm the relation between the distance of the center of the angle sensor to the...
We experimentally demonstrate a scheme for improving the intrinsic pressure sensitivity of fiber Bragg-gratings (FBGs) inscribed in polymer optical fibers by applying pre-strain in order to suppress the pressure induced mechanical contraction of the fiber. This contraction would otherwise contribute to a blueshift of the Brag-wavelength, counteracting the dominant redshift caused by the stress-optic...
This paper presents a spiral bevel gear strain measurement using optical fiber gratings. High-speed and heavy-duty spiral bevel gear (SBG) is the key component of the power transmission of intersection axes. Its dynamic mechanical properties greatly influence the working performance of the machine. By building a strain detecting system based on FBG demodulation, we carried out real-time measurements...
Three different fibre Bragg grating strain sensors were tested for their suitability for measuring high strain. The sensor types were: a bare epoxied fibre Bragg grating, a standard fibre Bragg grating epoxied into a metal capillary and, finally, a metal coated fibre Bragg grating brazed into a metal capillary. The sensors were calibrated on a steel specimen up to 1400MPa (equivalent to 7.3mε). The...
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