Fiber Bragg Grating Temperature Sensor Research Articles

Temperature monitoring of nuclear reactor cores with multiplexed fiber Bragg grating sensors

In-core temperature measurement is a critical issue for the safe operation of nuclear reactors. Classical thermocouples require shielded connections and are known to drift under high neutron fluence. As an alternative, we propose to take advantage of the multiplexing ca- pabilities of fiber Bragg grating (FBG) temperature sensors. Our experi- ments show that sensitivity to radiation depends on both the radiation field and the grating characteristics. For some FBGs installed in an air- cooled graphite-moderated nuclear reactor the difference between the measurements and the readings of calibrated backup thermocouples was within the measurement uncertainty. In the worst case, the differ- ence saturated after 30 h of reactor operation at about 5°C. To reach megagray per hour level gamma-dose rates and 10 19 neutron/cm 2 flu- ences, we irradiated multiplexed FBG sensors in a material testing nuclear reactor. At room temperature, FBG temperature sensors can sur- vive in such radiation conditions, but at 90°C a severe degradation is observed. We evidence the possibility to use FBG sensing technology for in-core monitoring of nuclear reactors with specific care under well- specified conditions. © 2002 Society of Photo-Optical Instrumentation Engineers.

Fiber Bragg grating temperature sensor for practical use

Fiber Bragg grating (FBG) is a promising measurement technology for future sensor system applications. Little attention has been given to the FBG sensor housing, however it is important that the FBG is embedded in a conventional electrical sensor housing so that it may be installed easily in instrumentation systems. We have experimentally fabricated a practical pass-through type FBG temperature sensor which is embedded in the conventional thermocouple housing. A small radius U-turn fiber spliced to the FBG is placed inside the top of a stainless sheath. Employing a high numerical aperture fiber with polyamide recoating, we have determined that the bending loss of the small radius U-turn fiber and heat resistance is less than 0.1 dB and up to 250°C respectively. The wavelength shift of this sensor due to temperature change is 10.3 pm/°C equal to that of general FBG. Consequently the practical use of this sensor has been confirmed.

In situ substrate temperature measurements during radio frequency sputtering of ZnO thin film using fiber Bragg grating

Several research groups throughout the world are currently working on fiber acousto-optic components, principally phase modulators, made by depositing a film of piezoelectric materials such as zinc oxide (ZnO) directly onto the optical fiber. It is well known that the quality of the resulting film is highly dependent on the temperature of the substrate (i.e., the fiber), but this has not been directly measured in situ. We present for the first time in situ measurements of the fiber temperature during the deposition process using a fiber Bragg grating temperature sensor. We show that the fiber temperature may rise substantially above that of its immediate surroundings. We also present a simple model for the heat flow for the fiber and the holder based on the heat gain from the plasma and the radiation loss between the various components in the sputtering chamber.

Fiber Bragg grating temperature sensor with controllable sensitivity

We demonstrate a fiber Bragg grating (FBG) sensor with controllable sensitivity by connecting two metal strips that have different temperature-expansion coefficients. By changing the lengths of the metal strips we successfully controlled and improved the temperature sensitivity to 3.3 times of that of bare FBG.

Embedded Fiber Bragg Grating Sensors for Industrial Composite Cure Monitoring

An embedded Fiber Bragg Grating (FBG) strain sensor and an FBG temperature sensor have been shown to be able to accurately monitor the industrial composite cure process of a glass/ epoxy plate devoted to aeronautical applications. The internal absolute strain level in the plate was determined, free of temperature effect thanks to a differential method. After curing, a residual compression strain of about -0.22% was observed, which represents a short part of the range in compression for a single mode fiber. Later on, the embedded FBG strain sensor could be used as a smart sensor for the health monitoring of composite structures, e.g. for impact or layer delamination detection.

Simultaneous measurement of displacement and temperature using a low finesse cavity and a fiber Bragg grating

An optical sensor capable of simultaneously measuring displacement and temperature is presented. It incorporates a fiber Bragg grating temperature sensor and a low-finesse extrinsic Fabry-Perot cavity. A white light tandem interferometric technique is used to recover signal from the low finesse cavity. Signals obtained from the interferometer and the Bragg grating provide required information to simultaneously determine temperature and displacement. Experimental results are presented which demonstrate the feasibility of this sensor topology in practical applications.