Fiber Bragg Grating Temperature Research Articles

A Passive Optical Fiber Anemometer for Wind Speed Measurement on High-Voltage Overhead Transmission Lines

Measurement of wind speed is an essential part of overhead transmission line monitoring. To overcome the drawbacks of the existing anemometer, such as the requirement on field power, the sensitivity to electromagnetic interference, and the unavailability of real-time measurement, a novel anemometer is developed on the basis of the fiber Bragg grating (FBG) sensing technique. In the anemometer, a beam with uniform strength was used to measure the force generated by the wind; two naked FBGs were symmetrically glued on the upper and lower surfaces of the beam to solve the problem of cross-sensitivity between strain and temperature of FBG sensing. Furthermore, the temperature effect on the zero output was investigated by putting the FBG anemometer into a temperature-controlled cabinet, and the experimental results indicated that the temperature effect on the zero output of the wind speed was less than ±5 pm (-10° C to 50 °C). The results from the wind tunnel experiment indicated that the measurement error of the anemometer was less than ±0.5 m/s.

Feedback Stabilized Interrogation Technique for EFPI/FBG Hybrid Fiber-Optic Pressure and Temperature Sensors

This paper discusses a Single Wavelength Interrogation (SWI) technique used to measure fast changing pressure related signals and over a large operational temperature range. The novel technique is based on a fiber-optic pressure and temperature hybrid sensor, and a feedback stabilization technique for a tunable laser source. The fiber-optic hybrid sensor consists of a miniature diaphragm based all-silica Extrinsic Fabry-Perot Interferometric (EFPI) Fiber-Optic Pressure Sensor (FOPS) which additionally incorporates a Fiber Bragg Grating (FBG) temperature sensor. The FBG temperature sensor is used as a feedback element to stabilize the output wavelength of the tunable laser source to operate always in the linear range of the EFPI FOPS.

基于动态法布里珀罗腔的光纤光栅温度传感

基于动态法布里珀罗腔的光纤光栅温度传感

Fiber Bragg Grating Temperature Sensors Applied in Intelligent Monitoring of Cable Trench and Cable Pit

Cable is the bridge connecting electrical equipment, such as transformers, circuit breakers and switchgear, etc, but also a power equipment. The long-running of cable will probably cause insulation material aging, leakage sparking and local overheating occur, which eventually lead to a cable fire and accident, the temperature of cable surface usually reflected the situation of the cable. In the paper, fiber bragg grating temperature sensor, insensitive to external stress was applied in monitoring cable temperature. The temperature of cable surface ranges in the similar curve with ambient temperature.

A PDMS-Coated Optical Fiber Bragg Grating Sensor for Enhancing Temperature Sensitivity

We proposed a poly-dimethylsiloxane (PDMS)-coated fiber Bragg grating (FBG) temperature sensor for enhancing temperature sensitivity. By embedding the bare FBG in a temperature-sensitive elastomeric polymer, the temperature sensitivity of the proposed structure could be effectively improved by 4.2 times higher than those of the conventional bare-type FBG sensors due to the high thermal expansion coefficient of the PDMS. We analyzed the temperature-sensitivity enhancement effect with the increased Bragg wavelength shift in our structure and dependence on the temperature sensitivity with respect to the cross-section area of the PDMS.

Design and Application of Long Distance Oil & Gas Pipeline Stress & Strain Monitoring Sensor

As Oil & Gas Pipeline of Long Distance has potential mechanical risks caused by geologic hazards, based on sensing technique, Fiber Bragg Grating (FBG) strain sensor, for which unstressed grating temperature compensation method is adopted, is designed to solve problems of FBG temperature and strain cross sensitivity. According to experimental tests, strain sensitive coefficients of the sensor before and after sticking on pipeline sample are 1.20 pm/με and 1.09 pm/με in separate. Finally, applied to a landslide area for monitoring pipeline stress, the sensor got the impact of Wenchuan Earthquake on May 12, 2008 on the pipeline.

Characteristics of a Fiber Bragg Grating Temperature Sensor Using the Thermal Strain of an External Tube

Characteristics of a Fiber Bragg Grating Temperature Sensor Using the Thermal Strain of an External Tube

Performance analysis of a fiber Bragg grating filter-based strain/temperature sensing system based on a modified Gaussian function approximation method

This paper analyzes the performance of a fiber Bragg grating (FBG) filter-based strain and/or temperature sensing system based on a modified Gaussian function (MGF) approximation method. Instead of using a conventional Gaussian function, we propose the MGF, which can capture the characteristics of the sidelobes of the reflected spectrum, to model the FBG sensor and filter. We experimentally demonstrate that, by considering the contributions of the sidelobes with the MGF approximation method, behaviors of the FBG filter-based FBG displacement and/or temperature sensing system can be predicted more accurately. The predicted behaviors include the saturation, the sensitivity, the sensing range, and the optimal initial Bragg wavelengths of the FBG sensing system.

Design, characterization and implementation of a fiber Bragg grating temperature sensor for application in solar power electronic inverters

This paper reports the design, characterization and implementation of a fiber Bragg grating (FBG) temperature sensor in a power electronic inverter which has a high electromagnetic interference (EMI) radiation. The performance and characteristics of the sensor are investigated by monitoring the temperature variation of the insulated gate bipolar transistor (IGBT) in photovoltaic (PV) arrays inverter. The thermal expansion of the optical fiber is enhanced by mounting the FBG sensor to a metal sheet. Due to this enhancement, the FBG temperature sensor recorded an improvement in terms of linearity and sensitivity. A comparison is made between the performance of the enhanced FBG sensor and a thermocouple in a high EMI environment, and the results show that the FBG sensor performs better.

Enhanced temperature sensitivity of fiber Bragg grating temperature sensor using thermal expansion of copper tube

AbstractThe temperature sensitivity of fiber Bragg grating (FBG) temperature sensor is enhanced when using a copper tube to jacket of the FBG.Both sides of the FBG are glued with epoxy to cylindrical ferrules tubes that in turn is inserted and glued to a cylindrical copper tube. As the high thermal expansion coefficient of the cylindrical copper tube pulls both sides of the FBG, the temperature sensitivity is improved 3.3‐fold when compared to that of a bare FBG. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26032

Modified simulated annealing evolutionary algorithm for fully distributed fiber Bragg grating temperature sensing

In this paper, we present a simple and fast spectra inversion method to reconstruct the temperature distribution along single fiber Bragg grating (FBG) temperature sensor. This is a fully distributed sensing method based on the simulated annealing evolutionary (SAE) algorithm. Several modifications are made to improve the algorithm efficiency, including choosing the most superior chromosome, setting up the boundary of every gene according to the density of resonance peaks of the reflection spectrum, and dynamically modifying the boundary with the algorithm running. Numerical simulation results show that both the convergence rate and the fluctuation are significantly improved. A high spatial temperature resolution of 0.25 mm has been achieved at the time cost of 86 s.

Development of FBG Sensing System for Outdoor Temperature Environment

We have experimentally designed a practical pass-through type FBG temperature sensor. The objective of this study is to design and built a prototype outdoor fibre Bragg grating (FBG) temperature sensor system. Its performance is evaluated at different times of the day. In order to reduce the optical losses of the FBG system, the shortest optical fiber path used to connect the FBG system is 55.5m. It has a total connector loss 4.0dB and fibre loss of 0.3dB thus giving a total loss of the system as 4.3dB. The FBG sensor system is connected to the tunable laser source (TLS) and optical spectrum analyzer (OSA). The TLS is used to provide a broadband light source via a fibre optic cable of wavelength 1550nm. The OSA is used to display the transmission and reflection spectrum to give the Bragg wavelength _B, bandwidth and power dip. The output spectrum can be obtained through direct connection to the FBG. Result of transmission and reflection spectrum show the sensitivity which is calculated from the slope of the graph. The FBG temperature sensor system has an average sensitivity of 9.1 pm (°C)-1 based on the transmission spectrum. It has an average sensitivity of 10.6 pm (°C)-1 based on the reflection spectrum.

Demodulation of the FBG temperature sensor with the tunable twin‐core fiber

AbstractA novel linear edge filter based on a piece of tunable twin‐core fiber is proposed in this article.The transmission spectrum of the twin‐core fiber can be adjusted by pulling and twisting the twin‐core fiber to match the central wavelength of the Fiber Bragg Grating (FBG) used for the temperature sensor. The feasibility of the method is analyzed and demonstrated experimentally. This demodulation filter, which is based on the all‐fiber component, can be designed and adjusted according to the measurement sensitivity and range of FBG temperature sensor, so its characteristics of compact scheme and low cost would make this method more applicable. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:81–84, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25681

Fiber Bragg Grating Temperature Sensor System on a Twin-Deck Continuous Rigid Frame Bridge for Long Term Monitoring

In structural health monitoring, evaluation of bridge serviceability performance is based on vibration method. The vibration properties are influenced by temperature, humidity, wind and traffic load. Temperature differential in rigid frame bridge causes additional stress, which affects dynamic characteristics and induces concrete cracks. Thus analysis of temperature distribution is the basement of damage identification. Fiber Bragg grating (FBG) sensors are advanced materials for SHM. This paper introduces a temperature sensor monitoring system consisting of 52 temperature sensors on a twin-deck continuous rigid frame concrete bridge and analyzes temperature distribution on the twin decks of the bridge through August to December, 2006. Temperature at the same height sections differs little in the longitudinal direction along this bridge. The comparisons between maximum and minimum temperature each month reveal the asymmetry of transverse temperature distribution. The pavement has significant impact to the top slab temperature. In November the temperature declines sharply. The temperature on the external surface of top slab is lower than that of bottom for short box girders in winter because of shelters of flanges.

Enhanced Sensitivity of the FBG Temperature Sensor Based on the PbO-GeO$_{2}$-SiO$_{2}$ Glass Optical Fiber

We developed and demonstrated a highly sensitive fiber Bragg grating (FBG) temperature sensor by using the PbO-GeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> glass optical fiber. Temperature sensitivity of the FBG sensor based on the PbO-GeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> glass optical fiber was about 40% improved to the 0.0173 nm/°C by the thermal expansion increase of the fiber.

Temperature and strain sensing characteristics of the tilted fiber Bragg grating

Theoretical and experimental studies on the tilted fiber Bragg grating (TFBG) temperature and strain sensing characteristics are conducted. The TFBG is stuck to the surface of the beam along the axis direction. When the free end of the beam is forced, both the strain and temperature will induce wavelength shifts. The temperature characteristic of TFBG cladding modes is similar to that of the core mode while the strain characteristics of TFBG core mode and cladding modes are different. A novel method to discriminate the temperature and strain simultaneously is put forward based on TFBG sensing characteristics.

A Simple Demodulation Method for FBG Temperature Sensors Using a Narrow Band Wavelength Tunable DFB Laser

A simple demodulation method for a fiber Bragg grating (FBG) temperature sensor is proposed and demonstrated, which uses a low cost commercial temperature-controlled wavelength scanning distributed-feedback (DFB) laser, a sensing FBG and a low-speed photodetector (PD). Relative high resolution is achieved by utilizing an FBG with enhanced temperature sensitivity design. Such a method may be suitable for applications requiring moderate resolution and low cost implementations.

Design of Fiber Bragg Grating Acoustic Sensor for Structural Health Monitoring of Nuclear Power Plant

Nuclear power plant (NPP) is commonly categorized as a harsh environment that gives rise to age-related degradation on the structures of plant and eventually leads to radiation leakage that threatens human. Integrated structural health monitoring (ISHM) technology is a strong candidate for NPP accidents. The emergence of optical fiber technology into SHM system for NPP was greatly interested by researchers, and also prior research works have shown that the fiber Bragg grating (FBG) was able to retain its reflectivity under radiation exposure. In this paper, a metal-coated fiber was newly used to develop a FBG acoustic sensor for ISHM of NPP. The 7 mm length of aluminum, copper/carbon coatings were successfully removed with sodium hydroxide and nitric acid solutions. A 5 mm FBG was successfully inscribed in the silica core through the 7 mm long coating-removed silica section of copper/carbon-coated fiber and the initial reflectivity was 71%. Then, the FBG acoustic sensor was developed in one-end-free FBG configuration on the stainless steel vessel using a high temperature metallic adhesive. The reflective power of the sensor was stabilized at 345°C during the high temperature elevation cyclic process. The FBG acoustic sensor showed good response to the acousto-ultrasonic waves during pencil-lead breaking and laser ultrasonics tests. The high temperature FBG acoustic sensor written in the cost-effective metal/carbon is feasible to be used for ISHM of the NPP.

Polymer coated fiber Bragg grating thermometry for microwave hyperthermia

Measuring tissue temperature distribution during electromagnetically induced hyperthermia (HT) is challenging. High resistance thermistors with nonmetallic leads have been used successfully in commercial HT systems for about three decades. The single 1 mm thick temperature sensing element is mechanically moved to measure tissue temperature distributions. By employing a single thermometry probe containing a fixed linear sensor array temperature, distributions during therapy can be measured with greater ease. While the first attempts to use fiber Bragg grating (FBG) technology to obtain multiple temperature points along a single fiber have been reported, improvement in the detection system's stability were needed for clinical applications. The FBG temperature sensing system described here has a very high temporal stability detection system and an order of magnitude faster readout than commercial systems. It is shown to be suitable for multiple point fiber thermometry during microwave hyperthermia when compared to conventional mechanically scanning probe HT thermometry. A polymer coated fiber Bragg grating (PFBG) technology is described that provides a number of FBG thermometry locations along the length of a single optical fiber. The PFBG probe developed is tested under simulated microwave hyperthermia treatment to a tissue equivalent phantom. Two temperature probes, the multiple PFBG sensor and the Bowman probe, placed symmetrically with respect to a microwave antenna in a tissue phantom are subjected to microwave hyperthermia. Measurements are made at start of HT and 85 min later, when a 6 degrees C increase in temperature is registered by both probes, as is typical in clinical HT therapy. The optical fiber multipoint thermometry probe performs highly stable, real-time thermometry updating each multipoint thermometry scan over a 5 cm length every 2 s. Bowman probe measurements are acquired simultaneously for comparison. In addition, the PFBG sensor's detection system drift over 10 h is measured separately to evaluate system stability for clinical applications. The temperature profiles measured by the two probes simultaneously under microwave HT are in good agreement showing mean differences of 0.25 degrees C. The stability of the detection system is better than 0.3 degrees C with response times of the PFBG sensor system of 2 s for each scan over ten points. The single fixed multipoint fiber thermometry capability compares favorably with the scanning Bowman probe data. This offers an enabling alternative to either scanning or bundled single point temperature probes for distributed thermometry in clinical applications.

Fibre Bragg grating sensors for monitoring the metal inert gas and friction stir welding processes

Fibre Bragg grating (FBG) sensors are finding increased usage in experimental mechanics for monitoring service conditions in structures and other equipment and are currently being tested for process monitoring. In FBG sensors, strain and temperature cause a shift in the Bragg wavelength reflected by the grating contained in these fibres. In situ monitoring of strain and temperature during welding processes increases knowledge of the welded material and the welding process itself. In the present work, two welding processes are monitored using FBG sensors and the complete measurement approach including sensor selection, calibration, instrumentation, welding monitoring and result interpretation is presented. Calibration for strain measurements at constant temperature was performed using a four-point bending test, and temperature calibration was carried out using an oven. Results for a sensor length of 5 mm are presented. Both transient and residual strains were recorded during experiments on metal inert gas and friction stir welding and the possible impact of this monitoring technology is discussed in the light of process optimization and subsequent structural health monitoring.