A Fiber-Optical Intrusion Alarm System Based on Quasi-Distributed Fiber Bragg Grating Sensors

A fiber-optical intrusion alarm system based on quasi-distributed fiber Bragg grating （FBG） sensors is demonstrated in this paper. The algorithms of empirical mode decomposition （EMD） and wavelet packet characteristic entropy are adopted to determine the intrusion location. The intrusion alarm software based on the Labview is developed, and it is also proved by the experiments. The results show that such a fiber-optical intrusion alarm system can offer the automatic intrusion alarm in real-time.

Experimental study on cross-sensitivity of temperature and vibration of embedded fiber Bragg grating sensors

In view of the principle for occurrence of cross-sensitivity, a series of calibration experiments are carried out to solve the cross-sensitivity problem of embedded fiber Bragg gratings(FBGs) using the reference grating method. Moreover, an ultrasonic-vibration-assisted grinding(UVAG) model is established, and finite element analysis(FEA) is carried out under the monitoring environment of embedded temperature measurement system. In addition, the related temperature acquisition tests are set in accordance with requirements of the reference grating method. Finally, comparative analyses of the simulation and experimental results are performed, and it may be concluded that the reference grating method may be utilized to effectively solve the cross-sensitivity of embedded FBGs.

Long-term performance of packaged fiber Bragg grating sensors for strain monitoring inside creep medium

To investigate the long-term performance of the packaged fiber Bragg grating(FBG)sensors embedded in civil infrastructure for strain monitoring,in this paper,the influence of host matrix’s creep effect on the behavior of the FBG sensors was systematically studied through theoretical,numerical,and experimental analysis.A theoretical strain transfer analysis between the optic fiber,packaging layer,and host matrix to consider the creep effect of the host matrix was performed accordingly for long-term strain monitoring.Parametric studies were carried out using numerical analysis for FBG sensors packaged with glass fiber reinforced plastic(GFRP),also known as FBG-GFRP sensors in concrete,as an example.The results show that embedded in a creep medium,an acceptable long-term performance of packaged FBG sensors requires the packaging layer to have a minimum length and maximum thickness.Laboratory long-term creep tests using epoxy resin and concrete as host matrix for FBG-GFRP sensors also clearly demonstrated that the influence of creep effect cannot be ignored for strain measurements if the host matrix has a creep potential and the developed correction model performed well to reduce measurement errors of such sensors in creep medium.

Use of fiber Bragg grating sensors for monitoring delamination damage propagation in glass-fiber reinforced composite structures

Embedded fiber Bragg grating（FBG）sensors have been widely used for damage monkoring of fiber composite structures for a few decades.However,many remaining engineering challenges have delayed FBG based in situ structural health monitoring（SHM）systems.One of the major problem associated with FBG based SHM system is the unavailability of reliable data processing algorithms.The present work details a study which has been undertaken for identification of delamination crack propagation in composite plate under fiber reinforced polymer（FRP）uniaxial loading.The strain measured by embedded FBG sensors closer to the crack tip was used to qualitatively and quantitatively analyze delamination damage propagation using recently proposed elasto-plastic model.Strain energy release rate was calculated and compared with the model prediction.The study has concluded that the delamination crack propagation in a FRP composite can be monitored successfully using an integral approach of FBG sensors measurements and the predictions of proposed elasto-plastic model.

Magneto-Optic Fiber Bragg Gratings with Application to High-Resolution Magnetic Field Sensors

Magneto-optic fiber Bragg gratings （MFBG） based on magneto-optic materials have a lot of potential applications for sensing and optical signal processing. The transmission and reflection spectra of guided optical waves in the MFBG are investigated. According to the sensitivity of MFBG spectral lines to the magneto-optic coupling intensity varying with applied magnetic field, a novel magnetic field sensor of high-resolution up to 0.01 nm/（kA/m） is predicted.

Packaging Effects on Fiber Bragg Grating Sensor Performance

In this paper, the effects of packaging material and structure of fiber Bragg grating sensor performance are investigated. The effects of thermal expansion coefficient of different embedding materials on the temperature sensitivities of the FBG sensors are studied both theoretically and experimentally with good agreement, which provides a means for selection of FBG packaging material to achieve desired temperature sensitivity. We also demonstrate a 4-point bending structured FBG lateral force sensor that measures up to 242N force with well-preserved reflection spectrum, whereas for 3-point bending structure, multiple-peaks start to occur when applied force reaches 72N.

Interrogating a Fiber Bragg Grating Vibration Sensor by Narrow Line Width Light

A method to interrogate fiber Bragg grating vibration sensor by narrow line width light is demonstrated. The interrogation scheme takes advantage of the intensity modulation of narrow spectral bandwidth light, such as distributed feedback laser, when a reflection or transmission spectrum curve of an fiber Bragg grating （FBG） moves due to the strain which is applied on the sensor. The sensor＇s response to accelerating frequency and amplitude is measured by experiment. The factors which have impacts on the sensitivity of the interrogation system are also discussed.

Fiber Bragg Grating Sensor Array System Based on Digital Phase Generated Carrier Demodulation and Reference Compensation Method

A novel fiber Bragg grating （FBG） sensor array system based on digital phase generated carrier （PGC） demodulation and reference compensation method is proposed and set up. Experimental results confirm that the digital PGC demodulation can be used for wavelength-division-multiplexed FBG sensor array and the reference compensation method can reduce the environmental interference by approximately 40 dB in the frequency range from 20 Hz to 2 kHz. The minimum detectable wavelength-shift of the sensor system is 1 × 10^-3 pm/Hz^1/2.

Characteristics of Smart Concrete with Fiber Optical Bragg Grating Sensor

Based on the advantages of the fiber Bragg grating sensing technology,this paper presents a principle of a novel smart concrete with fiber optical Bragg grating sensor,analyses the theory and characteristics,illustrates the key technology and method to make the fiber Bragg grating sensor for the smart concrete,and proves the feasibility with experiments.The results indicate that the smart concrete with fiber Bragg grating sensors is feasible in the structure monitoring and damage diagnosing in the long run.

Dissolution and Deformation Characteristics of Limestones Containing Different Calcite and Dolomite Content Induced by CO_(2)-Water-Rock Interaction

To investigate the impacts of mineral composition on physical and mechanical properties of carbonate rocks,limestone specimens containing different contents in calcite and dolomite are selected to perform CO_(2)-water-rock reaction experiments.The X-ray Diffraction(XRD) and Nuclear Magnetic Resonance(NMR) are carried out to examine the change characteristics of mineral dissolution and pore structure after reaction.The core flooding experiments with Fiber Bragg gratings are implemented to examine the stress sensitivity of carbonate rocks.The results show that the limestones containing pure calcite are more susceptible to acid dissolution compared to limestone containing impure dolomite.The calcite content in pure limestone decreases as the reaction undergoes.The dissolution of dolomite leads to the formation of calcite in impure limestone.Calcite dissolution leads to the formation of macropore and flow channels in pure limestone,while the effects of impure dolomite in impure limestone results in mesopore formation.When confining pressure is lower than 12 MPa,pure limestones demonstrate higher strain sensitivity coefficients compared to impure limestone containing dolomite after reaction.When confining pressure exceeds 12 MPa,the strain sensitivity coefficients of both pure and impure limestones become almost equal.

Fiber Bragg grating pressure sensor with enhanced sensitivity

A novel fiber Bragg grating （FBG） pressure sensor with the enhanced sensitivity has been demonstrated. A piston-like diaphragm with a hard core in the center is used to enhance the sensitivity. Both the theoretical analysis and the experimental result show that the radius of the hard core has significant effect on the pressure sensitivity. When the radius of the hard core is 1.5 mm, a pressure sensitivity of 7.23 nm/MPa has been achieved.

Hybrid fiber Bragg grating sensor for vibration and temperature monitoring of a train bearing

We report a fiber Bragg grating（FBG）-based sensor for the simultaneous measurement of a train bearing’s vibration and temperature. A pre-stretched optical fiber with an FBG and a mass is designed for axial vibration sensing. Another multiplexed FBG is embedded in a selected copper-based alloy with a high thermal expansion to detect temperature. Experiments show that the sensor possesses a high resonant frequency of 970 Hz, an acceleration sensitivity of 27.28 pm/g, and a high temperature sensitivity of 35.165 pm/℃. A resonant excitation test is also carried out that demonstrates the robustness and reliability of the sensor.

Time/Wavelength Fiber Bragg Grating Multiplexing Sensor Array

A novel time/wavelength-multiplexed fiber Bragg grating sensor array is presented. This type of sensor array has the advantages of more points for multi-point measurement, simple structure and low cost.

Fiber Bragg Grating Sensor Network Optimization

This study introduces the optimization of the fiber Bragg grating （FBG） network and the load identification. Current researches on the optimal placement and reliability of the FBG network and the static load identification are generally analyzed. And then, the optimal placement of sensors and reliability of the FBG network are studied. Through the analysis of structural response characteristics, the general rules of sensors placement in structural static response parameters monitoring are proposed. The probability calculation is introduced, and the numerical analyses of the FBG sensor network reliability of several simple topologies are given.

A Novel Fiber Bragg Grating with Triangular Spectrum and Its Application in Strain Sensor

A novel fiber Bragg grating with triangular spectrum is presented. A strain sensor based on this fiber grating is proposed. Experiments showed that the sensor has advantages of high sensitivity, wider measuring range and immunity to fluctuation of the light source power.

New Demodulation System for Fiber Bragg Grating Sensor

The mechanism of measuring temperature and strain using FBG has been studied deeply, however , signal demodulation has not been thoroughly solved. A novel demodulation system using CCD and a temperature sensing system are designed.

Optical Properties of High Sensitivity Fiber Bragg Grating on Temperature Sensor

In this paper, the spectrum shift properties of the center reflection wavelength detected to be based on the FBG sensor with ambient temperature change. The basic theoretical methods and numerical simulation for the spectral properties of uniform Bragg grating is analyzed by using coupling mode theory which is optical properties of high sensitivity fiber Bragg grating on temperature sensor in accordance with experiment.

A Practical Detection System of Multiplexed Wavelength Fiber Bragg Gratings

A practical demodulation of multiplexed wavelength FBGs is proposed. The detection wavelength of adjacent FBGs and the wavelength resolution are discussed. Experimental results show the wavelength resolution is 0.01nm and strain resolution is 8.27× 10-6.

An optimized distributed fiber Bragg grating sensing system based on optical frequency domain reflectometry

In this paper, the waveforms in time domain and frequency domain of two kinds of optical frequency domain refleetometry （OFDR） sensing systems are com- pared, which use common fiber Bragg grating （FBG） and chirped grating, respectively. The results show that chirped fiber grating with about 3 nm of full width at half maximum （FWHM） is helpful to reduce frequency noise evidently and makes the characteristic frequency distinct. OFDR distributed sensing system with chirped grating also offers longer available time, which makes it convenient to measure slow time-varying signal. Such OFDR distributed sensing system is supposed to be more suitable to be applied in bridge health monitoring, and it will improve the accuracy and reliability of the measurement.

Recent Advances in Long-distance FBG Sensor Systems at UESTC

Recent progress in long-distance in-Fiber Bragg Grating （FBG） sensor systems at University of Electronic Science ＆ Technology of China （UESTC） is reviewed in this paper. Two novel approaches with a 50km transmission distance are proposed and demonstrated. The first one is based on the combination of bidirectional Raman amplification and a dual Erbium-Doped Fiber （EDF） configuration. A good Signal-to-Noise Ratio （SNR） of ～16dB is achieved with only a pump power of ～280 mW, which is ～10 dB higher than that without amplification. The second is based on a novel tunable fiber ring laser configuration with hybrid Raman/EDFA configuration. Experimental results show that an excellent optical SNR of-～60 dB has been achieved for a 50 km transmission distance with a low Raman pump power of ～170 mW and a low EDFA pump power of～40 mW at wavelength of 980 nm. It is anticipated that these long-distance FBG sensing systems could find important applications in health monitoring of large infra-structures, such as oil or gas pipelines, ultra-long bridges and tunnels, river banks, and so on.