Determination of the Postmortem Interval Using Fiber Bragg Grating Sensors

Fiber Bragg grating(FBG)sensors are often used in monitoring activities and to ensure that environmental parameters satisfy industrial requirements.They offer crucial safety measures in the early detection of hazards due to their greatly reduced size,low weight,flexibility,and immunity to electromagnetic interference.These characteristics make FBGs suitable also for use in relation to the human body for in vivo measurements and long-term monitoring.In this study,recent developments are presented with regard to the utilization of these sensors to measure the so-called post-mortem interval(PMI).Such developments rely on numerical simulations based on the Matlab software and monitoring of the rectal temperature,which is one of the main parameters for estimating the PMI.First,the Matlab software is used to solve the Henssge equation for different ambient temperatures and for different body masses;then a Bragg grating sensors is used for post-mortem dating.The results and their accuracy are discussed.

Demodulation System for Fiber Bragg Grating Sensors Using Digital Filtering Technique

A discrimination measurement method and demodulation technique for fiber Bragg grating (FBG) sensors were presented using digital filtering technique. The system can control a tunable fiber Fabry-Perot filter with sawtooth wave voltage generated by digital clock to interrogate FBG sensors. Using the analogue digital converter (ADC), the reflected FBG signals were sampled with synchronous digital clock. With the aid of digital matched filtering technique, the sampled FBG signals were processed to obtain the maximum signal-to-noise ratio (SNR) and the Bragg wavelength shift from the FBG signals was recovered. The results demonstrate that this system has a scanning range of 1 520 nm-1 575 nm,and the wavelength detection accuracy is less than 2 pm with 1.5 Hz scanning frequency.

Advances in femtosecond laser direct writing of fiber Bragg gratings in multicore fibers:technology,sensor and laser applications

In this article,we review recent advances in the technology of writing fiber Bragg gratings(FBGs)in selected cores of multicore fibers(MCFs)by using femtosecond laser pulses.The writing technology of such a key element as the FBG opens up wide opportunities for the creation of next generation fiber lasers and sensors based on MCFs.The advantages of the technology are shown by using the examples of 3D shape sensors,acoustic emission sensors with spatially multiplexed channels,as well as multicore fiber Raman lasers.

Resistance Spot Welding Method for Metal-Based Fiber Bragg Grating Sensors

Aiming at the requirements of installation and work environment of metal-based fiber Bragg grating(FBG)sensor,a resistance spot welding method is presented.Firstly,the effect of welding parameters on welding quality is discussed theoretically,and a suitable resistance spot welding method for the metal-based FBG sensor is proposed for the first time.Then through serial resistance spot welding tests,the feasibility and practicability of the method are verified,and optimal welding parameters for two different tested metals are obtained.Fatigue performance test validates FBG sensors installed by the proposed method with good fatigue properties and long-term stable measurement performance.The research results can provide technical guidance for engineering structure long-term safety monitoring.

An active temperature compensated fiber Bragg grating vibration sensor for high-temperature application

An active temperature compensated fiber Bragg grating(FBG)vibration sensor with a constant section cantilever beam is proposed for the simultaneous measurement of temperature and vibration,and the sensor is verified by a temperature compensation feedback system.The high-temperature vibration sensor is composed of a quartz cantilever beam and a femtosecond Bragg grating.The feedback control demodulation system of active temperature compensation can adjust the laser wavelength to stabilize the grating offset point and realize simultaneous measurement of temperature and vibration.On this basis,the performance of the sensor is tested and analyzed within the range of 20-400℃by setting up a high-temperature vibration test system.The experimental results show that the sensitivity of the sensor is about 132.33 mV/g,and the nonlinearity is about 3.33%.The sensitivity between the laser wavelength and temperature is about 0.01307 nm/℃.In addition,the active temperature compensated fiber Bragg grating vibration sensor has the advantages of a simple structure,stable performance,easy demodulation and high sensitivity.Moreover,the sensor can achieve high temperature vibration signal monitoring and has good practical application value.

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.

High sensitivity micro-displacement sensor based on fiber Bragg grating and amplification substrate

A micro-displacement sensor based on fiber Bragg grating(FBG) is proposed. The device consists of a pair of FBGs with different central wavelengths fabricated by femtosecond laser phase mask method and a metal substrate with lever structure. The displacement is amplified by lever structure and it converts into axial tension of FBG, which has a high displacement sensitivity. The amplification factors obtained by theoretical analysis and finite element simulation are 2.67 and 2.50, respectively. The experimental results show that in the range of 0-50 μm the shift of FBG center wavelength is linearly related to the displacement of measured object and displacement sensitivity reaches 121 pm/μm. In addition, the cascaded FBG is used to compensate the temperature.

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.

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.

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.

Optical fiber Bragg grating sensors in smart structures

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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.

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.

准确检测液位的光纤Bragg光栅弹性膜片传感器

为了准确测量液位,研制了一种耦合光纤布喇格光栅和弹性膜片的液位传感器。该传感器由两个光纤光栅(FBG_1和FBG_2)、弹性膜片、弹性橡胶密封垫片、空心管(导气管)和光纤光栅固定装置组成。光纤光栅固定装置材料为聚甲基丙烯酸甲酯。FBG_1和FBG_2固定在弹性膜片表面。FBG_1用于监测液位高度和温度。将FBG_2封装在不锈钢毛细管中进行温度检测,消除液相温度变化对液位测量的负面影响。为了提高传感器检测液位的线性度,实验研究了弹性膜片厚度对液位测量结果的影响,并在此基础上研究了液位变化率和外部振动对液位测量精度的影响。结果表明,当弹性膜片厚度为2 mm时,传感器检测液位的线性范围为0~380 cm,灵敏度为(19.65±6.3)pm/cm。该传感器可在0~100 cm/min液位变化速率和0~5.27 mm/s外部振动强度范围内准确监测液位,最大检测误差为7.2%。

Engineering approach to in-situ bridge health monitoring with fiber bragg gratings

In this presentation the feasibility and capability of fiber Bragg gratings （FBG） employed in bridge health monitoring are demonstrated on a real bridge. FBG＇ s wavelength shift depending on strain variance has been tested. The technique of FBG installation on bridges has been developed. 12 FBG strain sensors and 3 temperature sensors have been successfully embedded in the prestressed concrete box girder during the construction of Heilongjiang Hulan River Bridge. The prestressing tension process and quasi-static loading process of the girder were monitored with those sensors before it was installed onto the bridge. After the bridge was completed, the FBG sensors embedded have been utilized to monitor the strain shift of the beam under quasi-static load, traffic load and temperature. The results show that the traffic fluxes, possible tatigue damage and deflection of the bridge can be revealed conveniently through strain measurements with these FBG sensors, which provide key information for structural health diagnosis. The fact that the FBG strain sensors have withstood the ordeal of harsh construction process and lasted for more than one year proves that their durability and stability can satisfy the requirements for bridge health monitoring. It is also shown that the FBG strain sensor is more adaptive to long-term structural health monitoring than the electric resistance strain gauge.

Study on rock deformation monitoring using fiber Bragg grating in simulation experiment

Presented the fiber Bragg grating （FBG） sensors for rock strain monitoring in the 1.2 m long plane stress model of the simulation experiment. In the past, for the lack of appropriate technique to measure the deformation of rock structures, the measurement of deflection was restricted to just a few discrete points along rock, and the measuring points were limited to the location installed with displacement transducers. We developed a method to monitor the deformation of rock structures using fiber optical Bragg grating strain sensors. The sensors were embedded in rock layers of simulation experiment before the materials were put in. These sensors were then used to monitor the experienced strain with different face advancing distance. The test results indicate that, if properly installed, FBG sensors can survive under severe conditions associated with embedment process and yield accurate measurements of strains response. At the same time, we make comparisons of the data obtained by FBG sensors with those by centesimal gauge. The interest in FBG sensors was motivated by the potential advantages that they can offer more than existing sensing technologies.

Cascaded tilted fiber Bragg grating for enhanced refractive index sensing

We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating(TFBG)for enhanced refractive index sensing.The TFBG is UV-inscribed in series in ordinary single-mode fiber(SMF)and reduced-diameter SMF with the same tilt angle,and then excites two sets of superposed spectral combs of cladding modes.The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF,enabling an enlarged range and a higher accuracy of refractive index measurement.The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.

Fiber Bragg Gratings in Small-Core Ge-Doped Photonic Crystal Fibers

This paper reports fiber Bragg gratings （FBGs） inscribed in a small-core Ge-doped photonic crystal fibers with a UV laser and a Talbot interferometer. The responses of such FBGs to temper- ature, strain, bending, and transverse-loading were systematically investigated. The Bragg wavelength of the FBGs shifts toward longer wavelengths with increasing temperature, tensile strain, and transverse-loading. The bending and transverse- loading properties of the FBGs are sensitive to the fiber orientations.

Study on Refraction Index Sensors Using Fiber Grating F-P Cavity

In this paper, the reflective spectra of a refraction index sensor were analyzed based on fiber grating F-P cavity. The sensor was constituted by two identical fiber gratings. Compared with the refraction index sensor using one fiber grating, the fiber grating F-P cavity sensor has narrower resonant peak and it can be used for more accurate measurement. The resonant peaks in the reflective spectra of the sensor are changed with small changes of the refraction index of the measured chemical liquids or cell samples. So it has potential applications in biology and chemistry.

Fabrication of High Quality Broadband Type IIA Chirped Fiber Bragg Gratings

Chirped fiber Bragg gratings have found many applications in optical communication and sensing systems. High quality filters based on chirped fiber Bragg gratings with reflection bandwidth of 2.6 and 32nm and high reflectivity are demonstrated experimentally with 2 and 4cm long phase masks, respectively. These filters with flat reflection band and high reflectivity are achieved by writing type IIA chirped Bragg gratings.