Wavelength Shift Of Fiber Bragg Grating Research Articles

Multi-Beam Surveying Ocean Exploration Model and Applications

With the development of artificial intelligence, fiber Bragg grating (FBG) sensing technology has garnered increasing attention. This paper first proposes a surface reconstruction algorithm based on curvature information, which is applicable to two different sensor structures: implanted FBG sensors and whisker array sensors. The design and analysis of these sensors are based on a pure bending model, where the corresponding bending curvature is obtained by measuring the wavelength shift of the fiber Bragg grating at the measurement points. Next, the paper elaborates on the surface reconstruction algorithm for the implanted FBG sensor. This sensor contains FBG sensing points that are evenly distributed. Curvature information corresponding to the position can be obtained based on the direction and magnitude of the wavelength shift. The fiber bending is considered as a connection of multiple arc segments, and the coordinates of the sensing points are calculated in the Cartesian coordinate system using the properties of the tangents. The fiber bending curve is then reconstructed by connecting the arc segments in MATLAB. Finally, the paper provides a detailed introduction to the surface reconstruction algorithm for the whisker array sensor. When the whiskers bend, the FBGs fixed on them act as curvature sensors. The curvature is determined by the FBG wavelength shift, and the three-dimensional coordinates of the whisker tip relative to the base are calculated based on a geometric model. MATLAB is then used to connect the whisker tip coordinates, completing the construction of the surface.

Estimation of Li-ion battery SOH based on factors combination of FBG wavelength shift and charge-discharge process

For the purpose of daily battery maintenance, safety forecasting, and energy ladder use, it is crucial to accurately estimate the state of health (SOH) of Li-ion batteries. The external fiber Bragg grating (FBG) sensor is used in this work to collect the signal fluctuations of the wavelength shift in different areas during the Li-ion battery's charge-discharge cycle using a combination of feature analysis and data-driven method, and the characteristics of the wavelength shift and the charge- discharge process in different regions under 125 cycles are statistically analyzed. The reaction degree of Li-ion battery in different areas was compared by wavelength shift value. The wavelength shift factor and charge-discharge process factor related to battery SOH were extracted and trained in the NGO-BP regression model. The experimental results show that the combination of fiber Bragg grating wavelength shift factor and charge-discharge process factor can accurately estimate the SOH of Li-ion battery, and the prediction effect of three areas combination is the best, the goodness of fit R2 is 0.99958, the mean square error MSE is 2.71 × 10−4, the mean absolute error MAE is 1.3373 × 10−2, the root mean square error RMSE is 1.6462 × 10−2, and the mean absolute percentage error MAPE is 1.3679 × 10−2%.The combination of negative electrode and middle area uses fewer sensors to obtain higher prediction accuracy, and its cost performance is the highest. The utilization of fiber Bragg grating wavelength shift factor and charge-discharge process factor has essentially led to the accurate calculation of Li-ion battery SOH, which holds significance for battery health monitoring as well as the design and development of battery management systems.

Tac-scope: An endoscope integrated with soft sensor for real-time tactile feedback

In order to improve the safety of endoscopic surgery, a flexible endoscope with real-time tactile feedback (Tac-scope) has been proposed. It integrates a soft sensor at the end embedded with fiber Bragg grating (FBG) to detect the contact force with the lumen wall, while retaining the original function of the endoscope. In this article, theoretical analysis, simulated analysis, and experiments have been implemented, obtaining the mapping from FBG wavelength shifts to the force magnitude and orientation. To verify the real-time detection and feedback capability, tests are conducted on the bronchial model. The results show an average reduction of 60% in contact force and 30% in operation time. The linearity of Tac-scope force detection is 0.991, the repeatability error is 6.46%, the resolution is 8.8 mN, the sensitivity is 0.693 nm/N, the average error is 4.4%, and the error of orientation detection is 3.57%. Such merits indicate that the proposed Tac-scope has huge potential in endoscopic surgeries.

Effects of bonding on Fiber Bragg Grating (FBG) sensor for monitoring steel corrosion condition in concretes

Steel corrosion in concrete is harmful but invisible. Until now, it is still very hard to measure the steel corrosion condition by non-destructive method accurately. In this paper, Fiber Bragg Grating (FBG) sensors include single and three grating sensors, are proposed to bond with steel bar and embed in concrete for monitoring the steel corrosion condition. The steel corrosion condition is evaluated by the corrosion ratio and volume expansion coefficients of steel, which are derived from the wavelength shift of FBG. Bonding materials and bonding ways are investigated in detail for improving the accuracy of FBG sensors. The mechanism of bonding effects on FBG sensor for optimizing the accuracy, has been discussed. The results suggested that the steel corrosion condition is successfully monitored by calculating the corrosion ratio of 2.02–4.24%, and volume expansion coefficient of 2.18–2.65 in this test. The research work is more quantify than the traditional methods for monitoring the steel corrosion condition in concretes. It is helpful for ensuring the safety operation of infrastructures efficiently.

Real-time monitoring of urea slow release through fiber Bragg grating sensors

This research aimed at using fiber Bragg grating (FBG) sensors for monitoring the slow release of urea. Urea granules were coated with ethyl cellulose for controlled-nitrogen release. The FBGs were fabricated using a 10 mm single-mode glass fiber optic, and silver nanoparticle coating was deposited on the partially removed cladding of the FBG using the electroless technique. The silver-coated FBGs at three operating wavelengths (FBG1: 1534 nm, FBG2: 1559 nm, and FBG3: 1565 nm) were used to monitor the slow release of urea in water and soil. The Bragg wavelength shift of FBG 1, 2, and 3 to the controlled-release rate in water was 0.028, 0.12, and 0.20 nm, respectively. In soil, the coated fertilizer responded to the FBG 1, 2, and 3 showing wavelength shifts of 0.028, 0.10, and 0.12 nm, respectively. This study demonstrates the potential of FBG sensors in agricultural applications.

Cascade Edge Filter for Demodulation of Quasi-Distributed FBG Sensor

The realization of multiple demodulation sche- mes of fiber Bragg grating (FBG) sensor is important for its engineering application. Here, we proposed a new edge filter that is formed by cascading dispersion compensation fiber (DCF) and no-core fiber (NCF) structure between two single-mode fibers (SMFs) for demodulation of quasi-distributed FBG sensor. The edge filter can be suitable for FBG with different center wavelengths by changing its structure parameters to achieve a wide range of FBG demodulation. In order to verify the performance of the edge filter, a demodulation system for quasi-distributed FBG sensor is successfully designed by introducing an optical time-domain reflectometer (OTDR), the wavelength shift of FBG caused by the change of temperature and strain is converted into power change through the edge filter, so as to realize temperature and strain demodulation. In the experiment, two FBG sensors separated by 500 m were set at the end of a 3000-m optical fiber for temperature and strain monitoring. The results show that the temperature sensitivity is 0.23 dB/°C from 50 °C to 100 °C, and the strain sensitivity is 0.01658 dB/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \epsilon $ </tex-math></inline-formula> from 0 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$669.6\,\mu \epsilon $ </tex-math></inline-formula> . The edge filter for FBG demodulation has the advantages of high sensitivity, adjustable structural parameters, low cost, and independent multipoint/multiparameter demodulation.

Integrated fiber-optic sensor based on inscription of FBG in seven-core fiber for curvature and temperature measurements

An integrated fiber-optic sensor with cross-sensitivity elimination effect is proposed and experimented for simultaneous measurements of curvature and temperature. The sensor structure mainly consists of a section of seven-core fiber (SCF) that fiber Bragg gratings (FBGs) were inscribed in each fiber core by phase-mask technique. Since the FBG in the central-core of SCF is only sensitive to temperature, and others in six outer-cores have same temperature responses and different sensitivity for curvature, the sensor can simultaneously measure temperature and curvature through analyzing the wavelength shifts of central-core FBG and every-two cores of FBG. The experiment results show that the maximum curvature sensitivity reaches 0.39 nm/m−1 in the curvature range of 2.53 m−1–8.62 m−1, and temperature response sensitivity is 9.97 pm/°C, which is consistent with ordinary single-mode FBG in temperature range of 30 °C–70 °C. Furthermore, the verified experiment for simultaneous measurement are performed, the central-core FBG can be used as a temperature calibration during the curvature measurement. The relative errors of curvature and temperature are 2.22 % and 2.58 %, respectively. The SCF-based FBG sensor has the advantages of small dimension, easy fabrication, better repeatability, and potential application values in many fields such as machine structure motion monitoring.

Proof-of-concept study of bolt connection status monitoring using fiber Bragg grating curvature sensor

For connection status monitoring of bolted joint groups, a novel method with fiber Bragg grating (FBG)-based curvature sensor is proposed. An FBG curvature sensor with an inextensible elastic matrix and an offset grating is adopted and clamped between a fixed support and the monitored bolt in a plane bending status. Based on the shape deformation of the FBG curvature sensor induced by the bolt loosening, the bending curvature change of the elastic matrix is measured by the FBG. By detecting the wavelength shift of the FBG induced by the matrix curvature variation, the relationship between the bolt loosening angle and the wavelength shift of FBG can be obtained, and hence the bolt connection status can be determined by the wavelength shift of FBG. Details of the proposed method are presented, and a surface-bonded FBG curvature sensor is designed, fabricated, and experimentally studied to verify the proposed method, and the parameters on sensing performance are also investigated. Experimental results show that the proposed method can monitor bolt loosening angle with high sensitivity and linear output by adjusting the parameters of the FBG curvature sensor. The looseness angle resolution of the proposed sensor can reach 0.0767°. This paper presents the first attempt to monitor bolt loosening angle using an FBG curvature sensor. With the advantages of high sensitivity and resolution, strong applicability, convenience and reusability for the maintenance of bolts, and ease of forming quasi-distributed sensor networks, the proposed method is able to provide a general solution for the on-line monitoring of bolt connection status for large-span distributed bolted-joint groups.

Real-Time Battery Temperature Monitoring Using FBG Sensors: A Data-Driven Calibration Method

Battery storage has an important role to play in integrating large-scale renewable power generations and in transport decarbonization. Real-time monitoring of battery temperature profiles is indispensable for battery safety management. Due to the advantages of small size, resistance to corrosion, immunity to electromagnetic interference, and multiplexing, fiber Bragg-grating (FBG) sensing has received substantial interest in recent years for battery temperature measurement. However, traditional temperature calibration for FBG sensors often requires a high-standard reference and causes the sensors to fail to be consistent during the calibration or recalibration processes. To tackle the challenges, an ensemble data-driven calibration method is developed in this article for FBG sensors. The calibration model consists of a linear part and a nonlinear part. First, the fuzzy <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> -means (FCM) algorithm is used to extract the linear relationship between the measured FBG wavelength shift and temperature variation. Then, the empirical mode decomposition (EMD) technique is used to classify the intrinsic mode functions (IMFs) and the remainder of the unmodeled nonlinear information. The unmodeled nonlinear information is further compensated using battery state of charge (SOC) and cycle number information. The experimental results confirm that the proposed temperature calibration method achieves desirable accuracy and reliability, with both the mean absolute error (MAE) and root mean square error (RMSE) being around 0.2 °C, respectively. Compared with the traditional temperature calibration method, the proposed approach can be used online in real-life applications.

Simultaneous measurement of refractive index and temperature based on tapered no-core fiber cascaded with a fiber Bragg grating

A Mach-Zehnder interference fiber-optic sensor for simultaneous measurement of temperature and refractive index (RI) is proposed and fabricated. In the sensing structure, no-core fiber (NCF) is cascaded with fiber Bragg grating (FBG), two enlarged tapers between NCF and the single-mode fiber serve as the light coupler, and the shrinked taper between two NCFs is used to enhance the interference effect. The different diameter influence of the shrinked taper on the sensing performance of RI and temperature has been evaluated, and the optimum diameter has been obtained. By monitoring the wavelength shift of FBG and the interference dip in the transmission spectra, the simultaneous measurement of temperature and RI is achieved. The maximum sensitivities of the attenuation peak to RI and temperature are 201.7157 nm/RIU and 87.4 pm/°C, respectively. The sensitivities of FBG to RI and temperature are 80.6 pm/RIU and 13.5 pm/°C, respectively. The transformation matrix has also been given. Own to the simple fabrication and high sensitivity, the sensor has the potential application in simultaneous measurement of multiple parameters.

A flexible multiplexing method of FBG sensors based on OFDR

A flexible multiplexing method of fiber Bragg grating (FBG) sensors based on optical frequency domain reflectometer (OFDR) is proposed in this paper to reduce the influence of spectral shadow effect on measurement and improve the reliability and measurement flexibility of FBG sensing network. In this method, the interrogation principle of FBG position and wavelength shift based on OFDR is analyzed, and as a guide, the flexible multiplexing FBG array is designed, in which multi-channel identical weak reflection FBGs are interrogated using a photoelectric detector. Meanwhile, the crosstalk beat noise generated by the flexible multiplexing FBG array is avoided so as to improve the performance of the measurement. The experiment results show that the method presented in this paper can achieve the flexible multiplexing of multi-channel FBGs with a single acquisition channel, while the measurement accuracy can be guaranteed.

Sealing state monitoring of watertight door using fiber Bragg grating sensor with arc-shaped structure

The sealing state of the watertight door (SSWD) is important information for the safe operation of a ship. A monitoring method for the SSWD based on fiber Bragg grating (FBG) sensor is designed, which can monitor the opening and closing state of the watertight door in real-time. A highly sensitive and temperature-independent sensor is installed under the rubber of the watertight door, the relationship between the displacement of the door panel and the wavelength shift of FBG is linearly fitted with the sensitivity of about 314.511 pm / mm, and the error percentage with the finite element analysis is 6.22%. The watertight door is opened and closed many times, the results show that the sensor has good stability and reliability, and the opening state, closing state, and the degree of opening and closing can be accurately judged by the wavelength shift of FBG. At the same time, the sensor can also identify the foreign body within a certain range on the rubber surface.

Thermal stability of fiber Bragg gratings fabricated by 193 nm excimer laser

The thermal stability of uniform fiber Bragg gratings (FBGs) inscribed in single mode double cladding fiber (DCF), standard single mode fiber (SMF-28) and dispersion shifted fiber (DSF) by 193 nm excimer laser was experimentally investigated. When the temperature rises from 30 °C to 800 °C, the grating contrast of FBGs with the saturated refractive index modulation drops slowly, and the corresponding 3 dB bandwidth gradually decrease After annealing at 400 °C for 2000 h, it is found that the resonance wavelength shift of FBGs mainly occur during the first 200 h. It is also observed that the FBG inscribed in DCF requires a longer time to stabilize wavelength than the FBG written in SMF-28, about 1500 h, which suggests that long-term pre-annealing is required to ensure accurate wavelength measurement. After 2000 h of annealing treatment, the FBGs can still have excellent sensing performance in the temperature range of 0–400 °C.

Fiber Bragg grating accelerometer based on symmetrical double flexure hinges

A compact fiber Bragg grating (FBG) accelerometer based on symmetrical double flexure hinges structure is designed and demonstrated, which integrates the elastic elements and the inertial masses. The resonant frequency and sensitivity of the accelerometer are theoretically analyzed, and then the sensing performance of the accelerometer is researched through experiment. In the experiment, the wavelength shift of FBG shows a good linear response to external acceleration, the linearity is better than 99.6%. The measured resonant frequency of the accelerometer is about 890 Hz, and the sensitivity is about 41 pm/G. The experimental results are in good agreement with the theoretical values. The proposed accelerometer is capable of measuring the vibration acceleration in a wide range of 50–600 Hz, which makes the accelerometer have a good application prospect in the engineering fields.

Simultaneous AC and DC measurement based on an FBG-magnetostrictive fiber sensor.

Simultaneous alternating current (AC) and direct current (DC) measurement is demonstrated with a new fiber sensor that combines fiber Bragg gratings (FBGs) with giant magnetostrictive materials (GMMs). Deformation of GMMs, proportional to the central wavelength shift of FBGs, is different when applying DC and AC to a solenoid where the whole sensing structure is located. DC introduces a constant deformation while AC causes a periodic variation. Therefore, the central wavelength of FBG has a periodic harmonic variation, which makes it possible to demodulate the values of DC and AC at the same time. In addition, the proposed method has potential significance for reducing temperature cross talk caused by the thermal sensitivity of FBGs. The experimental results show that the sensitivity of the AC current can reach up to 0.090576 nm/A in the range of 0 to 1 A, and in different AC environments, the sensitivity of the DC current can reach up to 0.2378 nm/A.

A fiber Bragg grating accelerometer based on Y-shaped symmetrical beam structure

A novel fiber Bragg grating (FBG) accelerometer is proposed. The accelerometer is based on a compact symmetrical structure consisting of a Y-shaped beam and an FBG. The mechanical model and sensing principle of the accelerometer are well illustrated. Then, the structural parameters are numerically studied. In experiment, the measured resonant frequency is 700 Hz, and the stable working frequency range is 50 ~ 400 Hz with an average sensitivity of 57.4 pm/g. The wavelength shift of FBG is linearly related to the acceleration with linearity better than 99.9%. Moreover, temperature effect on the accelerometer is also tested. The accelerometer exhibits good dynamic performance, as well as the advantages of compact structure and easy manufacturing, making it a candidate for vibration measurement.

Shape reconstruction based on a multicore optical fiber array with temperature self-compensation.

Temperature variations affect the accuracy of fiber-optic shape sensors; thus, temperature compensation is particularly important. This study developed a temperature self-compensation algorithm and verified the measuring accuracy of shape sensors after temperature compensation. A multicore fiber Bragg grating (FBG) sensor array was calibrated to confirm the consistency of sensor characteristics, and the relationship between the curvature and wavelength shift of FBGs was studied. A variable-temperature experiment revealed the temperature sensitivity of the FBG sensors, and these results were used by the temperature self-compensation algorithm. Further, shape reconstruction before and after temperature compensation was studied. The deformed shapes of the multicore FBG sensor array under different bending conditions were reconstructed. The results obtained after temperature compensation show that the average error between the measured and the theoretical coordinate values as less than 0.33 mm, the maximum error as less than 5.61 mm, and the relative error as less than 3.50%. The proposed temperature self-compensation algorithm has excellent prospects for application to flexible structures.

Continuous monitoring of crude oil movement in an electromagnetic-assisted enhanced oil recovery process using a modified fiber Bragg grating sensor

The Fiber Bragg grating (FBG) sensor used for distinguishing the oil movement offers detailed insights about the reservoir oil and is the key to quantifying the impact on improvement and the integrity and efficiency of the wells. The modified FBG sensors proposed in this paper through a partially un-cladding process and magnetostrictive nanolayer coating could advantageously monitor the crude oil mobility in electromagnetic-assisted enhanced oil recovery operations. The remaining ∼400 nm thickness of cladding after partial removal was coated with ∼100 nm magnetostrictive Ni-Fe nanolayer. The structures of Ga-doped magnetite and Ga-doped hematite were found orthorhombic with Pnma space group and rhombohedral with R3C space group, with the corresponding remnant magnetization (retentivity) value of 94 Oe and 150 Oe, respectively. The magnetization values at 1.5 T were 30 for Ga-doped magnetite and 21 emu/g for Ga-doped hematite nanoparticles. The interfacial tension of crude oil and brine dropped for 16.9 % and 4.1 % when the Ga-doped magnetite and the Ga-doped hematite nanofluid were injected, respectively. The correlated contact angle for the Ga-doped magnetite was 65.2˚, while for the Ga-doped hematite, it was 57.4˚. The FBG’s responses to different nanofluids and surfactant injection at the presence of electromagnetic field indicated the high sensitivity of the probe against the induced magnetic field, which was varied as a function of distance, nanofluids type, and nanoparticles accumulation near the FBG sensing point. The increase in the wavelength shift of FBG by flowing the nanofluids through the sandstone and opposite behavior was recorded by surfactant flowing. The maximum wavelength shift was 0.21 nm when Ga-doped magnetite nanofluid was injected, whereas it was 0.14 when Ga-doped hematite was injected.

Experimental Study on Glaze Icing Detection of 110 kV Composite Insulators Using Fiber Bragg Gratings.

Icing detection of composite insulators is essential for the security and stability of power grids. As conventional methods have met difficulties in harsh weather, a 110 kV composite insulator with embedded Fiber Bragg Gratings (FBGs) was proposed for detecting glaze icing in this paper. FBG temperature compensation sensors in ceramic tubes were adopted for simultaneous measurement of icicle loads and temperature. Then, temperature calibration experiments and simulated icicle load experiments were carried out to obtain temperature and icicle load characteristics of FBGs. The results showed that temperature sensitivities of FBG strain sensors and FBG temperature compensation sensors were 18.16 pm/°C, and 13.18 pm/°C, respectively. Besides, wavelength shifts were linearly related to icicle loads within the polar angle range of −60° to 60°, and the load coefficient of FBG facing the icicle was -34.6 pm/N. In addition, the wavelength shift generated by several icicles was equal to the sum of wavelength shifts generated by each icicle within the polar angle range of −15° to 15°. Finally, icicles can cause wavelength shifts of FBGs within a big shed spacing. The paper provides a novel icing detection technology for composite insulators in transmission lines.

Investigation of Low-Cost Interrogation Technique Based on Modulated Distributed Feedback Laser

In this paper a new low-cost fiber Bragg grating (FBG) interrogation technique for static applications is demonstrated. The idea is based on the multiplication between the FBG reflectivity profile and the emission of a sawtooth modulated distributed feedback (DFB) laser source. The variation of the FBG wavelength generates a modification in the shape, in time domain, of the reflected light signal. The concept has been proven, using simulation, to cover FBG wavelength shift up to 1.7 nm. Experimental validation was performed for FBG temperature ranging from 6 °C to 50 °C (equivalently 440 pm) with a modulation frequency of 1 kHz. Sensitivity higher than 3.5 mV/pm is achieved in all circumstances with an estimated resolution of 8 pm.