Sensitive Fiber Bragg Grating Research Articles

High Sensitivity Fiber Bragg Grating Humidity Sensors Made With Through-the-Coating Femtosecond Laser Writing and Polyimide Coating Thickening

High Sensitivity Fiber Bragg Grating Humidity Sensors Made With Through-the-Coating Femtosecond Laser Writing and Polyimide Coating Thickening

A highly sensitive diaphragm pressure sensor based on fiber Bragg grating with multiprobe configuration

The demand for accurate low-pressure sensing has become indispensable across diverse industries and research domains, where meticulous pressure monitoring holds paramount significance. This research work presents the development of a multiprobe extrinsically sensitive low pressure fiber Bragg grating (FBG) sensor. Three distinct diaphragm-based FBG sensing probes, equipped with silicone diaphragms of 0.5 mm, 1 mm, and 2 mm thickness, are developed within a unified assembly. This design offers the flexibility to select a probe based on the pressure magnitude and desired sensitivity and resolution. The displacement of diaphragm centers within the probes, caused by pressure variations in gas pipe channels, is actuated through an FBG-cantilever system. The sensor exhibits a dynamic range spanning 0 to 10 psi, featuring a peak sensitivity of 1.635 nm/psi. With a negligible hysteresis of 0.2 % observed in a complete operational cycle, the sensor demonstrates consistent stability across various constant pressure conditions, characterized by an average transient of <1 %. Furthermore, cyclic testing reveals an average deviation of 1.58 % in sensor response. This innovative sensor offers promising avenues for industrial applications and research and development endeavors that necessitate precise and reliable pressure measurements in the low pressure domains.

Augmentation of Sensitivity of FBG Sensor Using Microwave Photonics and Nonlinear Effect

A simple and unique scheme of high sensitive Fiber Bragg Grating(FBG) interrogation system based on microwave signal measurement utilizing the concept of microwave photonics and nonlinear Four wave mixing(FWM), is proposed. The concept of FWM process is combined with microwave photonics to enhance the sensitivity of FBG sensor. The strain induced wavelength shift of the sensing FBG is translated to higher wavelength shift of the corresponding higher order FWM signals on either side of FBG sensor wavelength in opposite directions. Thus the wavelength separation between the FWM signals increases with small increase in strain. Utilizing the FWM effect and microwave photonics technique, the microwave phase difference is altered, which ultimately is converted to significant change in RF intensity. A novel mathematical relationship relating FWM, applied strain and the microwave power of the proposed scheme is established. A high strain sensitivity of 36.52 μV/με (26.67 μW/με) is attained using the proposed FWM and microwave photonics technique against initial sensitivity of 4.9 μV/με (0.48 μW/με) using only microwave photonics technique. The proposed scheme automatically compensates the temperature variations and eliminates the requirement of high dispersive component to enhance the sensitivity.

High sensitivity fiber Bragg grating (FBG) sensor based on hollow core silica tube (HCST) sensitization for gas pressure and temperature discrimination

A fiber Bragg grating (FBG) based sensor is proposed for the measurement of gas pressure under extreme temperature condition. Two FBG sensors of different cladding diameters are encapsulated and sealed in a fine hollow-core silica tube (HCST) by using a high temperature resistant ceramic adhesive (HTA). In the observation, the FBG sensors are practically insensitive to pressure change at room temperature and their pressure sensitivities are negatively higher at higher temperature. This can be attributed to the temperature dependence of the HTA’s Young’s modulus. The findings show that the sensors have a maximum pressure and temperature sensitivity of −0.993 nm/MPa and 13.8 pm/°C for a pressure range of 0–1 MPa over the temperature range of 17–400 °C. Despite the high pressure–temperature cross sensitivities, an interesting approach based on a 2 × 2 characteristics matrix is demonstrated for discriminative measurement of pressure and temperature

Highly Sensitive Fiber Bragg Grating Sensing System Based on a Dual-Loop Optoelectronic Oscillator With the Enhanced Vernier Effect

In this paper, a highly sensitive fiber Bragg grating (FBG) interrogation system based on a dual-loop optoelectronic oscillator (OEO) with the enhanced Vernier effect has been proposed and experimentally demonstrated. Light reflected from the FBG sensor is used as the optical source of the OEO. By introducing dispersion in the OEO loop, the sensor information encoded in the FBG wavelength can be interrogated by detecting the frequency of microwave signal generated by the OEO loop. The dispersive media in OEO has two paths, one path is formed with a roll of dispersion compensation fiber (DCF), and the other path is formed with a roll of single-mode fiber (SMF). By designing the length of two paths with slightly difference, the Vernier effect is generated in the OEO. Since the dispersion of the two paths is opposite, an enhanced Vernier effect can be realized, which can significantly enhance the sensitivity. The experimental results prove the possibility of applying the concept of enhanced Vernier effect to the OEO for temperature sensing. The sensitivity is about 0.926 kHz/°C and 0.0912 kHz/°C for a single-loop OEO with DCF and SMF, respectively. By employing the enhanced Vernier effect, the sensitivity can be improved to 141.13 kHz/°C, which is estimated about 152.4 and 1547.5 times higher than that of the two single loops, respectively. Furthermore, sensitivity can be further improved by using a dispersive link with larger dispersion.

High Figure of Merit and Low Cross Sensitivity Fiber Bragg Grating Accelerometer Based on Double Grid-Diaphragms

Use of a detailed parallel theoretical model has allowed the design of a high figure of merit and low cross sensitivity accelerometer based on fiber Bragg grating (FBG), and the good response characteristics have been demonstrated experimentally. The relationship between the sensitivity and resonant frequency is downplayed, the mechanism of expanding the frequency band and maintaining higher sensitivity has been analyzed. A FBG accelerometer with a good performance of higher main-axis sensitivity and lower cross sensitivity has been presented. The experimental results obtained indicate that the FBG accelerometer has a broad frequency range from 1 to 60Hz, the corresponding sensitivity range from 754.3 to 763.2pm/G, while the fluctuation is less than 3dB. The resonant frequency is 103Hz, and the corresponding cross sensitivity is less than −24.76dB (< 5%). The figure of merit is 78.61nm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> Hz/G, it shows that the sensor has better comprehensive characteristics. An accelerometer with this performance thus has the potential for application in low frequency oil and gas seismic exploration.

Temperature compensated diaphragm based Fiber Bragg Grating (FBG) sensor for high pressure measurement for space applications

A temperature compensated diaphragm-type Fiber Bragg Grating (FBG) sensor for high pressure measurement, with a maximum pressure up to 700 bar, has been developed and packaged for different applications including space. In this device, a pressure sensitive FBG is bonded at the centre of a Martensitic Stainless Steel (APX-4) diaphragm and a temperature compensation FBG is bonded in the strain-free region of the same diaphragm. The experimental results obtained indicate a pressure sensitivity of 3.64 pm/bar and a non-linearity + Hysteresis error of 0.75% of full-scale pressure in the range of 0 to 700 bar, with a correlative coefficient of 99.99%. Structural and thermal stress analyses of the diaphragm and strain transfer analysis from the diaphragm to FBG have been carried out using Comsol Multiphysics software, to validate the experimental results. Shock tube and vibration tests have also been carried out to study the dynamic characteristics and stability of the sensor. The pressure sensor developed, can be used to measure both static/dynamic pressures of cryogenic propellants as well as pneumatic pressure in rockets, missiles and launch vehicles.

Real‐time device tracking under MRI using an acousto‐optic active marker

This work aims to demonstrate the use of an "active" acousto-optic marker with enhanced visibility and reduced radiofrequency (RF) -induced heating for interventional MRI. The acousto-optic marker was fabricated using bulk piezoelectric crystal and π-phase shifted fiber Bragg grating (FBGs) and coupled to a distal receiver coil on an 8F catheter. The received MR signal is transmitted over an optical fiber to mitigate RF-induced heating. A photodetector converts the optical signal into electrical signal, which is used as the input signal to the MRI receiver plug. Acousto-optic markers were characterized in phantom studies. RF-induced heating risk was evaluated according to ASTM 2182 standard. In vivo real-time tracking capability was tested in an animal model under a 0.55T scanner. Signal-to-noise ratio (SNR) levels suitable for real-time tracking were obtained by using high sensitivity FBG and piezoelectric transducer with resonance matched to Larmor frequency. Single and multiple marker coils integrated to 8F catheters were readout for position and orientation tracking by a single acousto-optic sensor. RF-induced heating was significantly reduced compared to a coax cable connected reference marker. Real-time distal tip tracking of an active device was demonstrated in an animal model with a standard real-time cardiac MR sequence. Acousto-optic markers provide sufficient SNR with a simple structure for real-time device tracking. RF-induced heating is significantly reduced compared to conventional active markers. Also, multiple RF receiver coils connected on an acousto-optic modulator can be used on a single catheter for determining catheter orientation and shape.

An experimental approach to evaluate machine learning models for the estimation of load distribution on suspension bridge using FBG sensors and IoT

AbstractMost of the tragedies on any bridge structure have been the cause of high‐density crowd behavior as a response to trampling as well as the crushing scenario. Therefore, it is most important to monitor such unforeseen situations by sensing the load imposed on the bridge structures. This scenario may arise where crowd movement is huge on these types of bridges. Similarly, the fiber Bragg grating (FBG) is a promising technology for structural health monitoring applications. In this work, an Internet of Things based FBG optical sensing scheme is proposed to monitor real‐time strain distribution throughout the bridge structures and localization of load imposed on the structure from a central control room. A suspension bridge model is designed by referring to a real bridge scenario and these FBG sensors are deployed to validate the proposed machine learning models. In this article, the performances of two machine learning strategies are discussed for the accurate estimation of load and its position by acquiring high sensitive FBG sensors signals at a very high data rate. The algorithms include K‐nearest neighbor (KNN) and random forest (RF); which are applied on each sensing data source, and then validated using a prototype suspension bridge model integrated with three FBG sensors (1532 nm, 1538 nm, and1541 nm) on a single optical fiber cable.

Highly sensitive FBG pressure sensor based on square diaphragm

A highly sensitive fiber Bragg grating (FBG) based square diaphragm pressure sensor has been designed and verified both in theory and experiment. The square diaphragm deflects due to the pressure difference generated at both sides of the square, and causes the compression along the axis of the pre-stretched FBG. The experimental results indicate that the pressure sensitivity of the proposed sensor reaches 3.402 pm/kPa in the range of 0–200 kPa with a higher coefficient of determination of 0.9985. Meanwhile, the sensor is found to present low hysteresis, good repeatability and resolution. Relative error recorded at 3.13 % represents that the effect of the temperature compensation is remarkable. Furthermore, the designed pressure sensor is simple, cost-effective and suitable for low pressure measurement.

Broadband and High Sensitivity FBG Accelerometer Based on Double Diaphragms and h-Shaped Hinges

A novel broadband and high sensitivity fiber Bragg grating (FBG) accelerometer is designed and analyzed. The accelerometer is based on a compact structure consisting of double diaphragms and h-shaped hinges. The h-shaped hinge structure is used to break through the restriction between sensitivity and resonance frequency. The FBG accelerometer is demodulated by an interferometric method and test results show that the acceleration sensitivity is 32 dB re pm/g between 1 Hz and 1 kHz, with a fluctuation less than ±3 dB, and the resonant frequency is above 1.6 kHz. The cross-sensitivity is less than -26 dB in the flat frequency of 15μg/√ Hz in a wide frequency range, making it promising range. The sensor shows a high acceleration resolution for cross-well seismic, micro-seismic monitoring and electromechanical equipment vibration monitoring, etc.

High Sensitivity Fiber Bragg Grating Acceleration Sensor Based on Rigid Hinge

In order to break through low sensitivity limitation of the existing fiber Bragg grating (FBG) acceleration sensor, a new high sensitivity FBG acceleration sensor based on rigid hinge is proposed. The working principle innovation is that the sensor uses the rigid body rotation motion instead of the existing elastic deformation. The novel structure is that the pendulum rotates around the rigid hinge and the structure is symmetrically designed, which increases the elongation of the fiber grating by twice. The resonance frequency and sensitivity formula of FBG acceleration sensor is theoretically obtained by analysis. The influence of size parameters of the structure on sensor sensitivity and resonance frequency is further analyzed by MATLAB, and finally the structural parameters are optimized. On the basis, the first-order natural frequency of the sensor is simulated by ANSYS Workbench17.0. Experimental studies show that the natural frequency of the acceleration sensor designed in this paper is 39 Hz, the sensitivity of the sensor is 949.2 pm/g at 15 Hz, and the cross-interference is less than 6.49%, which is suitable for precision measurement under low frequency micro-vibration.

A novel modified fiber Bragg grating (FBG) based ammonia sensor coated with polyaniline/graphite nanofibers nanocomposites

Abstract The sensing of ammonia leakage at room temperature has potential applications in many areas such as industry. A sensitive etched-tapered fiber Bragg grating (FBG) based ammonia sensor is developed and investigated towards different concentrations of ammonia. The investigations are performed at room temperature. FBGs are etched with 50 µm diameter and tapered with 15 and 30 µm waist diameters. These FBGs are coated with polyaniline/graphite nanofibers (PANI/GNF) nanostructures as a sensing layer using spray method. The developed FBG sensors are based on Bragg wavelength shift on exposure to different ammonia concentrations due to change in refractive index of the sensing layers as interact with ammonia molecules. FBG sensors proved a linear Bragg wavelength shift with ammonia concentrations. The developed sensors exhibited linear, stable response, high sensitivity and good repeatability. Furthermore, FBGs sensors proved strong response towards NH3 by exhibiting high Bragg wavelength shift. This is because of porous structures of PANI\GNF nanostructures which improves the capability to adsorb additional NH3 molecules. This is in turn eventually enhances the interaction between NH3 and PANI\GNF nanocomposites. PANI\GNF coated FBG sensor with 15 µm waist diameter shows the highest sensitivity and good selectivity towards NH3.

A Model Test for the Influence of Lateral Pressure on Vertical Bearing Characteristics in Pile Jacking Process Based on Optical Sensors.

Photoelectric integrated testing technology was used to study precast piles during pile jacking at the pile–soil interface considering the influence of the earth and pore water pressures on its vertical bearing performance. The low temperature sensitive fiber Bragg grating (FBG) strain sensors and miniature silicon piezoresistive sensors were implanted in the model pile to test the changes of earth pressure, pore water pressure and pile axial force of the jacked pile at the pile–soil interface, and the influence of lateral pressure on pile axial force was studied. The test results showed that the nylon rod is feasible as a model pile. The FBG strain sensor had a stable performance and monitored changes in the axial force of the model pile in real time. The miniature earth and pore water pressure sensors were small enough to avoid size effects and accurately measured changes in the earth and pore water pressures during the pile jacking process. During pile jacking, the lateral earth pressure increased gradually in depth, and the lateral earth pressure at the same depth tended to decrease at greater depths. Lateral pressures caused the axial force of the pile to increases by a factor of 1–2, where the maximum was 2.7. Therefore, the influence of the lateral pressure must be considered when studying the residual pile stress.

Magnetic field detection using a highly sensitive FBG probe

A partially unclad fiber Bragg grating (FBG) coated with Fe3O4 nanoparticles as a magnetic field sensor is experimentally demonstrated. A series of six FBGs reflecting different wavelengths at an efficient length of 30 mm are fixed on the top and outside of a cylindrical glass chamber. The chamber is equipped with a solenoid that acts as a magnetic field generator and is filled up with air, saline solution, and crude oil separately to detect the changes in the magnetic field. The magnetic–hysteresis loops confirm the super-paramagnetic properties of the synthesized Fe3O4 nanoparticles with size smaller than 20 nm. The sensor response time of ∼21 s confirms the high reliability and repeatability of the sensing scheme. The change in the magnetic field strength depended from FBG–solenoid distance, propagating at different media and function generator frequency leads to shift in the reflected wavelength of each single FBG’s accordingly. The magnetic field strength outside the solenoid obeys the inverse-cubic law, and the decrease in the wavelength shift with an increase in the FBG–solenoid distance is in excellent agreement with the Biot–Savart law. The shift is caused by the interference of different propagating modes that are reflected from the core-cladding and cladding-magnetite layer interfaces; these modes have different phases because of the changes in the refractive index of the magnetite layer resulting from the change in the magnetic field. Our precise fabrication of the FBG probe with a maximum sensitivity of ∼11 000 pm mT−1 and the proposed design of experiment may be appropriate for detecting small changes in magnetic fields in the oil industry.

Highly Sensitive FBG Strain Sensor With Enhanced Measurement Range Based On Higher Order FWM

To meet the simultaneous requirement of high sensitivity and high measurement range is an uphill task in the development of fiber Bragg grating (FBG) strain sensor. A unique scheme of highly sensitive FBG strain sensor is proposed based on nonlinear four wave mixing (FWM) with a high measuring range. In this paper, both the edges of FBG reflection spectrum are used without increasing the number of sources. The FWM products generated are tuned to the reflection edges of the FBG. The signals reflected from the edges of the FBG are then utilized in the subsequent FWM process to enhance the sensitivity of the system. The proposed scheme can provide a strain measurement range of 2310 με with strain sensitivity of 91.21 dBm/nm.

Highly Sensitive FBG Pressure Sensor Based on a 3D-Printed Transducer

In this work, we describe a fiber Bragg grating (FBG) pressure sensor with high sensitivity. The sensor exploits a three-dimensional printed mechanical transducer capable of converting the external pressure very efficiently into strain, measured by a first FBG, whereas a second one is used for temperature compensation. The pressure sensitivity of this sensor is found as high as 240 pm/kPa with an accuracy of 112 Pa over 10 kPa, which makes this sensor up to 80,000 times more sensitive than a bare fiber Bragg grating. Moreover, it is experimentally shown that it is capable of detecting fast dynamic pressure change up to 100 Hz. Thanks to these performances, this device can be used in many static and dynamic low-pressure measurement applications, and it is here demonstrated as a sub-millimetric surface water waves detector.

A High Sensitivity FBG Strain Sensor Based on Flexible Hinge.

For the purpose of improving the sensitivity of the fiber Bragg grating (FBG)-based strain sensor. A novel FBG-based strain sensor with high sensibility was designed by means of a flexible hinge bridge displacement magnification structure. This sensor can be used to accurately measure the strain of a mechanical structure surface. In this paper, the strain sensitization amplification factor of the sensor was calculated by using the flexible matrix method and the strain energy theory. The magnification had been verified by using simulation analysis and experimental results, and the error between theoretical calculation and simulation analysis was less than 7%. The result shows that the strain sensitivity of the sensor is 10.84 pm/με, which is about 10 times to that of the bare FBG sensor. This sensor is sensitive to micro-strain, so it can be well applied to health monitoring of a mechanical system.

Application of Additive Layer Manufacturing Technique on the Development of High Sensitive Fiber Bragg Grating Temperature Sensors

This paper presents the development of temperature sensors based on fiber Bragg gratings (FBGs) embedded in 3D-printed structures made of different materials, namely polylatic acid (PLA) and thermoplastic polyurethane (TPU). A numerical analysis of the material behavior and its interaction with the FBG sensor was performed through the finite element method. A simple, fast and prone to automation process is presented for the FBG embedment in both PLA and TPU structures. The temperature tests were made using both PLA- and TPU-embedded FBGs as well as an unembedded FBG as reference. Results show an outstanding temperature sensitivity of 139 pm/°C for the FBG-embedded PLA structure, which is one of the highest temperature sensitivities reported for FBG-based temperature sensors in silica fibers. The sensor also shows almost negligible hysteresis (highest hysteresis below 0.5%). In addition, both PLA- and TPU-embedded structures present high linearity and response time below 2 s. The results presented in this work not only demonstrate the feasibility of developing fully embedded temperature sensors with high resolution and in compliance with soft robot application requirements, but also show that the FBG embedment in such structures is capable of enhancing the sensor performance.

Field test of a 16 channel high sensitivity FBG geophone array

In this paper we report the development and field test of a 16 channel high sensitivity fiber Bragg grating (FBG) geophone array for oil and gas exploration application. A high sensitivity FBG geophone is designed, and its sensitivity is about 1000pm/g. The wavelength change of the FBG geophone is interrogated by using interferometric demodulation method, and the demodulation system noise is below 10−3pm/. And the minimum detectable seismic signal is below 1μg/. We are presenting field test results for the FBG geophone and comparing its performance with regular exploration geophones. In comparison, FBG geophone has the advantages of higher signal-to-noise ratio and better low-frequency response. This work shows that using FBG technology to develop geophone for oil and gas exploration is both advantageous and feasible.