High Sensitivity 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 Novel Compact High-Sensitivity Fiber Bragg Grating Sensor for Microvibration Measurement of Robot Joints

A Novel Compact High-Sensitivity Fiber Bragg Grating Sensor for Microvibration Measurement of Robot Joints

Temperature self-compensating and high-sensitivity FBG inclination sensor based on the sliding mass principle

This paper presents a temperature self-compensating, high-sensitivity fiber Bragg grating (FBG) inclination sensor. A sliding mass block and a spring are selected as the inclination-force conversion components to induce strain in the substrate where the FBGs are located, resulting in a change in the center wavelength. Both sides of the sliding mass block are arranged with one FBG on each side to play the role of temperature self-compensating. By calculating the variation of the center wavelength of the two FBGs, the variation of the inclination angle can be obtained. The detailed mechanical construction and sensing mechanism of the sensor are introduced, and the theoretical sensitivity factor formula of the sensor is given. The calibration test and static characteristics analysis of the sensor are carried out with the inclination angle change as the parameter. The experimental results show that there is a good linear relationship between the inclination angle and the FBG central wavelength, and the sensor possesses good repeatability and creep resistance. The maximum angular sensitivity is 427.3 pm/°, avoiding the cross-sensitivity between temperature and strain of the FBG. The sensitivity of the sensor can be easily adjusted by replacing the sliding mass block and the spring.

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 Three-Axis FBG Accelerometer Based on Elliptical Spring

We propose an elliptical spring-based three-axis fiber Bragg grating (FBG) accelerometer fabricated by appropriately arranging and encapsulating three identical one-axis sensing structures in a cylindrical shell. The derived theoretical equations and the established simulation model of the sensing structure are in good agreement with the experimental results. Sensors on three axes operate in a frequency band of 10–70 Hz; the sensitivities of the proposed accelerometer in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z$ </tex-math></inline-formula> directions are 1197.82, 1157.78, and 1223.04 pm/g, respectively, showing high sensitivity, good consistency, directional response, and resistance to transverse interference.

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

High-sensitivity fiber Bragg grating strain sensor of the substrate type.

Strain measurement has important applications in mechanical engineering, civil engineering, aerospace, earthquake monitoring, and other fields. Aiming at the problem of low sensitivity of existing fiber Bragg grating (FBG) strain sensors, a high-sensitivity FBG strain sensor of the substrate type with a sensitization structure is proposed. The sensitivity of the sensor is analyzed theoretically, the sensor is simulated by Solidworks and ANSYS software, and the structural parameters are optimized. According to the simulation results, the real sensor is developed, and the strain test system is built to test the performance of the sensor. The results show that the strain sensitivity of the sensor is 3.21p m/µε, which is about 2.7 times that of the bare FBG strain sensor, which is basically in line with the theoretical value. The fitting linear correlation coefficient is 0.9999, and the repeatability error is 3.9%FS. The research results provide a reference for developing the same type of sensors and further improving the sensitivity of fiber strain sensors.

Design and Investigation of a High-Sensitivity Tilt Sensor Based on FBG

In this paper, a high-sensitivity fiber Bragg grating (FBG) tilt sensor using a cantilever-based structure is introduced. Two FBGs are fixed on a specially designed elastomer. One end of the elastomer is connected to the mass block, and the other end is connected to the shell. The principle of the tilt sensor is introduced in detail, and the mathematical model is established. The performance of the sensor is studied. The results show that there is a good linear relationship between the central wavelength difference of the two FBGs and the tilt angle in the range of −5° to 5°. The repeatability of the sensor is good, and the tilt sensitivity can reach 231.7pm/°. The influence of the silicone oil on the damping capacity of the sensor is studied. The results show that the damping capacity of the sensor has been improved by sealing the silicone oil inside the shell of the sensor. The field test is carried out on a pier of an elevated bridge, and the result is good, which verifies the practicability of the sensor.

Design and experimental study of a fiber Bragg grating strain sensor with enhanced sensitivity.

A novel high-sensitivity fiber Bragg grating (FBG) strain sensor is reported, to the best of our knowledge. The sensitivity of the sensor is improved by fixing the FBG on an elastic substrate with a sensitization function. The sensitization principle of the designed sensor is introduced, and the mathematical model of the sensor is established. In the static and dynamic experiments of the sensor, the effect of adhesive between the sensor and the measured structure on the sensitivity of the FBG strain sensor is experimentally investigated. The experimental results show that the adhesive with high shear strength is beneficial to the realization of a high-sensitivity sensor. The sensor fixed with planting bar glue can achieve a sensitivity of 9.42 pm/µε, a repeatability error of 4.79%, and a hysteresis error of 3.36%, which is consistent with theoretical and simulation results. The designed high-sensitivity strain sensor has a simple structure, small size, and convenient installation, so it has a good application prospect in micro-strain monitoring.

Sensitivity Enhancement of Fiber Bragg Grating Accelerometer Based on Short Grating

We propose and develop a high-sensitivity fiber Bragg grating (FBG) accelerometer based on a flexible hinge for vibration sensing. The proposed method employs a 1-mm FBG that is inscribed pointwise using a femtosecond laser such that the resultant stress concentration at the FBG is improved significantly by reducing the distance between the two bonding points of the FBG structure. Through theoretical calculations and finite element simulations, the relationship between sensitivity and distance was found to be inversely proportional. Using this structure, the sensitivity was enhanced to 804 pm/g at 15 and 30 Hz. The resonant frequency of the proposed accelerometer is 102 Hz, and the working frequency bandwidth is from 10 to 50 Hz. The performance of the accelerometer allows the detection of vibrations in seismic explorations with high reliability.

A High-sensitivity FBG Accelerometer Based on a Bearing

We present the modelling, design, and characterization of a novel fiber Bragg grating (FBG) accelerometer based on a bearing. A cantilevered mechanical structure with bearings can effectively decrease energy loss during vibration and enhance sensitivity. The principle of the accelerometer is analysed by a simplified model. The influence of the structural parameters of the proposed sensor on its sensitivity and resonance frequency is further analysed for structural optimization. Meanwhile, its dynamic behaviour and frequency response characteristics are analysed by numerical simulations. In addition, dual-FBG not only enables temperature compensation but also enhances sensitivity. Experimental results indicate that the FBG accelerometer provides a linear response over a broad frequency range from 0.5 Hz to 40 Hz, with a high sensitivity of 575.8 pm/g. This FBG accelerometer with low frequency and high sensitivity provides effective support for the design of sensors of the same type.

Torsional bandgap switching in metamaterials with compression–torsion interacted origami resonators

Torsional vibrations are unavoidable in beam-type structures in various engineering practices, and the advent of metamaterials provides a solution through the generation of bandgaps. However, unlike their flexural counterparts, tunable torsional bandgaps are seldomly studied due to two major difficulties: the existing metamaterial's units are less torsional-sensitive and the reliable torsional sensing techniques for validations are less available. In this work, switchable torsional bandgaps are realized in a metamaterial beam with a bistable resonator design based on Kresling origami with attached eccentric balls. We find that, through compression–torsion interaction of the proposed origami resonators and the corresponding wave-coupling phenomenon, torsional bandgaps can be generated and efficiently tuned, which leads to lower and wider vibration isolation frequency zones. Thanks to bistability, Kresling resonators arranged with eccentric balls can achieve bandgap switching. Specifically, based on the compression–torsion interaction of the bistable Kresling origami, wave coupling will be weakened/enhanced when the Kresling resonators arranged with eccentric balls turn from the 1st/2nd state to the 2nd/1st state, and, thus, the switching of torsional bandgaps can be realized. In order to experimentally validate the tunable torsional bandgaps, a high-sensitive fiber Bragg grating (FBG) displacement sensing system containing two parallel FBG sensors is set up to extract the torsional responses. This research will be helpful for future studies focusing on regulating torsional waves through compression–torsion interaction and mode conversion utilizing wave coupling.

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.

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 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.

High-sensitivity FBG microphone with static pressure equalization and optimized response

We present a high-sensitivity fiber Bragg grating (FBG)-based microphone with a flat response and static pressure equalization. A very high dynamic sensitivity of the microphone is achieved by a pressure sensing structure based on a carbon fiber diaphragm. Static pressure equalization is realized by a balance structure with a capillary glass tube. The resonances of the sensor are suppressed by air damping structures, and a broadened flat response is achieved. An acoustic-solid interaction model was used to analyze the response characteristics of the microphone. An experimental prototype was produced and tested, and the results are well consistent with the design. The tested sensitivity was −10 dB re 1 pm/Pa from 10 Hz to 2.5 kHz with a fluctuation of less than ±1.5 dB. Combined with the phase-generated-carrier-based coherent detection scheme, the microphone can achieve a sound resolution of the milli-pascal level. The static pressure sensitivity is measured to be −0.27 pm/atm, which is 100 dB lower than the dynamic sensitivity.

基于单模-多模-单模拉锥结构的高灵敏度光纤布拉格光栅应变传感器

基于单模-多模-单模拉锥结构的高灵敏度光纤布拉格光栅应变传感器

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.