Dual Fiber Bragg Gratings Research Articles

Dual straight-wing FBG accelerometer for low-frequency vibration measurement

Fiber optic accelerometers have a wide range of applications in low-frequency vibration measurement, such as in earthquake monitoring, disaster early warning, underground resource exploration, and anti-seismic monitoring projects for critical structures like dams and bridges. In response to the current issues of Fiber Bragg Gratings (FBG) accelerometers being insensitive to low-frequency vibration signals and challenging to apply in engineering, a dual straight-wing FBG accelerometer for low-frequency vibration measurement is proposed. Firstly, a sensor model is established and theoretically analyzed. Secondly, the impact of the sensor's main structural parameters on sensitivity and natural frequency is analyzed, and the sensor is simulated using ANSYS. Finally, a prototype of the sensor is developed, and a low-frequency vibration testing system is set up to test the sensor's performance. Experimental results show that the accelerometer has a natural frequency of 39.1 Hz, operates in the 5–22 Hz frequency band, and has a sensitivity of 171.7 p.m./g, a dynamic range of 69.82 dB, and a transverse interference resistance of less than 9.5%. This research provides a new reference for the development of similar sensors.

Spectral Failsafe System of High-Power Laser Using Dual Fiber Bragg Gratings.

Phase-modulated (PM) spectral failsafe systems are necessary to promptly terminate amplification processes following accidental seeding of a high-power laser chain with a non-PM pulse to prevent optical damage. In this work, we present a reliable spectral failsafe system that can indicate the presence or absence of sufficient PM light. This requirement is met by combining dual temperature-sensitive fiber Bragg gratings detection with high-speed RF amplitude comparisons. The failsafe trigger signal is generated when the spectral power at the peak sideband exceeds that at the center. The spectral failsafe system has the ability to distinguish between adequate and inadequate PM pulses, and it exhibits significant robustness in pulse width, TEC temperature drift, and DFB wavelength drift in experiments, making it valuable for safe high-power laser operations and providing a useful reference for other detection system designs.

Dual-FBG arrays hybrid measurement technology for mechanical strain, temperature, and thermal strain on composite materials

The response measurement of spacecraft during reentry is very important for designing the base composite structure. This paper proposes a hybrid measurement method to measure the mechanical strain, the temperature, and the thermal strain using dual fiber Bragg grating (FBG) arrays. The decoupling of temperature and stain is illustrated by a three-step process such that triple physical variables are measured simultaneously. For the base composite structure, four heating scenarios with thermal steady and non-steady states encountered during the lifting re-entry were designed to illustrate the feasibility of the proposed method. Under the thermal non-steady state, the average absolute error of the temperature measured by the dual-FBG and the thermocouple did not exceed 2.799 K. Meanwhile, the dual FBG-based thermal strain was compared with the thermally measured strain with an average relative error of no more than 2.913%. A finite element model at different temperatures was developed to calculate mechanical responses and was compared with the results obtained by FBG. The results show significant agreement between the measurement and the simulation, with a maximum error of 3.61%.

Three-dimensional force-tactile sensors based on embedded fiber Bragg gratings in anisotropic materials.

Three-dimensional force-tactile sensors have attracted much attention for their great potential in the applications of human-computer interaction and bionic intelligent robotics. Herein, a flexible haptic sensor based on dual fiber Bragg gratings (FBGs) embedded in a bionic anisotropic material is proposed for the detection of 3D forces. To achieve the discrimination of normal and tangential force angles and magnitudes, FBGs were orthogonally embedded in a flexible silicone cylinder for force determination. Fe3O4 nanoparticles were used as a modifying agent to induce anisotropic elasticity of the silicone structure to improve the angle detection resolution. The results show that the flexible tactile sensor can detect the angle and magnitude of the 3D force.

An FBG Temperature–Pressure Sensor Based on Diaphragm and Special-Shaped Bracket Structure

A fiber Bragg grating (FBG) sensor capable of simultaneous temperature–pressure measurement is presented and experimentally verified, which consists of a diaphragm, a special-shaped bracket, dual FBGs, and protective housing. The principle of simultaneous temperature and pressure measurement with dual FBGs is theoretically illustrated and simulated by a finite-element analysis. The experimentally investigated results demonstrate that the sensor can be employed to measure temperature and pressure in environments where the temperature ranges from 50 °C to 200 °C and the pressure ranges from 0 to 40 MPa. The temperature sensitivity of the sensor is 31.8 pm/°C with a linear correlation coefficient of 0.9997; the pressure sensitivity is 50.6 pm/MPa, the linearity is 0.21%, and the repeatability and hysteresis error are 0.024% and 0.16%, respectively. The sensor exhibits a large measuring range, high-temperature resistance, miniaturized structure, and easily multiplexed, which allows it for temperature and pressure dual parametric measurements in high-temperature and high-pressure environments such as oil and gas wells.

Design of a Modular 3-D Force Sensor With Fiber Bragg Gratings for Continuum Surgical Robot

An instrument usually is installed at the distal end of a continuum surgical robot to perform specific tasks. The driving wire of the instrument needs to pass through the central channel of the continuum robot. And force perception of the continuum robot is often lacking. Based on this application background, a novel Fiber Bragg Gratings (FBG)-based 3-D force sensor is proposed. This sensor consists of an axial force perceptive zone and a radial force perceptive zone. Four optical fibers with dual FBG nodes are arranged to the sensor. Thanks to the novel arrangement of FBGs, one central channel is retained to arrange the driving wire of the instrument. A novel force perceptive model is established through the temperature decoupling algorithms and Bernoulli-Euler beam theory. Calibration experiments show that the proposed sensor can achieve a resolution of 1.9 mN, 2.4 mN, and 9.8 mN for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_x</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_y</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_z</i> , respectively. Dynamic performance and temperature decoupling algorithms show that the proposed FBG sensor can accurately realize 3-D force perception.

Development of a Fiber Bragg Grating-Based Force Sensor for Minimally Invasive Surgery–Case Study of Ex-Vivo Tissue Palpation

In this paper, a one-dimensional distal force sensor design is proposed for minimally invasive surgery based on fiber Bragg grating (FBG) sensing principle. The sensor is made with a miniaturized force-sensitive flexure within which an optical fiber is embedded. The former includes a spiral elastomer utilized for high axial force sensitivity, while the fiber includes dual FBGs that are tightly suspended around the distal parts of the flexure and along elastomer’s centerline, respectively. Theoretical model of the flexure was derived based on its components and a design approach for decoupling strain and temperature cross-effects during sensor usage. In addition, design parameters of the flexure were analyzed on physics-based model optimization using fmincon function, while the static and dynamic properties were analyzed in-silico using finite element method. Further experiments were also carried out to analyze the sensor’s performance, and the data obtained was used for calibration study. The latter was done by training a feed-forward neural network designed for predicting the force vs. wavelength-shift relationship. The experimental results show the designed force sensor design can sense force values in a range of 1N with an average relative error less than 2% of full scale. Ex-vivo tissue palpation experiments were further done on pig liver organs to verify the effectiveness and applicability of the proposed sensor design in minimally invasive surgery.

In-place fiber-optic inclinometer based on a vertical cantilever beam and dual FBGs

Inclinometers are commonly used in boreholes to monitor the profile of land/soil displacement, which is vital in geotechnical engineering. A new in-place fiber-optic inclinometer (FOI) is developed based on a vertical cantilever beam and dual fiber Bragg gratings (FBGs). This FOI is characterized by its robust design, bidirectional large range, multiplexing capability, and push-pull configuration with temperature insensitivity. A pair of pre-stretched FBGs with different reflection wavelengths are respectively glued on the opposite surfaces of a vertical cantilever beam with tip mass to form a push-pull structure, which is further encapsulated by a solid cylinder made of aluminum alloy. Calibration tests of the proposed inclinometer are performed in the laboratory to examine its measurement performance, revealing a measurement sensitivity of ∼ 0.1 nm/°, resolution of ∼ 0.01°, and a maximum bidirectional measurement range of ± 30°. The numerically calculated sensitivity based on actual parameters agrees well with the experimental result. Furthermore, three inclinometer units are connected by spacers to conduct an assembled inclinometer test in the laboratory, four typical profile patterns are validated with a sensing error of <6.73 %.

An FBG-Based 3-DOF Force Sensor With Simplified Structure for Retinal Microsurgery

Retinal microsurgery, which requires surgeons to perform precise operations on delicate tissue in a tiny eye, is considered one of the most technically demanding operations. Lack of force perception is one of the major problems faced during retinal microsurgery. In order to solve the problem of lack of force sensing, many 3 degree of freedom (DOF) force sensing instruments have been developed. However, they all adopt complex structures, and the accuracy of axial force still has room for improvement. In this paper, we presented a 3-DOF force sensor based on fiber Bragg grating (FBG) sensors for retinal microsurgery. An improved FBG configuration which simplifies the structure of the force sensor and the corresponding temperature compensation method was designed. Two optical fibers with single FBG sensor and an optical fiber with dual FBG sensors are longitudinally attached along the grooves of a stainless steel tube. The calibration method used in the force sensor is a combination of linear calibration method and the least squares support vector regression (LSSVR), which can effectively reduce the influence of linear and nonlinear errors. The results of calibration experiment demonstrate that the hybrid calibration method has better accuracy than using linear or nonlinear method alone. Verification experiment and temperature compensation experiment show that the 3-DOF force sensor proposed has the ability to provide accurate and stable estimation of 3 dimensional forces in a temperature changing environment.

A flexible hinge accelerometer based on dual short fiber Bragg grating

Fiber Bragg gratings (FBGs) are a type of optical element with several advantages. In this study, we propose a vibration monitoring system consisting of a flexible hinge and a dual FBG. The novel design enables the dual short FBG to be tensile and compressed separately during vibration, while achieving sensitivity enhancement and self-temperature compensation. Through theoretical analysis and experiments, the resonant frequency was 150 Hz. The working frequency bandwidth of the accelerometer ranged from 10 to 100 Hz with a sensitivity of 1711 pm/g. The minimum resolution and detectable acceleration of the proposed system were 0.584 mg and 3 mg, respectively, which are significantly better than similar systems with a single FBG.

A Non-Invasive Measurement Method of Pipeline Flow Rate Based on Dual FBG Sensors

Combining fiber Bragg grating (FBG) sensors and finite element simulation analysis, an online monitoring method for non-invasive distributed flow velocity in pipelines has been proposed. A placement strategy has been proposed for the deployment of these FBG sensors to ensure effective sensing of strain. The cross-sensitivity problem of FBG sensors can be solved by differential FBG measurements. The principle of online monitoring of flow velocity based on the flow velocity function and finite element analysis is described and derived. Finite element analysis results show the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\varepsilon }_{1}- \boldsymbol {\varepsilon }_{2}$ </tex-math></inline-formula> at 45° of the elbow of the bend is quadratically proportional to the flow velocity. Meanwhile, the feasibility of the method is verified by experiments. The calibration results show a fitted correlation coefficient R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.9982 in the velocity range of 4.25-10.62m/s, fitted by least squares to the wavelength data. The repeatability error of the flow measurement of the proposed sensor is no more than 5.06%FS. Compared with the existing literature, the method proposed in this paper has a wider range of flow velocity measurement and applications, especially suitable for applications with strong electromagnetic interference capability and harsher environment, showing great potential for engineering applications, especially in the distributed detection of long-distance pipeline networks.

Performance Optimization of Apodized FBG Biomedical Sensor for Variation in Temperature and Presence of Noise

In this work, comprehensive analysis on single and dual mode, uniform and apodized Fiber Bragg Grating (FBG) based gas concentration measurement sensor performance in the presence of noise and temperature variations is presented. Different scenarios are formulated. Firstly, the indirect sensing method for gas concentration measurement is presented, followed by the discussion on single and dual mode uniform FBG sensor design. Thereafter single and dual mode Gaussian apodized FBG sensor design and its pros and cons are discussed. The effect of temperature variations and noise on FBG sensor is also discussed. Afterwards as per referred literature the simulation results for uniform and apodized FBG in the presence or absence of noise, temperature variations and strain applications are validated. The quantitative analysis shows that the single mode apodized FBG has highest side lobes suppression ratio which is 88.21%. In terms of FWHM single mode apodized FBG has narrowest bandwidth of amplitude 0.18. While dual mode apodized FBG has highest reflectivity, that is, −0.20571. It is observed that reflection spectrum of uniform FBG sensor contains large strength of side lobes at adjacent wavelength. Moreover, the dual mode FBG sensor performance is more affected by variation in temperature and noise but dual mode FBG sensor works better as compared to single mode FBG sensor in context of minimum side lobes, high absorption depth and enhanced reflectivity. The presented investigation will be helpful to prescribe the correct amount of dosage for biomedical application. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Performance analysis of long band passive optical network using amplifier spontaneous noise and fiber Bragg gratings

Abstract Long band (L-Band) passive optical networks (PONs) are attracting a lot of attention these days, thanks to rising capacity demands. Because of PONs requesting more and more channels, fault detection/monitoring is critical. Fault detection in the conventional band (C-Band) employing reflecting Fiber Bragg Gratings (FBGs) and a probe signal integrating an additional amplified spontaneous noise (ASEN) source has been frequently demonstrated. However, interference occurs when ASEN and transmitter signals are in the same wavelength band, and adding additional ASEN sources to the network raises the overall cost. So, in L-Band PONs, a cost-effective, low-complexity fault detection/monitoring system is required. Therefore, in this work, a fault detection/monitoring system for L-Band PON using C-Band ASEN from inline erbium doped fiber amplifier (EDFA) and dual purpose FBG, i.e. (1) ASEN reflection for fault monitoring and (2) dispersion compensation is proposed. A 4 × 10 Gbps L-Band PON is investigated over 40 km feeder fiber (FF) and 1 km drop fibers (DFs) that serve 32 optical network units (ONUs)/different input powers, dispersion values, and laser linewidths in terms of reflective power of FBGs, eye opening factor, and bit error rate (BER), respectively.

New Method of Temperature and Strain Decoupling Based on Directivity of Fiber Bragg Grating Sensing

Fiber Bragg Grating (FBG) has been widely used in temperature and strain measurement. Its center wavelength drift is affected by both temperature and strain. The influence of temperature and strain on center wavelength should be decoupled when measuring. In this paper, the sensing characteristics of FBG which pasted at different angles were simulated and analyzed, and it was found that FBG sensing for strain has strong directivity. A dual FBG composite construction based on the directivity of FBG sensing was proposed. Two FBGs were at an Angle of 62°. One FBG was sensitive to both temperature and strain, and the other was only sensitive to temperature. The structure can realize the decoupling of temperature and strain, and it doesn’t depend on feature of cantilever beam. It was verified by experimental analysis that the decoupling result was good by utilizing the combined FBG structure, and decoupling was realized easily.

Broadband elastic wave detection based on dual FBGs capable of automatically matching the spectra

Fiber Bragg grating (FBG)-based sensors can be used to detect middle/high frequency elastic waves via intensity demodulation. Temperature change or structural deformation at the location where the sensing FBG is adhered to may shift the FBG spectrum and mismatch the interrogator filter and sensing FBG spectra, leading to sensing failure. This paper proposes a broadband elastic wave measurement system with a trackable work point based on dual FBGs together with a piezoelectric transducer (PZT), wherein one FBG is pasted on the PZT as a filter and tracker. By applying AC + DC excitation to the PZT and sweeping the DC bias, the two FBGs’ spectra are autonomously matched by searching the max amplitude of the receiving AC signals to maintain high sensitivity. It is experimentally demonstrated that the proposed system can detect up to 500 kHz broadband elastic waves. The proposed system is replicated to produce four sets that are successfully used to detect and locate the impact on an aluminum plate.

A Novel 3-DOF Force Sensing Microneedle With Integrated Fiber Bragg Grating for Microsurgery

Retinal microsurgery requires precise manipulation of delicate tissue in the interior of the eye. Force sensing instruments can provide surgeons the imperceptible force information, thereby improving the safety of retinal microsurgery. Previous force sensing microneedles have demonstrated robust performance in transverse force measurement. However, in some surgical operations such as puncturing the vessel, the axial force sensing function is critical. In this article, we present a three degrees of freedom force sensing microneedle based on fiber Bragg grating (FBG) sensors. A novel configuration of the FBG sensors is arranged to detect the transverse and axial forces. Three optical fibers with dual FBGs are longitudinally attached along the outside surface of a Nitinol tube. Benefiting from the novel configuration of the FBG sensors, a hollow channel can be used to pass through injection catheter. A new force calculation algorithm was developed to decouple the transverse forces and axial forces. Experimental results demonstrate the proposed force calculation algorithm can achieve a resolution of 0.124 and 0.74&#x00A0;mN for transverse forces and axial forces, respectively. Validation and temperature compensation experiments show the force sensor can provide consistent and accurate measurement of 3-D forces within 35&#x2013;37 &#x00B0;C temperature variation.

Terfenol-D Based Magnetic Field Sensor With Temperature Independence Incorporating Dual Fiber Bragg Gratings Structure

A magnetic field sensor with temperature insensitivity implemented by two fiber Bragg gratings (FBGs) structure is presented and experimentally demonstrated. In the proposed sensing probe, a Terfenol-D piece is bonded with the same type of two FBGs in different direction relative to magnetic field. Two center wavelengths of the notches of FBG filters are mainly determined by the magnetic field, and the two FBGs experience different magnetic-field-induced strain and the same thermal expansion, leading to the linear relationship between the wavelength drift difference and the magnetic field and temperature insensitivity. By monitoring the shift of the wavelength drift difference, the magnetic field measurement for thermal-insensitive interrogation of the magnetic field sensor can be realized. Owing to its compact and temperature independent advantages, the proposed sensor has potential application especially in the unstable direction of magnetic field. Moreover, the sensor can also serve the purpose of temperature measurement by monitoring one of the center wavelengths. The measured sensitivity of the magnetic field intensity of the proposed sensor is 8.77 pm/mT.

Sensitivity-Enhanced Fiber Bragg Grating Pressure Sensor Based on a Diaphragm and Hinge-Lever Structure

A high-sensitivity and small-size pressure sensor based on dual fiber Bragg grating (FBG), a diaphragm and hinge-lever structure is proposed. Its measurement principle is described and simulation analysis is conducted. We compensate for temperature cross-sensitivity by using an additional FBG to accurately measure the ambient temperature. Sensing experiments indicate that the pressure sensitivity is 5.227 pm/kPa within the range of 0-1.0 MPa, which is three times greater than that of a single-diaphragm pressure sensor without a flexible hinge lever. The sensor is suitable for accurate and stable pressure measurement in oil and gas pipelines and similar environments.

Distributed Curvature Sensing and Shape Reconstruction for Soft Manipulators With Irregular Cross Sections Based on Parallel Dual-FBG Arrays

This article presents a distributed curvature sensing and shape reconstruction method based on parallel dual fiber Bragg grating (FBG) arrays for a type of cable-driven soft manipulator with irregular cross sections. The curvature at each measured point can be detected by the differential response of the relevant dual-FBG sensing unit with less interference from the temperature and axial driven force. The shape of the manipulator can be completely reconstructed by using the integration of the piecewise curvature functions. The measurement principle of curvature and shape reconstruction method have been investigated and derived. Experiments indicate that the constant temperature-induced error for the detected curvature is less than 0.1042 m−1. The error of the detected curvature is small less than −0.0824 m−1 within a changing temperature from 30 °C to 50 °C. The shape of the manipulator can be reconstructed with a small error of less than 1 mm under a constant or changing temperature environment. Static and dynamic grasping experiments for the manipulator have been implemented, which indicates a feasible shape tracking with resistance for axial force effect. Such merits further validate the effectiveness of the proposed approach for distributed curvature sensing and shape tracking of the manipulator with irregular cross sections.

Compact Dual Fiber Bragg Gratings for Simultaneous Strain and High-Temperature Measurement

We present a compact simultaneous strain and high-temperature measurement scheme using dual fiber Bragg gratings (FBGs) written in single mode fiber (SMF) and thin-core fiber (TCF). The different effective refractive indexes between the cores of SMF and TCF are the key point because such FBGs support two separate resonances in the reflection spectrum for sensing measurement. These two resonances have different optical parameters, elastic-optic coefficient, and thermal-optic coefficient, they shift with different sensitivities under axial strain and temperature variations. The etching process is utilized on the grating of TCF to increase the sensitivity differences of the dual FBGs. In the experiment, simultaneous measurement of strain and temperature with the high strain sensitivity of 3.25 pm/ $\mu \varepsilon $ and high temperature up to 800 °C is realized respectively. This sensor scheme suits the practical application for strain and high-temperature measurement simultaneously.