Bragg Grating-based Sensor Research Articles

Etched Fiber Bragg Grating-Based Novel Tilt Sensor Employing Effective Refractive Index Induced Intensity Modulation Mechanism

Etched Fiber Bragg Grating-Based Novel Tilt Sensor Employing Effective Refractive Index Induced Intensity Modulation Mechanism

Fiber Bragg Grating-based sensor for measuring supersonic inlet terminal shock at different angles of attack

This study presents a multipoint pressure measurement system using fiber Bragg grating sensors to detect terminal shock positions. The system consisted of a fiber optic string encapsulated with multiple diaphragm-based fiber Bragg grating sensors, capable of detecting flow field characteristics at fourteen different axial positions of the inlet. The calibration results indicated a sensitivity of 46.47 pm/kPa, a linear correlation coefficient of 0.9997, and a maximum repeatability error below 1.44%. In supersonic wind tunnel tests, the system effectively measured pressure and located the terminal shock across varying angles of attack and throttling degrees. The maximum difference compared to conventional pressure sensors was 4.7%, and the terminal shock positioning error was limited to 1.2%. Overall, the system has robust multipoint measurement capabilities and is priced at only one-tenth of traditional sensors, showing great potential in the field of inlet measurements.

Visible-light fiber Bragg grating-based wearable optical sensor

In this work, we proposed, for what we believe to be the first time, a wearable optical sensor based on the higher-order harmonic fiber Bragg grating (FBG), which has the advantages of easy fabrication, visible window operation and cross-talk removal. The fifth-order harmonic Bragg grating was inscribed by use of the conventional C-band phase masks and excimer laser but resonated in the visible spectrum. The visible window FBG can not only significantly improve the bandwidth of utilization, but also endow the sensor with visual perception. As was encapsulated by the PDMS pad, the wearable FBG held the temperature and bending sensitivity of 7.16 pm/°C and 4 pm/deg, respectively. Furthermore, taking advantage of the abundant resonances in harmonic FBG, a sensitivity matrix was established based on the orchestration of fifth and second-order harmonic resonances to discriminate the cross-sensitivity between temperature and bending. Our research provides new sight for the future development of wearable optical sensors.

Fiber Bragg grating-based touch-slip sensor for surface roughness detection

To enable humanoid prosthetic hands to accurately identify and grasp objects, a touch-slip sensor based on fiber Bragg grating (FBG) was proposed in this paper. The sensor was designed with a double-layer sensing structure to detect three-dimensional force, sliding information, surface roughness, and compensate for ambient temperature using a reference grating. To analyze the relationship between the sensor surface structure parameters and FBG's vibration signal, the contact sliding model was introduced. By using a finite element simulation, the contact sliding model was validated, and the surface structure parameters of the sensor were determined. A series of experiments were conducted on the sensor’s three-dimensional force detection, temperature calibration, sliding measurement, and surface roughness detection. Using machine learning methods, a regression prediction model was created. The sensor could detect the surface roughness on the sample plate surface more accurately with a maximum error of 8.58×10−4. This sensor has the following advantages: a simple structure, low cost, high linearity, and quick response time. It provides a new design solution for the detection of touch-slips on humanoid prosthetic hands.

Experimental development and evaluation of a fiber bragg grating-based outside air temperature sensor for aircraft applications

This study presents the development and rigorous evaluation of a Fiber Bragg Grating (FBG)-based Outside Air Temperature (OAT) sensor designed for aircraft applications. Employing a Design of Experiments (DoE) approach, the research optimized the sensor's performance for reliability, accuracy, and durability in aviation environments. Experimental assessment covered detailed installation of the FBG sensor on an aircraft, considering influential parameters such as outside dimensions and varying temperature. The OAT sensor's design focused on robustness and precision for accurate real-time temperature recording, vital for operational efficiency and safety. Extensive statistical analysis assessed the sensor's performance under differing conditions, providing valuable insights into operational capabilities and overall efficacy. Thermo-climatic chamber tests simulated extreme environmental conditions to validate the sensor's durability and function under potential aircraft operational scenarios. This research enhances understanding of FBG-based OAT sensors for aircraft applications, demonstrating their superior robustness and performance capabilities, thereby contributing to aviation safety, operational efficiency, and data precision.© 2017 Elsevier Inc. All rights reserved.

Design of optical fiber Bragg grating-based sensors for flow measurement in pipes

In this work, optical Fiber Bragg grating (FBG) sensors were used to measure water flow in pipes. Several types of coatings were incorporated into the design of the sensors to examine their effects on the elastic strain that the fiber underwent as a result of the water flow. ANSYS-CFX V2020 R2 software was used to model the elastic strain encountered by the fiber under various flow rates in order to assess the performance of the FBG sensors. The calculations and experimental data exhibited good convergence, demonstrating the accuracy of the FBG sensors in determining water flow. These calculations and procedures can be extrapolated to any other fluid.

Optical fiber Bragg grating-based pressure sensor for soil monitoring applications

Optical fiber Bragg grating-based pressure sensor for soil monitoring applications

Fiber Bragg grating-based fingertip tactile sensors for normal/shear forces and temperature detection

Fiber Bragg grating-based fingertip tactile sensors for normal/shear forces and temperature detection

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.

A Fiber Bragg Grating-Based Gap Elongation Sensor for The Detection of Gap Elongation in Bolted Flange Connection

Many attempts havebeen madeby embedding a strain gauge sensor into thebolt shank to directly monitor the looseness of bolted structures. This application is constrained by many factors,including massive cabling connection, shortcomings of this sensor in harsh conditions,and low efficiency forhigh temperature applications.Therefore, fiber Bragg grating (FBG) sensingtechnology isa good alternative to solve the problem. In this article, an FBG-based gap elongation sensor wasdeveloped by embedding the sensor into a Teflon tube and clampingon the metal base structure. Several tests were carried out to calibrate the strain-sensitive coefficient of the sensor and also to determine the stability, linearity, and repeatability of the sensor for gap strain measurement. The strain sensitivity of the sensor was determined by a standard tensile test,with the strain sensitivity values ranging from 0.4221 pm/με to 0.5245 pm/με. During the calibration test, the FBG sensors showed excellent linearity and repeatability of less than 0.1% and 5% errors, respectively. Theexperimental resultsdemonstrated a linear relationship between the applied force and the FBG sensorwavelength. Furthermore, the experimental resultsdemonstrated acceptable linearity and stabilityof the sensor when subjected to bending loadswith overall repeatability errorsof less than 10%. This proposed method provides an alternativeapproach to monitor bolted gapelongation andcharacterize bolt looseness.

Fiber Bragg Grating-based sensor system for sensing the shape of flexible needles

Shape sensing is of importance for the manipulation of flexible needles. In this work, a 0.6 mm diameter stylet with five Fiber Bragg Gratings (FBGs) installed as triplets was designed and implemented and a novel model of local curvature was established. A gradient-based optimization method has been integrated into the complete algorithm for shape sensing and this was used to reduce the difference between the midpoint curvature and the mean curvature. The experimental results obtained show that the mean tip errors are 0.35 mm, 0.30 mm, 0.38 mm in the single-bending, double-bending and space-bending experiments, respectively. In a torsion test experiment which was performed, when the rotation angle of the tip was less than 25°, the error seen was less than 0.5 mm. Furthermore, when the needle designed in this work was used to puncture a 60 mm thickness, ex vivo biological tissue, the mean error of the measurement of the needle tip was 0.39 mm.

City-wide monitoring and contributing factors to shallow subsurface temperature variability in Nanjing, China

Shallow temperatures down to a depth of 100 m were measured over one year in 19 closed boreholes located in Nanjing, China, to reveal the conditions and factors influencing the subsurface thermal regime. A monitoring concept with distributed temperature sensing, fiber Bragg grating-based sensor, and a type of Resistance Temperature Detectors, is implemented, providing spatial distribution characteristics of subsurface temperatures. The results show that temperatures near the surface are most dynamic, influenced by the air temperature. The temperature remains stable at the depth of 10–20 m. The mean transition temperature is 18.1 °C. Borehole measurements are interpolated by using satellite images and surface temperature records to obtain large-scale surface temperature distributions and temporal variations of subsurface temperature. Geological and hydrological conditions are primary factors by affecting subsurface upward heat flux and heat loss. Urban land cover change and enhanced heat release from urbanization contribute to a subsurface urban heat island with intensities of 1.0–4.4 °C. The altered subsurface thermal regime is of primary concern for the management of shallow geothermal energy use. The monitoring concept in this study can provide spatially-temporally continuous profiles of subsurface temperature and become a reference for city-wide geothermal monitoring in other urban areas.

Smart Polymer Composite Deck Monitoring Using Distributed High Definition and Bragg Grating Fiber Optic Sensing.

Fiber-reinforced polymer composites are an excellent choice for bridge decks due to high strength, lightweight, resistance to corrosion, and long-term durability with a 100-year design life. Structural health monitoring is useful for the long-term assessment of the condition of the bridge structure and obtaining a response to complex loads considering environmental conditions. Bridge structures have been studied primarily using distributed fiber optic sensing, such as Brillouin scattering; however, critical events, including damage detection, can be missed due to low spatial resolution. There is also a critical need to conduct a comprehensive study of static and dynamic loading simultaneously for fiber-reinforced composite bridge structures. In this study, a novel approach was implemented using two sensor technologies, optical frequency domain reflectometry and fiber Bragg grating-based sensors, embedded in a glass-fiber-reinforced composite bridge deck to simultaneously monitor the deformation response of the bridge structure. The optical frequency domain reflectometry sensor utilizing Rayleigh scattering provides high spatial strain resolution were positioned strategically based on expected stress distributions to measure strain in the longitudinal, transverse, and diagonal directions along the span of the composite bridge. Furthermore, fiber Bragg grating based sensors are used to monitor the response to dynamic vehicular loading and deformations from an automotive-crash-type event on the bridge structure. To monitor environmental variables such as temperature, a custom wireless configured sensor package was developed for the study and integrated with a composite bridge located in Morgan County, Tennessee. Additionally, a triaxial accelerometer was used to monitor the vehicular dynamic loading of the composite bridge deck in parallel with fiber Bragg grating sensors. When appropriate, mid-point displacements were compared with strain-distribution measurements from the fiber optic sensor-based data.

A Fiber Bragg Grating-Based Sensor for Passive Cavitation Detection at MHz Frequencies.

Fiber Bragg gratings (FBGs) are a potential alternative to piezoelectric ultrasound sensors for applications that demand high sensitivity and immunity to electromagnetic interference (EMI). However, limited data exist on the quantitative performance characterization of FBG sensors in the MHz frequency range relevant to biomedical ultrasound. In this work, we evaluated an FBG to detect MHz-frequency ultrasound and tested the feasibility of measuring passive cavitation signals nucleated using a commercial contrast agent (SonoVue). The sensitivity, repeatability, and linearity of the measurements were assessed for ultrasound measurements at 1, 5, and 10 MHz. The bandwidth of the FBG sensor was measured and compared to that of a calibrated needle hydrophone. The FBG showed a sensitivity of 0.99, 0.769, and 0.818 V/MPa for 1, 5, and 10 MHz ultrasound, respectively. The sensor also exhibited linear response ( 0.975 ≤ R -Squared ≤ 0.996) and good repeatability with a coefficient of variation (CV) less than 5.5%. A 2-MHz focused transducer was used to insonify SonoVue microbubbles at a peak negative pressure of 175 kPa and passive cavitation emissions were measured, in which subharmonic and ultraharmonic spectral peaks were observed. These results demonstrate the potential of FBGs for MHz-range ultrasound applications, including passive cavitation detection (PCD).

High-Resolution Optical Fiber Temperature Sensor Based on Draw Tower Grating Array.

Ocean temperature monitoring is of great significance to marine fishing, aquaculture, and marine operations. Traditional electric sensors lack the potential to multiplex several sensors, and may suffer from electromagnetic interference. Meanwhile, fiber Bragg grating-based sensors have the advantages of high sensitivity, possibility for large-scale multiplexing, and immunity to electromagnetic interference. In this paper, we propose a Fabry–Pérot (FP) interferometer based on the draw tower grating array and combine it with the phase measurement method for demonstration and testing. In the sensor system, two adjacent fiber Bragg gratings (FBGs) are used as mirrors and an optical fiber connects them, forming a sensor unit. The signal was detected through the compensation of the optical path difference via two-arm path differences in an unbalanced interferometer. The sensor is calibrated in the range of 36.00–36.50 °C, and back to 36.00 °C, in steps of 0.10 °C. A thermocouple (DW1222) is used as a reference. Experimental testing demonstrates that under the thermal loop, the temperature and phase can be approximated as a linear relationship, the Pearson square correlation coefficient is 0.9996, and the temperature sensitivity is −9846 rad/°C. To prove that our experimental device can achieve a higher temperature resolution, we measured the background noise of the system. The experimental results indicate that the order of magnitude of our system temperature resolution can reach 10−5 °C. Thus, we believe that the sensor system is promising for the application of ocean temperature detection, and owing to the ultraweak reflection characteristics of the FBG, this method provides the possibility for large-scale multiplexing of the system.

Optical transmission and dimensional stability of single-crystal sapphire after high-dose neutron irradiation at various temperatures up to 688 °C

The use of single-crystal sapphire optical fibers has been considered to extend fiber-optic sensing to the extreme temperature (>1000 °C) environments encountered in nuclear applications. However, before these sapphire fiber–based sensors can be deployed, their optical transmission and dimensional stability (which impacts drift of some sensors) must be characterized under representative testing conditions. Data regarding the optical transmission of sapphire following high-dose neutron irradiation at temperatures >100 °C is extremely limited. This work provides measurements of optical density (i.e., attenuation) and directional dimensional changes in bulk single-crystal sapphire materials irradiated to a fast neutron fluence of 2.4 × 10 21 n/cm 2 (3.5 displacements per atom) at temperatures ranging from 95 to 688 °C. Optical density measured after irradiation at 95 and 298 °C showed ultraviolet and visible absorption bands corresponding to known defect centers and temperature trends that were generally consistent with previous ex situ and in situ measurements made at much lower neutron fluence. However, optical density measured after irradiation at 688 °C was as much as two orders of magnitude higher, indicating that the fundamental mechanism for radiation-induced attenuation changes at this irradiation temperature. Additional analysis and comparison with previous works suggest that the attenuation may result from void formation, leading to increased Rayleigh scattering losses in the material and increased swelling that would also result in drift of Bragg grating-based sensors in sapphire fibers. These results pose serious questions regarding the feasibility of sapphire fiber–based sensors for high-temperature nuclear applications.

Research progress and development tendency of sapphire fiber Bragg grating-based high-temperature sensors (invited)

Research progress and development tendency of sapphire fiber Bragg grating-based high-temperature sensors (invited)

Toward a Fiber Bragg Grating-Based Two-Dimensional Force Sensor for Robot-Assisted Cardiac Interventions

Coronary heart disease (CHD) has one of the highest contribution to global health risks. In essence, CHD’s economic burden cum the goal of achieving sustainable human health has attracted attention toward procedural innovations for better diagnosis and treatment of CHD. Despite having robotic systems paving the way towards reducing the perioperative risks faced by interventionists and patients, modeling and sensing of distal force feedback remain as an unsolved challenge. Of all sensing techniques adopted to solve this challenge, a fiber Bragg grating-based technique seems to be the most promising. In this letter, a prototype of a 3-D-printed 2-D distal force sensor is proposed for acquiring tool-vessel contact forces during robot-assisted cardiac procedures. The prototype consists of a symmetrical sensing structure designed with four optical fibers. Simulation and experimental studies were carried out to validate the applicability of the sensor. The simulation result shows that the force sensor could experience a minimal deformation under lateral forces of up to 1.0 N, whereas the in-lab temperature characterization study indicates that the sensor prototype has good linearity with increasing temperature between 35 and 54 °C. Thus, the fiber Bragg grating-based technique could enhance robot-assisted treatments of CHD.

Fiber Bragg Grating-Based Sensor System for Sensing the Shape of Flexible Needles

Fiber Bragg Grating-Based Sensor System for Sensing the Shape of Flexible Needles

Fiber Bragg Grating-Based Three-Axis Vibration Sensor

This paper proposed a fiber Bragg grating (FBG)-based three-axis vibration sensor by using only five sensing elements. A composite structure of the cross-beam-type elastomer with multiplexed FBGs has been designed for three-axis vibration sensing. Because of the mechanical decoupling function of the structure and the reasonable arrangement of FBG sensing elements, the designed sensor possesses great advantages of low cross coupling and self temperature compensation capability. Theoretical model of the composite structure has been established, strain distribution and dynamic characteristics of the composite structure have been studied by the finite element analysis method. Amplitude-frequency test result shows that resonant frequencies of the sensor in X, Y, and Z directions were 980Hz, 960Hz, and 640Hz, respectively. Vibration sensitivities in X, Y, and Z directions were 9.7pm/g, 10.13pm/g, and 7.45pm/g, respectively. Vibration calibration test have validated that the designed sensor possess the capability to measure three-axis vibration.