Fiber Bragg Grating Sensors Research Articles

Steel corrosion process in ultra-high performance concrete monitored by fiber bragg grating sensor

The steel corrosion in Ultra-High Performance Concrete (UHPC) would cause degradation of structural performance or even structural failure. It is an urgent need to monitor and predict the steel corrosion in UHPC, however it is still a tough task. In this paper, Fiber Bragg Grating (FBG) sensors are applied for monitoring the steel corrosion process in UHPC, by combining with steel bar, which is equidistant winding with the sensors, and connected with power supply for accelerating corrosion. The UHPC specimens embedded with steel bars are surrounded by sodium chloride (NaCl) solution, and the steels are artificially corroded with different current densities for investigation. The steel corrosion in Original C60 and Marine Concrete 60 (Marine C60) are applied for comparison. The volume expansion coefficient for monitoring the steel corrosion process, is carried out by FBG sensors, and further comprehensively monitored by three grating sensors. The results suggest that the steel corrosion process in UHPC is slowly with current density lower than 100 μA/cm2, and largely increases with current density higher than 500 μA/cm2, the volume expansion coefficient of corroded steel in UHPC is in range of 2.02–2.62 in this test, which is much different from Original C60 and Marine C60.

Fiber Bragg grating sensing system for temperature measurements based on optically injected DFB-LD with an OEO loop

A novel fiber Bragg grating (FBG) sensing system, based on an optically injected distributed feedback laser diode (DFB-LD) with an optoelectronic oscillating (OEO) loop, is proposed and experimentally demonstrated for temperature measurements with high and tunable sensitivity. The FBG sensor device works as an edge filter to adjust the optical power of the injected beam in response to temperature variations. The optically injected DFB-LD works at Period-one (P1) oscillating state, and the central wavelength of the oscillating mode of the DFB-LD can be tuned by the variable power of the injected beam. Furthermore, an OEO loop is implemented to improve the signal quality of the generated P1 microwave signal. Hence, the sensing parameter of temperature is converted to the frequency variation of the generated P1 microwave signal in the proposed sensing system. In the proof-of-concept experiment, a series of P1 microwave signals are generated while different temperatures are applied to the FBG sensor. The sensitivity of the proposed FBG sensing system for temperature measurements can be tuned from 0.44322 GHz/°C to 1.25952 GHz/°C. The stability and repeatability experiments are also performed, demonstrating the high measurement accuracy (0.0629°C) and low error of the system. The proposed FBG-based sensing and interrogation system exhibits high sensitivity, large tunability, good linearity, and flexible sensing generality.

Cooperative vs. Teleoperation Control of the Steady Hand Eye Robot with Adaptive Sclera Force Control: A Comparative Study.

A surgeon's physiological hand tremor can significantly impact the outcome of delicate and precise retinal surgery, such as retinal vein cannulation (RVC) and epiretinal membrane peeling. Robot-assisted eye surgery technology provides ophthalmologists with advanced capabilities such as hand tremor cancellation, hand motion scaling, and safety constraints that enable them to perform these otherwise challenging and high-risk surgeries with high precision and safety. Steady-Hand Eye Robot (SHER) with cooperative control mode can filter out surgeon's hand tremor, yet another important safety feature, that is, minimizing the contact force between the surgical instrument and sclera surface for avoiding tissue damage cannot be met in this control mode. Also, other capabilities, such as hand motion scaling and haptic feedback, require a teleoperation control framework. In this work, for the first time, we implemented a teleoperation control mode incorporated with an adaptive sclera force control algorithm using a PHANTOM Omni haptic device and a force-sensing surgical instrument equipped with Fiber Bragg Grating (FBG) sensors attached to the SHER 2.1 end-effector. This adaptive sclera force control algorithm allows the robot to dynamically minimize the tool-sclera contact force. Moreover, for the first time, we compared the performance of the proposed adaptive teleoperation mode with the cooperative mode by conducting a vessel-following experiment inside an eye phantom under a microscope.

On-line cure monitoring of phenol formaldehyde resin using embedded fiber Bragg grating sensor

On-line cure monitoring techniques have shown advantages for identifying the stages of curing and can lead to smart curing process of resin system and its composites. In this study, an on-line measuring technique with fiber Bragg grating (FBG) sensors was used to gain clear understanding of the curing stages of phenolic resin, as well as to determine its chemical shrinkage level. The FBG sensors were embedded in phenolic resin and worked under temperature raising and isothermal conditions. Through the interface between FBG sensor and resin, curing shrinkage strain was transferred to the grating, changing the central wavelength of FBG and producing strain. The feasibility of FBG sensors for monitoring chemical shrinkage during curing was verified by employing epoxy and benzoxazine resins that exhibits low chemical shrinkage. For cure monitoring of phenolic resin, the results show that the strain signal can be corresponded to various responses, such as solvent volatilization, hydroxylation and dehydration condensation reactions during temperature raising curing process. Through these strain characteristics, the curing state of phenolic resin can be obtained, which degree of cure ranges from 0.05 to 0.9. In isothermal curing process of phenolic resin, an exponential correlation between chemical shrinkage induced compressive strain and degree of cure of resin was identified, indicating that the real-time compressive strain is proportional to the degree of cure of phenolic resin. By evaluating real-time curing shrinkage levels, the estimation of curing degree of phenolic resin can be achieved utilizing exponential correlation of curing degree and curing shrinkage level.

Exploring the Needle Tip Interaction Force with Retinal Tissue Deformation in Vitreoretinal Surgery.

Recent advancements in age-related macular degeneration treatments necessitate precision delivery into the subretinal space, emphasizing minimally invasive procedures targeting the retinal pigment epithelium (RPE)-Bruch's membrane complex without causing trauma. Even for skilled surgeons, the inherent hand tremors during manual surgery can jeopardize the safety of these critical interventions. This has fostered the evolution of robotic systems designed to prevent such tremors. These robots are enhanced by FBG sensors, which sense the small force interactions between the surgical instruments and retinal tissue. To enable the community to design algorithms taking advantage of such force feedback data, this paper focuses on the need to provide a specialized dataset, integrating optical coherence tomography (OCT) imaging together with the aforementioned force data. We introduce a unique dataset, integrating force sensing data synchronized with OCT B-scan images, derived from a sophisticated setup involving robotic assistance and OCT integrated microscopes. Furthermore, we present a neural network model for image-based force estimation to demonstrate the dataset's applicability.

Design of Wearable Human Physiological Parameter Acquisition System Based on Fiber Bragg Grating Sensors

Design of Wearable Human Physiological Parameter Acquisition System Based on Fiber Bragg Grating Sensors

Evaluation of an Erbium-Doped Fiber Ring Laser as an Edge Filtering Device for Fiber Bragg Grating Sensor Interrogation

An easy-to-implement and cost-effective Fiber Bragg Grating (FBG) sensor interrogation technique based on a ring Erbium-Doped Fiber Laser (EDFL) topology is proposed and experimentally assessed. The FBG sensor is part of the EDFL cavity and must have a central wavelength located within the linear region of the EDF’s amplified spontaneous emission (ASE) spectrum, which occurs at between 1530 and 1540 nm. In this manner, the wavelength-encoded response of the FBG under strain is converted to a linear variation in the laser output power, removing the need for spectrum analysis as well as any limitations from the use of external edge-filtering components. In addition, the laser linewidth is significantly reduced with respect to the FBG bandwidth, thus improving the resolution of the system, whereas its sensitivity can be controlled through pumping power. The performance of the system has been characterized by modeling and experiments for EDFs with different lengths, doping concentrations, and pumping power levels. The influence of mode-hopping in the laser cavity on the resolution and accuracy of the system has also been investigated.

Fiber Bragg Gratings Sensor Strain-Optic Behavior with Different Polymeric Coatings Subjected to Transverse Strain.

This research work is based on a previous study by the authors that characterized the behavior of FBG sensors with a polyimide coating in a structural monitoring system. Sensors applied to structural health monitoring are affected by the presence of simultaneous multidirectional strains. The previous study observed the influence of the transverse strain (εy) while keeping the longitudinal strain constant (εx), where the x direction is the direction of the optical fiber. The present study develops an experimental methodology consisting of a biaxial test plan on cruciform specimens with three embedded FBG sensors coated with polyimide, acrylate, and ORMOCER®. Applying the Strain-Optic Theory as a reference, a comparison of the experimental values obtained with the different coatings was studied. This experimental work made it possible to study the influence of the transverse strain (εy) on the longitudinal measurements of each FBGS and the influence of the coating material. Finally, the calibration procedure was defined as well as K (strain sensitivity factor) for each sensor.

Design and analysis of a fiber Bragg grating-based foot pressure assessment system.

This research presents a comprehensive study focused on the design, implementation, and analysis of an innovative fiber Bragg grating (FBG) based foot pressure assessment system. FBG sensors strategically placed on the great toe, metatarsal 1, metatarsal 2, and heel provided distinct peak resonant wavelengths, strains, and pressures during experimental cycles. Participant 1 exhibited peak resonant wavelength of 1537.745 nm for great toe, 1537.792 nm for metatarsal 1, 1537.812 nm for metatarsal 2, and 1537.824 nm for heel. Participant 2 showcased distinct graphical representations with peak resonant wavelengths ranging from 1537.903 to 1537.917 nm. In a fracture patient condition, the FBG-based system monitored weight-bearing capacity, integrated with real-time X-ray imaging for dynamic insights of rehabilitation as distinct approach. The strains and pressures at each position exhibited notable variations along with the sensitivity of 1.31με obtained across all positions, underscoring the FBG-based system's reliability in capturing subtle foot pressure.

Research on Decoupling Model of Six-Component Force Sensor Based on Artificial Neural Network and Polynomial Regression.

A two-stage decoupling model based on an artificial neural network with polynomial regression is proposed for the six-component force sensor load decoupling problem in the case of multidimensional mixed loading. The six-dimensional load categorization stage model constructed in the first stage combines 63 load category label sets with a deep BP neural network. The six-dimensional load regression stage model was constructed by combining polynomial regression with a BP neural network in the second stage. Meanwhile, the six-component force sensor with a fiber Bragg grating (FBG) sensor as the sensitive element was designed, and the elastomer simulation and calibration experimental dataset was established to realize the validation of the two-stage decoupling model. The results based on the simulation data show that the accuracy of the classification stage is 93.65%. The MAPE for the force channel in the regression stage is 6.29%, and 3.24% for the moment channel. The results based on experimental data show that the accuracy of the classification stage is 87.80%. The MAPE for the force channel in the regression phase is 5.63%, and 4.82% for the moment channel.

A novel packaging method for FBG temperature sensors based on ultrasonic-assisted soldering technology

The packaging technology of fiber Bragg grating (FBG) sensors is the key to determining their operational performance. A method for encapsulating FBG temperature sensors using ultrasonic-assisted soldering technology has been proposed and attempted. This packaging method is based on the successful connection between SiO2 quartz glass and Invar alloy. Implementing this soldering connection depends on the active components in the solder, which are dispersed into SiO2 and metal alloys to form more stable substances. The FBG with the removed coating is reliably connected to the metal capillary through ultrasonic soldering. The fragile FBG is adequately protected in the capillary. Sn-based solder with a melting point of 297 ℃ has been selected. The soldering temperature of 330 ℃ avoids significant residual stress caused by the difference in the thermal expansion coefficient of the material at the joint. Excellent bonding strength between optical fibers, solder, and capillaries is necessary for encapsulating sensors. Compared to adhesive, solder packaging is no longer affected by the creep of the sealant. The results show that the working range of FBG temperature sensors encapsulated in epoxy resin is −25 ℃ −115 ℃, while temperature sensors encapsulated by welding can operate stably at −50 ℃ −280 ℃. Sensors packaged using ultrasonic-assisted soldering technology have the potential to be embedded in metal substrates, creating favorable conditions for the development of intelligent electromechanical components.

Recent Applications of Fiber Bragg Grating Sensors in Humidity and Water Content Detection in Agriculture: A Comprehensive Review of Development, Challenges, and Future Trends

Recent Applications of Fiber Bragg Grating Sensors in Humidity and Water Content Detection in Agriculture: A Comprehensive Review of Development, Challenges, and Future Trends

Dual-parameter combined measurement sensor based on tri-metal structure

Simultaneous measurement of strain and temperature in vibrating environments has always been a key technical issue in the field of structural health monitoring. To address the bottleneck of inadequate dual-parameter measurement performance in existing Fiber Bragg Grating (FBG) strain and temperature sensors, a new type of fiber optic grating sensor with anti-vibration capabilities for the measurement of both strain and temperature is proposed. The sensor utilizes a flexible hinge structure made of 304 steel with high elastic modulus for strain sensitization and a bimetallic structure composed of 7075 aluminum and 4 J36 Invar alloy for temperature sensitization, integrating both types of sensors. Theoretical analysis of the sensor was conducted, followed by the fabrication of a prototype and the establishment of a testing system for performance evaluation. The results show that the designed dual-parameter FBG sensor has a strain sensitivity of approximately 3.06 pm/µε, about 2.62 times that of a bare FBG, and a temperature sensitivity of about 50.2 pm/℃, roughly 4.97 times that of a bare FBG. In anti-vibration performance tests between 5–100 Hz, the wavelength drift of the strain and temperature sections of the FBG in the sensor were both within 1 pm, meeting the requirements for simultaneous measurement of strain and temperature in vibrating environments. These findings provide a reference for the development of similar sensors and further improvement of the measurement performance of FBG strain and temperature sensors.

Dynamic characterization of Fiber Bragg Grating temperature sensors

To reliably characterize fast dynamic heat transfer mechanisms, fast-response temperature sensors are crucial, including knowledge about the temporal response. In this paper, the dynamic behavior of a Fiber Bragg Grating temperature sensor is investigated and compared to different types of fast-response thermocouples using two different experimental dynamic characterization methods. A temperature step is generated by either plunging the sensor into a fluid or exposing it to a fluid droplet at different temperatures. The step response is evaluated to determine the sensor response time. Calibration runs are performed for a silica-based 0.125mm FBG sensor, as well as for 0.16mm and 0.8mm exposed tip and 0.25mm sheathed tip type K thermocouples. Water, glycerin, oil and GaInSn were used to cover a broad range of applications regarding different thermal diffusivities and viscosities. The FBG sensor showed the shortest response times compared to the thermocouples, ranging from 60ms in oil down to 3ms in liquid metal, which is 20% up to 70% faster compared to a 0.25mm sheathed tip type K thermocouple. Additional plunging calibration runs of the FBG sensor were performed in a ternary nitrate molten salt mixture (HITEC) to determine its overall and dynamic behavior in corrosive fluids at elevated temperatures. It turns out that the FBG sensor is not affected by the molten salt and shows similar response times to those measured in water. Regarding the characterization methods, both techniques show reproducible results, even though the droplet method is inapplicable for sensors with higher heat capacity or lower thermal conductivity than the calibration fluid. Furthermore, splashing effects for fluids with low viscosity reduce the reliability of the droplet method. The results also show that a dynamic characterization is indispensable for temperature measurements with high temporal resolution because the response time depends on the sensor size and the heat transfer coefficient between sensor and surrounding, which in turn depends on the sensor type, fluid properties and the flow parameters.

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

Membrane-based optical fiber Bragg grating pressure sensor for health monitoring of pile foundations

A fiber Bragg grating (FBG) pressure sensor is proposed, designed, and fabricated for lateral earth pressure sensing, in which the FBG sensor is mounted on a 3D printed trestle structure combined with a membrane. The applied pressure can cause a deformation on the membrane, and then this deformation applied on the trestle structure causes tensile strain on the FBG. The proposed sensor is functionalized as a high-sensitive pressure transducer capable of converting the pressure into strain on the FBG. Here, the performance of the proposed sensor is numerically and experimentally investigated. The results show that the pressure sensitivity at 30°C is 10.62 pm/kPa within a range of 0–0.6 MPa. Due to the thermal expansion of the structure, the pressure sensitivity coefficient decreases with the increase of temperature; however, the cross effect between the temperature and strain on the sensing sensitivity is investigated and can be eliminated. The fabricated sensor has advantages of high sensitivity, good stability, and high pressure resolution, so it has potential in the field of structural health monitoring.

Optimizing Parameters and Applications of Femtosecond Laser Technology in Fiber Bragg Grating Manufacture

Fiber Bragg Grating (FBG) sensors have garnered extensive attention for their pivotal role in diverse domains, including strain, pressure, hydroacoustics, and temperature monitoring, especially within the ambit of the Internet of Things (IoT). The femtosecond laser point-by-point fabrication methodology stands out in this context, primarily for its flexibility in altering FBG periods through precise control of the fiber’s movement velocity. This adaptability facilitates the creation of FBGs with varied periodicities, significantly broadening their application spectrum. A notable aspect of FBG sensors is their sensitivity to temperature variations, which manifest as changes in both the grating pitch and the refractive index of the FBG. These alterations consequently induce shifts in the FBG’s reflection and transmission spectra. Specifically, temperature fluctuations lead to a discernible drift in the central wavelength of the light reflected by the Bragg grating. This wavelength drift is linearly proportional to the temperature change, rendering it a reliable metric for assessing both the magnitude and rate of temperature variations. Experimental framework was centered around the femtosecond laser point-by-point fabrication technique for FBG creation. Within this setup, we delved into four critical factors influencing the spectral quality of the FBGs: grating length, periodicity, laser energy, and grating position. By meticulously adjusting these parameters, we aimed to optimize the performance and applicability of FBG sensors in real-world IoT scenarios.

A miniature triaxial force sensor based on fiber Bragg gratings for flexible endoscopic robot

Contact force sensing is an important means to ensure the safe operation of surgical robots. This paper presents a miniature triaxial force sensor based on fiber Bragg grating (FBG) for detecting the interaction forces between the tip of flexible endoscopic surgical robots and tissue. The proposed sensor mainly consists of a force-sensitive flexure structure, a support body, and four FBG sensors. A composite hollow structure with a parallel helical slot and elliptical hinge has been utilized to design the force-sensitive flexure with an excellent linear measurement range. The four optical fibers arranged along the circumference of the flexure are configured as a tightly stretched status with their two points fixed. This configuration can improve sensitivity and avoid the drawbacks of FBG chirping and low repeatability. Finite element method-based simulation has been implemented to optimize the flexure’s structural parameters for balancing the force sensor’s axial and radial resolution. The prototyped sensor has been calibrated and achieves a high resolution of 0.77 mN and 0.79 mN for both lateral forces within −1 to 1 N and 1.25 mN for axial force within 0 to 2 N. Loading experiments have been conducted to validate the effectiveness of the proposed designs. The results show that the sensor can provide a high-accuracy measurement of three force components with an average RMS error of less than 3% in the total operating ranges. Such a result validates the feasibility of the designed sensor to measure the robot-tissue interaction forces.

Integration of Piezoelectric Energy Harvesting Systems into Building Envelopes for Structural Health Monitoring with Fiber Optic Sensing Technology

This paper presents a study about the integration of Piezoelectric Energy Harvesting Systems (PE-EHSs) into building envelopes for powering Fiber Bragg Grating (FBG) sensors, enabling efficient and low-consumption monitoring with the objective of leveraging structural health monitoring (SHM). The research includes preliminary tests conducted in a real environment to validate the PE-EHS when fully integrated into a ventilated façade, capturing mechanical vibrations generated mainly by wind loads. Based on these activities, the final configuration of PE-EHSs is defined to provide a complete system for façade monitoring. This integrated system includes the piezoelectric generator (PEG), supercapacitor (SC), Power Conditioner Circuit (PCC), Fiber Optic Sensing (FOS) interrogator, and the IoT gateway transmitting measurement data within an Internet of Things (IoT) monitoring platform. This configuration is tailored to address the challenges related to the structural integrity of building envelopes. Results demonstrate a potential for a stand-alone solution in the façade sector but raise issues for certain limitations, requiring further investigation. In particular, the study emphasizes constraints related to the energy production of PE-EHSs for façade integration. It highlights the necessity to carefully consider these limitations within the broader context of their applicability, providing insights for the informed deployment of piezoelectric energy harvesting technology in building envelope monitoring.

Blast wave pressure measurement and analysis in air and granular media inside a shock tube using a fiber Bragg grating sensor.

In this work, we have demonstrated the use of a fiber Bragg grating (FBG) sensor to measure the pressure profile of blast waves generated inside a vertical shock tube (VST). An FBG pressure sensor probe has been designed and developed that can be incorporated into the wall of the VST. The VST facility is used to generate blast waves with decay times of the order of a few milliseconds to simulate explosive events. Pressure measurement experiments have been carried out at different incident blast wave peak pressures inside the VST. The FBG pressure sensor measurements are validated against a standard piezoelectric pressure transducer at an acquisition rate of 1MHz. The pressure signals of both sensors are found to match well with similar rise times and decay profiles. The validated FBG pressure sensor is then incorporated into a sand column mounted in the test section of the VST to measure the pressure profile of blast wave-induced stress waves in granular media. The FBG and piezoelectric pressure sensor data are compared using fast Fourier transform analysis and continuous wavelet transform. The feasibility of FBG sensors for blast pressure measurement under harsh conditions imposed inside shock tube environments is established.