Proposed Fiber Bragg Grating Sensor Research Articles

2D Shape Estimation of a Pneumatic‐Driven Soft Finger with a Large Bending Angle Based on Learning from Two Sensing Modalities

A shape estimation method that utilizes two sensing modalities of a customized fiber Bragg grating (FBG) sensor and a commercial air pressure sensor for a pneumatically driven soft finger with an extensive bending angle range based on an artificial neural network model is proposed. The proposed FBG sensor utilizes two tiny nitinol rods as a backbone to attach the long‐grating FBG element fiber, enabling high strain transfer, shape sensing for large bending deformation, and preventing chirping failure and fiber sliding when bending. Its distal end is set free to slide and synchronizes with the extended length and reflects shapes for large bending deformation (up to 320° with a linearity of 99.96%), while its proximal end is fixed. The small packaged sensor unit enables modular design, easy assembly, and high repeatability with negligible effects on the soft finger's bending performances. The artificial neural network model is utilized to process the input of two sensing modalities, reducing errors from material nonlinearity, fabrication, and assembly of soft fingers while improving shape estimation's accuracy and transferability with average errors of 0.90 mm (0.69%) and 1.55 mm (1.19%) for whole shape and distal end position, respectively. Preliminary experiments also verify the potential for pressing force prediction and hardness recognition.

A Fiber Bragg Grating Sensor Based on Cladding Mode Resonance for Label-Free Biosensing

A fiber-optic biosensing platform based on ultra-narrowband cladding mode resonances was developed on a high-reflectivity fiber Bragg grating (FBG) for targeting biomolecular detection. The multiple cladding modes with a high sensitivity to the refractive index (RI) were excited in the FBG by coupling between the forward-propagating guided core mode of the multimode fiber and the backward-propagating guided cladding mode of the FBG without any damage to the fiber structure or any change to the standard FBG manufacturing process. The full width at half maximum and the Q-factor of the typical cladding mode resonance operation of the proposed sensor are 80 pm and 19,270, respectively, which are better than those of most fiber-optic biosensors reported to date. In addition, the FBG sensor demonstrated a high sensitivity in protein detection and a high selectivity in serum sample assays. The sensitivity of this sensor was further increased simply by coating it with graphene oxide (GO) sheets on the sensing surface without using a signal amplification strategy. Furthermore, an ultra-low limit of detection (LOD) of 32 pM was obtained by the GO-coated FBG sensor for IgG detection. The proposed FBG sensor provides a competitive fiber-optic platform for biomolecular detection. It has a great potential for applications in label-free biosensing.

Cladding Modified Fiber Bragg Grating for Copper Ions Detection

This paper reports a fiber Bragg grating (FBG) as a biosensor. The FBGs were etched using a chemical agent,namely,hydrofluoric acid (HF). This implies the removal of some part of the cladding layer. Consequently, the evanescent field propagating out of the core will be closer to the environment and become more sensitive to the change in the surrounding. The proposed FBG sensor was utilized to detect toxic heavy metal ions aqueous medium namely, copper ions (Cu2+). Two FBG sensors were etched with 20 and 40 μm diameters and fabricated. The sensors were studied towards Cu2+ with different concentrations using wavelength shift as a result of the interaction between the evanescent field and copper ions. The FBG sensors showed a good response in terms of significant wavelength shift in corresponding to varying Cu2+ concentrations when immersed in aqueous mediums. The sensors exhibited excellent repeatability towards Cu ions.The results demonstrate that the smaller FBG etching diameter, the better optical response in terms of wavelength and linearity.

Reliable self-healing FBG sensor network for improvement of multipoint strain sensing

In this paper, we proposed and designed reliable self-healing fiber Bragg grating (FBG) sensor network for improvement of multipoint strain sensing. We use an optical switch (OSW) to reconfigure the sensor network and improve the self-healing function during fault happen in the sensor network. In this work, to prove and validate the detection performance of our proposed Bragg wavelength detection technique even when the number of overlap spectra of FBGs increases, we conduct three experiments and collect three different cases of strain data (namely case 1, case 2, and case 3) by applying different strain steps to FBGs. In case 1 experiment, strain was applied to only FBG1 sensor, while the other four FBGs keeps fixed. In case 2 experiment, strain was applied to FBG1 and FBG2 sensors at the same time and with different strain steps. In case 3 experiment, strain was applied to FBG1, FBG2 and FBG3 sensors at the same time and with different strain steps. As a result, in all cases of the experiment, three situations of spectra were introduced between FBGs like non-overlapped, partially overlapped and completely overlapped spectra. To solve this overlap problem, we used deep learning technique to accurately identify the Bragg wavelength of FBGs in the condition of the partially or fully overlapped spectra. Therefore, our proposed FBG sensor system can improve the reliability and detection accuracy of the sensor system even the number of overlaps FBGs spectra increases.

Fiber Bragg Grating Pressure Sensor Integrated with Epoxy Diaphragm.

A fiber Bragg grating (FBG) sensor integrated with an epoxy diaphragm was developed for the measurement of pressure and water level. The bending strain of a circular diaphragm induced by uniform pressure was transferred to the FBG sensor. The response of the FBG sensor to the pressure was observed in terms of the Bragg wavelength shift which is linearly proportional to the strain. The effect of epoxy diaphragm thickness on the sensitivity and accuracy was investigated. The experimental results show that the sensitivity of FBG/epoxy diaphragm pressure sensor is decreasing with the increase of the diaphragm thickness. The sensitivities of the FBG pressure sensors with diaphragm thicknesses of 0.5 mm, 0.7 mm, and 1.0 mm were 175.5 pm/kPa, 89.5 pm/kPa, and 43.7 pm/kPa, respectively. The pressure measured by the proposed FBG sensor was compared with theoretical prediction and a close agreement was observed.

Design and Experiment of FBG Sensors for Temperature Monitoring on External Electrode of Lithium-Ion Batteries

Lithium-ion (Li-ion) battery becomes a promising energy storage element in the power grid. Temperature monitoring is a key tool to guarantee the safe service and durable life of Li-ion batteries. In this study, an optical fiber sensor was proposed for the temperature monitoring of Li-ion batteries. The proposed sensor consists of a metal ring and a fiber Bragg grating (FBG), which is gloved on the external electrode of the cell. This installation is not only easy to assemble but also no interference to the circuit connection. The results of calibration test on proposed FBG sensors show good linearity (0.99) and high sensitivity (12 pm/°C). A comparison test illustrates the response of proposed FBG sensors has a good agreement with PT100 sensors. The FBG sensor can be fabricated as sensor arrays to monitor the temperature of multiple cells during charge/discharge cycles, simultaneously. The experimental results show that the FBG sensors have good repeatability during several cycles. FBG sensor arrays can be used to achieve distributed temperature measurement for multiple cells. It provides a solution to monitor the thermal behavior of each cell in battery packs and an available tool to improve the thermal management and safety of Li-ion batteries.

Study of Calorimetric Self-Field AC Loss Measurement of HTS Stacks Using FBG Sensors

AC loss plays an important role in the design of the device employing HTS magnet. Therefore, it is important to measure the AC loss in HTS magnet. In this work, we studied the calorimetric self-field AC loss measurement of a four-tape HTS stacks using Fiber Bragg Grating (FBG) sensors. Three cryogenic FBG temperature sensors with different coating and installation were selected for the AC loss measurement. The calibration between power loss and wavelength shift was carried out by a resistance heater before the AC loss measurement. With the calibrated FBG sensors, the AC loss measurement was measured at 67 Hz and 89 Hz. These measurements were carried out at 77 K through conduction cooling by sealing the sample in a thermal insulator. The measured loss results were verified through comparison with the Norris models as well as the electrical measurements of AC loss. Finally, the magnetic strain effect on loss measurement was evaluated experimentally. The results in our paper shows that the calorimetric method based on the proposed FBG sensor can be used for the AC loss measurement of a four-tape HTS stack, and the magnetic strain of a four-tape stack has no effect on the AC loss measurement, which provides the possibility of using FBG sensors for ac loss measurement on HTS stacks.

External Electrode Temperature Monitoring of Lithium Iron Phosphate Batteries Based on Fiber Bragg Grating Sensors

Lithium-ion (Li-ion) batteries have become a promising candidate for the electrical energy storage and power delivery solutions. Thermal management is a key tool to improve performance and safety of Lithium-ion batteries. Currently, the common method is using electric sensors to monitor the thermal behaviour of batteries. In this work, an optical fiber sensor was proposed for temperature measurement of cells. The proposed sensor consists of a metal ring and a fiber Bragg grating (FBG). The FBG sensor calibration test shows a good linearity and high sensitivity. The FBG sensors were gloved on the external electrodes to monitor the temperature variation during charge/discharge cycles, and the PT100 sensors were attached on the electrodes as a comparison. Comparison test illustrates the response of proposed FBG sensors has a good agreement with PT100 sensors. It provides that the proposed FBG sensor can be used to monitor the temperature variation of cells, which provides a promising tool to improve the thermal management and safety of Li-ion batteries.

Development and experimental validation of a Nuttall apodized fiber Bragg Grating sensor with a hydrophobic polymer coating suitable for monitoring sea surface temperature

Abstract Continuous monitoring of Sea Surface Temperature (SST) is essential for predicting and understanding various complex meteorological processes. In this work, a novel fiber optic temperature sensor based on an apodized Fiber Bragg Grating (FBG) is proposed for measuring variations in SST. The sensor head is fabricated based on optimized grating profile and coating material. Experimental analysis reveals that the proposed sensor yields a temperature sensitivity of 13 pm/ ° C with a resolution of 0.023 ° C in the temperature ranging from 16 ° C to 30 ° C . Performance of the proposed temperature sensor is validated against commercial ocean sensors which provides a mean error of 0.2342 ° C thereby proving the potential of the proposed FBG sensor for efficient SST monitoring in real-time.

Design and investigation of a sensitivity-enhanced fiber Bragg grating sensor for micro-strain measurement

The fiber Bragg grating (FBG) sensors are widely used in strain measurement. However, the current FBG sensors are not sensitive enough to monitor the micro-strain. In order to provide a feasible method to monitor the micro-strain of lithium-ion battery, a novel fiber Bragg grating (FBG) strain sensors with enhanced sensitivity was developed in this paper. A lever mechanism was adopted to enhance the sensor sensitivity and flexure hinges as well as serpentine springs were used in sensor structure. The sensor structure dimension was optimized through theoretical calculation and finite element analysis, and the optimized sensor was manufactured and tested. The results of calibration test show that in the measuring range of ±500 με, the sensor has strain sensitivity of 11.49 pm/με, good linearity and repeatability as well as tiny hysteresis error. The battery experimental results illustrate there is a same trend between strain and voltage of battery, and a good uniformity under three working modes of battery. This proposed FBG sensor will provide a solution for strain measurement of battery.

Selection and Characterization of Packaged FBG Sensors for Offshore Applications.

With the development in the exploitation of maritime resources, the structural health monitoring (SHM) of offshore structures becomes necessary. This study focuses on addressing the practical issues of application of fiber Bragg grating (FBG) sensors for the SHM of offshore structures, in particular an FPSO (floating, production, storage, and offloading unit) vessel. Due to the harsh marine environment and tough working conditions, the FBG sensors must have sufficient protection and good repeatability for long-term monitoring. Thorough research has been conducted to identify the most suitable, commercially available protection packaging for FBG sensors for offshore applications. Further, the performance of the selected FBG sensor packaging is tested under conditions of strong sunlight, heavy rain, and salty water in order to emulate the marine environment. Moreover, the installation method of the packaged FBG sensors is equally important, as it ensures the repeatability and durability of the sensors for their long-term performance. It is shown that the packaged FBG sensors can be installed using resin-based epoxy to maintain the repeatability of the sensor over the long-term. Further, the packaged FBG sensors are installed and tested on a simple FPSO model. The experimental results under full load and ballast draft conditions show that the proposed FBG sensors are competent for the SHM of offshore structures.

Capacity and capability enhancements of FBG sensor system by utilizing intensity and WDM detection technique

In this paper, we demonstrate a multipoint fiber Bragg grating (FBG)-based sensor system by using intensity and wavelength-division-multiplexing (I-WDM) technique to enhance the sensing capacity and capability. In the proposed multipoint sensor system, a three output port optical splitter with different output ratios of 50%, 35% and 15% is proposed to connect each intensity coding FBG sensor for strain and temperature sensing simultaneously. Different output ratios of connected ports can produce different intensity-coding for I-WDM application. Nine FBGs with different Bragg wavelengths are employed for demonstration. The proposed FBG sensor system not only can sense the strain and temperature simultaneously, but also can increase the capacity and capability.

Fault Self-Detection Technique in Fiber Bragg Grating-Based Passive Sensor Network

In this paper, we propose and experimentally investigate a fault self-detection technique in fiber Bragg grating (FBG)-based passive sensor network. Here, once a fault occurs on connecting fiber or FBG sensor, it can be detected directly by the proposed sensing network. Moreover, in the proposed FBG sensor system, the multiple wavelength-division-multiplexing FBG sensor numbers can be reduced significantly and also increase the sensing capability for sensing temperature and strain simultaneously. In the measurement, when the temperature variation is from 20 °C to 75 °C, the measured Bragg wavelength shift of tension is nearly 0.74 nm. While the strain shift of 0.3 mm is applied on FBG, the Bragg wavelength shift of nearly 1.88 nm is observed.

Investigation of the dynamic strain responses of sandstone using multichannel fiber-optic sensor arrays

In the process of rock mechanical experiments, strain-response measurement is a most fundamental and most essential procedure for geomechanical researchers. The main objective of this paper is to point out the feasibility and the superiority of the application of a novel multichannel fiber Bragg grating (FBG) sensor arrays for dynamic strain-response measurements of cylindrical specimen subjected to uniaxial compression. The principle, design, and embedment of multichannel FBG sensors used in the experiment are briefly described. To fully monitor the strain history of the sandstone cylinder in uniaxial compression, six circumferential FBG sensors, four lateral FBG sensors, linear variable differential transformers (LVDT) built-in machine have been utilized for spatially monitoring small radial and axial strains along the height of the specimen, respectively. The experimental results indicate that the proposed FBG sensors can successfully provide a full-field view of the surface strains, as well as detect the potential crack locations within the specimen, and strains measured by multichannel FBG sensors are in good agreement with the results of LVDT, especially in the axial strains. Hence, it could be inferred that multichannel FBG sensor arrays are capable of measuring dynamic strain responses of sandstone specimen in multistage compression, which would greatly strengthen experimental basis for further application and theoretic research of in-situ field monitoring.

High-resolution fiber Bragg grating based transverse load sensor using microwave photonics filtering technique.

In this paper, a new fiber Bragg grating (FBG) sensor exploiting microwave photonics filter technique for transverse load sensing is firstly proposed and experimentally demonstrated. A two-tap incoherent notch microwave photonics filter (MPF) based on a transverse loaded FBG, a polarization beam splitter (PBS), a tunable delay line (TDL) and a length of dispersion compensating fiber (DCF) is demonstrated. The frequency response of the filter with respect to the transverse load is studied. By detecting the resonance frequency shifts of the notch MPF, the transverse load can be determined. The theoretical and experimental results show that the proposed FBG sensor has a higher resolution than traditional methods based on optical spectrum analysis. The sensitivity of the sensor is measured to be as high as 2.5 MHz/N for a sensing fiber with a length of 18mm. Moreover, the sensitivity can be easily adjusted.

Spiral-structured fiber Bragg grating for contact force sensing through direct power measurement.

A high-sensitivity fiber Bragg grating (FBG) force sensor based on direct optical power measurement is presented. The approach utilizes a novel structure where the FBG is mounted on a thin tube-like fixture spirally. Contact force measurement is achieved through direct measurement of the FBG reflection power at a single wavelength using a power meter. The measuring system in our approach is simple and does not require processing of massive amount of spectral data, enabling real-time contact force monitoring. When force is applied to the FBG sensor, the unique spiral structure leads to FBG chirping and reflection spectrum broadening. A proportional relationship and linear fit are found between the force applied (up to 1.55 N) and the optical power reflected by the proposed FBG sensor. An average sensitivity of 11.16 dB/N is experimentally achieved. This design significantly reduces system complexity and improves data processing speed, which has great practical value in real-time FBG sensing applications.

A high reading rate fiber Bragg grating sensor system using a high-speed swept light source based on fiber vibrations

We propose a fiber Bragg grating (FBG) sensor array system using a high-speed swept light source. The light source is an external cavity semiconductor laser using an optical fiber coupling with a Littrow-mounted grating spectroscope, where the fiber end is vibrated in the cantilever bending mode using a piezoelectric transducer. The incident angle to the grating is scanned at an ultrasonic frequency, and the output wavelength is swept according to the vibration displacement amplitude. The maximum sweep rate of 172 kHz was achieved for the sweep range of 70 nm. In this paper, the light source is used for high-speed and high sensitivity FBG sensor interrogation. First, to test the operation of the proposed FBG sensor, the center wavelength variation due to temperature shift is measured in water. Second, we experimentally demonstrate the measurements of dynamic strain oscillating at 10 and 28 kHz. The observation of high frequency vibrations is achieved with a sufficient sampling rate.

Pointwise fiber Bragg grating displacement sensor system for dynamic measurements

A method for setting up a fiber Bragg grating (FBG) sensor which can measure the pointwise, out-of-plane or in-plane dynamic displacement is proposed. The proposed FBG sensor is reusable. A multiplexing demodulation system based on a single long-period fiber grating is used in this study. The experimental results of the steady-state motion for a multilayer piezoelectric actuator and the dynamic response of a cantilever beam subjected to impact loadings are presented. These results indicate that the proposed displacement sensor has the ability to measure the out-of-plane dynamic displacement with high sensitivity. Measurements for a piezoceramic plate excited by high frequency show that the proposed displacement sensor also has the ability to provide the in-plane dynamic displacement up to 20 kHz.

A hybrid star-ring architecture for fiber Bragg grating sensor system

In this letter, we present a hybrid star-ring architecture for a highly reliable fiber Bragg grating (FBG) sensor system and demonstrate its effectiveness. The main trunk of the proposed sensor network is star topology and the sensing branches comprise a series of concatenated ring subnets. The weakness in reliability of the star network is overcome by the ring subnets with a self-healing function based on the reconfigurable optical switches between each subnet. To enhance the signal-to-noise ratio (SNR) of the sensor system, we adopt a linear-cavity FBG laser scheme to construct our proposed hybrid star-ring architecture. Such a fiber-laser scheme results in the SNR over 48 dB for the sensor network. The network survivability of a ten-point FBG sensor is experimentally examined. It is shown that the proposed FBG sensor system can increase the reliability of a sensing network.