FBG-based System Research Articles

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.

The Effect of Infill Pattern and Density on the Response of 3-D-Printed Sensors Based on FBG Technology

Fiber Bragg gratings (FBGs) are known for their uses in applications ranging from civil engineering to medicine. A bare FBG is small and light; hence, it can be easily embedded into hosting materials. However, conventional fabrication methods are generally time-consuming with reproducibility issues. A more recent strategy has been proposed to develop novel FBG-based systems by encapsulating the grating within 3-D-printed structures. This process, known as 3-D printing, is characterized by several advantages like rapid prototyping, printing precision, and high customization. The possibility of quickly personalizing the 3-D-printed sensors by customizing the infill settings makes this technique very appealing for medical purposes, especially for developing smart systems. However, the influence of printing settings on the sensor response has not been yet systematically addressed. This work aimed at combining FBG with the most popular 3-D printing technique (the fused deposition modeling [FDM]) to develop four 3-D-printed sensors with different printing profiles. We chose two patterns (triangle and gyroid) and two infill densities (30% and 60%) to investigate their influence on the sensors’ response to strain, temperature, and relative humidity (RH), and on the hysteresis behavior. Then, we preliminary assess the sensor performance in a potential application scenario for FBG-based 3-D printing technology: the cardiorespiratory monitoring. The promising results confirm that our analysis can be considered the first effort to improve the knowledge about the influence of printing profiles on sensor performance and, consequently, pave the way to develop highly performant 3-D-printed sensors customized for specific applications.

FBG-Based Soft System for Assisted Epidural Anesthesia: Design Optimization and Clinical Assessment.

Fiber Bragg grating sensors (FBGs) are considered a valid sensing solution for a variety of medical applications. The last decade witnessed the exploitation of these sensors in applications ranging from minimally invasive surgery to biomechanics and monitoring physiological parameters. Recently, preliminary studies investigated the potential impact of FBGs in the management of epidural procedures by detecting when the needle reaches the epidural space with the loss of resistance (LOR) technique. In this article, we propose a soft and flexible FBG-based system capable of detecting the LOR, we optimized the solution by considering different designs and materials, and we assessed the feasibility of the optimized soft sensor (SS) in clinical settings. The proposed SS addresses some of the open challenges in the use of a sensing solution during epidural punctures: it has high sensitivity, it is non-invasive, the sensing element does not need to be inserted within the needle, and the clinician can follow the standard clinical practice. Our analysis highlights how the material and the design impact the system response, and thus its performance in this scenario. We also demonstrated the system’s feasibility of detecting the LOR during epidural procedures.

Design and analysis of Pound-Drever-Hall-based free-space and fiber-based frequency discriminators: A comparison

Lasers with high coherence and low frequency and amplitude noise are essential for applications requiring high-precision measurement. Laser frequency stabilization is therefore a critical component of lasers used in these applications. In this work, we investigate the frequency stability characteristics of a laser system utilizing Pound-Drever-Hall (PDH) frequency locking and two different frequency discrimination systems, one based on a free-space Fabry-Pérot (F-P) cavity and another based on fiber Bragg gratings (FBGs). The result shows that F-P-based systems offer better performance than FBG-based systems, with each system showing frequency drifts of 83 MHz and 197 MHz respectively over a period of 30 min. The advantages and limitations of both approaches are discussed.

Shape Sensing with Rayleigh Backscattering Fibre Optic Sensor.

In this paper, Rayleigh backscattering sensors (RBS) are used to realize shape sensing of beam-like structures. Compared to conventional shape sensing systems based on fibre Bragg grating (FBG) sensors, RBS are capable of continuous lateral sensing. Compared to other types of distributed fibre optic sensors (FOS), RBS have a higher spatial resolution. First, the RBS’s strain sensing accuracy is validated by an experiment comparing it with strain gauge response. After that, two shape sensing algorithms (the coordinate transformation method (CTM) and the strain-deflection equation method (SDEM)) based on the distributed FOS’ input strain data are derived. The algorithms are then optimized according to the distributed FOS’ features, to make it applicable to complex and/or combine loading situations while maintaining high reliability in case of sensing part malfunction. Numerical simulations are carried out to validate the algorithms’ accuracy and compare their accuracy. The simulation shows that compared to the FBG-based system, the RBS system has a better performance in configuring the shape when the structure is under complex loading. Finally, a validation experiment is conducted in which the RBS-based shape sensing system is used to configure the shape of a composite cantilever-beam-like specimen under concentrated loading. The result is then compared with the optical camera-measured shape. The experimental results show that both shape sensing algorithms predict the shape with high accuracy comparable with the optical camera result.

A Novel FBG-Based Triggering System for Cardiac MR Imaging at 3 Tesla: A Pilot Pre-Clinical Study

This first-ever study demonstrates the applicability of a fiber Bragg grating (FBG) system for MR cardiac triggering of cardiovascular magnetic resonance at 3 Tesla. The unique patented system senses body movements caused by cardiac activity using a non-invasive ballistocardiography (BCG) sensor. The pilot research compares a novel FBG-based system with clinically used triggering systems based on electrocardiography (ECG) and pulse oximetry (POX). The pilot pre-clinical study was conducted on 8 subjects at a Siemens Prisma 3T MR Scanner. The study compares images from two basic cardiac sequences, TRUE FISP (Free Induction Decay Steady-State Precession) and PSIR (Phase Sensitive Inversion Recovery), using objective methods and subjective evaluation by clinical experts. The study presents original results that confirm the applicability of optical sensors in the field of cardiac triggering having a number of advantages in comparison to conventional solutions, such as no eddy current interference, ease of placement of the sensor on the patient’s body, and senor reusability. The proposed FBG-based system achieves comparable results with the most frequently used and most accurate ECG-based and POX-based clinical systems. In terms of subjective evaluation by experts, the FBG system outperformed the POX-based system used in clinical practice.

Development and application of new FBG mini tension link transducers for monitoring dynamic response of a flexible barrier under impact loads

Flexible barriers, as an effective protective measure to mitigate landslide hazards, have attracted a lot of interest from the geotechnical community. The dynamic response of flexible barriers subjected to impact loads is of great concern. However, the forces developed on ring-net barriers during impacts have not been effectively measured and the dynamic behavior of barriers has not been fully understood. In this study, new mini tension link transducers based on fiber Bragg grating (FBG) sensing technology are uniquely developed to both link adjacent rings of a flexible barrier and measure the forces between rings. Besides, a novel monitoring system based on the new FBG mini tension link transducers is established for detecting dynamic response of a flexible barrier under impact loads. Calibration results of the FBG mini tension link transducers demonstrate that the wavelength shift of the FBG sensor has a linear relationship with the applied force with high accuracy. A single boulder impact test and a debris flow impact test were conducted to investigate the performance of the FBG-based system. The results reveal that the FBG mini tension link transducers are capable of capturing the evolution of the forces between rings of the flexible barrier, and the FBG-based system can be used for monitoring the dynamic response of the flexible barrier under impact loads.

Polymer-coated fiber optic probe for the monitoring of breathing pattern and respiratory rate.

In recent years, no-invasive and small size systems are meeting the demand of the new healthcare system, in which the vital signs monitoring is gaining in importance. In this context, Fiber Bragg grating (FBG) sensors are becoming very popular and FBG-based systems could be used for monitoring vital signs. At the same time, FBG could be able to sense chemical parameters by the polymer functionalization. The aim of our study was investigating the ability of a polymer-coated FBG-based probe for monitoring breathing patterns and respiratory rates. We tested the proposed FBG-based probe on 9 healthy volunteers during spirometry, the most common pulmonary function test. Results showed the high accuracy of the proposed probe to detect respiratory rate. The comparison between the respiratory rates estimated by the probe with the ones by the spirometer showed the absolute value of the percentage errors lower than 2.07% (in the 78% of cases <.91%). Lastly, a Bland Altman analysis was performed to compare the instantaneous respiratory rate values gathered by the spirometer and the FBG probe showing the feasibility of breath-by-breath monitoring by the proposed probe. Results showed a bias of 0.06± 2.90 $\mathrm{breaths}\square {\mathrm {min}}^{-1}$. Additionally, our system was able to follow the breathing activities and monitoring the breathing patterns.

A Fiber Bragg Grating Sensor for Radial Artery Pulse Waveform Measurement.

In this paper, we report the design and experimental validation of a novel optical sensor for radial artery pulse measurement based on fiber Bragg grating (FBG) and lever amplification mechanism. Pulse waveform analysis is a diagnostic tool for clinical examination and disease diagnosis. High fidelity radial artery pulse waveform has been investigated in clinical studies for estimating central aortic pressure, which is proved to be predictors of cardiovascular diseases. As a three-dimensional cylinder, the radial artery needs to be examined from different locations to achieve optimal pulse waveform for estimation and diagnosis. The proposed optical sensing system is featured as high sensitivity and immunity to electromagnetic interference for multilocation radial artery pulse waveform measurement. The FBG sensor can achieve the sensitivity of 8.236nm/N, which is comparable to a commonly used electrical sensor. This FBG-based system can provide high accurate measurement, and the key characteristic parameters can be then extracted from the raw signals for clinical applications. The detecting performance is validated through experiments guided by physicians. In the experimental validation, we applied this sensor to measure the pulse waveforms at various positions and depths of the radial artery in the wrist according to the diagnostic requirements. The results demonstrate the high feasibility of using optical systems for physiological measurement and using this FBG sensor for radial artery pulse waveform in clinical applications.

Novel Negative Pressure Wave-Based Pipeline Leak Detection System Using Fiber Bragg Grating-Based Pressure Sensors

In this paper, the design and underpinning technical principles of the novel design of a negative pressure wave (NPW)-based pipeline leak detection system has been reported, which is configured using fiber Bragg grating (FBG) pressure sensors. To evaluate this, a pipeline leakage test platform has been established and experiments have been conducted, to verify the performance of a system using this FBG-based approach. The results show that a system using FBG-based sensors can accurately determine the pressure change trends along the pipeline and thus allow the calculation of the NPW velocity online. A key comparison is made with traditional NPW detection techniques, showing that the novel detection system is capable of achieving the higher leak-location accuracy and the detection of smaller leakage volumes. This arises from the ability of the FBG-based system to allow an increased number of sensors to be multiplexed along the pipeline. Their corresponding output signals generated show a very satisfactory, high signal-to-noise ratio. The system has been evaluated, especially in its response to extraneous signals and thus disturbances caused by the pump starting or stopping can be eliminated. This was achieved through an analysis of the time sequence of the pressure changes captured by the multisensor array being carried out and thus immunity to such effects demonstrated. The system has thus been designed to minimize the instances where a false alarm occurs.

Fiber Bragg gratings-based sensing for real-time needle tracking during MR-guided brachytherapy.

The development of MR-guided high dose rate (HDR) brachytherapy is under investigation due to the excellent tumor and organs at risk visualization of MRI. However, MR-based localization of needles (including catheters or tubes) has inherently a low update rate and the required image interpretation can be hampered by signal voids arising from blood vessels or calcifications limiting the precision of the needle guidance and reconstruction. In this paper, a new needle tracking prototype is investigated using fiber Bragg gratings (FBG)-based sensing: this prototype involves a MR-compatible stylet composed of three optic fibers with nine sets of embedded FBG sensors each. This stylet can be inserted into brachytherapy needles and allows a fast measurement of the needle deflection. This study aims to assess the potential of FBG-based sensing for real-time needle (including catheter or tube) tracking during MR-guided intervention. First, the MR compatibility of FBG-based sensing and its accuracy was evaluated. Different known needle deflections were measured using FBG-based sensing during simultaneous MR-imaging. Then, a needle tracking procedure using FBG-based sensing was proposed. This procedure involved a MR-based calibration of the FBG-based system performed prior to the interventional procedure. The needle tracking system was assessed in an experiment with a moving phantom during MR imaging. The FBG-based system was quantified by comparing the gold-standard shapes, the shape manually segmented on MRI and the FBG-based measurements. The evaluation of the MR compatibility of FBG-based sensing and its accuracy shows that the needle deflection could be measured with an accuracy of 0.27 mm on average. Besides, the FBG-based measurements were comparable to the uncertainty of MR-based measurements estimated at half the voxel size in the MR image. Finally, the mean(standard deviation) Euclidean distance between MR- and FBG-based needle position measurements was equal to 0.79 mm(0.37 mm). The update rate and latency of the FBG-based needle position measurement were 100 and 300 ms, respectively. The FBG-based needle tracking procedure proposed in this paper is able to determine the position of the complete needle, under MR-imaging, with better accuracy and precision, higher update rate, and lower latency compared to current MR-based needle localization methods. This system would be eligible for MR-guided brachytherapy, in particular, for an improved needle guidance and reconstruction.

Influence of Fiber-Bragg Grating-Induced Group-Delay Ripple in High-Speed Transmission Systems

The implementation of a chirped fiber-Bragg grating (FBG) for dispersion compensation in high-speed (up to 120&#x00A0;Gbit/s) transmission systems with differential and coherent detection is, for the first time, experimentally investigated. For systems with differential detection, we examine the influence of group-delay ripple (GDR) in 40&#x00A0;GBd 2-, 4-, and 8-ary differential phase shift keying (DPSK) systems. Furthermore, we conduct a nonlinear-tolerance comparison between the systems implementing dispersion-compensating fibers and FBG modules, using a 5&#x00D7;80&#x00A0;Gbit/s 100-GHz-spaced wavelength division multiplexing 4-ary DPSK signal. The results show that the FBG-based system provides a 2 dB higher optimal launch power, which leads to more than 3&#x00A0;dB optical signal-to-noise ratio (OSNR) improvement at the receiver. For systems with coherent detection, we evaluate the influence of GDR in a 112&#x00A0;Gbit/s dual-polarization quadrature phase shift keying system with respect to signal wavelength. In addition, we demonstrate that, at the optimal launch power, the 112&#x00A0;Gbit/s systems implementing FBG modules and that using electronic dispersion compensation provide similar performance after 840 km transmission despite the fact that the FBG-based system delivers lower OSNR at the receiver. Lastly, we quantify the GDR mitigation capability of a digital linear equalizer in the 112 Gbit/s coherent systems with respect to the equalizer tap number (Ntap). The results indicate that at least Ntap=9 is required to confine Q-factor variation within 1&#x00A0;dB.

Impact localisation with FBG for a self-healing carbon fibre composite structure

We demonstrated the localisation of impacts in orthotropic carbon fibre reinforced polymer (CFRP) composite materials to within a few centimetres, using a sparse array of fibre Bragg grating (FBG) sensors. This type of sensor is easily embedded in composites permitting the development of structures with integrated sensing capability. Impact location was determined by measuring the differences in time-of-flight of ultrasonic Lamb waves at three surface-mounted sensors. An algorithm was developed taking into account the angle dependence of the optical fibre sensor sensitivity and the variation of Lamb waves propagation velocity with direction and wave mode. The performance of FBG sensors for impact localisation was compared to that of standard piezoelectric transducers (PZTs), which are already widely used for that purpose. The FBG-based system showed promising potential for a non-intrusive impact detection system applied to self-healing composite structures.

Enhanced FBG sensor-based system performance assessment for monitoring strain along a prestressed CFRP rod in structural monitoring

Fiber Bragg grating (FBG) sensor-based systems have been widely used for many engineering applications including most recently a number of applications in structural health monitoring. It is well known that strain and temperature both affect the FBG spectrum which in the interrogation system will be converted to a conventional electronic signal. This procedure provides the means for the FBG-based sensor system to be used for several monitoring applications. The aim of this research is to improve an existing monitoring system which has been used for several field test inspections. A brief description of the existing FBG-based system and the evaluation of the software developed to be compatible with a resolution reaching as high as ±0.15 μɛ is presented. The system has been tested under particular conditions where a prestressed CFRP (carbon fiber reinforced polymer) rod to which a FBG sensor is attached is used. The test procedure and results obtained are discussed in some detail.

Strain Measurement on a Rail Bridge Loaded to Failure Using a Fiber Bragg Grating-Based Distributed Sensor System

The paper reports results obtained from an unusual situation in structural monitoring - a test-to-destruction, measuring strain using a series of fiber Bragg gratings (FBGs) sensors on a decommissioned concrete Railway Bridge in Ornskoldsvik, Sweden. The study formed part of the EU Sustainable Bridges Project. To undertake the study, FBG-based sensors were chosen and embedded in carbon fiber reinforced polymers (CFRPs) composite rods incorporated into grooves specially created in the concrete structure and interrogated using a compact system based on wavelength-division multiplexing (WDM). Throughout the study, the FBG sensors were continuously monitored, allowing the incremental increases in the strain to be seen and through the yield point of the carbon composite reinforcement. The sensors were able to follow the resulting induced changes in strain of over a range in excess of 4000 muepsiv just prior to failure of the bridge and representing extreme levels of strain for such a mechanical structure. The measurements made with the FBG-based system were found to be in agreement with the changes expected in the structure (together with the embedded reinforcement), produced by the loading applied. The study has demonstrated the successful use of FBG-based technology premounted in smart carbon fiber composite reinforcements used in a test of this type on a typical bridge structure of a type found widely across the world.