[go: up one dir, main page]
More Web Proxy on the site http://driver.im/
You seem to have javascript disabled. Please note that many of the page functionalities won't work as expected without javascript enabled.
 
 
Sign in to use this feature.

Years

Between: -

Subjects

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Journals

Article Types

Countries / Regions

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Search Results (727)

Search Parameters:
Keywords = fiber bragg grating (FBG)

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
26 pages, 15681 KiB  
Article
Applications of Optical Fiber Sensors in Geotechnical Engineering: Laboratory Studies and Field Implementation at the Acropolis of Athens
by Elena Kapogianni and Michael Sakellariou
Sensors 2025, 25(5), 1450; https://doi.org/10.3390/s25051450 - 27 Feb 2025
Viewed by 81
Abstract
The current study investigates the feasibility and performance of Fiber Bragg Grating (FBG) optical sensors in geotechnical engineering applications, aiming to demonstrate their broader applicability across different scales, from controlled laboratory experiments to real-world field implementations. More specifically, the research evaluates the sensors’ [...] Read more.
The current study investigates the feasibility and performance of Fiber Bragg Grating (FBG) optical sensors in geotechnical engineering applications, aiming to demonstrate their broader applicability across different scales, from controlled laboratory experiments to real-world field implementations. More specifically, the research evaluates the sensors’ ability to monitor key parameters—strain, temperature, and acceleration—under diverse loading conditions, including static, dynamic, seismic, and centrifuge loads. Within this framework, laboratory experiments were conducted using the one-degree-of-freedom shaking table at the National Technical University of Athens to assess sensor performance during seismic loading. These tests provided insights into the behavior of geotechnical physical models under earthquake conditions and the reliability of FBG sensors in capturing dynamic responses. Additional testing was performed using the drum centrifuge at ETH Zurich, where physical models experienced gravitational accelerations up to 100 g, including impact loads. The sensors successfully captured the loading conditions, reflecting the anticipated model behavior. In the field, optical fibers were installed on the Perimeter Wall (Circuit Wall) of the Acropolis of Athens to monitor strain, temperature, and acceleration in real-time. Despite the challenges posed by the archaeological site’s constraints, the system gathered data over two years, offering insights into the structural behavior of this historic monument under environmental and loading variations. The Acropolis application serves as a key field example, illustrating the use of these sensors in a complex and historically significant site. Finally, the study details the test setups, sensor types, and data acquisition techniques, while addressing technical challenges and solutions. The results demonstrate the effectiveness of FBG sensors in geotechnical applications and highlight their potential for future projects, emphasizing their value as tools for monitoring structural integrity and advancing geotechnical engineering. Full article
(This article belongs to the Special Issue Optical Fiber Sensors Used for Civil Engineering)
Show Figures

Figure 1

Figure 1
<p>Laboratory equipment: (<b>a</b>) single-degree-of-freedom force generator, (<b>b</b>) amplifier, (<b>c</b>) data acquisition card, (<b>d</b>) LabView software, (<b>e</b>) interrogator, (<b>f</b>) optical fiber sensors.</p>
Full article ">Figure 2
<p>Unrestrained sensor, sensor with protective sheathing, and sensor attached to a geotextile.</p>
Full article ">Figure 3
<p>Saturated sand slope: model and geometrical characteristics.</p>
Full article ">Figure 4
<p>Saturated sand slope: model behavior and resulting failure mechanism.</p>
Full article ">Figure 5
<p>Saturated sand slope (<b>left</b>) and lower acceleration response (<b>right</b>): strain variation recorded by the optical fiber sensors.</p>
Full article ">Figure 6
<p>Pipe reinforcement effects: side view of the model (<b>left</b>) and the scaled pipe with optical fiber sensor placement (<b>right</b>).</p>
Full article ">Figure 7
<p>Pipe reinforcement effects: model structural response to applied loading, including scour at the slope base and shear initiation at the existing tensile crack.</p>
Full article ">Figure 8
<p>Pipe reinforcement effects: strain variation recorded by the optical fiber sensor.</p>
Full article ">Figure 9
<p>Reinforced vertical slope: cross-section and failure mechanism.</p>
Full article ">Figure 10
<p>Reinforced vertical slope: strain variation recorded by two optical fiber sensors.</p>
Full article ">Figure 11
<p>Scaled reinforced slope model (<b>left</b>), reinforcement layers incorporating optical fiber sensors (<b>middle</b>), and model cross-section (<b>right</b>).</p>
Full article ">Figure 12
<p>Test setup (<b>left</b>) and reinforced slope in the centrifuge (<b>right</b>).</p>
Full article ">Figure 13
<p>Strains captured during Test No. 1 (<b>left</b>) and strains captured during Test No. 2 (<b>right</b>).</p>
Full article ">Figure 14
<p>Flow vectors of soil grains, with vectors colored black representing 1 g and vectors colored red indicating 50 g (<b>left</b>). Normalized strain values calculated via GeoPIV and locations of the FBG sensors (<b>right</b>).</p>
Full article ">Figure 15
<p>Numerical model of full-scale slope (<b>left</b>) and maximum shear strains in Layers No. 8 and No. 4, at different SRF levels (<b>right</b>), using FEM.</p>
Full article ">Figure 16
<p>Cross-section of the southern part of the Circuit Wall (<b>left</b>) [<a href="#B29-sensors-25-01450" class="html-bibr">29</a>]. A panoramic view of the Acropolis Hill, the Circuit Wall, and the Parthenon from the southeast (<b>right</b>).</p>
Full article ">Figure 17
<p>Locations of the installed optical fiber sensors on the South Wall (<b>left</b>) and the plan view of Acropolis Hill (<b>right</b>) [<a href="#B29-sensors-25-01450" class="html-bibr">29</a>].</p>
Full article ">Figure 18
<p>Strain and temperature FBG sensors on the Wall, including anchoring plates (<b>left</b>) and acceleration FBG sensor (<b>right</b>).</p>
Full article ">Figure 19
<p>Configuration of Fiber Bragg Grating sensors, arranged in series and parallel on the South Circuit Wall.</p>
Full article ">Figure 20
<p>Comparison of strain variation with and without thermal compensation.</p>
Full article ">Figure 21
<p>Comparison of strain variation at the IN and OUT positions for the same smart rods.</p>
Full article ">Figure 22
<p>Strain variation of four sensors at both IN and OUT positions, with thermal compensation.</p>
Full article ">Figure 23
<p>Acceleration levels recorded by the single-axis acceleration sensor with and without thermal compensation using the initial wavelength value (<b>left</b>) and temperature variation (<b>right</b>).</p>
Full article ">Figure 24
<p>Acceleration levels, both with and without thermal compensation, using the mean wavelength as the reference value (<b>left</b>), and a comparison of results with the initial wavelength as the reference value versus those with the mean wavelength as the reference value (<b>right</b>).</p>
Full article ">Figure 25
<p>Calibration procedure for the monitoring system at the Acropolis.</p>
Full article ">
23 pages, 11715 KiB  
Article
An FBG-Based Hard Landing Monitoring System: Assessment for Drops on Different Soils
by Angela Brindisi, Cristian Vendittozzi, Lidia Travascio, Marika Belardo, Michele Ignarra, Vincenzo Fiorillo and Antonio Concilio
Photonics 2025, 12(3), 197; https://doi.org/10.3390/photonics12030197 - 26 Feb 2025
Viewed by 75
Abstract
This study aims to develop an integrated monitoring system using a fiber Bragg grating sensor network to record the structural response of a landing gear system under operational loads to detect hard landing conditions on soils with different absorbing characteristics and to differentiate [...] Read more.
This study aims to develop an integrated monitoring system using a fiber Bragg grating sensor network to record the structural response of a landing gear system under operational loads to detect hard landing conditions on soils with different absorbing characteristics and to differentiate between soil types during landings. This paper refers to drop tests carried out at a drop tower of the test article, an integrated leaf spring landing gear with fiber Bragg grating sensors, measuring strain to evaluate landings from different heights on different soil types: hard soil, sand, and gravel. Cross-correlation and fast Fourier transform analyses can help to assess the repeatability of the impact tests, to assess the developed system as very reliable in detecting landing conditions and ensure very low error in the accuracy of the sensor placement, or to assess whether different impacts under different conditions produce consistent responses. Full article
(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Photonics Sensors)
Show Figures

Figure 1

Figure 1
<p>The Test Article.</p>
Full article ">Figure 2
<p>The test article: the two legs of the LG are integrated with strain sensors.</p>
Full article ">Figure 3
<p>The test article. Installation details: (<b>a</b>) the test rig and the TA installed on the slit at a suitable drop height; (<b>b</b>) the drop tower with two containers deployed at its base; (<b>c</b>) detail over the two containers deployed at the drop tower base, with an FBG sensor installed in each of them. In the two containers, the impact areas of the wheels of the TA are highlighted in yellow.</p>
Full article ">Figure 4
<p>Free-fall height, h.</p>
Full article ">Figure 5
<p>The three different impact soils: rigid (<b>left</b>), sand (<b>center</b>), and gravel (<b>right</b>).</p>
Full article ">Figure 6
<p>Time histories of the reference sensors during a 0.20 m drop test over a rigid surface: accelerations (<b>left</b>) and deformations (<b>right</b>).</p>
Full article ">Figure 7
<p>Time histories of the reference sensors during a 0.20 m drop test over sand: accelerations (<b>left</b>) and deformations (<b>right</b>).</p>
Full article ">Figure 8
<p>Time histories of the reference sensors during a 0.20 m drop test over gravel: accelerations (<b>left</b>) and deformations (<b>right</b>).</p>
Full article ">Figure 9
<p>Deformation measurements of the FBG sensors for a drop test from 0.10 m on a rigid impact surface: in the first phase, the test article is suspended; then, there is the free-fall frame, up to the impact; a rebound then occurs, followed by an ascent and descent phase, up to the second impact, and finally a smooth oscillation until rest.</p>
Full article ">Figure 10
<p>Outcome of drop tests from (<b>a</b>) 0. 15 and (<b>b</b>) 0.20 m, featuring an impact on a rigid surface.</p>
Full article ">Figure 11
<p>On the <b>left</b> column, from <b>top</b> to <b>bottom</b>, are the 0.10, 0.15, and 0.20 drops on sand; on the <b>right</b> column are the 0.10, 0.15, and 0.20 drops on gravel.</p>
Full article ">Figure 12
<p>Correlation graphs between three consecutive drops from 0.10 m on rigid soil related to (<b>a</b>) sensor S3 and (<b>b</b>) sensor S4. The first drop is indicated with the blue dashed curve, the second drop with the red continuous curve, and the third drop with the black dashed curve.</p>
Full article ">Figure 13
<p>Correlation graphs between signals of sensor S3 for drops from a given height on the three different soils. From top to bottom: (<b>a</b>) drops from 0.10 m, (<b>b</b>) drops from 0.15 m, and (<b>c</b>) drops from 0.20 m.</p>
Full article ">Figure 14
<p>Correlation graphs between signals of sensor S3 for drops on the same soil from three heights. From top to bottom: (<b>a</b>) drops on rigid soil, (<b>b</b>) drops on sand, and (<b>c</b>) drops on gravel.</p>
Full article ">Figure 15
<p>Detailed analysis schematic and an indication of the two different analysis windows, whose description is reported in <a href="#photonics-12-00197-t011" class="html-table">Table 11</a>. An1 (0–16,384 ms) and An2 (2500–6596 ms).</p>
Full article ">Figure 16
<p>Analysis no 1. FFT analyses of the signal frames are defined in <a href="#photonics-12-00197-t011" class="html-table">Table 11</a>. The repeated peaks are evident, even though it is not possible to distinguish among the system responses in the supported (grounded) and floating (free) conditions. The FFT analyses are related to three drops from a height of 0.10 m on a rigid soil recorded by sensor no. 3. On the left, (<b>a</b>–<b>c</b>) are the complete frequency range from 0 to 500 Hz; on the right, (<b>a′</b>–<b>c′</b>) are zoomed in from 0 to 50 Hz.</p>
Full article ">Figure 17
<p>Analysis no 2. The FFT analyses are related to three drops from a height of 0.10 m on a rigid soil recorded by sensor no. 3. On the left, (<b>a</b>–<b>c</b>) are the complete frequency range from 0 to 500 Hz; on the right, (<b>a′</b>–<b>c′</b>) are zoomed in from 0 to 50 Hz.</p>
Full article ">
19 pages, 4591 KiB  
Article
Enhancing Orthotic Treatment for Scoliosis: Development of Body Pressure Mapping Knitwear with Integrated FBG Sensors
by Ka-Po Lee, Zhijun Wang, Lin Zheng, Ruixin Liang, Queenie Fok, Chao Lu, Linyue Lu, Jason Pui-Yin Cheung, Kit-Lun Yick and Joanne Yip
Sensors 2025, 25(5), 1284; https://doi.org/10.3390/s25051284 - 20 Feb 2025
Viewed by 184
Abstract
Bracing is a widely used conservative treatment for adolescent idiopathic scoliosis (AIS) patients, yet there is no consensus on the optimal amount of force applied. Although a number of different sensors have been developed to continuously monitor the applied pressure and force, they [...] Read more.
Bracing is a widely used conservative treatment for adolescent idiopathic scoliosis (AIS) patients, yet there is no consensus on the optimal amount of force applied. Although a number of different sensors have been developed to continuously monitor the applied pressure and force, they have several limitations, including inadequate overall force distribution and displacement. They also cause discomfort with limited wearability. In this study, body pressure mapping knitwear (BPMK) integrated with fourteen silicone-embedded fiber Bragg grating (FBG) sensors is developed to monitor immediate and overall changes in force during the bracing treatment. A wear trial of the BPMK is conducted by using a validated soft AIS mannequin, and prediction equations have been formulated for the FBG sensors at individual locations. The findings indicate that the measured forces are in good agreement with those obtained from clinical studies, with peak forces around the padding regions reaching approximately 2N. This was further validated by using finite element (FE) models. When comparing X-ray images, the estimated differences in Cobb angles were found to be 0.6° for the thoracic region and 2.1° for the lumbar region. This model is expected to provide valuable insights into optimal force application, thus minimizing the risk of injury and enhancing bracing compliance and efficacy. Ultimately, this innovative approach provides clinicians with data-driven insights for safer and more effective bracing applications, thus improving the quality of life of AIS patients. Full article
(This article belongs to the Special Issue Advances in Optical Fiber-Based Sensors)
Show Figures

Figure 1

Figure 1
<p>Inter-FBG sensor intervals on four series of optical fibers.</p>
Full article ">Figure 2
<p>(<b>a</b>) Structure of optical fiber inlaid into single jersey fabric in warp direction, (<b>b</b>) silicone membrane with a groove, (<b>c</b>) FBG sensor embedded in silicone membrane, and (<b>d</b>) cross-section of BPMK.</p>
Full article ">Figure 3
<p>Placement of FBG sensors on BPMK.</p>
Full article ">Figure 4
<p>Equipment setup and schematic of transverse force applied to BPMK on artificial tissues.</p>
Full article ">Figure 5
<p>Models of: (<b>a</b>) torso, (<b>b</b>) skeletal structure, (<b>c</b>) textile materials and hinge bone of FIA.</p>
Full article ">Figure 6
<p>(<b>a</b>) Fixed boundary condition: all six degrees of freedom were set to zero, and (<b>b</b>) stretched boundary condition: the FIA was stretched to the dressed state.</p>
Full article ">Figure 7
<p>Schematic of Cobb angle measurements.</p>
Full article ">Figure 8
<p>Linear regression between Bragg wavelength shift and force when applying force to different FBG Series 1 to 4.</p>
Full article ">Figure 9
<p>Force on interface between torso and FIA.</p>
Full article ">Figure 10
<p>Displacement of skeletal model on: (<b>a</b>) FE model, and (<b>b</b>) X-ray images.</p>
Full article ">Figure 11
<p>Comparison of spinal curves: (<b>a</b>) FEA, (<b>b</b>) X-ray images, and (<b>c</b>) their in-brace effects.</p>
Full article ">
13 pages, 4545 KiB  
Article
An Optimized PZT-FBG Voltage/Temperature Sensor
by Shangpeng Sun, Feiyue Ma, Yanxiao He, Bo Niu, Cheng Wang, Longcheng Dai and Zhongyang Zhao
Micromachines 2025, 16(2), 235; https://doi.org/10.3390/mi16020235 - 19 Feb 2025
Viewed by 180
Abstract
The piezoelectric grating voltage sensor has garnered significant attention in the realm of intelligent sensing, attributed to its compact size, cost-effectiveness, robust electromagnetic interference (EMI) immunity, and high network integration capabilities. In this paper, we propose a PZT-FBG (piezoelectric ceramic–fiber Bragg grating) voltage–temperature [...] Read more.
The piezoelectric grating voltage sensor has garnered significant attention in the realm of intelligent sensing, attributed to its compact size, cost-effectiveness, robust electromagnetic interference (EMI) immunity, and high network integration capabilities. In this paper, we propose a PZT-FBG (piezoelectric ceramic–fiber Bragg grating) voltage–temperature demodulation optical path architecture. This scheme effectively utilizes the originally unused temperature compensation reference grating, repurposing it as a temperature measurement grating. By employing FBGs with identical or similar parameters, we experimentally validate two distinct optical path connection schemes, before and after optimization. The experimental results reveal that, when the input voltage ranges from 250 V to 1800 V at a frequency of 50 Hz, the goodness of fit for the three fundamental waveforms is 0.996, 0.999, and 0.992, respectively. Furthermore, the sensor’s frequency response was tested across a frequency range of 50 Hz to 20 kHz, demonstrating that the measurement system can effectively respond within the sensor’s operational frequency range. Additionally, temperature measurement experiments showed a goodness of fit of 0.997 for the central wavelength of the FBG as the temperature increased. This research indicates that the improved optical path connection method not only accomplishes a synchronous demodulation of both temperature and voltage parameters but also markedly enhances the linearity and resolution of the voltage sensor. This discovery offers novel insights for further refining sensor performance and broadening the applications of optical voltage sensors. Full article
Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) The optical path connection before optimization; (<b>b</b>) optimized optical path connection.</p>
Full article ">Figure 2
<p>(<b>a</b>) The spectral overlap area before optimization; (<b>b</b>) optimized spectral overlap area.</p>
Full article ">Figure 3
<p>The optimized physical diagram of the PZT-FBG voltage/temperature sensor.</p>
Full article ">Figure 4
<p>Experimental test platform.</p>
Full article ">Figure 5
<p>(<b>a</b>) 1.2 kV, 50 Hz sine wave input and output response; (<b>b</b>) 1.2 kV, 5 kHz sine wave input and output response; (<b>c</b>) 1.2 kV, 50 Hz rectangular wave input and output response; (<b>d</b>) 1.2 kV, 5 kHz rectangular wave input and output response; (<b>e</b>) 1.2 kV, 50 Hz triangular wave input and output response; (<b>f</b>) 1.2 kV, 5 kHz triangular wave input–output response.</p>
Full article ">Figure 6
<p>(<b>a</b>) Output fitting results of three basic waveforms at 50 Hz before optimization; (<b>b</b>) the output fitting results of three basic waveforms at 50 Hz after optimization.</p>
Full article ">Figure 7
<p>Frequency response test results.</p>
Full article ">Figure 8
<p>(<b>a</b>) The central wavelength shifts to the right with the increase in temperature. (<b>b</b>) Fitting results of center wavelength with increasing temperature.</p>
Full article ">
13 pages, 4934 KiB  
Article
Design, Calibration, and Application of a Wide-Range Fiber Bragg Grating Strain Sensor
by Gang Wang, Jiajian Wang, Jian Meng, Liang Ren and Xing Fu
Sensors 2025, 25(4), 1192; https://doi.org/10.3390/s25041192 - 15 Feb 2025
Viewed by 213
Abstract
To address the issue of extra-large structural deformation or strain in infrastructures such as bridges, buildings, railroads, and pipelines during catastrophic events, this study proposes a wide-range fiber Bragg grating (FBG) strain sensor utilizing a snake spring desensitization mechanism to share large parts [...] Read more.
To address the issue of extra-large structural deformation or strain in infrastructures such as bridges, buildings, railroads, and pipelines during catastrophic events, this study proposes a wide-range fiber Bragg grating (FBG) strain sensor utilizing a snake spring desensitization mechanism to share large parts of the strains. Initially, the axial stiffness of the snake spring desensitization mechanism was derived using the strain energy method, which was applied for stiffness calculation, range determination, and parameter design of the entire structure, where the snake spring and the FBG strain sensor were connected in series. Then, the snake springs were fabricated using 3D printing technology and assembled with the FBG sensor to construct a wide-range strain sensor. The wide-range sensor was subsequently calibrated, achieving a strain range of 10,000 με and a linearity coefficient above 0.9995. Finally, the sensor was installed in a pipeline for testing, yielding favorable results. These results demonstrate that the proposed sensor exhibits a wide strain monitoring range and can be effectively used for real-time structural safety analysis by continuously monitoring localized large structure strains. Full article
(This article belongs to the Special Issue Sensors for Non-Destructive Testing and Structural Health Monitoring)
Show Figures

Figure 1

Figure 1
<p>Three-dimensional diagram of the wide-range FBG strain sensor (① FBG strain sensor; ② fixed plate; ③ snake spring desensitization mechanism; ④ sensor support).</p>
Full article ">Figure 2
<p>Principle of the wide-range FBG strain sensor.</p>
Full article ">Figure 3
<p>The structure of the unilateral snake spring: (<b>a</b>) boundary conditions of the unilateral snake spring; (<b>b</b>) the size of the snake spring element; (<b>c</b>) load analysis of the unilateral snake spring; and (<b>d</b>) moment diagram of the snake spring element.</p>
Full article ">Figure 4
<p>Influence of key parameters on the stiffness and length of snake spring: (<b>a</b>) element number <span class="html-italic">n</span>; (<b>b</b>) element length <span class="html-italic">a</span>; (<b>c</b>) element half width <span class="html-italic">b</span>; and (<b>d</b>) section width <span class="html-italic">w</span>.</p>
Full article ">Figure 5
<p>The prototype of the wide-range FBG sensor.</p>
Full article ">Figure 6
<p>The calibration test: (<b>a</b>) testing machine and (<b>b</b>) a wide-range FBG strain sensor.</p>
Full article ">Figure 7
<p>Calibration test results: (<b>a</b>) test data; (<b>b</b>) local test data; (<b>c</b>) sensitivity coefficients, and (<b>d</b>) linear coefficients.</p>
Full article ">Figure 8
<p>Schematic descriptions of the calibration test and loading conditions (unit: mm).</p>
Full article ">Figure 9
<p>The application test: (<b>a</b>) testing machine and (<b>b</b>) a wide-range FBG strain sensor and ESG.</p>
Full article ">Figure 10
<p>Application test results: (<b>a</b>) large deformation of the HDPE pipeline and (<b>b</b>) sensor data of the wide-range FBG strain sensor and ESG.</p>
Full article ">
19 pages, 7591 KiB  
Article
Measurement and Decoupling of Hygrothermal-Mechanical Effects with Optical Fibers: Development of a New Fiber Bragg Grating Sensor
by Pietro Aceti, Lorenzo Calervo, Paolo Bettini and Giuseppe Sala
Sensors 2025, 25(4), 1037; https://doi.org/10.3390/s25041037 - 9 Feb 2025
Viewed by 637
Abstract
Composite materials are increasingly used in the aviation industry for various aircraft components due to their lightweight and mechanical performances. However, these materials are susceptible to degradation due to environmental factors such as hot–wet environments and freeze–thaw cycles, which can compromise their performance [...] Read more.
Composite materials are increasingly used in the aviation industry for various aircraft components due to their lightweight and mechanical performances. However, these materials are susceptible to degradation due to environmental factors such as hot–wet environments and freeze–thaw cycles, which can compromise their performance and safety over time. This study develops an innovative Fiber Bragg Grating (FBG) sensor system capable of not only measuring but also decoupling the simultaneous effects of temperature, humidity and strain. Unlike existing FBG systems, our approach integrates a novel theoretical framework and sensor configuration that accurately isolates these parameters in an epoxy resin material. The system incorporates three FBG sensors: one for temperature, one for temperature and humidity and a third one for all three factors. A theoretical framework based on linear strain superposition and constitutive laws was developed to isolate the individual contributions of each factor. Experimental validation in controlled hygrothermal conditions demonstrated the system’s ability to accurately detect and decouple these effects, enabling the monitoring of moisture absorption and composite degradation over time. The proposed system provides a reliable, lightweight and efficient solution for the long-term monitoring of composite structures in extreme conditions. Additionally, it enhances predictive maintenance by improving the accuracy of Health and Usage Monitoring Systems (HUMSs) and provides a method to correct data inconsistencies in already installed sensors, further extending their operational value. Full article
(This article belongs to the Special Issue Advances in Optical Fiber-Based Sensors)
Show Figures

Figure 1

Figure 1
<p>A typical optical fiber structure.</p>
Full article ">Figure 2
<p>Arrangement of three FBGs in three different fibers to create the sensor.</p>
Full article ">Figure 3
<p>Manufacturing of the thermal sensor.</p>
Full article ">Figure 4
<p>Realization of the micro-perforated capillary tube FBG sensor.</p>
Full article ">Figure 5
<p>Optical microscope analysis.</p>
Full article ">Figure 6
<p>Silicone mold.</p>
Full article ">Figure 7
<p>Detail of the sensor arrangement and assembly process.</p>
Full article ">Figure 8
<p>Time history of the Bragg wavelength for the three sensors.</p>
Full article ">Figure 9
<p>Time history comparison between the temperature measured by the optical thermal sensor and the sensor of the climate chamber controller.</p>
Full article ">Figure 10
<p>Time history of the relative humidity (hygrothermal sensor).</p>
Full article ">Figure 11
<p>Time histories of temperature and relative humidity.</p>
Full article ">Figure 12
<p>Relative humidity comparison: superposition of the RH time-histories measured by hygrothermal and hygrothermal-mechanical sensors.</p>
Full article ">Figure 13
<p>Strain time-history measured by the hygrothermal-mechanical sensor.</p>
Full article ">Figure 14
<p>Saturated sensorized specimen at 50 °C temperature loaded by 110 g weights.</p>
Full article ">Figure 15
<p>Measured mass from bulk specimens and comparison with estimated mass from the hygrothermal sensor.</p>
Full article ">
17 pages, 12188 KiB  
Article
Wearable and Thermal Drift-Compensated Monitoring System Based on Fiber Bragg Grating Sensors for a 3D-Printed Foot Prosthesis
by Sara Del Chicca, Gennaro Rollo, Andrea Sorrentino, Emanuele Gruppioni, Marco Tarabini and Paola Saccomandi
Sensors 2025, 25(3), 885; https://doi.org/10.3390/s25030885 - 31 Jan 2025
Viewed by 623
Abstract
Monitoring foot prostheses is essential, as their performance impacts users’ daily lives. Fiber Bragg Grating (FBG) sensors represent a gold standard in monitoring applications, but traditional optoelectronic units are too cumbersome for wearable applications. This research addresses this issue by using a lightweight [...] Read more.
Monitoring foot prostheses is essential, as their performance impacts users’ daily lives. Fiber Bragg Grating (FBG) sensors represent a gold standard in monitoring applications, but traditional optoelectronic units are too cumbersome for wearable applications. This research addresses this issue by using a lightweight and compact optoelectronic unit and developing a compensation algorithm to overcome the signal drift phenomena caused by the light source instability. The proposed method uses an FBG as a reference to provide the algorithm with information on the signals drift. The developed algorithm is based on the assumptions of linearity among drift in different detection channels and the absence of drift at the initial time instant. The compensation variable was experimentally identified and validated. Experimental validation through temperature tests showed the algorithm reduces the drift error by 60%. Finally, mechanical tests were conducted on a foot prosthesis equipped with two FBGs: one used as a reference and the other for strain sensing. An electrical strain gauge was used to validate the FBG-based sensing system. The results of the mechanical tests indicate the possiblity to monitor a foot prosthesis using FBGs. The FBG and strain gauge measurements comparison aligns with previous studies where high-performance optoelectronic units were used. Full article
(This article belongs to the Special Issue Intelligent Medical Sensors and Applications)
Show Figures

Figure 1

Figure 1
<p>(<b>a</b>) Working principle of the integrated Gaussian WDM demodulator adapted from [<a href="#B31-sensors-25-00885" class="html-bibr">31</a>]. (<b>b</b>) Voltage signal of undisturbed FBG affected by drift.</p>
Full article ">Figure 2
<p>(<b>a</b>) Illustration of the sensorized prosthesis. (<b>b</b>) Carbon-fibre reinforced composite specimens with glued FBG sensor.</p>
Full article ">Figure 3
<p>Set-up implemented to perform sensor validation tests: (<b>a</b>) Focus on the MTS loading machine and the foot prosthesis. (<b>b</b>) Focus on the FBG-based monitoring system highlighting the MOFIS<span class="html-italic"><sup>TM</sup></span> optoelectronic unit, the reference FBG sensor, and the upper portion of the strain gauge, the sensing FBG is on the prosthesis sole in correspondence with the strain gauge as shown in <a href="#sensors-25-00885-f002" class="html-fig">Figure 2</a>a.</p>
Full article ">Figure 4
<p>(<b>a</b>) Identification of parameter <span class="html-italic"><b>k</b></span>: the orange dots represent the dataset used to identify the compensation variable <span class="html-italic"><b>k</b></span>, whereas the blue line shows the drift on the sensing channel estimated using the identified linear model. (<b>b</b>) Effect of the drift compensation.</p>
Full article ">Figure 5
<p>Validation of the identified linear model. (<b>a</b>) Comparison between the measured data (light-blue dots) and the estimated data (bordeaux straight line). (<b>b</b>) Resembles between the wavelength expected value and the <math display="inline"><semantics> <msub> <mi>λ</mi> <mrow> <mi>e</mi> <mi>x</mi> <mi>p</mi> <mi>e</mi> <mi>c</mi> <mi>t</mi> <mi>e</mi> <mi>d</mi> </mrow> </msub> </semantics></math> (red line) and the wavelengths <math display="inline"><semantics> <mover accent="true"> <mi>λ</mi> <mo stretchy="false">˜</mo> </mover> </semantics></math> obtained from the experimental data by applying the voltage to the wavelength conversion model after the drift compensation procedure was completed.</p>
Full article ">Figure 6
<p>Static temperature test. In light blue (<math display="inline"><semantics> <msub> <mi>T</mi> <mrow> <mi>P</mi> <mi>T</mi> <mn>100</mn> </mrow> </msub> </semantics></math>) is the temperature measured by the reference PT100 sensor. In orange (<math display="inline"><semantics> <msub> <mi>T</mi> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>s</mi> <mi>u</mi> <mi>r</mi> <mi>e</mi> <mi>d</mi> </mrow> </msub> </semantics></math>) is the temperature measured by the FBG sensing system obtained without performing the drift compensation procedure. In green (<math display="inline"><semantics> <mover accent="true"> <mi>T</mi> <mo stretchy="false">˜</mo> </mover> </semantics></math>) is shown the temperature measured by the FBG sensing system obtained by applying the proposed compensation algorithm.</p>
Full article ">Figure 7
<p>Induced deformation for positive tilt angles. (<b>a</b>) Quasi-static tests. (<b>b</b>) Dynamic tests.</p>
Full article ">Figure 8
<p>(<b>a</b>) Fitting relationship between the deformation measure with SG and the related wavelength shift. (<b>b</b>) Relationship between force and strain: the solid line represents the signals acquired with FBG sensors, and the dashed line the signals measured by the strain gauge.</p>
Full article ">
10 pages, 3072 KiB  
Communication
Acoustic Sensing Fiber Coupled with Highly Magnetostrictive Ribbon for Small-Scale Magnetic-Field Detection
by Zach Dejneka, Daniel Homa, Logan Theis, Anbo Wang and Gary Pickrell
Sensors 2025, 25(3), 841; https://doi.org/10.3390/s25030841 - 30 Jan 2025
Viewed by 546
Abstract
Fiber-optic sensing has shown promising development for use in detecting magnetic fields for downhole and biomedical applications. Coupling existing fiber-based strain sensors with highly magnetostrictive materials allows for a new method of magnetic characterization capable of distributed and high-sensitivity field measurements. This study [...] Read more.
Fiber-optic sensing has shown promising development for use in detecting magnetic fields for downhole and biomedical applications. Coupling existing fiber-based strain sensors with highly magnetostrictive materials allows for a new method of magnetic characterization capable of distributed and high-sensitivity field measurements. This study investigates the strain response of the highly magnetostrictive alloys Metglas® 2605SC and Vitrovac® 7600 T70 using Fiber Bragg Grating (FBG) acoustic sensors and an applied AC magnetic field. Sentek Instrument’s picoDAS interrogated the distributed FBG sensors set atop a ribbon of magnetostrictive material, and the corresponding strain response transferred to the fiber was analyzed. Using the Vitrovac® ribbon, a minimal detectable field amplitude of 60 nT was achieved. Using Metglas®, an even better sensitivity was demonstrated, where detected field amplitudes as low as 3 nT were measured via the strain response imparted to the FBG sensor. Distributed FBG sensors are readily available commercially, easily integrated into existing interrogation systems, and require no bonding to the magnetostrictive material for field detection. The simple sensor configuration with nanotesla-level sensitivity lends itself as a promising means of magnetic characterization and demonstrates the potential of fiber-optic acoustic sensors for distributed measurements. Full article
(This article belongs to the Section Chemical Sensors)
Show Figures

Figure 1

Figure 1
<p>Magnetic domains in a magnetostrictive material lattice at equilibrium (top) and under an external magnetic field at saturation strength (bottom) with a maximum magnetostrictive strain λ.</p>
Full article ">Figure 2
<p>Experimental test setup with air-core solenoid connected to function generator and amplifier. The magnetostrictive ribbon is positioned in the middle of the solenoid with the sensing fiber on top.</p>
Full article ">Figure 3
<p>Single-sided amplitude spectrums with an applied AC magnetic field at 350 Hz with amplitudes of 274 nT (<b>a</b>) and 2740 nT (<b>b</b>) from a Metglas<sup>®</sup> ribbon sample.</p>
Full article ">Figure 4
<p>Vitrovac<sup>®</sup> ribbon fiber sensor: 100 Hz amplitude spectrum intensity vs. 100 Hz AC magnetic-field amplitude.</p>
Full article ">Figure 5
<p>Three air-core solenoids containing Vitrovac<sup>®</sup> ribbon.</p>
Full article ">Figure 6
<p>Software capture of 3-dimensional matrix showing position, strain, and time for a half-second interval along 16 m of the fiber and 8 broadband FBG pairs.</p>
Full article ">Figure 7
<p>Metglas<sup>®</sup> ribbon fiber sensor: 200 Hz amplitude spectrum intensity vs. 100 Hz AC magnetic field amplitude.</p>
Full article ">Figure 8
<p>Metglas<sup>®</sup> ribbon fiber sensor: 350 Hz amplitude spectrum intensity vs. 350 Hz AC magnetic-field amplitude. (<b>a</b>) up to 60 nT and; (<b>b</b>) up to 6000 nT.</p>
Full article ">
14 pages, 4762 KiB  
Article
Trigger-Free and Low-Cross-Sensitivity Displacement Sensing System Using a Wavelength-Swept Laser and a Cascaded Balloon-like Interferometer
by Jianming Zhou, Jinying Fan, Junkai Zhang, Jianping Yao and Jiejun Zhang
Sensors 2025, 25(3), 750; https://doi.org/10.3390/s25030750 - 26 Jan 2025
Viewed by 552
Abstract
A wavelength-swept laser (WSL) demodulation system offers a unique time-domain analysis solution for high-sensitivity optical fiber sensors, providing a high-resolution and high-speed method compared to optical spectrum analysis. However, most traditional WSL-demodulated sensing systems require a synchronous trigger signal or an additional optical [...] Read more.
A wavelength-swept laser (WSL) demodulation system offers a unique time-domain analysis solution for high-sensitivity optical fiber sensors, providing a high-resolution and high-speed method compared to optical spectrum analysis. However, most traditional WSL-demodulated sensing systems require a synchronous trigger signal or an additional optical dispersion link for sensing analysis and typically use a fiber Bragg grating (FBG) as the sensing unit, which limits displacement sensitivity and increases fabrication costs. We present a novel displacement sensing system that combines a trigger-free WSL demodulation method with a cascaded balloon-like interferometer, featuring a simple structure, high sensitivity, and low temperature cross-sensitivity. The sensor is implemented by bending a short length of single-mode fiber with an optimal radius of around 4 mm to excite cladding modes, which form an interference spectral response with the core mode. Experimental findings reveal that the system achieves a high sensitivity of 397.6 pm/μm for displacement variation, corresponding to 19.88 ms/μm when demodulated using a WSL with a sweeping speed of 20 nm/s. At the same time, the temperature cross-sensitivity is as low as 5 pm/°C or 0.25 ms/°C, making it a strong candidate for displacement sensing in harsh environments with significant temperature interference. Full article
(This article belongs to the Special Issue Advances in Microwave Photonics)
Show Figures

Figure 1

Figure 1
<p>The schematic of a wavelength-swept laser sensing system with a reference sensor and a displacement sensor. (<b>a</b>) Structure of the entire system. (<b>b</b>) Transmission spectrum of the cascaded balloon-like bent fiber sensors. WSL, wavelength-swept laser; PD, photodetector; OSC, oscilloscope.</p>
Full article ">Figure 2
<p>The structure of the balloon-like bent fiber sensor and photograph. (<b>a</b>) Schematic diagram of the coupling between core and cladding modes. (<b>b</b>) Structure of the balloon-like bent fiber sensor. (<b>c</b>) Photograph of real product. R, radius.</p>
Full article ">Figure 3
<p>The schematic diagram of the radius variation of the displacement sensor. (<b>a</b>) No displacement. (<b>b</b>) After displacement. (<b>c</b>) Data point for curvature radius fitting without displacement. (<b>d</b>) Data point for radius curvature fitting after displacement. R, the initial radius; R’, the radius after the change.</p>
Full article ">Figure 4
<p>Analysis of the effective refractive index for different curvature radii. (<b>a</b>) Mode 1 at a radius of 2 mm; (<b>b</b>) Mode 2 at a radius of 2 mm; (<b>c</b>) Mode 1 at a radius of 4 mm; (<b>d</b>) Mode 2 at a radius of 4 mm; (<b>e</b>) Fitting curve of the refractive index difference as a function of the radius.</p>
Full article ">Figure 5
<p>Waveguide simulation of different bending radii. (<b>a</b>) R = ∞; (<b>b</b>) R = 10 mm; (<b>c</b>) R = 4 mm; (<b>d</b>) R = 2 mm; (<b>e</b>) R = 1 mm; (<b>f</b>) R = 0.5 mm.</p>
Full article ">Figure 6
<p>The displacement sensing system based on the WSL and the cascaded balloon-like bent fiber sensor. (<b>a</b>) Schematic diagram of the WSL sensing system. (<b>b</b>) Photograph of the WSL sensing system. WSL, wavelength-swept laser; PD, photodetector; OSC, oscilloscope.</p>
Full article ">Figure 7
<p>The optical spectra and time waveforms of the reference sensor and the displacement sensor within a range of 10 μm to 50 μm. (<b>a</b>) Wavelength intensity data from the optical spectrum analyzer (<b>b</b>) Voltage curve data from the oscilloscope.</p>
Full article ">Figure 8
<p>The measured waveform on the oscilloscope with a 20 μm step in a continuous 50 s sampling.</p>
Full article ">Figure 9
<p>Linear fitting results of displacement measurements under different scanning processes. (<b>a</b>) Forward scanning process with a step size of 20 μm (<b>b</b>) Backward scanning process with a step size of 20 μm. (<b>c</b>) Forward scanning process with a step size of 10 μm. (<b>d</b>) Forward scanning process with a step size of 5 μm.</p>
Full article ">Figure 10
<p>The temperature effect on the displacement sensing system. (<b>a</b>) Transmission spectrum of the cascaded balloon-like bending sensor from 35 °C to 60 °C. (<b>b</b>) Linear fit of Dip1 and Dip2.</p>
Full article ">
11 pages, 5329 KiB  
Communication
Radiation-Induced Wavelength Shifts in Fiber Bragg Gratings Exposed to Gamma Rays and Neutrons in a Nuclear Reactor
by G. Berkovic, S. Zilberman, Y. London, M. Rosenfeld, E. Shafir, O. Ozeri, K. Ben-Meir, A. Krakovich and T. Makmal
Sensors 2025, 25(2), 323; https://doi.org/10.3390/s25020323 - 8 Jan 2025
Viewed by 533
Abstract
Fiber Bragg gratings (FBGs) inscribed by UV light and different femtosecond laser techniques (phase mask, point-by-point, and plane-by-plane) were exposed—in several irradiation cycles—to accumulated high doses of gamma rays (up to 124 MGy) and neutron fluence (8.7 × 1018/cm2) [...] Read more.
Fiber Bragg gratings (FBGs) inscribed by UV light and different femtosecond laser techniques (phase mask, point-by-point, and plane-by-plane) were exposed—in several irradiation cycles—to accumulated high doses of gamma rays (up to 124 MGy) and neutron fluence (8.7 × 1018/cm2) in a research-grade nuclear reactor. The FBG peak wavelengths were measured continuously in order to monitor radiation-induced shifts. Gratings inscribed on pure silica core fibers using near-IR femtosecond pulses through a phase mask showed the smallest shifts (<30 pm), indicating that these FBGs are suitable for temperature measurement even under extreme ionizing radiation. In contrast, the pointwise inscribed femtosecond gratings and a UV-inscribed grating showed maximal shifts of around 100 pm and 400 pm, respectively. Radiation-induced red shifts are believed to arise from gamma radiation damage, which may partially recover after irradiation is stopped. At the highest neutron exposures, grating peak blue shifts started to appear, apparently due to fiber compaction. Full article
(This article belongs to the Special Issue Optical Fiber Sensors in Radiation Environments: 2nd Edition)
Show Figures

Figure 1

Figure 1
<p>A visual demonstration of the difference between femtosecond phase mask and femtosecond point-by-point FBGs. (<b>left</b>) The green spool is a connectorized fiber containing point-by-point FBGs, and the smaller blue spool is a fiber with phase mask FBGs. Both fibers are illuminated using red light from fiber fault locators. In a bright room, scattering is visible from the point-by-point FBGs but not from the phase mask FBGs. (<b>right</b>) Weak scattering from the phase mask FBGs can only be observed when the room is completely darkened.</p>
Full article ">Figure 2
<p>The reflection spectra of the FBGs used in this study, as measured by an Optical Spectrum Analyzer (OSA). All graphs are presented with the FBG reflected power normalized with respect to its maximum. In all graphs, the full scale along the x-axis is the same (5 nm), enabling an easy comparison of the bandwidths of the different FBGs.</p>
Full article ">Figure 3
<p>(<b>a</b>) A photograph of fibers on an aluminum bar and the irradiation tube into which they are placed and lowered into the reactor. The five FBGs and the thermocouple sensing head are all positioned (to within 1 cm) at the same location on the bar to ensure equal exposures during the experiment. (<b>b</b>) Experimental set-up for monitoring FBG peaks and temperature during the experiment.</p>
Full article ">Figure 4
<p>Changes in the FBG peak wavelengths (corrected for temperature variations) during and after the first reactor operation shift.</p>
Full article ">Figure 5
<p>Accumulated changes in the FBG peak wavelengths (corrected for temperature variations) before, during, and after the second reactor operation shift.</p>
Full article ">Figure 6
<p>Changes in the FBG peak wavelengths (corrected for temperature variations) during and after the fifth reactor operation shift (first operation in the stronger irradiation site). The inset at the bottom also shows the partial recovery of the peak shift after shutdown and rapid erasure at the start of the next shift.</p>
Full article ">Figure 7
<p>Cumulative shifts in FBG peak wavelengths at the conclusions of all reactor operations expressed as a function of radiation exposure. The bottom horizontal axis is the accumulated dose of γ-rays, and the neutron doses accumulated in parallel are given on the top axis and in the table at bottom.</p>
Full article ">
17 pages, 5679 KiB  
Article
Fiber Bragg Grating Thermometry and Post-Treatment Ablation Size Analysis of Radiofrequency Thermal Ablation on Ex Vivo Liver, Kidney and Lung
by Sanzhar Korganbayev, Leonardo Bianchi, Clara Girgi, Elva Vergantino, Domiziana Santucci, Eliodoro Faiella and Paola Saccomandi
Sensors 2025, 25(1), 245; https://doi.org/10.3390/s25010245 - 3 Jan 2025
Viewed by 965
Abstract
Radiofrequency ablation (RFA) is a minimally invasive procedure that utilizes localized heat to treat tumors by inducing localized tissue thermal damage. The present study aimed to evaluate the temperature evolution and spatial distribution, ablation size, and reproducibility of ablation zones in ex vivo [...] Read more.
Radiofrequency ablation (RFA) is a minimally invasive procedure that utilizes localized heat to treat tumors by inducing localized tissue thermal damage. The present study aimed to evaluate the temperature evolution and spatial distribution, ablation size, and reproducibility of ablation zones in ex vivo liver, kidney, and lung using a commercial device, i.e., Dophi™ R150E RFA system (Surgnova, Beijing, China), and to compare the results with the manufacturer’s specifications. Optical fibers embedding arrays of fiber Bragg grating (FBG) sensors, characterized by 0.1 °C accuracy and 1.2 mm spatial resolution, were employed for thermometry during the procedures. Experiments were conducted for all the organs in two different configurations: single-electrode (200 W for 12 min) and double-electrode (200 W for 9 min). Results demonstrated consistent and reproducible ablation zones across all organ types, with variations in temperature distribution and ablation size influenced by tissue characteristics and RFA settings. Higher temperatures were achieved in the liver; conversely, the lung exhibited the smallest ablation zone and the lowest maximum temperatures. The study found that using two electrodes for 9 min produced larger, more rounded ablation areas compared to a single electrode for 12 min. Our findings support the efficacy of the RFA system and highlight the need for tailored RFA parameters based on organ type and tumor properties. This research provides insights into the characterization of RFA systems for optimizing RFA techniques and underscores the importance of accurate thermometry and precise procedural planning to enhance clinical outcomes. Full article
Show Figures

Figure 1

Figure 1
<p>Experimental setup of RFA in liver, kidney, and lung. The experimental setup includes the RF generator connected to the water-cooled electrode(s) and the grounding pad; the biological tissue sample (bovine liver, kidney, or lung tissue); the optical interrogation unit connected to the optical fiber(s), embedding a chain of FBG sensors, and a laptop for displaying temperature evolution and distribution measured by the FBG sensors.</p>
Full article ">Figure 2
<p>Placement of the electrodes and FBG sensors in the organs and definition of the ablation axes ‘a’ and ‘b’. On the left, the experimental setup is illustrated, while an enlargement of the position of the electrodes and optical fibers in the sample is shown on the right.</p>
Full article ">Figure 3
<p>Bovine liver. Single-electrode configuration: (<b>a</b>) trends of maximum temperature variation at distances of 1 cm (blue) and 2 cm (red) from the RF electrode, and 2D temperature evolution maps along the sensor over time at a distance of (<b>b</b>) 1 cm and (<b>c</b>) 2 cm from the electrode. Double-electrode configuration: (<b>d</b>) trends of maximum temperature registered between the electrodes (blue), at 1 cm (red) and 2 cm (yellow) from the RF electrode; 2D temperature evolution maps along the sensor over time (<b>e</b>) between the two electrodes, at a distance of (<b>f</b>) 1 cm and (<b>g</b>) 2 cm from the electrode.</p>
Full article ">Figure 4
<p>Bovine kidney. Single-electrode configuration: (<b>a</b>) trends of maximum temperature change at distances of 1 cm (blue) and 2 cm (red) from the RF electrode, and 2D temperature evolution maps along the sensor over time at a distance of (<b>b</b>) 1 cm and (<b>c</b>) 2 cm from the electrode. Double-electrode configuration: (<b>d</b>) trends of maximum temperature registered between the electrodes (blue), at 1 cm (red) and 2 cm (yellow) from the RF electrode; 2D temperature evolution maps along the sensor over time (<b>e</b>) between the two electrodes, at a distance of (<b>f</b>) 1 cm and (<b>g</b>) 2 cm from the electrode.</p>
Full article ">Figure 5
<p>Bovine lung. The results of the single-electrode configuration experiments are shown in the upper panel: (<b>a</b>) trends of maximum temperature change at distances of 1 cm (blue) and 2 cm (red) from the electrode, and 2D temperature change maps along the sensor over time at a distance of (<b>b</b>) 1 cm and (<b>c</b>) 2 cm from the electrode. Double-electrode configuration (lower panel): (<b>d</b>) trends of maximum temperature registered between the electrodes (blue), at 1 cm (red) and 2 cm (yellow) from the RF electrode; 2D temperature evolution maps along the sensor over time (<b>e</b>) between the two electrodes, at a distance of (<b>f</b>) 1 cm and (<b>g</b>) 2 cm from the electrode.</p>
Full article ">Figure 6
<p>Bovine liver: ablation axes obtained from ex vivo experiments compared with the manufacturer’s data at different settings (i.e., 200 W for 12 min in the case of single-electrode configuration and 200 W for 9 min for the double-electrode configuration).</p>
Full article ">Figure 7
<p>Bovine kidney: ablation axes obtained from ex vivo experiments compared with the company’s data at different settings (i.e., 200 W for 12 min in the case of single-electrode configuration and 200 W for 9 min for the double-electrode configuration).</p>
Full article ">Figure 8
<p>Bovine lung: ablation axes obtained from ex vivo experiments compared with the company’s data at different settings (i.e., 200 W for 12 min in the case of single-electrode configuration and 200 W for 9 min for the double-electrode configuration).</p>
Full article ">
17 pages, 5024 KiB  
Article
Comparative Study of γ Radiation-Induced Effects on Fiber Bragg Gratings by Femtosecond Laser Point-by-Point Method and Line-by-Line Method
by Mingyang Hou, Yumin Zhang, Xin Xiong and Lianqing Zhu
Photonics 2025, 12(1), 32; https://doi.org/10.3390/photonics12010032 - 3 Jan 2025
Viewed by 618
Abstract
In the realm of advanced optical fiber sensing (OFS) technologies, Fiber Bragg Grating (FBG) has garnered widespread application in the monitoring of temperature, strain, and external refractive indices, particularly within high-radiation environments such as high-energy physics laboratories, nuclear facilities, and space satellites. Notably, [...] Read more.
In the realm of advanced optical fiber sensing (OFS) technologies, Fiber Bragg Grating (FBG) has garnered widespread application in the monitoring of temperature, strain, and external refractive indices, particularly within high-radiation environments such as high-energy physics laboratories, nuclear facilities, and space satellites. Notably, FBGs inscribed using femtosecond lasers are favored for their superior radiation resistance. Among various inscription techniques, the point-by-point (PbP) and line-by-line (LbL) methods are predominant; however, their comparative impacts on radiation durability have not been adequately explored. In this research, FBGs were inscribed on a single-mode fiber using both the PbP and LbL methods, and subsequently subjected to a total irradiation dose of 5.04 kGy (radiation flux of 2 rad/s) over 70 h in a 60Co-γ radiation environment. By evaluating the changes in temperature- and strain-sensing performance of the FBG pre-irradiation and post-irradiation, this study identifies a more favorable technique for writing anti-irradiation FBG sensors. Moreover, an analysis into the radiation damage mechanisms in optical fibers, alongside the principles of femtosecond laser inscription, provides insights into the enhanced radiation resistance observed in femtosecond laser-written FBGs. This study thus furnishes significant guidance for the development of highly radiation-resistant FBG sensors, serving as a critical reference in the field of high-performance optical fiber sensing technologies. Full article
(This article belongs to the Special Issue Emerging Trends in Optical Fiber Sensors and Sensing Techniques)
Show Figures

Figure 1

Figure 1
<p>Schematic diagram of FBG sensing principle.</p>
Full article ">Figure 2
<p>Schematic of femtosecond inscription FBG.</p>
Full article ">Figure 3
<p>Micrograph of writing FBG by femtosecond laser.</p>
Full article ">Figure 4
<p>Schematic of sensing experiment.</p>
Full article ">Figure 5
<p>Sensing experiment setup.</p>
Full article ">Figure 6
<p>Schematic of radiation experiment.</p>
Full article ">Figure 7
<p>Temperature-sensing spectral diagram and central wavelength drift diagram written by the PbP method before irradiation: (<b>a</b>) 3d spectrum of heating; (<b>b</b>) center wavelength drift diagram of heating; (<b>c</b>) 3d spectrum of cooling; (<b>d</b>) center wavelength drift diagram of cooling.</p>
Full article ">Figure 8
<p>Temperature-sensing spectral diagram and central wavelength drift diagram written by the PbP method after irradiation: (<b>a</b>) 3d spectrum of heating; (<b>b</b>) center wavelength drift diagram of heating; (<b>c</b>) 3d spectrum of cooling; (<b>d</b>) center wavelength drift diagram of cooling.</p>
Full article ">Figure 9
<p>The strain-sensing spectrum and the central wavelength drift diagram written by the PbP method before irradiation: (<b>a</b>) 3d spectrum of applying strain; (<b>b</b>) center wavelength drift diagram of applying strain; (<b>c</b>) 3d spectrum of unloading strain; (<b>d</b>) center wavelength drift diagram of unloading strain.</p>
Full article ">Figure 10
<p>The strain-sensing spectrum and the central wavelength drift diagram written by the PbP method after irradiation: (<b>a</b>) 3d spectrum of applying strain; (<b>b</b>) center wavelength drift diagram of applying strain; (<b>c</b>) 3d spectrum of unloading strain; (<b>d</b>) center wavelength drift diagram of unloading strain.</p>
Full article ">
18 pages, 5268 KiB  
Article
Vibration Control of Flexible Launch Vehicles Using Fiber Bragg Grating Sensor Arrays
by Bartel van der Veek, Hector Gutierrez, Brian Wise, Daniel Kirk and Leon van Barschot
Sensors 2025, 25(1), 204; https://doi.org/10.3390/s25010204 - 2 Jan 2025
Viewed by 710
Abstract
The effects of mechanical vibrations on control system stability could be significant in control systems designed on the assumption of rigid-body dynamics, such as launch vehicles. Vibrational loads can also cause damage to launch vehicles due to fatigue or excitation of structural resonances. [...] Read more.
The effects of mechanical vibrations on control system stability could be significant in control systems designed on the assumption of rigid-body dynamics, such as launch vehicles. Vibrational loads can also cause damage to launch vehicles due to fatigue or excitation of structural resonances. This paper investigates a method to control structural vibrations in real time using a finite number of strain measurements from a fiber Bragg grating (FBG) sensor array. A scaled test article representative of the structural dynamics associated with an actual launch vehicle was designed and built. The main modal frequencies of the test specimen are extracted from finite element analysis. A model of the test article is developed, including frequency response, thruster dynamics, and sensor conversion matrices. A model-based robust controller is presented to minimize vibrations in the test article by using FBG measurements to calculate the required thrust in two cold gas actuators. Controller performance is validated both in simulation and on experiments with the proposed test article. The proposed controller achieves a 94% reduction in peak–peak vibration in the first mode, and 80% reduction in peak–peak vibration in the second mode, compared to the open loop response under continuously excited base motion. Full article
(This article belongs to the Special Issue Spacecraft Vibration Suppression and Measurement Sensor Technology)
Show Figures

Figure 1

Figure 1
<p>Instrumented flexible beam test article representative of slender launch vehicle structural dynamics. (<b>a</b>) slender launch vehicle example, (<b>b</b>) experimental setup for active control of flexible structure with similar natural frequencies to (<b>a</b>), (<b>c</b>) cold gas thrusters shown on test specimen, (<b>d</b>) Placement of FBG sensors on test specimen.</p>
Full article ">Figure 2
<p>Vibration spectrum of the test article measured with capacitance probe and FBG.</p>
Full article ">Figure 3
<p>(<b>a</b>) Operating principle of the fiber Bragg grating (FBG) sensor. (<b>b</b>) FBG sensor interrogation system. In this study, only one fiber channel was used.</p>
Full article ">Figure 4
<p>Thruster assembly and components.</p>
Full article ">Figure 5
<p>(<b>a</b>) Thruster transient model, (<b>b</b>) thruster model response vs. measured thrust for experimentally measured current input.</p>
Full article ">Figure 6
<p>Augmented SIMO plant for mixed sensitivity problem.</p>
Full article ">Figure 7
<p>Definition of MISO controller input weights.</p>
Full article ">Figure 8
<p>Weighting filters used for H-infinity synthesis.</p>
Full article ">Figure 9
<p>Double-MISO H-infinity controller response with initial deflection in first mode shape, simulation results (<b>left</b>), experimental results (<b>right</b>). Top row: displacement at top thruster location, Bottom row: displacement at bottom thruster location.</p>
Full article ">Figure 10
<p>Double-MISO H-infinity controller with initial deflection in second mode shape, simulation results (<b>left</b>), experimental results (<b>right</b>). Top row: displacement at top thruster location, Bottom row: displacement at bottom thruster location.</p>
Full article ">Figure 11
<p>Double-MISO H-infinity controller with continuous base excitation at first modal frequency. Simulation results (<b>left</b>), experimental results (<b>right</b>). Top row: displacement at top thruster location, Bottom row: displacement at bottom thruster location.</p>
Full article ">Figure 12
<p>Double-MISO H-infinity controller with continuous base excitation at second modal frequency. Simulation results (<b>left</b>), experimental results (<b>right</b>). Top row: displacement at top thruster location, Bottom row: displacement at bottom thruster location.</p>
Full article ">Figure 13
<p>Performance assessment of the double MISO H-infinity controller after step base motion excitation. Simulation results (<b>left</b>), experimental results (<b>right</b>). Top row: displacement at top thruster location, bottom row: displacement at bottom thruster location.</p>
Full article ">Figure 14
<p>Bode diagram of the controller, showing notches at the natural frequencies.</p>
Full article ">Figure 15
<p>Frequency response of the full order SIMO plant vs. reduced order SIMO plant.</p>
Full article ">
22 pages, 2053 KiB  
Review
Research Progress in Fiber Bragg Grating-Based Ocean Temperature and Depth Sensors
by Xinyu Zhao, Chenxi Wei, Lina Zeng, Li Sun, Zaijin Li, Hao Chen, Guojun Liu, Zhongliang Qiao, Yi Qu, Dongxin Xu, Lianhe Li and Lin Li
Sensors 2025, 25(1), 183; https://doi.org/10.3390/s25010183 - 31 Dec 2024
Viewed by 626
Abstract
Fiber Bragg gratings (FBGs) are widely used in stress and temperature sensing due to their small size, light weight, high resistance to high temperatures, corrosion, electromagnetic interference, and low cost. In recent years, various structural enhancements and sensitization to FBGs have been explored [...] Read more.
Fiber Bragg gratings (FBGs) are widely used in stress and temperature sensing due to their small size, light weight, high resistance to high temperatures, corrosion, electromagnetic interference, and low cost. In recent years, various structural enhancements and sensitization to FBGs have been explored to improve the performance of ocean temperature and depth sensors, thereby enhancing the accuracy and detection range of ocean temperature and depth data. This paper reviews advancements in temperature, pressure, and dual-parameter enhancement techniques for FBG-based sensors. Additionally, the advantages and disadvantages of each method are compared and analyzed, providing new directions for the application of FBG sensors in marine exploration. Full article
(This article belongs to the Section Optical Sensors)
Show Figures

Figure 1

Figure 1
<p>Principle of Fiber Bragg Grating Reflection and Transmission [<a href="#B38-sensors-25-00183" class="html-bibr">38</a>].</p>
Full article ">Figure 2
<p>Spectral Shift in Fiber Bragg Grating under External Influences [<a href="#B40-sensors-25-00183" class="html-bibr">40</a>].</p>
Full article ">Figure 3
<p>Schematic Diagram of Pressure Sensor Structure [<a href="#B74-sensors-25-00183" class="html-bibr">74</a>].</p>
Full article ">Figure 4
<p>(<b>a</b>–<b>c</b>) Principle and Physical Diagram of π-FBG Sensor [<a href="#B67-sensors-25-00183" class="html-bibr">67</a>].</p>
Full article ">Figure 5
<p>Schematic Diagram of the Structure of an FBG Pressure Sensor [<a href="#B84-sensors-25-00183" class="html-bibr">84</a>].</p>
Full article ">Figure 6
<p>Schematic Diagram of the Sensor Structure Based on Membrane and Lever [<a href="#B86-sensors-25-00183" class="html-bibr">86</a>].</p>
Full article ">
15 pages, 4143 KiB  
Article
Digitalized Optical Sensor Network for Intelligent Facility Monitoring
by Esther Renner, Lisa-Sophie Haerteis, Joachim Kaiser, Michael Villnow, Markus Richter, Torsten Thiel, Andreas Pohlkötter and Bernhard Schmauss
Photonics 2025, 12(1), 18; https://doi.org/10.3390/photonics12010018 - 28 Dec 2024
Viewed by 570
Abstract
Due to their inherent advantages, optical fiber sensors (OFSs) can substantially contribute to the monitoring and performance enhancement of energy infrastructure. However, optical fiber sensor systems often are standalone solutions and do not connect to the main energy infrastructure control systems. In this [...] Read more.
Due to their inherent advantages, optical fiber sensors (OFSs) can substantially contribute to the monitoring and performance enhancement of energy infrastructure. However, optical fiber sensor systems often are standalone solutions and do not connect to the main energy infrastructure control systems. In this paper, we propose a solution for the digitalization of an optical fiber sensor system realized by the Open Platform Communications Unified Architecture (OPC UA) protocol and the Internet of Things (IoT) platform Insights Hub. The optical fiber sensor system is based on bidirectional incoherent optical frequency domain reflectometry (biOFDR) and is used for the interrogation of fiber Bragg grating (FBG) arrays. To allow for an automated sensor identification and thus measurement procedure, an optical sensor identification marker based on a unique combination of fiber Bragg gratings (FBGs) is established. To demonstrate the abilities of the digitalized sensor network, a field test was performed in a power plant test facility of Siemens Energy. Temperature measurements of a packaged FBG sensor fiber were performed with a portable demonstrator, illustrating the system’s robustness and the comprehensive data processing stream from sensor value formation to the cloud. The realized network services promote sensor data quality, fusion, and modeling, expanding opportunities using digital twin technology. Full article
(This article belongs to the Special Issue Advanced Optical Fiber Sensors for Harsh Environment Applications)
Show Figures

Figure 1

Figure 1
<p>Optical sensor system based on the bidirectional incoherent optical frequency domain (biOFDR): (<b>a</b>) Schematic of the biOFDR setup; (<b>b</b>) image of the portable demonstrator.</p>
Full article ">Figure 2
<p>Optical sensor identification markers (ID markers) based on three FBGs with different wavelength combinations: (<b>a</b>) measurement results of marker 1-1-1 from the biOFDR; (<b>b</b>) different wavelength and position combinations with applied markers 1-1-1 and 1-1-2 in blue and red, respectively.</p>
Full article ">Figure 3
<p>Digital sensor network architecture. Data flow from left (DigiMonet biOFDR system) to right (cloud applications). The different communication paths are marked by type.</p>
Full article ">Figure 4
<p>Measurement value Open Platform Communications Unified Architecture (OPC UA) node with properties, exemplarily shown for the full-width half-maximum (FWHM) bandwidth of FBG 1.</p>
Full article ">Figure 5
<p>Automated cloud onboarding based on the Siemens MindSphere Digital Service Platform (MDSP).</p>
Full article ">Figure 6
<p>Power plant generator mockup at Siemens Energy AG with installed fiber sensor arrays. The black dots on the sensor strip mark the position of the FBG. Each sensor strip consists of a standard single-mode fiber with 10 FBGs.</p>
Full article ">Figure 7
<p>Configuration scheme of the OPC UA service structure. Service connections are depicted in grey, OPC UA connections in yellow, and file transfers in green.</p>
Full article ">Figure 8
<p>Measurement results acquired with the bidirectional iOFDR setup: (<b>a</b>) FBG sensor elements and marker configuration; (<b>b</b>) temperature measurements for all 10 FBGs over the whole measurement time (each color represents the temperature measurement of one FBG).</p>
Full article ">Figure 9
<p>Screenshot of the ThingsBoard during the field test. The measured temperature values (as depicted in <a href="#photonics-12-00018-f008" class="html-fig">Figure 8</a>) are transferred from the biOFDR demonstrator unit to the cloud via the OPC UA data servers.</p>
Full article ">Figure 10
<p>Insights Hub Monitor dashboard (simplified screenshot). The calculated temperature values (Max, Mean, Min) are derived from the Statistics µ-service.</p>
Full article ">
Back to TopTop