Optical strain gauge with high spatial resolution

A technique to enhance the spatial resolution of typical fiber Bragg grating–based strain gauges has been experimentally verified in this study. Just analyzing the intensity of the reflection spectrum of a sampled fiber Bragg grating, its inner deformation profile has been obtained with a spatial resolution of Formula L<1mm. The proposed method employs a synthesis algorithm to retrieve the longitudinal axis strain profile of a sampled fiber Bragg grating glued to an asymmetric plate. The achieved experimental results have been compared to the mechanical simulations of the employed plate, exhibiting a good response even without compensating the residual stress provoked during the installation process.This study was supported by the project TEC2010-20224-C02-02 and grant AP2009-1403

Recovering a fiber Bragg grating axial strain distribution from its reflection spectrum

A processing scheme able to obtain any arbitrary intragrating strain distribution of a fiber Bragg grating (FBG) is proposed and demonstrated. The processing method employs just the intensity of the FBG reflection spectrum to obtain its deformation profile by combining a geometrical processing scheme with the particle swarm optimization technique. The technique has been evaluated using several spectra generated from very heterogeneous strain distributions and with a real spectrum obtained from a 5 mm length FBG under an asymmetric perturbation. The achieved results exhibit a good spatial resolution (Δ≈0.5 mm) and repeatability.This work has been supported by the project TEC2010-20224-C02-02 and grant AP2009-140

Laser-induced breakdown spectroscopy: fundamentals, applications, and challenges

Laser-induced breakdown spectroscopy (LIBS) is a technique that provides an accurate in situ quantitative chemical analysis and, thanks to the developments in new spectral processing algorithms in the last decade, has achieved a promising performance as a quantitative chemical analyzer at the atomic level. These possibilities along with the fact that little or no sample preparation is necessary have expanded the application fields of LIBS. In this paper, we review the state of the art of this technique, its fundamentals, algorithms for quantitative analysis or sample classification, future challenges, and new application fields where LIBS can solve real problems

Focal beam position detection in a laser induced breakdown spectroscopy system by using a fiber Bragg grating sensor

Chemical analysis of dangerous materials entails a safety issue for the researchers. Laser Induced Breakdown Spectroscopy offers the possibility to analyze these materials away from them using Stand-Off Set-ups. To optimize the plasma induction, the remote focalization of the laser beam is of paramount importance. A custom Fiber Bragg Grating sensor system able to correct the laser beam focalization errors is proposed and experimentally checked. The optical transducer architecture and the preliminary obtained results are reported in this paper.This work has been co-supported by the Spanish Government through the project TEC2010-20224-C02- 02 and the grant AP2007-02230

Real options of distributed DAS sensing applied to road transport engineering

Distributed Acoustic Sensing (DAS) techniques with Optical Fibers are able to provide a wide range of data for very long distances. The technique is used for monitoring purposes on the energy sector (i.e.: oil &gas pipes, electricity transport lines, etc..), where the resiliency of the infrastructure linear layout is low, and the associated loss-of-service costs are high. The significant cost barriers of the technology are changing due to the scientific advances and the economy of scale effects; however, the use within the road transport engineering is still not widespread and limited to specific applications. This work explores the cost-benefit analysis of using the DAS technique for transport engineering, including a sensitivity analysis on the foreseeable cost reductions and technical characteristics of the technology applied to planning, operation and maintenance purposes. The real options of installing new fiber optic layout vs using dark fiber networks is also analysed and compared to the use of standard ITS systems.We thank the support of PID2019-107270RB-C21 (funded by MCIN/ AEI/ 10.13039/501100011033) and PDC2021-121172-C22 funded by MCIN/AEI /10.13039 /501100011033 and European Union Next Generation EU/PRTR. Our sincere gratitude Alayn Loayssa (Public University of Navarra), Victor Centeno (WSP) and to William Fawcett, Ian Ellinghan, Martin Hughes, Lars Mikalsen and the CILECCTA project (FP7-NMP 229061) for the LCC and Real Options methodology

Smart material using fiber Bragg grating transducers and shape memory alloy actuators

A structure based on a smart material and a PID control loop is presented in this paper. A glass fiber reinforced plastic material is instrumented with Fiber Bragg Gratings (FBG) and Shape Memory Alloy (SMA) actuators. The smart material and the smart structure are both successfully checked by being subjected to different operational conditions at the laboratory. Very good responses are obtained under both slow and quicker varying conditions.This work has been supported by the Spanish TEC2010-20224-C02-02 project and grant AP2009-140

Radial processing scheme of speckle patterns for sensing applications

A processing scheme to enhance the speckle sensitivity to dynamic perturbation has been proposed and tested. Considering different areas within speckle patterns where highest order modes interfere, a better dynamic sensitivity has been achieved.This work has been supported by the Spanish Government through CYCIT projects DA2TOI (FIS2010-19860), TFS (TEC2010-20224-C02-02) and the Alma’s Eguizabal PhD Grant (FPU12/04130

Acoustic detection of laser-induced plasma emission by means of a fiber-Bragg grating sensor

Laser-induced breakdown spectroscopy (LIBS) is an analytical tool able to estimate the atomic composition of materials, without sample preparation and in a short time. One drawback of this technique is that the quantitative analysis is not as precise as other established methods, in part because of the pulse-to-pulse fluctuations of the energy delivered to the sample. These fluctuations can be compensated by monitoring the acoustic wave emitted by the plasma, which is related to the ablated mass. In this paper, we propose the use of a fiber-Bragg grating sensor to detect and measure the acoustic shockwave. A processing scheme is proposed to derive the acoustic energy from the sensor waveform. The experiments show that there is a correlation between the sensor’s response and the laser pulse energy, so it can be used as a monitoring signal of the ablation process

Fiber Bragg Grating sensors for on-line welding diagnostics

In this work Fiber Bragg Grating transducers (FBGs) are used to perform an on-line monitoring of an arc-welding process by means of the combined temperature and strain profile. The main goal of this approach is to establish a correlation between the appearance of defects in the seams and the response offered by the FBGs, exploring the optimal disposition of the FBGs in terms of their sensitivity to weld defects. The proposed solution will be explored by means of welding tests and a comparison with a plasma spectroscopic analysis.This work has been supported by the project TEC2010-20224-C02-02 and grant AP2009-1403. Authors would also like to thank Roberto Perez Sierra for his valuable help during the FBGs fabrication process

Reflection-based fiber specklegram sensor

In this paper, a Fiber Specklegram Sensor (FSS) based on Plastic Optical Fiber (POF) has been proposed with a reflection-based configuration. A HeNe laser is launched through a coupler, reflected by a mirrored fiber end and detect the specklegram sequence using a commercial camera. Different sensor performance metrics have been analyzed in terms of final sensitivity to external vibration applied to the fiber. The results confirm the performance reduction of the reflection-based scheme in comparison with the transmission-based approach but it can be also employed as sensing system where only a single fiber end is available.This work has been supported by the project TEC2013-47264-C2-1-R