Stimulated Brillouin scattering modeling for high-resolution, time-domain distributed sensing.

Starting from the standard three-wave SBS coupled equations, we derive a novel expression describing Brillouin interaction between a pulsed pump wave with a finite cw component, and a Stokes continuous wave counter-propagating along a single-mode optical fiber. The derived integral equation relates the time-domain Stokes beam amplification to the Brillouin frequency distribution. The proposed model permits an accurate description of the Brillouin interaction even for arbitrarily-shaped pump pulses, and can be efficiently employed for improving the accuracy and the resolution of SBS-based distributed sensors. The validity and the limits of the proposed model are numerically analyzed and discussed

An Experimental Investigation on the Progressive Failure of Unsaturated Granular Slopes

Slope failure is a complex process which depends on several factors concerning nature and properties of soil, slope morphology and structure, past stress history, groundwater regime, boundary conditions, and their changes. As a consequence, the mechanism of slope failure is typically characterized by the development of a highly non-uniform strain field, which does not allow an easy prediction of the failure conditions. Usually, the process which will bring the slope to final collapse starts with local soil failure, which then leads to formation and propagation of a shear zone, and finally to general slope failure. This mechanical process is called progressive failure. However, in spite of the progresses in the knowledge of the slope behavior, a complete framework about the progressive failure is still missing; in particular, information about the response of granular unsaturated sloping soils is very poor. This paper reports the results of a couple of small-scale experiments on slopes reconstituted with unsaturated pyroclastic soils and subjected to continuous rainfall. The use of miniaturized sensors and optical fibers provided useful data to read some aspects of the mechanics of failure

Brillouin Optical Time Domain Analysis Sensor for Active Vibration Control of a Cantilever Beam

The paper reports the use of a distributed optical fiber sensor based on stimulated Brillouin scattering, for structural vibration control. A cantilevered flexible aluminum beam was used as test-bed for vibration control. The proposed approach allows acquiring simultaneously the dynamic strain at several locations. The dynamic strain measured at one (or more) fiber location can be used to implement any vibration control algorithm. Experimental results are reported in which a voice coil, positioned near the fixed end of the cantilever beam, was employed as actuator for the reduction of the vibrations related to the first bending mode of the beam

Lamb Wave Detection for Structural Health Monitoring Using a ϕ-OTDR System

In this paper, the use of a phase-sensitive optical time-domain reflectometry (phi-OTDR) sensor for the detection of the Lamb waves excited by a piezoelectric transducer in an aluminum plate, is investigated. The system is shown to detect and resolve the Lamb wave in distinct regions of the plate, opening the possibility of realizing structural health monitoring (SHM) and damage detection using a single optical fiber attached to the structure. The system also reveals the variations in the Lamb wave resulting from a change in the load conditions of the plate. The same optical fiber used to detect the Lamb waves has also been employed to realize distributed strain measurements using a Brillouin scattering system. The method can be potentially used to replace conventional SHM sensors such as strain gauges and PZT transducers, with the advantage of offering several sensing points using a single fiber

Performance of Ground Anchors Built in a Flysch Deposit

AbstractThe ultimate pull-out tensile load of ground anchors is strongly dependent onsoil nature,grout injection and effective stress state around the bulb. In this paper, the comparison between the results of conventional pull-out testson instrumented anchors built in a flysch formation and those of small scale pull-out tests performed in the laboratory,on undisturbed soil samples recovered at the depth of the anchor bulb,allowed to closely examine the skin friction that can be mobilizedin undrained conditionsat the soil-structure interface. The experiments highlight a strong scale effect, probably depending on the real size androughness ofthe lateral surface of the bulb. In fact, theirregular bulb profiledue to flysch features strongly contributes to the pull-outstrength

Experimental demonstration of a Brillouin optical frequency-domain reflectometry (BOFDR) sensor

To measure the strain and/or temperature along an optical fiber with one-end access, a Brillouin optical frequency-domain reflectometry (BOFDR) technique is presented in this paper. It is based on detecting the spontaneous Brillouin scattering from a sinusoidally modulated pump light. Compared to the Brillouin optical frequency-domain analysis (BOFDA), this new BOFDR sensor approach presents the advantage that the measurements are free from the distorting components related to acoustic wave modulation, thus simplifying the associated data processing.This work has been supported by the projects MIUR-PON03PE_00155_1-OPTOFER and MIUR-PON03PE_00171_1-GEOGRID of the Italian government, and by the project TEC2013-47264-C2-1-R and TEC2016-76021-C2-2-R of the Spanish government

Wind Turbine Blade Monitoring with Brillouin-Based Fiber-Optic Sensors

Wind turbine (WT) blade is one of the most important components in WTs, as it is the key component for receiving wind energy and has direct influence on WT operation stability. As the size of modern turbine blade increases, condition monitoring and maintenance of blades become more important. Strain detection is one of the most effective methods to monitor blade conditions. In this paper, a distributed fiber-optic strain sensor is used for blade monitoring. Preliminary experimental tests have been carried out over a 14 m long WT composite blade, demonstrating the possibility of performing distributed strain and vibration measurements

An integrated approach for rock slope failure monitoring: The case study of Coroglio tuff cliff (Naples, Italy) - Preliminary results

The paper re ports the i mple mentation of an integrate d syste m ai me d at the real-ti me monitoring of a series of physical parame ters controlling the r ock slope stability. The system has bee n installe d on the Cor oglio tuff cliff, loc ate d in the highly ur banize d coastal area of Naples (Italy) at the bor der of the acti ve volcanic cal der a of Campi Flegrei. Preliminar y results obtai ne d during the first ye ar of data ac quisition and monitoring acti vi ty (Dece mber 2014 – January 2016) are also discussed on the basis of statistical models. (3) (PDF) An integrated approach for rock slope failure monitoring: the case study of Coroglio tuff cliff (Naples, Italy) – preliminary results. Available from: https://www.researchgate.net/publication/299340773_An_integrated_approach_for_rock_slope_failure_monitoring_the_case_study_of_Coroglio_tuff_cliff_Naples_Italy_-_preliminary_results [accessed Feb 27 2020].Published242-2471IT. Reti di monitoraggio e sorveglianzaN/A or not JC

Low distortion Brillouin slow light in optical fibers using AM modulation

Stimulated Brillouin scattering (SBS) has been recently shown to offer a mechanism for generating tunable all-optical delays in room temperature single-mode optical fibers at telecommunication wavelengths. This technique makes use of the rapid variation of the refractive index that occurs in the vicinity of the Brillouin gain resonance. When the slow light pulse delay is subject to a constraint on the allowable pulse distortion, it has been shown that the use of a pair of closely-spaced Brillouin gain lines can increase the distortion-constrained delay, with respect to the single-line configuration. In this paper, we numerically and experimentally demonstrate that the same experimental apparatus usually employed for generating a Brillouin gain doublet, can also be used for achieving three equally-spaced Brillouin gain resonances, further increasing the distortion-constrained pulse delay