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

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

Brillouin Optical Time Domain Analysis in silica fibers at 850 nm wavelength

Brillouin scattering properties of silica fibers at 850 nm wavelength were experimentally investigated using a Brillouin optical time-domain analysis (BOTDA) scheme. In the single-mode 780-HP fiber, the Brillouin frequency shift (BFS) and FHWM of the Brillouin Gain Spectrum were found to be ∼ 19795 MHz and 90 MHz, respectively. The estimated peak Brillouin gain is 0.32(mW)-1. The temperature and strain dependences of BFS were determined as well. Distributed sensing capability was demonstrated at a minimum spatial resolution of 1.5 m and a fiber length of 100 m. As a proof-of-principle, the temperature and strain dependencies of the BFS in SFM-28 fiber have been determined at 850 nm and 1550 nm wavelengths, suggesting its possible use for temperature/strain discrimination

NSTH New Smart distributed optical fiber Transducers made of Hybrid composite material for civil and enviromental monitoring

Il trasduttore è stato sviluppato con sensore in fibra ottica distribuito in tecnologia ibrida vetro-carbonio e resina poliestere. Il sistema di monitoraggio con trasduttori in fibra ottica distribuita con tecnologia ibrida vetro-carbonio, offre enormi vantaggi se associato a sistemi convenzionali di monitoraggio. Tali vantaggi sono connessi alla possibilità di riconoscere in tempi compatibili con la definizione di un sistema Early Warning, lo sviluppo di fenomeni deformativi. Le limitazioni delle tradizionali tecniche di monitoraggio possono essere superate grazie all’uso di sensori in fibra ottica distribuiti incorporati all’interno del nuovo trasduttore ibrido vetro-carbonio basati sul fenomeno fisico dello “scattering di Brillouin” laddove una singola fibra ottica consente di ricostruire, con elevata risoluzione spaziale, il profilo termico e/o deformativo per tutto il tratto strumentato, sino a lunghezze di centinaia di metri. Il trasduttore realizzato è caratterizzato da uno spessore “s” di 5 cm e può assumere una lunghezza che può raggiungere centinaia di metri con un interasse “i” per connessioni di 50 cm. È possibile realizzare tre prototipi di trasduttore che presentano tre diverse configurazioni. Il primo prototipo presenta la seguente configurazione di base, caratterizzata da fibre di vetro e fibre di carbonio con una grammatura di 200 gr/mq: Il secondo prototipo presenta una configurazione di elevata flessibilità caratterizzata da fibre di vetro disposte sia superiormente che inferiormente con una grammatura di 200 gr/mq: Il terzo prototipo presenta una configurazione di elevata rigidezza e resistenza meccanica, caratterizzata da fibre di carbonio disposte sia superiormente che inferiormente con grammatura di 200 gr/mq

High-Pass Filtering for Accurate Reconstruction of the Brillouin Frequency Shift Profile From Brillouin Optical Frequency Domain Analysis Data

In this work, we propose and demonstrate a new method to reconstruct the Brillouin Frequency shift (BFS) profile in high spatial resolution Brillouin Optical Frequency Domain Analysis (BOFDA) sensors. The method aims to compensate the distorting terms affecting BOFDA measurements, which originate from the modulation impressed on the acoustic wave involved in the scattering phenomenon. We show that these terms can be easily removed by applying a high-pass filter to the data acquired in the frequency-domain, at the cost of a degradation of the signal-to-noise ratio. A numerical analysis, as well as experimental tests carried out at 8-mm spatial resolution, validate the proposed technique

Modal analysis of a cantilever beam by use of Brillouin based distributed dynamic strain measurements

In this work we report an experimental modal analysis of a cantilever beam, carried out by use of a Brillouin optical time-domain analysis (BOTDA) setup operated at a fixed pump–probe frequency shift. The employed technique permitted us to carry out distributed strain measurements along the vibrating beam at a maximum acquisition rate of 108 Hz. The mode shapes of the first three bending modes (1.7, 10.8, 21.6 Hz) were measured for the structure under test. The good agreement between the experimental and numerical results based on a finite-element method (FEM) analysis demonstrates that Brillouin based distributed sensors are well suited to perform the modal analysis of a vibrating structure. This type of analysis may be useful for applications in structural health monitoring where changes in mode shapes are used as indicators of the damage to the structure

Distributed Optical Fiber Sensor Applications in Geotechnical Monitoring

We report the experimental application of distributed optical fiber sensors, based on stimulated Brillouin scattering (SBS), to the monitoring of a small-scale granular slope reconstituted in an instrumented flume and subjected to artificial rainfall until failure, and to the monitoring of a volcanic rock slope. The experiments demonstrate the sensors’ ability to reveal the sudden increase in soil strain that foreruns the failure in a debris flow phenomenon, as well as to monitor the fractures in the tuff rocks. This study offers an important perspective on the use of distributed optical fiber sensors in the setting up of early warning systems for landslides in both rock and unconsolidated materials