Brillouin optical time-domain analysis for geotechnical monitoring

AbstractIn this paper, we show some recent experimental applications of Brillouin optical time-domain analysis (BOTDA) based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting early movements of soil slopes by the direct embedding of suitable fiber cables in the ground is presented. Furthermore, the same technology can be used to realize innovative inclinometers, as well as smart foundation anchors

NSHT: New Smart Hybrid Transducer for Structural and Geotechnical Applications

This work describes the application of a new transducer prototype for continuous monitoring in both the structural and geotechnical fields. The transducer is synthetically constituted by a wire of optical fiber embedded between two fiber tapes (fiberglass or carbon fiber) and glued by a matrix of polyester resin. The fiber optical wire ends have been connected to a control unit whose detection system is based on Brillouin optical time-domain frequency analysis. Three laboratory tests were carried out to evaluate the sensor's reliability and accuracy. In each experiment, the transducer was applied to a sample of inclinometer casing sets in different configurations and with different constraint conditions. The experimental collected data were compared with theoretical models and with data obtained from the use of different measuring instruments to perform validation and calibration of the transducer at the same time. Several diagrams can compare the transducer and highlight its suitability for the monitoring and maintenance of structures. The characteristic of the transducer suggests its use as a mixed system for reinforcing and monitoring, especially in the lifetime maintenance of critical infrastructures such as transportation and service networks, and historical heritag

Distributed dynamic strain sensing based on brillouin scattering in optical fibers

Over the past three decades, extensive research activity on Brillouin scattering-based distributed optical fiber sensors has led to the availability of commercial instruments capable of measuring the static temperature/strain distribution over kilometer distances and with high spatial resolution, with applications typically covering structural and environmental monitoring. At the same time, the interest in dynamic measurements has rapidly grown due to the relevant number of applications which could benefit from this technology, including structural analysis for defect identification, vibration detection, railway traffic monitoring, shock events detection, and so on. In this paper, we present an overview of the recent advances in Brillouin-based distributed optical fiber sensors for dynamic sensing. The aspects of the Brillouin scattering process relevant in distributed dynamic measurements are analyzed, and the different techniques are compared in terms of performance and hardware complexity

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

Sweep BOTDA for fast distributed sensing

A new scheme for fast distributed sensing based on Brillouin Optical Time-Domain Analysis (BOTDA) is proposed and demonstrated, based on the use of a frequency swept microwave source for the generation of the probe wave. The entire BOTDA measurement is taken within the duration of the frequency sweep, at a frequency granularity depending on the duration of the sweep, the repetition rate of the pump pulses and the number of averages

Dual Wavelength Botda for Strain/Temperature Discrimination

The sensitivity of Brillouin Frequency Shift (BFS) to strain and temperature has been studied in a bending-loss insensitive fiber (BIF), at two different wavelengths (850 and 1550, nm). The results show that the ratio between strain sensitivity at the two wavelengths is different from the ratio between temperature sensitivity, which can be conveniently used for simultaneous and distributed measurement of the two parameters using a single sensing element. Experimental results, carried out at 1-m spatial resolution, demonstrate the feasibility of the proposed method

High-Pass Filtering for Accuracy Enhancement in Dark-Pulse Brillouin Optical Time Domain Analysis

In this letter, we demonstrate a simple technique aimed to enhance the accuracy in dark-pulse Brillouin optical time-domain analysis (BOTDA) sensors. Modeling the stimulated Brillouin scattering in the frequency domain, we show that the degrading features related to the pump background can be removed by applying a high-pass filter to the raw data, at the cost of some degradation of the signal-to-noise ratio. A numerical analysis, as well as experimental tests carried out at 20-cm spatial resolution, validate the proposed technique