Massimo L. Filograno

Coherent Noise Reduction in High Visibility Phase-Sensitive Optical Time Domain Reflectometer for Distributed Sensing of Ultrasonic Waves

Phase-sensitive optical time domain reflectometry (φOTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, φOTDRs have been used mostly for the measurement of sub-kHz vibrations, normally in the context of intrusion sensing. In this paper, the authors present an experimental and theoretical description of a high-visibility φOTDR and its performance when used for ultrasonic vibration measurements. The use of a semiconductor optical amplifier in the setup allows to suppress coherent noise and also to improve the spectral response of the pump pulses. These two advantages greatly decrease the detected intra-band noise thus allowing frequency measurements in the limits set by the time of flight of the light pulses while maintaining the simplicity of the scheme, as no post-processing, extremely high coherence lasers or coherent detection methods are required. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a fully distributed measurement of ultrasonic waves was achieved. The statistical behavior of the system was also described theoretically and characterized experimentally.

Real-Time Monitoring of Railway Traffic Using Fiber Bragg Grating Sensors

In this work, we present field tests concerning the application of fiber Bragg grating (FBG) sensors for the monitoring of railway traffic. The test campaigns are performed on the Spanish high-speed line Madrid-Barcelona, with different types of trains (S-102 TALGO-BOMBARDIER, S-103 SIEMENS-VELARO, and S-120 CAF). We located the FBG sensors in the rail track at 70 km from Madrid in the country side, where the trains primarily are tested during commercial operation with maximum speeds between 250-300 km/h. The FBG sensor interrogation system used allows the simultaneous monitoring of four FBG sensors at 8000 samples/s. The different position of the FBG sensors in relation with the rail can be used for different purposes such as train identification, axle counting, speed and acceleration detection, wheel imperfections monitoring, and dynamic load calculation.

Phase-sensitive Optical Time Domain Reflectometer Assisted by First-order Raman Amplification for Distributed Vibration Sensing Over >100 km

In this study, the authors present an experimental and theoretical description of the use of first order Raman amplification to improve the performance of a Phase-sensitive optical time domain reflectometer (φOTDR) when used for vibration measurements over very long distances. A special emphasis is given to the noise which is carefully characterized and minimized along the setup. A semiconductor optical amplifier and an optical switch are used to greatly decrease the intra-band coherent noise of the setup and balanced detection is used to minimize the effects of RIN transferred from the Raman pumps. The sensor was able to detect vibrations of up to 250 Hz (close to the limits set by the time of flight of light pulses) with a resolution of 10 m in a range of 125 km. To achieve the above performance, no post-processing was required in the φOTDR signal. The evolution of the φOTDR signal along the fiber is also shown to have a good agreement with the theoretical model.

Wheel Flat Detection in High-Speed Railway Systems Using Fiber Bragg Gratings

Wheel flats are a major source of problems in railway systems since they cause strong wear both in the infrastructure and in the train vehicles. In this paper, we present field tests concerning the application of Fiber Bragg Grating (FBG) sensors for the detection of out-of-roundness in high-speed train wheels. Wheel flats are shown to cause high-energy impacts on the rails that can be monitored using FBGs located in the rails. The results point out a great potential of this technology for the development of reliable wheel flat detection systems.

Comparison of the use of first and second-order Raman amplification to assist a phase-sensitive optical time domain reflectometer in distributed vibration sensing over 125 km

We report on the use of second-order Raman amplification to assist a phase-sensitive optical time domain reflectometer (ΦOTDR ) used for vibration measurements over very long distances. The sensor was able to measure vibrations of up to 380 Hz (limit set by the time of flight of light pulses) in a distance of 125 km with a resolution of 10 m and no post-processing. Balanced detection is used to reduce the relative intensity noise. A comparison with a sensor using first-order Raman amplification under similar conditions is presented and a clear improvement of performance is demonstrated.

High visibility phase-sensitive optical time domain reflectometer for distributed sensing of ultrasonic waves

In structural health monitoring, the propagation of ultrasonic waves along a structure can reveal interesting data relevant to the integrity of the whole structure. The availability of a system for distributed sensing of ultrasonic waves could, in some cases (e.g. pipelines) provide extremely valuable information to civil engineers. Phase-sensitive optical time domain reflectometry (ΦOTDR) is a simple and effective tool allowing the distributed monitoring of vibrations along single-mode fibers. Up to now, ΦOTDRs have been used mostly for the measurement of sub-kHz vibrations. In this work, the authors present an experimental characterization of a high-visibility ΦOTDR and its performance when used for ultrasonic vibration measurements. The sensor was able to measure vibrations of up to 39.5 kHz with a resolution of 5 m over a range which could go up to 1.25 km. This is the first time to our knowledge that a ΦOTDR is demonstrated for distributed measurement of ultrasonic waves.

Real Time Monitoring of Railway Traffic Using Fiber Bragg Grating Sensors

In this work we present field tests concerning the application of Fiber Bragg Grating (FBG) sensors for the monitoring of railway traffic. The test campaigns are performed on the Spanish high speed line Madrid–Barcelona, with different types of trains (S-102 TALGO–BOMBARDIER, S-103 SIEMENS-VELARO and S-120 CAF). We located the FBG sensors in the rail track at 70 km from Madrid in the country side, where the trains primarily are tested during commercial operation with maximum speeds between 250–300 km/h. The FBG sensor interrogation system used allows the simultaneous monitoring of four FBG sensors at 8000 samples/s. The different position of the FBG sensors in relation with the rail can be used with different purposes such as train identification, axle counting, speed and acceleration detection, wheel imperfections monitoring and dynamic load calculation.Copyright

Triaxial fiber optic magnetic field sensor for MRI applications

In this paper, we report a fiber-optic triaxial magnetic field sensor, based on Fiber Bragg Gratings (FBGs) integrated with giant magnetostrictive material, the Terfenol-D. The realized sensor has been designed and engineered for Magnetic Resonance Imaging (MRI) applications. A full magneto-optical characterization of the triaxial sensing probe has been carried out, providing the complex relationship among the FBGs wavelength shift and the applied magnetostatic field vector. Finally, the developed fiber optic sensors have been arranged in a sensor network composed of 20 triaxial sensors for mapping the magnetic field distribution in a MRI-room at a diagnostic center in Naples (SDN), equipped with Positron emission tomography/magnetic resonance (PET/MR) instrumentation. Experimental results reveal that the proposed sensor network can be efficiently used in MRI centers for performing quality assurance tests, paving the way for novel integrated tools to measure the magnetic dose accumulated day by day by MRI operators.

Identification of a “thermodynamic consistent” model of magneto-mechanical hysteresis

Smart or multi-functional materials are receiving more and more attention in the last decade, due to their strong potentialities to provide new and remarkable functionalities. With the aim to identify the operator by a systematic approach based on first order reversals, the device reported has been developed. The box contains the magnetostrictive material equipped with a strain sensor based on Fiber Bragg Grating. A screw is also employed to apply a specified prestress to the sample. The availability of an electromagnet with air-gap fields up to 2T allows to apply sufficiently large fields able to lead the Terfenol samples close to saturation, for a wide set of applied pre-stresses. The magnetostrictive response of the Terfenol sample for a wide range of pre-stresses is displayed.

Non-intrusive measurement of internal pressure and flow in pipelines using fiber Bragg grating

In this paper we propose and demonstrate a non-intrusive measurement method for internal pressure and water flow in hydraulic pipeline systems. Fiber Bragg Gratings are used to measure deformations in the external side of pipes under different working conditions for two different experiments. In the first experiment a PVC sewerage pipeline with a diameter of 90 mm was subjected to a variable air pressures up to 4 bars; in the second a PVC sewerage pipeline with a diameter of 32 mm was subjected to a water flow between 10 and 35 liters per minute.