C. Ambrosino

Sensitivity Tuning in Terfenol-D Based Fiber Bragg Grating Magnetic Sensors

In this work, the dependence of the magnetostrictive response on the prestress has been used to improve and fit the performance of Terfenol-D based fiber Bragg grating magnetic sensor. The possibility to tune sensitivity allows to work at different operative conditions and to develop advanced sensors with reconfigurable sensitivity. Performance improvements in terms of magnetic resolution up to 0.0116 A/m have been demonstrated.

Damage detection by using experimental modal analysis technique and fiber Bragg gratings

In this work, the application of fiber Bragg gratings (FBGs) to damage detection tests is reported. The presence of alterations on a mechanical structure can be evaluated from variations of the resonances (frequency and amplitudes) of its frequency response function (FRF). This latter can be evaluated through experimental approaches, like the modal analysis, involving mechanical excitation systems (instrumented hammers and piezoelectric elements) and adequate sensing systems. Here, results of preliminary tests performed with FBGs externally bonded on a simply steel structure are reported. FBG sensors have been interrogated with a low cost passive technique based on optical filtering As previous step, in order to test FBGs capability to retrieve the dynamic features of a test sample in a wide frequency range, results of high frequency (1.5kHz) modal analysis tests are reported. In both cases, i. e. modal analysis and damage detection tests respectively, laser Doppler vibrometers and accelerometers, representative of the state of the art for this application field, have been used as reference sensors. As future work, an algorithm to quantify the damage level of a structure from experimental data will be determined

Dynamic measurements on a star tracker prototype of AMS using fiber optic sensors

An aluminum prototype of the AMICA (Astro Mapper for Instrument Check of Attitude) Star Tracker Support (ASTS) of the AMS_02 (Alpha Magnetic Spectrometer) space experiment has been instrumented with Fiber Bragg Gratings (FBGs). In this work the use of FBGs to perform dynamic tests on the ASTS prototype is reported. The excitation has been provided by an instrumented impact hammer, the mechanical response of the structure has been obtained by bonded FBGs and accelerometers. All time histories have been recorded, transformed in the frequency domain to retrieve Frequency Response Functions (FRFs)-accelerometer responses- and Strain Frequency Response Functions (SFRFs) -FBG responses-, both providing resonant frequencies and displacements (strain) shapes of the ASTS. Numerical simulations of this structure have been performed to predict its resonant frequencies and vibrational displacement (strain) shapes. Experimental results demonstrate the capability of FBGs to perform in situ experimental modal analysis as confirmed by the comparison of the optical response with the accelerometers one and the good agreement with the numerical analysis.

Influence of the pre-stress in Terfenol-Fiber Bragg Grating integrated magnetic field sensors

This paper presents the first results on the use of the pre-stress to improve the performance of a magnetic field sensor based on a Terfenol-Fiber Bragg Grating integrated device. Indeed, since the pre-stress modifies the response of the magnetostrictive material, this should allow to fit the performances of the sensor to different operative conditions or to exploit also the stress as a control variable to optimize the design of the sensor.

High sensitivity magnetic sensor by using fiber Bragg grating bonded to magnetic shape memory alloys

In this work, the experimental demonstration of fiber Bragg grating based sensors as magnetic transducers is reported. Up to now, FBGs based magnetic sensors have been proposed by using Terfenol, metallic alloy with a giant magnetostriction coefficient. Here, a novel configuration is proposed employing a new class of magnetic materials, Magnetic Shape Memory alloys (MSMs), instead of Terfenol. This class of material, with a very giant magnetostriction coefficient, changes its shape when magnetic fields are applied. High strain values, up to 10 percent can be obtained with fast response times (less than 1 ms). A fiber Bragg grating has been bonded on a MSM sample and sensor characterization has been carried out. Experimental results and the comparison with Terfenol based FBGs sensors performances are reported, showing, for MSM, a sensitivity expressed as (▵λB/λB)/( ▵H/Hm) of 1.1e-4.

Fiber Bragg Grating Sensors and Piezoelectric Actuators in Co-Located Configuration for Active Vibration Control Applications

An active vibration control hybrid system using Fiber Bragg Grating (FBG) sensors and piezoelectric (PZT) actuators for vibration suppression is presented. An aluminum test-structure have been provided with FBGs sensors bonded below the same number of PZT actuators in a co-located configuration. A novel bonding procedure was used to realize the co-located sensors/actuators cells combining epoxy based glue filled with glass micro-balloons matching the size of optical fibers. Closed loop operation was implemented by using a Proportional-Derivative controller and proper designed power amplifiers to drive the actuators based on the FBGs response. Positioning criteria based on sensitivity considerations have been implemented to define the positioning of the sensors/actuators cells. The system was first validated through open loop tests comparing experimental results with numerical predictions. Finally, “closed loop” configuration tests have been carried out demonstrating of vibration-noise reduction up to 17 dB.

Magnetic Shape Memory alloy based Fiber Bragg Grating magnetic field sensor

The paper discusses a new device for magnetic field sensing, based on the integration of a fiber Bragg grating (FBG) with a magnetic shape memory alloy (MSMA). The latter is a new kind of material able to show extremely large strains in response to a magnetic field. Differently from classical shape memory alloys (SMA), actuated by temperature, they normally show quite fast responses. In the paper the basic features of the proposed device are illustrated and field range and sensitivity of the device are also discussed. Moreover, comparison with Terfenol based FBG sensor performances is reported showing for MSM based one a sensitivity expressed as (DeltalambdaB/lambdaB)/(DeltaH/Hm) of 1.81ldr10-4 , where lambdaB is the Bragg wavelength and Hm the mean magnetic field in the considered range.

Magnetic Field sensors employing Fiber Bragg Grating and Magneto-Elastic active material

This paper proposes a new device for magnetic field sensing that integrates a magneto-elastic rod as active material, with a Fiber Bragg Grating (FBG) strain sensor. Due to rate independent memory effects of the material, the response of the device is hysteretic and this lowers the device accuracy. Accurate modeling of material allows to embed in the device an algorithm for fast compensation of hysteresis so, yielding to a practically linear response of the sensor.