Dynamics characterization of optical Fiber Bragg Grating sensors (FBGs) and related integration tecniques

The main purpose of this thesis, realized in collaboration with the DIMEAS (Mechanical and Aerospace Engineering Department) and the ISMB (Mario Boella Higher Institute), is to study the dynamic characterization of the Fiber Bragg Grating sensors in order to exploit them as regular vibration sensors. The advantages over the traditional electronic sensors such as their light weight, small cable size and resistance to electromagnetic and radio frequency interferences, are leading them to be the favourites in the aerospace field. In particular, during this work a geometry that allows to change the disposition of the support on the shaker has been developed and printed 3D in order to study the effects of the vibration in two different oscillation directions. By comparing the results on the FFT (Fourier Fast Transform) spectrum has been demonstrated that it possible to recognize the vibration direction. Then, after a preliminary analysis aiming to find the resonant frequencies of the fiber and the support, carried using respectively a stroboscope and the Solidworks Simulation modal analysis, a control process has been automated in order to speed up and enhance the reliability of the measurements made to obtain the Bode diagrams and confirm experimentally what obtained preliminary. The tests have been conducted both on an empty-ends and on a full supports to demonstrate and remark the fact that the support response is influenced by its first vibration frequency which depends on stiffness and density; in fact, as expected, the natural frequency of the empty-ends support has resulted to be higher than that of the full one because the stiffness/mass ratio is higher. Moreover, since the fiber pre-tensioning strain is revealed to be suffering from environmental conditions such as temperature and humidity, a comparison with a fiber glued using resin instead of cyanoacrylate has been made and a new possible pre-tensioning solution geometry has been proposed, providing inspiration for future works.