Experimental modal analysis of an aluminum rectangular plate by use of the slope-assisted BOTDA method

We report an experimental modal analysis of an aluminum rectangular plate (50 cm x 30 cm x 0.3 cm), carried out by use of a Brillouin optical time-domain analysis (BOTDA) sensor operating in the slope-assisted configuration, i.e. at a fixed pump-probe frequency shift. Strain measurements were acquired along an optical fiber attached to the structure, at a maximum acquisition rate of 250 Hz, a spatial resolution of 30 cm and a sampling distance of 5 cm in both x-and y-directions. A sequence of dynamic tests, aimed to evaluate the resonant frequencies and strain modal shapes of the structure, were performed on the plate for various boundary conditions (plate clamped with four, three or two bolts). Comparison with finite element method (FEM) analysis and dynamic strain measurements with strain gauges shows that Brillouin based distributed sensors can be usefully employed to perform the modal analysis of a vibrating structure, even if the spatial resolution is comparable with the plate dimensions.