Modal analysis of a cantilever beam by use of Brillouin based distributed dynamic strain measurements

In this work we report an experimental modal analysis of a cantilever beam, carried out by use of a Brillouin optical time-domain analysis (BOTDA) setup operated at a fixed pump-probe frequency shift. The employed technique permitted us to carry out distributed strain measurements along the vibrating beam at a maximum acquisition rate of 108 Hz. The mode shapes of the first three bending modes (1.7, 10.8, 21.6 Hz) were measured for the structure under test. The good agreement between the experimental and numerical results based on a finite-element method (FEM) analysis demonstrates that Brillouin based distributed sensors are well suited to perform the modal analysis of a vibrating structure. This type of analysis may be useful for applications in structural health monitoring where changes in mode shapes are used as indicators of the damage to the structure.