Ice detection for vibrating beams based on fibre Bragg grating sensors

Abstract

In this paper, a method based on fibre Bragg gratings (FBGs) is proposed to detect ice in vibrating beam-like mechanical structures. For this, two points of an optical fibre, with a pretensioned FBG sensor in the middle, are glued on the upper surface of a cantilever beam. The fibre is placed in a way that the central fibre section containing the FBG remain unglued and loose when the cantilever is placed at the most upward bending position. This way, the vibrating beam and dangling FBG are constructed into a bowstring structure. To validate the method, ice is induced on the upper surface of the cantilever beam by applying a freezing spray in laboratory. Results point out that when no ice is present in the vibrating beam, the FBG response shows a quasi-sine wave response with a flat-bottom section, which indicates the condition of the loose FBG. On the contrary, when ice cumulated on top of the cantilever, the ice induces a gluing effect that bonds the FBG to the vibrating beam, so that its strain response corresponds to an almost undistorted sine wave. By analysing the shape of the time-domain and frequency-domain strain response of the FBG, an effective method for ice detection is demonstrated.