Dynamic strain measurements of a cantilever using the improved bonding fiber Bragg grating

Abstract

For a surface mounted fiber Bragg grating (FBG) strain sensor, this study used an improved bonding method that distributes cement only on the two ends of the grating and leaves the grating free from cement. According to a recent numerical study, for a conventional surface mounted FBG strain sensor its relationship between average strains (within its glued grating) and voltage signals is nonlinear and changeable depending on the variation patterns of strain gradients (within its glued grating) in a strain history. By contrast, the relationship for the improved bonding one is linear because of the constant zero strain gradient within the glue-free grating. To experimentally verify the linear relationship for the improved bonding fiber Bragg grating (IBFBG), this study set up a cantilever with both the IBFBG and a resistance strain gauge surface mounted in close proximity, and the vibration responses were induced by impactions of a free-falling steel ball on the cantilever's surface. Experimental results indicate that dynamic calibrations of an IBFBG by using a commonly used resistance strain gauge are possible because both sensors in close proximity have their changes of voltage signals almost proportional to each other.