Directional bending sensor based on triangular shaped fiber Bragg gratings.

We propose a directional bending sensor by mechanically bonded FBGs in a radially placed triangular shape to measure the bending moment and its applied direction. Bending measurement and the determination of its direction is essential to get the maximum bending stress and to figure out the deflection shape by the curvature information in a wide range of engineering applications. The proposed sensor configuration is original in terms of a pointwise sensing scheme based on the mechanically bonded scheme of three optical fibers and its simple fabrication process only using optical fibers. This set-up made of three FBG sensors provides a simple relationship of the bending moment to the independent strain measurement of each FBG. We demonstrate two sensor configurations such as the self-bending measurement and the structural bending measurement in a surface-mount (or embedded) measurement. Through the verification experiments, the proposed bending sensor is successfully shown to measure the applied bending moment and its direction.