Analytical Optimization of Optical Fiber Curvature Gauges

`The ldquocurvature gaugerdquo sensor monitors deflection of structures under mechanical loading in applications in which strain gauges have traditionally been used. Structural deflection-curvature is measured rather than material strain. The sensitive zone of the curvature gage is precision machined into the plastic optical fiber on grinding or milling machines. The cutout produced removes a part of the fiber core and introduces light loss that is related to the bend-radius of the fiber. This modulation mechanism is described analytically in this paper. Results relate the relative light loss to the fiber curvature for different parameters of the sensitive zone (depth, length, number of cuts, bend radius, and pitch of cuts). This allows a quantitative optimization of the gauge without having to produce thousands of sensors with slightly different combination of parameters in order to accomplish a similar objective experimentally.