Fiber optic micro sensor for the measurement of tendon forces

A fiber optic sensor developed for the measurement of tendon forces is designed, numerically modeled, fabricated, and experimentally evaluated. The sensor incorporates fiber Bragg gratings and micro-fabricated stainless steel housings. A fiber Bragg grating is an optical device that is spectrally sensitive to axial strain. Stainless steel housings are designed to convert radial forces that are applied to the housing into axially forces that can be sensed by the fiber Bragg grating. The metal housings are fabricated by several methods including laser micromachining, swaging, and hydroforming. Designs are presented that allow for simultaneous temperature and force measurement as well as simultaneous resolution of multi-axis forces.;Sensor geometries are analyzed by closed form calculation and the finite element method. The axial strain on the fiber Bragg grating is determined by the models and used to estimate the change in the reflected spectrum.;The sensors are experimentally evaluated by hydrostatic loading and in vitro testing. A commercial hydraulic burst tester is used to provide programmable pressures that are exerted on the sensor. The in vitro experiments are performed in excised tendon. Experimental results are compared to the analytical models. Results of these experiments suggest that this sensor may prove useful in a variety of biomechanical measurements.