Fiber Bragg Grating-based sensor system for sensing the shape of flexible needles

Shape sensing is of importance for the manipulation of flexible needles. In this work, a 0.6 mm diameter stylet with five Fiber Bragg Gratings (FBGs) installed as triplets was designed and implemented and a novel model of local curvature was established. A gradient-based optimization method has been integrated into the complete algorithm for shape sensing and this was used to reduce the difference between the midpoint curvature and the mean curvature. The experimental results obtained show that the mean tip errors are 0.35 mm, 0.30 mm, 0.38 mm in the single-bending, double-bending and space-bending experiments, respectively. In a torsion test experiment which was performed, when the rotation angle of the tip was less than 25°, the error seen was less than 0.5 mm. Furthermore, when the needle designed in this work was used to puncture a 60 mm thickness, ex vivo biological tissue, the mean error of the measurement of the needle tip was 0.39 mm.