Design of Optical Fibre Goniometer for Measurement of Complex Human Joint

Abstract

Optical signal gets attenuated when subjected to bending within an optical fiber, but it still attracts the various sensing applications based on bending losses. The optical fiber is subjected to macrobending losses when the optical fiber’s bend radius exceeds its core diameter. Tribology is the science of friction, lubrication and wear. Biotribology provides the important information for biological systems (human joints such as knees and hips) which continuously move relative to one another. This research is based on implementation of optical fiber goniometer in order to study joint biotriboilogy. The goniometer is a device to measure bend angles between two planes of contact. Goniometers are widely used for robotics and human prosthetic devices, but mechanical goniometers have performance limitations for very small bend angles. The use of optical fiber for goniometer provides the flexibility of measurement of smaller bend angles. The optical goniometer makes use of polarization controller to maintain the state of polarization of optical signal. The effect of macrobending loss on radius of curvature of bend, bending angle, number of wrapping turns and wavelength is observed. A mathematical model presenting macrobending loss dependence on these parameters is presented in this paper. A Single mode fiber with core size 5 µm is subjected to bend angles ranging from 0° to 180° and its influence on macrobending losses have been investigated for wavelength of 850 nm, 1310 nm and 1550 nm. The bending angle is measured with precision accuracy of less than 1° in this setup.