Distributed torsion sensor based on cascaded coaxial cable Fabry–Perot interferometers

Abstract

Cascaded coaxial cable Fabry–Perot interferometers (FPI) are studied and demonstrated for distributed torsion measurement. Multiple weak reflectors are implemented on a coaxial cable so that any two consecutive reflectors can form a Fabry–Perot cavity. By fixing the cable sensor in a helical form on a shaft, the distributed torsion of the shaft can be measured by the cascaded Fabry–Perot cavities. A test on a single section shows that the sensor has a linear response with a sensitivity of 1.834 MHz (rad/m)−1 in the range of twisted rate from 0 to 8.726 rad m−1. The distributed torsion sensing capability is useful in drilling process monitoring, structure health monitoring and machine failure detection.