Highly sensitive detection of distorted points in a cable by frequency domain reflectometry

This paper demonstrates that the location in an electric cable where some mechanical distortion appears can be estimated very precisely by a method based on frequency domain reflectometry and inverse fast Fourier transform. A coaxial communication cable insulated by low density polyethylene or a triplex cable insulated with flame-retardant ethylene propylene diene copolymer was distorted at different positions, and electromagnetic waves in a frequency range from one to several hundred MHz or 1.5 GHz were transmitted through the cable. The ratio between the incident power and the reflected power was measured using a network analyzer. As a result, the position in each cable where the distortion was given can be located with a spatial resolution as short as 1.0 cm, which indicates high sensitivity of this method.