Transfer impedance of braided coaxial cables under applied longitudinal torsion

The surface transfer impedance ZT of several braided coaxial cables was measured under applied longitudinal torsion to determine the electromagnetic shielding characteristics of the cables under such conditions. The results cover the frequency range 100 kHz to 150 MHz with torsion angles varying between 0°, +360° m¿1 and ¿180°m¿1. It was found that ZT increases with torsion angle and depending on the degree of optimisation in the braid, increases of up to 800% can occur at a torsion angle of 360° m¿1. Further, when a cable is returned to its original position, after being subjected to torsion, the resulting value of ZT is higher than the original value.