Analysis of low-frequency magnetic coupling in cables grounded at both ends

The experiments and theoretical considerations about several cable configurations grounded at both ends are described. The theory of magnetic coupling and shielding is reviewed. In the experiment, a constant magnetic field is generated at 4 frequencies and 10 different cable configurations are tested at each frequency. 40 measurement results are presented and they are compared with 6 measurements in the literature. The results point out that cables grounded at both ends exhibit high susceptibility to radiated electromagnetic interference (EMI) due to the ground loop and it is quite difficult to construct a good cable configuration in this mode. All double-grounded cable configurations have been found to provide poor protection performance against magnetic fields, in the frequency range between 100 Hz and 50 kHz. However, some configurations utilizing magnetic shields made of mumetal are found to be advantageous. Furthermore, cables with a nonmagnetic shield grounded at both ends are shown to provide some protection above the shield cutoff frequency and the results are discussed.