Attenuation of low frequency magnetic fields using active shielding

Attenuation of environmental low-frequency magnetic fields is important to reduce undesirable electromagnetic interference on electric and electronic equipment. This paper presents an analytical study of an active shielding arrangement to attenuate the 60 Hz magnetic fields produced by a transmission line at p points inside a cubic space. The shield consists of three sets of n orthogonal square coils, placed around the x, y and z-axes. Each coil is energized independently by a current source in such a way that all the B_x, B_y and B_z values detected at the p points, are cancelled when the set of coils generates opposite components. Computer simulation is performed to demonstrate the attenuation achieved and the current requirement for each coil.