Active, Passive and Dynamic Shielding of Static and Low Frequency Magnetic Fields

Three kinds of static and low-frequency magnetic fields shielding are known, namely, active, passive and dynamic. In this paper we discuss each of them, while a special emphasis is put on active shielding. Such a shielding uses coils with currents that generate magnetic fields of the same frequency and amplitude as the external field but in the opposite direction. From mathematical point of view these problems belong to ill posed nonlinear inverse problems and require special treatment. A method for designing a shape of the coils is given in the paper.