Inductive coupling
A time varying external current i1(t) generates a magnetic field B(t), which induces a disturbing voltage udist(t) in a neighbouring circuit. In an equivalent circuit model this may be described by a coupling of both circuits via a coupling inductance M. The voltage udist(t) generates a common mode current i2(t), which itself generates a magnetic field to weaken the external field. The current i2(t) is superimposed on the currents of the disturbed system and may lead to malfunctions of the system. The coupling of magnetic fields of the different systems can be modelled by an equivalent circuit model by mutual inductances of the coupled circuits (Figure 4).