Proximity effect (electromagnetism)

In electromagnetics, proximity effect is a redistribution of electric current occurring in nearby parallel electrical conductors carrying alternating current (AC), caused by magnetic effects. In adjacent conductors carrying AC current in the same direction, it causes the current in the conductor to concentrate on the side away from the nearby conductor. In conductors carrying AC current in opposite directions, it causes the current in the conductor to concentrate on the side adjacent to the nearby conductor. Proximity effect is caused by eddy currents induced within a conductor by the time-varying magnetic field of the other conductor, by electromagnetic induction. For example, in a coil of wire carrying alternating current with multiple turns of wire lying next to each other, the current in each wire will be concentrated in a strip on each side of the wire facing away from the adjacent wires. This "current crowding" effect causes the current to occupy a smaller effective cross-sectional area of the conductor, increasing current density and AC electrical resistance of the conductor. The concentration of current on the side of the conductor gets larger with increasing frequency, so proximity effect causes adjacent wires carrying the same current to have more resistance at higher frequencies.