Eddy Current

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Figure 1. Induced magnetic fields in a loaded coil.

Eddy current is an electrical phenomenon that occurs when a conductor is exposed to a varying magnetic field which causes a current flow within the conductor.

Why "Eddy"?

An Eddy is a term used in fluid mechanics which describes a fluid's swirl and its reverse current after the fluid has overcome an obstacle, like those produced by a dragging oar. A similar phenomenon occurs when a current is induced in a large conductor.

How does it work?

Figure 2. Eddy currents.

Whenever a current travels in a coil, a magnetic field, or electromagnetic induction, is produced around the coil. This is explained by the Faraday's Law of Induction, which states that a change in the magnetic environment of a coil will induce an electromagnetic force in the coil. The polarity of that emf generated by the change in magnetic flux will also produce a current whose magnetic field is opposed to the change that produces it. This is know as Lenz's Law.

Applications

Eddy current is used as a method of measurement, inspection of defects, and correction.