Definition of Eddy Current

What are Eddy Currents?

Eddy currents are loops of electrical current induced within conductors (any conductive material) by a changing magnetic field in the conductor's vicinity according to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.

The Effect of Eddy Currents

According to Lenz’s Law, eddy currents generate a magnetic field that always opposes the change that caused them. This opposition leads to several noticeable effects in conductive materials exposed to changing magnetic fields:

• Magnetic drag: The interaction between the magnetic field and induced eddy currents creates resistance to motion. This is why a magnet falls slowly through a copper pipe—its motion is dampened by the opposing magnetic force.
• Joule heating: As eddy currents circulate within the conductor, they produce heat due to electrical resistance. This can lead to unwanted energy loss in systems like transformers, electric motors, or induction coils.
• Energy conversion: Eddy currents convert kinetic or electrical energy into thermal energy. In magnetic braking systems, for instance, a moving object's kinetic energy is transformed into heat to slow it down effectively.

These effects are fundamental in both designing and troubleshooting electromagnetic systems, especially where efficiency, heat management, or precise magnetic field control is critical.

How are Eddy Currents Created?

They are induced by changing magnetic fields. They can be created when a conductor is moving through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying i.e. anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field can produce eddy currents.

Factors Influencing the Size of Eddy Currents

The size/intensity of the eddy current is proportional to the change of the magnetic field's intensity in certain directions, the area of the loop and the rate of change of magnetic flux, and it is inversely proportional to the resistivity of the conductor.

Everyday applications where we benefit from Eddy currents

Examples include electromagnetic braking, metal detectors, aluminium can separation non-destructive testing, identification of metals , proximity and displacement sensors, detection of coins in vending machines, and also for measurements of coating thickness.