Eddy currents: Induced currents in conductive materials

Eddy currents are electric currents that occur in conductive materials when they are exposed to a changing magnetic field. These currents flow in a circle in the plane of the conductive material and generate their own magnetic field, which is opposite to the original magnetic field. The phenomenon was first described by the French physicist Jean-Bernard Léon Foucault in 1851, which is why eddy currents are also known as Foucault currents.

How do eddy currents occur?

Eddy currents are caused by **electromagnetic induction**, a principle discovered by Michael Faraday. When a conductive material is placed in a changing magnetic field or moves through a magnetic field, electrical voltages are generated in the material. These tensions lead to circular currents, known as eddy currents.

The strength of the eddy currents depends on various factors:

• The speed of the magnetic field change
• The conductivity of the material
• The geometry of the conductive material

Negative effects of eddy currents

In many applications, eddy currents cause unwanted energy losses, which are referred to as **eddy current losses**. These losses occur due to the conversion of electrical energy into heat and are particularly problematic in:

• Transformers: Eddy current losses in the core material lead to heat generation and reduce efficiency.
• Electric motors: The heat generated by eddy currents can reduce the service life of the components.
• Generators: Unwanted currents can impair energy conversion.

Reduction of eddy currents

To minimise losses due to eddy currents, various measures are taken in technical applications:

• Laminated cores: In transformers and electric motors, the core materials are produced in thin layers, known as laminations, which are electrically insulated from each other. This significantly reduces eddy currents.
• Use of special materials: Materials with low electrical conductivity, such as ferrites, are often used to minimise eddy currents.
• Optimised geometry: The design of the components can be adapted to minimise the areas in which eddy currents can flow.

Positive applications of eddy currents

Although eddy currents are often regarded as a loss factor, there are also applications in which they can be utilised in a targeted manner:

• Eddy current brakes: These brakes utilise the thermal energy generated by eddy currents to slow down movements, e.g. in trains or fitness equipment.
• Induction heaters: Eddy currents are specifically generated in a material in order to heat it quickly and efficiently.
• Non-destructive material testing: Eddy current testing is used to detect defects or irregularities in materials, particularly in aviation and manufacturing.

Interesting facts about eddy currents

Did you know that eddy currents even occur in nature? When a conductive material, such as an aluminium ring, falls into a strong magnetic field, the eddy currents create a repulsion between the ring and the magnet. This principle is often used in experiments to demonstrate the basics of electromagnetic induction.