Eddy currents

Eddy Currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor, according to Faraday's law of electromagnetic induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced by moving a conductor through a stationary magnetic field or by varying the intensity of a stationary magnetic field around a stationary conductor.

Overview

Eddy currents are named after the vortices or "eddies" that are formed in fluids when the fluid is stirred. Similarly, eddy currents are circular currents induced in conductors when there is a relative motion between the magnetic field and the conductor or when the magnetic field itself changes with time. These currents can generate opposing magnetic fields, which can cause repulsive or drag forces between the conductor and the magnet, a principle utilized in magnetic braking and other applications.

Generation

Eddy currents are generated by the relative motion between a magnet and a conductor or by time-varying magnetic fields. This phenomenon is described by Faraday's law of electromagnetic induction, which states that a changing magnetic field within a loop of wire induces a voltage across the wire, which in turn causes a current to flow. In the case of eddy currents, the "loop" is not a physical wire but a path taken by induced currents within the bulk material of the conductor.

Effects

Eddy currents generate heat as electrical energy is dissipated in the material in which they are induced. This effect is used beneficially in induction heating applications. However, in many other applications, such as transformers and electric motors, eddy currents are undesirable as they lead to energy losses. To minimize these losses, materials with high electrical resistance or laminated magnetic cores are used, which restrict the paths available for eddy currents.

Applications

Eddy currents have a wide range of applications in various fields. In non-destructive testing, eddy current testing is a technique used to detect cracks and defects in metal parts. In electromagnetic braking, eddy currents are used to provide a contactless braking mechanism for trains and amusement park rides. They are also utilized in induction heating for cooking and industrial heating processes.

Mitigation

To mitigate the undesirable effects of eddy currents, several strategies can be employed. Using materials with higher resistivity can reduce the magnitude of eddy currents. Laminating the core material in transformers and electric motors can disrupt the path of eddy currents, significantly reducing their effects. Additionally, designing the magnetic circuit to minimize the area enclosed by the path of the eddy currents can also help in reducing their impact.

See Also

• Faraday's law of electromagnetic induction
• Magnetic braking
• Induction heating
• Non-destructive testing