What Is an Eddy Current?

This phenomenon of electromagnetic induction occurring inside the entire conductor to generate induced current is called eddy current phenomenon. The longer the outer circumference of the conductor, the higher the frequency of the alternating magnetic field and the larger the eddy current.

Eddy current

As shown in the figure, put a coil around a conductor and let the coil pass in.

Eddy currents, like normal currents, produce thermal effects, and the heat production is somewhat consistent with Joule's law.

Mine detectors work with eddy currents. When a long-handled coil with a varying current is swept across the ground, underground metal objects generate eddy currents in an alternating magnetic field. The eddy currents generate a magnetic field that affects the coil's magnetic field, thereby triggering an alarm. Insulation materials other than metal cannot generate eddy currents, so that mines with metal shells can be detected. ^[3]

Eddy current phenomenon electromagnetic damping

When a conductor moves in a magnetic field, the amperage of the conductor caused by the eddy current always hinders the movement of the conductor.

The electrician's measuring instrument requires that the pointer's swinging stop quickly in order to quickly read the reading (such as ammeter, voltmeter, etc.). To achieve this, the coil of the ammeter should be wound on the aluminum frame. When the measured current passes through the coil, the coil drives the pointer and the aluminum frame to rotate together. When the aluminum frame rotates in a magnetic field, eddy currents are generated. They sway, and the pointer quickly stabilizes to the reading position. ^[2]

Eddy current phenomenon electromagnetic drive

When the conductor is stationary and the magnetic field is moving relative to the conductor, the amperage of the conductor caused by the eddy current will cause the conductor to move.

The AC induction motor uses three-phase electricity to generate a rotating magnetic field to rotate the lead frame.