Magnetic Attraction

Eric Blue
Gwen Jones

Eddy Currents

Eddy Currents are circulating currents that are induced when a conductive object moves through a magnetic field. When a moving conductive object comes within the range of a magnetic field the changing magnetic field induces a current in the conductive object. The currents create magnetic fields that are opposite of the external magnetic field, which is shown through Lenz Law: the direction of the Eddy Current must be opposite to the force that caused it.

Metal Detectors

Within a metal detector there is a transmitter coil and a receiver coil. When the metal detector is turned on an electromagnetic field is generated.

The receiver coil initially registers the electromagnetic field because the receiver coil detects changes and disturbances in the surrounding magnetic field.

After being turned on, the receiver coil detects any changes in the field created by the transmitter coil.

The change is measured by the time taken by the receiver coil to detect the change, and this is sent to the control board and the user can determine what type of object has been detected.

Conductive Objects

As the magnetic field from the metal detector changes, it interacts with any conductive objects it encounters, causing the object to generate weak magnetic fields. Ferrous metals (such as iron), take a longer time to respond initially than non-ferrous metals (such as aluminum) which have a shorter response time. The “Trash Eliminator” works because the time lags between ferrous and non-ferrous metals are slower and faster, respectively.

Only metals are conductive objects; all other materials are non-conductive and thus cannot be detected. That is why a metal detector cannot find a diamond alone, but can find a diamond ring, becaus