How does a metal detector work?

What make a metal detector buzz when you sweep it over buried treasure? Why is it important to keep the detector moving?

  1. A battery in the top of the metal detector activates the transmitter circuit (red) that passes electricity down through a cable in the handle to the transmitter coil(red) at the bottom.
  2. When electricity flows through the transmitter coil, it creates a magnetic field all around it.
  3. If you sweep the detector above a metal object (such as this old gray spanner), the magnetic field penetrates right through it.
  4. The magnetic field makes an electric current flow inside the metal object.
  5. This flowing electric current creates another magnetic field all around the object. The magnetic field cuts through the receiver coil (blue) moving about up above it. The magnetic field makes electricity flow around the receiver coil and up into the receiver circuit (blue) at the top, making a loudspeaker buzz and alerting you you’ve found something.