A metal detector is another way of seeing beneath the soil. It helps to find metal objects under the ground from above the ground. It works in the same sort of way as geophysics, but instead of using the Earth's own electrical and magnetic fields, it detects the electrical and magnetic fields of whatever metal objects are buried in the soil.
Metal detectors were originally invented for use by the army, to help soldiers to find bombs or landmines that had been buried during wars. Nowadays, they are usually used for searching for archaeological finds.
Metal detectors can be easily carried around. The metal detector user walks over an area holding the detector just above the ground. Metal detectors use a battery and a coil of metal wire that can conduct electricity to make a magnetic field. When the metal detector is switched on, electricity is passed through the wire coil and it generates a magnetic field around the coil.
This magnetic field is distorted when it is passed over a buried metal object and this change makes a beeping sound that tells you that you have found something. If you try exploring the village of West Mucking you will get the chance to try this! The exact location that the metal detector beeped, called the findspot, is recorded. The archaeologist can then carefully excavate the find spot to remove the object from the ground and see what it is.
When an object is in the ground it is preserved a little, but when it is removed from the ground it can start to very gradually rot away. It’s little bit like keeping a sandwich in the fridge – once you take it out of the fridge it slowly starts to go yucky! That’s why the object has to be carefully looked after when it has come out of the ground.
Metal detectors are good for finding objects that are near to the surface of the ground. They can also help find archaeological features like pits, ditches, walls or kilns as these things are sometimes made with material that has magnetic bits in it.