How do hobby Metal Detectors work?
The most basic form of a metal detector is made up of an instrument called an oscillator that sends off an alternating electrical current that moves through a coil which creates an alternating magnetic field.
Metal has properties that allow it to conduct electricity. When a piece of metal is near by the alternative current being produced by the coil something called eddy currents will be induced in the metal. This eddy current coming from the metal produces an alternating magnetic field of its own which is detected by another coil within the device which is called a magnetometer. So the metal causes a difference in the magnetic field which can be identified.
When the metal detector identifies an anomaly in the magnetic field caused by a piece of metal various electronic instruments feed this information to the user. This can take the form of a sound,vibration or even a visual cue on an LCD screen.
Sophisticated metal detectors not only indicate the presence of metal but can also indicate the depth of the metal under the ground, the size of the metal detected as well as the type of metal. Different metal give off different types of eddy currents when within a magnetic field and can thus be singled out.
One can also set the sensitivity of your hobby metal detector so that deeper or shallower items can be found and one can metal detect over very trashy soil. Trashy soil is soil filled with bottle caps and other metal items of no value. Unfortunately much of the hot spots for hobby metal detecting in South Africa are trashy.
A metal detector may even screen out certain types of metal. For example you can set your detector to pick up only gold or only silver and exclude iron. This also helps avoid trash.