How does the metal detector work?
According to Lenz's electromagnetism Act, when the conductor falls within a certain range of oscillating (alternating) magnetic fields, it generates its own oscillation fields against the primary field. The magnetometer can pick up the resulting changes in the overall field and signal the close presence of a conductive object, usually a piece of metal. The metal detectors range differs from several feet for the smallest coils, up to 10 feet (3 m) for 12 to 15 inches (30.5 to 38.1 cm) coil.
The key to a functioning metal detector is the presence of whirlpools generated by conductive objects in the environment. Like pushing the paddle through the water lake, it can cause small beliefs to appear on the surface and the producing oscillation fields in the environment cause electromagnetic vortions when electrons in the metal form their own oscillation fields. It is known that the frequency of 3 to 20 kHz brings the best results and some of the more modern metal detectors allow the operator to change the frequency of the AC field.
Another, newer type of metal detector uses technology called pulse induction. This metal detector fires the ground with a large electromagnetic pulse and observes the time required before the voltage is reduced to the ambient levels. If the ground is a conductive object, it will take a longer period of time for the voltage to be reduced. It is a small effect, but modern sensors can pick it up well. This technique has certain advantages over conventional metal detectors, such as the ability to detect objects under highly mineralized "black sand".
Metal detectors are numerous and well known. Perhaps the most important application for any metal detector is to find mines or improvised explosive devices buried just below the surface. In some countries who still remain from the old wars, such as Vietnam, it is recommended to use metal detectors to browse unknown areas known to be at risk of terrestrial mines. This can save many lives.
Another common use for metal detector is the search for a "buried treasure" - coins and relics from years or even millennia in the past. Searching the beach, which has many visitors, can bring lost items from several days. This is not a viable way to earn a living, but some people enjoy it as a hobby.