Most of today’s commercial metal detectors consists four main components; the Stabiliser, the control box, shaft and most importantly the search coil. The idea of VLF is simply the usage two coils where the transmitter emits an electric impulse in a very low frequency and receiver coil, where its wire of the coil is used as an antenna picks up any reflected from any metallic objects in the searched area.
Firstly, the current comes from the control box, which contains the batteries, sends down Alternating Current (AC) along the wire around the shaft to the Transmitter coil. As electrons pass through the loops of wire (inductor) in the coil, it creates an electromagnetic field. As the current changes direction thousands of times per second in the coil, so does its polarity; the frequency of the unit, from negative to positive. This results in the electric field being in constant motion, pushing into the ground then pulling out of it.
If there is a metal in the vicinity of the electric field, the metal, because of its high electric conductivity, will induce an electric current of its own. Simultaneously, the metal will produce its own magnetic field, opposite to that from the Transmitter coil. The Receiver coil, acting as an antenna will pick up the signature of the opposing magnetic field. This will lead to current passing through the speaker, where the small magnet will vibrate as electrons flow through. The vibration will in turn, create sound; alerting that metal has been detected.
More modern, high tech metal detectors consist of more sophisticated components that allow it to calculate the type of the metal being detected. All metals have different inductance, its ability to conduct electricity, as some metals being more resistant to electricity than others. More inductive metals has a larger phase shift than the more resistant ones, and will therefore be slower to react if the current changes. VLF metal detectors will be able to compare the magnitude...