A VLF metal detector uses Very Low Frequency technology, which is also known as induction balance. VLF metal detectors are probably the most commonly used presently. How a VLF metal detector works is by the use of two coils that create magnetic resistance with objects in the ground.
In a VLF metal detector there are two separate and distinct coils, one on the inside and one on the outside. The first is called the “transmitter coil.” This is the outer coil. Within this loop is a coil along which electricity is sent. Electricity runs through the metal detector coils first in one direction and then in the other, and this happens thousands of times per second. The number of times that the currency changes or switches direction is how the frequency is determined. For example, if your machine has a frequency of 6.6 kHz, this means that the current changes direction at a rate of 6,600 times per second.
The second coil is called the “receiver coil.” This is the inner loop, and it contains another coil of wire. In a VLF metal detector, this wire is an antenna that picks up then amplifies the frequencies that come from metal objects in the ground.
When current moves through a transmitter coil, it creates an electromagnetic field, like the one that is in an electric motor. The magnetic field’s polarity is perpendicular to the coil, and each time the current changes its direction, the polarity of the field changes as well. When the coil is parallel to the ground, a magnetic field is always pushing into the ground then pulling it back out.
When the magnetic field pulses in and out of the ground, it reacts with any objects that conduct electricity, causing them to generate their own magnetic fields. The polarity of the object in the ground is opposite of the transmitter’s field. If the metal detectors transmitter coil’s field is aimed and pulsing down, the objects is now pulsing up. The receiver coil is shielded from the transmitter coil, but it’s not shielded from the magnetic fields that come from the object in the ground. Therefore when the receiver passes over an object in the ground that has a magnetic field – a metal object – an electric current travels to the coil. The coil amplifies the frequency that’s created and you register a “hit” on your metal detector.
In short a VLF metal detector works through coils that can detect metal objects in the ground. One coil shoots a signal into the ground, and the other receives what signals come back. When you go over a metal object, your receiver coil recognizes this and you register a find on your machine. Most are VLF metal detectors, to determine if a VLF unit is the best metal detectors for you, then you need to know what target you are hunting (some resonate better with higher frequencies) and the depth (VLF metal detector has a good compromise between depth of detection and discrimination abilities).
