The majority of underground metal detectors used in the leisure detection use the VLF technology. The VLF band takes place from 3 kHz to 30 kHz in the frequency spectrum. The VLF is the traditional type of technology applied in most requisite or basic metal detectors. In a VLF metal detector, you find two distinct coils, each coil contains a wire coil within it: 1. Transmitter coil: Electric power is sent along this wire coil, first in one sense or direction and then in the other, many times each second. The number of times that the currant's direction switches each second establishes the frequency of the unit. So, single frequency sine wave detectors create an electro-magnetic field, which is transmitted into the ground in a continuous wave. 2. Receiver coil: This wire serves as an antenna to pick up and expand or amplify frequencies coming from objects in the ground.