Metal detector of transmitting and receiving antennas

Metal detectors are designed to detect special foil bags that are used by attackers for shoplifting. Such metal detectors are also called foil detectors or foil bags. They can be made as separate antennas installed at the entrance to the store or integrated into anti-theft systems. When you make a foil bag in the store, an alarm is issued and now the store staff will know that a potential thief has entered the trading floor.
Structurally, the metal detector consists of a transmitting and receiving antennas located at a distance from each other, the main electronics unit, connecting cables.
The gap between the antennas is considered to be the test area.

The principle of operation of the metal detector is based on the assessment of changes in the parameters of the magnetic flux in the controlled area of space when moving a metal object in it, the dimensions of which exceed 200x300 mm.

To search for a metal object in the control area, digital signal processing is performed in the main electronics unit. When moving the search object through the controlled opening metal detector produces light (changing the illumination of the antennas) and an alarm sound from the emitter built into the main electronics unit.