Types of metal detectors by the principle of operation

 A metal detector (metal detector, mine detector) is an electronic device that allows you to detect metal objects in a neutral or weakly conductive environment due to their conductivity. The metal detector detects metal in the ground, water, walls, in wood, under clothing and in luggage, in food, in human body and animals, etc. Thanks to the development of microelectronics, modern metal detectors are compact and reliable devices.

Types of metal detectors by the principle of operation

Devices of the "receiving-transmitting" type. They are based on two inductors - receiving and transmitting, arranged so that the signal emitted by the transmitting coil does not leak into the receiving coil. When a metal object appears near the device, the signal of the transmitting coil -emitted in all directions and enters the receiving coil, is amplified, and fed to the display unit.

Advantages: relatively simple circuitry, ample opportunities for determining the type of detected object.

Disadvantages: the complexity of manufacturing the sensor, the effect of soil mineralization, and relatively low sensitivity.

Induction metal detectors. They are a kind of "receiving-transmitting" device, but unlike the latter, they contain not two, but only one coil, which is both transmitting and receiving. The main difficulty in creating such devices is the allocation of a very small reflected (induced) signal against the background of a powerful transmitter (emitted).

Advantages: simplicity of sensor design.

Devices — frequency meters. They are based Ōnan LC generator. As the metal approaches the contour, its frequency changes. Various methods fix this change:

Mixing the frequency of the oscillator with the reference and measuring the frequency of the beats.

Supplying a signal from the generator to the PLL system and measuring the voltage in the feedback circuit.

Advantages: simplicity of sensor design, simple circuitry.

Disadvantages: worse possibilities of discrimination of detected objects, low sensitivity.

Devices that record the change in the Q factor of the oscillatory circuit, which is part of the LC generator. As a metal object approaches the coil, the Q factor of the circuit decreases, and the amplitude of the oscillations at the output of the LC generator also decreases.

Advantages: simplicity of design, low power consumption.

Disadvantages: low-temperature stability.

Pulsed metal detectors - the principle of operation is based on the excitation of pulsed vortex currents in the zone of location of a metal object and the measurement of the secondary electromagnetic field that these currents induce. In this case, the excitation signal is transmitted to the sensor coil not constantly, but periodically, in the form of pulses. In conductive objects, attenuated induce vortex currents, which excite the fading electromagnetic field. The field, in turn, induces an attenuated current in the sensor coil. Accordingly, depending on the conductive properties and size of the object, the signal changes its shape and duration.

Advantages: insensitivity to mineralized soil, simplicity of the sensor design.

Disadvantages: increased energy consumption, and weak opportunities for discrimination.

In professional metal detectors, several methods of detecting objects can be combined.