Metal detectors are devices capable of detecting metals. Devices that receive signals from signals sent underground are called detectors. Detectors usually transmit electromagnetic signals underground and display the received data to the user as a value.
They help detect dangerous objects in military mine searches, weapons, security checks at concerts, airports, and shopping centers, as well as in archaeological and geological excavations. Metal detectors detect metal objects but do not create images.
At airports, public buildings, and military facilities, portable detectors or portals are frequently used. Electromagnetic waves are sent into the detection area by the source coil. When the electromagnetic field of the transmitted wave hits a conductive body, it induces temporary currents on the surface of the body. These currents emit electromagnetic waves.
How does a metal detector work?
Detectors are devices that operate with radio frequency. The coils on them form the receiver and transmitter parts. The electromagnetic wave generated in the transmitter part induces a current when it meets metal.
The current induced on the metal generates a magnetic field, which allows a current to pass through the receiver coil on the detector. The obtained signal is amplified with the help of an amplifier and provides an audio and visual notification. Depending on the power of the detector, it can search up to 12 meters.
The position of the coils on the detector head must be adjusted correctly. A faulty production can cause the coils to influence each other and the detector to malfunction. Depending on the type and size of the metal, there may be variations in the detected magnetic field. The larger the metal surface, the shorter the detection time.
Certain minerals in the soil can increase soil conductivity and cause oxidation of metals, reducing their metallic properties. Natural gas pipelines, water pipes, and electrical cables can lead the detector to false detections.
Types of detectors
Low Frequency Oscillator Detector (VLF)
It is the most commonly used type of detector. It has two coils: receiver and transmitter.
Pulse Induction Detector (PI)
It is mainly used in sensitive works. It has a single coil. It has a wide detection depth range. It is used in saltwater and mineral soils.
Portable metal detectors, small enough to be held in the hand, are usually used at security checkpoints to locate metal objects detected on the human body. Some models are designed to be carried and used for scanning metals in the ground by manual scanning. All these devices operate based on the same variation of the physical principle of the passing metal detector. They emit time-varying electromagnetic fields and listen to signals reflected by objects.
Some ground search detector models analyze the reflected fields in more detail to differentiate various common metals. Portable detectors have long been used for detecting landmines. However, modern mines are mostly made of plastic to avoid this cheap and obvious countermeasure method. For detecting non-metallic mines, new technologies have been developed, especially neutron activation analysis and ground-penetrating radar.
Portal magnetic images are a fairly new technology. They illuminate the detection area with radio frequency electromagnetic waves, like traditional portable detectors. However, they use a series of small antennas arranged in a ring shape around the portal, oriented inward. Each of these antennas transmits to the farthest antennas in the series. A complete scan of the detection area can take place while a person passes through the portal.
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