The purpose of metal detectors is to detect the presence of metallic objects. For this, electromagnetic fields are used. Detectors, which come in different models, can be portable, vehicle-mounted, or used in checkpoint areas.
These devices, used discreetly at entrances to high-security places such as airports, schools, and courthouses, are also preferred for detecting unknown or underground objects.
Metal detectors detect only metallic objects but do not provide any image. For example, scanners or X-ray machines are not classified as metal detectors.
Metal detectors operate based on the electromagnetism system, using two fundamental principles: active and passive.
Active detection method
The active detection method involves a time-varying electromagnetic field. That is, opening the traffic portal or the area in front of the portable unit illuminates the detection zones. The energy passing through the illuminated area detects the presence of the object. The detector measures the values and determines the presence of metal.
Passive detection method
In passive detection, there is no illumination. Objects moving along the detection zone cause temporary but detectable changes in the natural field. Many metals, such as aluminum, are conductive but not ferromagnetic and cannot be detected by passive methods.
Use of detectors in enclosed spaces
Metal detectors are intensively used in enclosed spaces such as airports, public buildings, and military zones. These are framed by two large coils or ring-type antennas. Low-frequency radio waves are transmitted into the detection area by the source coil. The transmitted waves, when hitting an object, trigger temporary receptions on the surface. Thus, an alert is generated.
Portable metal detectors
Metal detectors can be portable. These systems are especially used in security checks to scan objects on the ground. All detectors operate on the same principle. That is, they emit time-varying electromagnetic fields and listen to waves reflected by objects. The quality of detectors becomes evident here. For example, some detectors alert all underground objects, while others reanalyze the received signals and alert only metals. Portable metal detectors have been used for a long time to detect landmines.
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