HOW DO METAL DETECTOR WORKS? ~ Suman Blogz

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How do metal detectors work?

Airport security gates, treasures sweepers for hunting lost change or jewellery on the beach, traffic lights and coin slots in vending machines have one thing common. They all exploit the fact that a piece magnetic force has one or more of its physical properties changed in away that can be picked up by a sensor. Each type of metal detector contains a transmission elements for generating a magnetic field and receiving element for translating a secondary physical change in to an electronic signal that registers on a dial or triggers a sonic alarm.

The simplest of these devices generates an electric current that runs through a coil of wire, producing a magnetic field. When the coil passes over a piece of metal, the metal induces a second magnetic field, which interferes with first one and reverses the flow of electricity in the coil. This reversal is picked up by electronic circuitry. More sophisticated detectors that screen for concealed weapons, bombs or bits of metal contamination food, paper pulp or raw plastic may contain additional coils and computer chips that increases their sensitivity.

Measuring magnetic fields:

When metallic objects pass through a security gate, the flux or strength and extend of the magnetic field, increases. The rise in flux is accompanied by a voltage increase in the current flowing through the receiver coils, which triggers an alarm.

Control box:

To make sure that a security alarm sounds only if there is an unusual amount of metal guards adjust the sensitivity on a control box.

Two magnetic responses:

Nickel, iron and other easily magnetized metals enhances a magnetic field, while copper, aluminium and other less easily magnetized ones do not.

Nickel or iron attracts magnetic lines of forces.

Copper repels the magnetic lines of forces.

Security checkpoint:

To ferret out hidden guns or other weapons, airports and office buildings rely on security gates like the one at right. A series of coils scan a person’s body and alert guards when sizable amount of metals – possibly caused by the presence of weapons – are detected.

Detecting ferromagnetic materials:

The ferromagnetic materials nickel, iron and cobalt become easily magnetized when exposed to as magnetic field. The special metal detector locates buried metals of this sort. The magnetic field in its two coils cancels each other out until exposed to a metal object. Then, the objects induced magnetism trips an electrical gate, sending a low current from the receiver coil to the detector’s electronic circuitry.