Metal detector

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Metal detector from World War 1

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Metal detector is a device that responds to the presence of metal nearby. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground. They consist of a handheld unit with a sensor probe which can be swept over the ground or other objects. If the sensor comes near a piece of metal, this is indicated by a changing tone in earphones, or a needle moving on an indicator. The device gives some indication of distance; the closer the metal is, the higher the tone in the earphone or the higher the needle goes. Another common type are stationary "walk through" metal detectors used for security screening at access points in prisons, courthouses, and airports to detect concealed metal weapons on a person's body.

History

The first industrial metal detectors were developed in the late 19th century and were used extensively for mineral prospecting and other industrial applications. Uses include de-mining (the detection of land mines), the detection of weapons such as knives and guns (especially in airport security), geophysical prospecting, archaeology, and treasure hunting. Metal detectors are also used in the construction industry to detect steel reinforcing bars in concrete and pipes and wires buried in walls and floors.

Technology

Modern metal detectors are powered by batteries and use the principle of electromagnetic induction to detect metal. The basic design consists of a coil of wire (the search coil) through which electricity is passed, creating a magnetic field around the coil. When the coil passes over a metal object, the magnetic field induces eddy currents in the metal. These eddy currents generate their own magnetic field, which is detected by a secondary coil or a magnetometer, signaling the presence of metal.

There are different types of metal detectors, including Very Low Frequency (VLF), Pulse Induction (PI), and Beat-frequency Oscillation (BFO). Each type uses a different technology to detect metal objects.

Applications

Metal detectors have a wide range of applications. They are used in:

• Archaeology: to locate and unearth historical artifacts.
• Security: for screening people at airports, buildings, and events to prevent prohibited metal objects from being carried in.
• Construction: to find buried pipes, rebar, and wires.
• Treasure Hunting: by hobbyists looking for coins, jewelry, and other valuable items.
• Military: for mine detection and clearing explosive devices.

Legal and Ethical Considerations

The use of metal detectors is subject to legal restrictions in many jurisdictions. These laws often relate to privacy, property rights, and the protection of archaeological sites. Users of metal detectors must be aware of and comply with any laws and regulations that apply to their activities.

See Also

• Electromagnetic induction
• Archaeology
• Security screening