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How_Do_Metal_Detectors_Work
| How Do Metal Detectors Work?
In 1881, Alexander Graham Bell constructed one of the worlds
first metal detectors in an attempt to find an assassin's bullet
in President James Garfield. Fischer patented a portable version
in 1931. From treasure hunting to security screening, metal
detectors are used in many a field.
Metal detectors are electronic devices that are used to find
traces of metal usually from the ground, a person, or cargo.
This metal could be anything from discarded pieces of aluminum
to buried treasures. These devices can penetrate sand, soil,
wood and other non-metallic substances.
A basic metal detector consists of an electronic box and a
battery case on one end, with a handle for the operator's arm.
There is a coil, which consists of an insulated wire around a
telescoping shaft and into a round plastic disk. This disk comes
off the shaft at an angle, which allows it to be held parallel
to the ground. The operator grips the electronic box and turns
on the power to slowly sweep the coil end over the ground until
an electronic signal is heard. This indicates the presence of
some metallic element buried beneath the area swept by the coil.
Metal detectors work on the principal of electromagnetism and
their effects on conductive metals. The high-powered coil of
metal, called the transmitter, uses the battery power to
generate a penetrating magnetic field. As the electromagnetic
field enters the ground, anything metallic will become charged
with magnetism. When the receiver in the coil detects the
electromagnetic signature, it sends a signal to the electronic
box. A speaker amplifies this signal and the operator hears a
beep. Microprocessors located in the electronic box can actually
measure the time between the charging and the receiving (called
a phase shift) and determine which metals may be present. This
is how high-end metal detectors can be adjusted to only search
for certain metals.
Metal detectors use one of three technologies:
A beat frequency oscillator detector uses a coil as an inductor
in an oscillator. When its frequency changes, so does its
inductance. Another oscillator produces a close frequency, and
audible beats between them signal metal.
An induction balance detector uses two coils that overlap each
other. A sine wave is transmitted with one coil and received
with the other. The coils are adjusted so that there is no
signal in the receiving coil when there is no metal nearby.
A pulse induction detector generates pulses by cutting off an
indicator. This pulse is sent through a coil and the detector
listens for echoes.
About the author:
Metal Detectors
Info provides detailed information about walk-through,
hand-held, and used metal detectors, as well as reviews of best
metal detectors. Metal Detectors Info is the sister site of Security Cameras
Web.
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