A
metal detector is a portable electronic device that penetrates the
ground magnetically in order to find traces of metal. This metal could
either be discarded pieces of aluminum or valuable coins, jewelry, or
other buried treasures. Part of the appeal of using the device is this
unknown factor, keeping amateurs and professionals on a constant scan
for new sources of metal and more promising locations. These tools can
usually penetrate sand, soil, wood, and other non-metallic substances,
making most areas fair game for treasure hunters.
A
basic metal detector consists of an electronic box and battery case on
one end, with a brace or handle for the operator’s arm. An insulated
wire wraps around a telescoping shaft and into a round plastic disk
called the coil. This disk comes off the shaft at an angle, which allows
it to be held parallel to the ground. The operator straps on or grips
the electronic box and turns on the power. The idea is to slowly sweep
the coil end over the ground until an electronic signal is heard. This
lets the user know that some metallic element is buried directly beneath
the area swept by the coil.
Some
devices can discriminate between various metals, allowing users to
decide if a particular discovery would be worth digging up. A
significant percentage of hits are indeed pieces of metallic trash or
discarded building materials. Part of the appeal of this hobby, however,
is discovering a lost class ring or a piece connected with local
history. Some professional treasure hunters use very discriminating
detectors set only for valuable metals, but hobbyists tend to explore
even the less lucrative hits.
Metal
detectors work on the principle of electromagnetics and their effects
on conductive metals. There are actually two separate elements in the
coil of a typical unit. The first is a high-powered coil of metal called
the transmitter that uses the battery power to generate a penetrating
magnetic field. As the elecromagnetic field enters the ground, anything
metallic will become magnetized, similar to how a paper clip reacts
after it comes into contact with a standard bar magnet.
The
coil also contains a very sensitive wire array called the receiver.
This receiver reacts to any charged magnetic field it passes over,
especially the newly-magnetized metal elements. When the receiver
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. The phase shifts of all
other metallic elements are electronically squelched by the
microprocessing unit.
These
devices must also be adjusted to eliminate false positives generated by
natural deposits of metal in the soil or sand itself. Most units allow
users to change the sensitivity of the coil in order to cancel out the
background clutter. Metal detecting technology is also used for security
inspections at airports, government buildings, and other public places.
Construction crews and woodworkers also use hand-held metal detectors
to find dangerous nails or other metallic debris in reclaimed building
materials and trees.