Making My Own Metal Detector!
Mention the words metal detector and you'll get completely different reactions
from different people. For instance, some people think of combing a beach in
search of coins or buried treasure. Other people think of airport security, or
the handheld scanners at a concert or sporting event.
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.
U.S. Army soldier uses a metal detector to search for weapons and ammunition in Iraq
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.
Metal detectors work on the principal of electromagnetics and their effects on
conductive metals. There are actually two separate elements in the coil of a
typical unit. One is a high-powered coil of metal which uses the battery power
to generate a penetrating magnetic field. This coil is called the transmitter.
As the elecromagnetic field enters the ground, anything metallic will become
charged with magnetism, similar to a paper clip become magnetized after contact
with a standard bar magnet.
Michael FARADAY observed (1831) that when a magnet is moved through a closed
coil of wire, a current is induced in the wire. The direction of the current
flow is such as to create a magnetic field opposite in direction to that of the
change in the field produced by the magnet. Faraday then replaced the magnet
with an electromagnet.
Two coils were wound close together, the first being connected to a battery and
the second to a galvanometer, which measures small currents.
Metal detectors 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.
Some other uses of metal detecting technology include 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.
Metal Detector for Treasure Hunting? Find out about Metal Detectors at