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History of the metal detector
History of the Modern Metal Detector                                                                          by Patrick O'Masters



Since man first discovered that metal was useful he has found myriad ways to utilize it. It has been used
for trade, tools, machines, art, and in so many other ways that it would be almost impossible to imagine
life today without it. As we found more and more ways to manipulate metals to our benefit it also was
used for harm. It is recorded in ancient manuscripts that approximately 200 years B.C. a Chinese
Emperor who was fearful of being assassinated constructed the first metal detector, a special doorway
built to attract iron weapons hidden under the clothing of visitors to his palace. The doorway was
reportedly made of a magnetic mineral like magnetite (lodestone) which had been heated and
hammered to enhance it's magnetic properties. Visitors may have also been "scanned" with lodestone
bits hanging from a string passed across their bodies.

As we learned how to harness the properties of metals to improve life we also learned how to use
magnetism for communication over distances. An effect of conducting electricity through a wire
conductor induces a magnetic field around that conductor. Experiments in the 1830's on both sides of
the Atlantic ocean studied the effects of electromagnetic induction which led to the invention of the
telegraph and later the telephone. As telephone technology was being advanced electromagnetic
induction was found to interfere with telephone signals transmitted on wires close to telegraph wires.
Alexander G. Bell was experimenting with conductor configurations when he accidentally discovered
that his patented "balanced" two wire system which eliminated interference was subject to a different
type of interference when he passed a silver coin across the two conductors. He and acquaintances
continued experimenting with coils and induction with the hopes creating a device to find underground
metallic ore deposits but a twist of history found the device being used in an attempt to locate a bullet in
a dying President Garfield who had been shot in the back. The seeds of the first modern metal detector
had been planted.

Pass-through metal detectors were later created to reduce theft at factories and found their way as
security devices in courthouses and airports. Metal detectors have also been used to save lives in the
battlefield detecting land mines. Later the hobby of "radio prospecting" began as surplus machines
were used by soldiers who had returned home and realized their detectors could be used to find buried
relics. The metal detector has not changed much over time but what has changed is the way that the
signal is processed by the equipment giving the modern detectorist a machine which can interpret what
type of material passes under his or her detector's coil and even eliminate the signal of undesirable
metals. Some detectors are very sensitive to small bits of gold and some over very great depth but with
little exception they operate on the same principle; a series of magnetic pulses is sent out from
transmitter coil which induces weak electromagnetic field around a metallic object buried in the ground.
The machine then detects and interprets the frequency of the signal being returned from the object. One
exception would be metal detectors that emit a radio frequency signal. A metallic object will interfere
with the signal frequency, the machine then interprets that interference.

The biggest recent change in metal detectors are the additions of microprocessors, global positioning
technology, programmablity, and internet connectivity. While these additions definitely make the modern
machine a more flexible and capable tool, no bells and whistles will change the fact that it will always
take time and practice for the detectorist to learn how to properly use their machine.


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