Metal Detectors

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.

The fact is that all of these scenarios are valid.
Metal-detector technology is a huge part of our lives, with
a range of uses that spans from leisure to work to safety.
The metal detectors in airports, office buildings, schools,
government agencies and prisons help ensure that no one is
bringing a weapon onto the premises. Consumer-oriented metal
detectors provide millions of people around the world with
an opportunity to discover hidden treasures (along with lots
of junk).

Anatomy of a Metal Detector
A typical metal detector is light-weight and consists of just
a few parts:

1. Stabilizer (optional) - used to keep the unit steady as
you sweep it back and forth
2. Control box - contains the circuitry, controls,
speaker, batteries and the microprocessor
3. Shaft - connects the control box and the coil; often
adjustable so you can set it at a comfortable level for your
height
4. Search coil - the part that actually senses the metal;
also known as the "search head," "loop" or "antenna"

Most systems also have a jack for connecting headphones, and
some have the control box below the shaft and a small display
unit above.

Operating a metal detector is simple. Once you turn the unit
on, you move slowly over the area you wish to search. In most
cases, you sweep the coil (search head) back and forth over
the ground in front of you. When you pass it over a target
object, an audible signal occurs. More advanced metal
detectors provide displays that pinpoint the type of metal it
has detected and how deep in the ground the target object is
located.

Metal detectors use one of three technologies:

* Very low frequency (VLF).
* Pulse induction (PI).
* Beat-frequency oscillation (BFO).