FAQS About Metal Detectors
How does a metal detector find metal?
a metal detector detects metal through the transmission and reception of
very low frequency (VLF) magnetic waves. Most of today's detectors operate
on a VLF and are referred to as VLF or motion detectors.
magnetic wave is transmitted through the transmitter portion of the detector's
searchcoil, which subsequently generates an invisible, intangible magnetic
field that balloons outward into the surrounding medium, such as air, earth,
clothing, water, etc.. The field size varies depending upon the size of the
searchcoil and the resistance of the medium into which the signal is transmitted.
metal enters this magnetic field, it absorbs some of the field's energy.
The remaining energy causes eddy currents to flow over the surface of the
metal, creating a smaller, secondary magnetic field that also flows into
the surrounding medium.
receiver coil in conjunction with the detector's circuitry measures the field's
power loss and detects the presence of the secondary field. Essentially,
a metal detector "finds" metal by simultaneously interpreting these two effects
and conveys the results via an audio and/or visual alarm.
metals are classified according to their ability to conduct electricity.
A metal is typically referred to as a good conductor (e.g., aluminum, gold,
and silver) or a poor conductor (e.g., iron and stainless steel).
You can find out more information about the art of metal detecting, in Charles Garrett's book, Modern Metal Detectors.
What does a searchcoil do?
searchcoil is the most vital part of a hobby detector. It is the device attached
to the control housing, which "connects" the metal detector to the ground
beneath it. It contains a transmitter and a receiver, which help the detector
retrieve and interpret information about a detected target.
are available in several shapes and sizes to meet a variety of hunting needs.
Generally speaking, small searchcoils are designed to detect small shallowly
buried objects, while large searchcoils are used to find large, deeply buried
objects, such as relics and Caches. Coils can range in size from four to
12 1/2 inches in diameter. An all-purpose detector usually comes equipped
with an eight- or nine-inch searchcoil that is practical for scanning parks,
playgrounds, beaches and other popular coin-hunting locations.
small searchcoil is often used in very trashy areas because its magnetic
field penetrates a small area and therefore is less likely to pick up unwanted
targets like trash. The Garrett four-inch Super Sniper is great for isolating
and identifying coins among trash.
large coil, whose magnetic field is wider and penetrates the ground more
deeply, is best used in relatively clean areas, where there's little risk
of good targets being masked by nearby pieces of junk metal. (Masking is
a phenomenon that can occur while hunting in discriminate search mode instead
of an all-metal or zero discrimination mode.)
Can I identify a detected object before I dig it up?
not 100% of the time. However, recent advances in microprocessor technology
have enabled many metal detectors to avoid trash and to better retrieve and
interpret information about a buried target.
microprocessor-driven detectors can be calibrated to include or exclude certain
metals from detection via a user-adjustable discrimination (also referred
to as elimination) mode. Metals are classified in a linear numerical scale
according their ability to conduct electricity. At the low end of the scale
are iron, foil and nickel, followed by nickel, aluminum and gold in the middle
and gold, zinc and silver at the high end.
discriminating detectors can determine to a relatively accurate degree, the
target's conductivity and if it's a coin, can also determine its depth. But
only Garrett's Power Master DSP-enhanced GTI detectors take target identification
a step further by revealing the target's true size and true depth no matter
what that target is.
GTI's unique ability to go beyond conductivity and retrieve information about
any detected target, including trash, means that you know what the object
is before you dig it up. Thanks to the GTI's easy-to-read Treasure Vision™
screen with graphic target imaging, a drink can is revealed it for what it
really is - a can - NOT a quarter. And it doesn't matter whether the can
is flattened or lying on its side, the GTI still identifies it as a can.
can find out more information about the capabilities and limitations of metal
detectors in the book, Modern Metal Detectors, by Charles Garrett.
At what depths can a detector find treasure?
depends. Many factors can affect how deep a detector can detect, such as
the condition of the soil, the material of a detected object and the quality
of the detector itself. The size and surface area of a target also affects
detection. For example, the larger a metal target, the easier and more deeply
it can be detected. Therefore, it's impossible to predict with complete certainty
how deep a specific detector can be expected to find something.
Generally speaking, a detector equipped with a standard-sized eight- or nine-inch searchcoil can be expected to detect:
Small jewelry (e.g., necklaces, thin gold rings) at 3 to 6 inches
Large jewelry (e.g., class ring) at 6 to 12 inches
Small coins (e.g., dime, penny) at 4 to 6 inches
Large coins: (e.g., quarter, silver dollar) at 6 to 12 inches
Mason jar lid at 9 to 16 inches
Coffee can at 1 to 2 feet
Cannonball, helmet, etc. at 2 to 3 feet
a searchcoil larger in diameter can also help a detector achieve greater
depth. A 12 1/2" searchcoil produces a more extensive magnetic field that
penetrates the ground more deeply to find objects at depths that a smaller
size searchcoil can't reach.
How can I pinpoint a detected target?
Proper pinpointing enables you to recover a detected target quickly without damaging it or the ground above it.
First it is important to ensure you are applying the proper scanning techniques.
and methodically sweep the searchcoil from side to side, keeping it one to
two inches above the surface. Overlap each sweep by advancing the searchcoil
by about one quarter to one half of its diameter. Scanning in a straight
line helps to keep the searchcoil level and the overlap sweeps uniform while
reducing the likelihood of lifting the searchcoil after each sweep.
for a peak in the audio sound. Hold the searchcoil one to two inches off
the ground and slowly sweep it back and forth in an X pattern. Note where
the sound becomes the loudest. The target should be located in the center
of the imaginary X.
What do I need to know about batteries?
(nickel/cadmium) and nickel metal hydrides are rechargeable batteries that
last between 8 and 12 hours and cost up to 10 dollars each. Alkalines are
disposable batteries that last between 25 and 30 hours and cost about two
extreme temperatures can drain battery power, it is recommended that you
always carry a spare set of batteries. In cold weather, attaching the battery
pack to your belt under your jacket can help keep batteries warm and dry.
Is overall depth compromised when searching with discrimination?
To achieve the greatest depths when searching for large, cache sized-objects,
many professionals hunt in the All-Metal mode and use a large searchcoil.