Metal Detector Principle
Metal detectors are electronic devices designed to detect metals, whether in their mineral form
or objects made of various metals such as gold, silver, and copper, for example gold coins, bronze
statues, or swords made of steel … etc.
The types of metal detectors vary according to the search technology present in the device and are
classified according to the research technology used according to the following:
Refer to the article: Metal Detectors Types for more details on each type.
The technologies present in these devices vary greatly and depend on various physical and electronic principles.
In each technology, certain tools are used for conducting search, for example antennas in long-range devices
and search coils in electromagnetic detectors.
In general, all devices contain an electronic circuit consisting of various elements to address the coming signals
from the search tool and then output the signal in some way, for example, as a number displayed on the screen
in electromagnetic metal detection devices or in the form of three-dimensional imaging displayed on a screen
or tablet as in imaging devices.
Applications & Uses of Metal Detectors
- Detection of ancient and antique coins of historical value that were made of gold, silver, copper, or bronze.
- Detection of raw gold (natural gold ores) in the earth’s crust in the form of small grains in some regions
such as Africa, or in the form of metals mixed with other minerals or in the form of rock clusters called veins of gold.
- Prospecting for metals in their natural form, such as silver – copper – iron.
- Searching for lost objects on the seashore or in rivers, as well as in parks and forests, for example, a gold ring – steel chain – gold jewelry – earrings …
- Excavating ancient relics from the remnants of historical civilizations
such as Roman, Persian, Babylonian… etc. Example: a statue made of bronze – an ancient mausoleum – a box containing gold coins, etc.
Metal Detector Principle
Electromagnetic metal detectors are the most widespread and diversified metal detectors due to their ease of manufacture,
economic prices and low production costs, as well as their spread among searchers and prospectors from amateurs and professionals.
There are many international companies that manufacture electromagnetic metal detectors, such as the American Fisher and Garrett,
Research techniques in electromagnetic metal detectors are classified into two main technologies:
1 – Very Low Frequency Technology – VLF
2 – Pulse Induction Technology (PI)
In the following paragraphs, we will give a detailed explanation of how the two technologies work, and the benefits and features of each technology.
Very Low Frequency Technology – VLF
VLF, also known as induction balance, is probably the most popular detection technology in use today among metal detectors due to its low production cost,
ease of manufacture, and the availability of electronic components and components.
In a metal detector that works according to the VLF technology, there is within the search tool,
which is the so-called search file or coil inside the plastic cover, two electrical coils of copper:
- Transmitter Coil
It is a coil of copper wire, wrapped several turns on each other and through which the electrical current coming from the
power source – usually ordinary batteries or lithium – ion batteries – is passed first in a particular direction and then in
the other direction or the opposite, thousands of times every second.
The number of times the direction of the current electric current changes every second reflects the search frequency,
which is usually measured in kHz unit, which is the number that expresses the device, where in some devices there
is only one search frequency, for example, 61kHz like a Gold Kruzer device, or there are several frequencies
available (for example 5-10-20 kHz )as in Impact Pro.
In some modern devices, as in the Equinox device from Minlab, several search frequencies can be used simultaneously
It is called concurrent multi-frequency technology Multi-IQ
See Equinox device link for more on available technology
- Receiver Coil
It is a coil similar to the structure of the transmitting coil (a coiled wire from several windings), but here this coiled wire works
as an antenna to capture and amplify the coming or reflected signals from the target objects in the ground, and that is where
the magnetic field resulting from the current passes within the coil is sent to a metal body underground Like a coin
, a reflex magnetic field is formed whose signal is received by the receiving coil.
How does the VLF metal detector distinguish between different minerals? It depends on a phenomenon known as the phase shift.
The phase shift is the difference in timing between the frequency of the transmitted magnetic field and the frequency of the magnetic
field reflected from the metal target.
That is, a target with a high induction will have a greater phase shift, because it takes longer to change its magnetic field.
A metallic object with a high electrical resistance will have a smaller phase shift and thus a distinction can be made between
metals and knowledge of the type of metal according to this shift as the received electrical signals are converted to a digital signal
displayed on the device screen in a digital form called a digital target identifier (Target ID) indicating the nature of the metal
if it is a ferrous magnetic metal or non-ferrous, such as gold, silver, and copper, as well as the device beeps in the form of an audible tone.
In some devices, a range of tones can be set according to the target ID.
Example of VLF Metal Detectors
Impact Pro gold and metal detector device is a new reliable device for any gold seeker
and treasure hunter in the world which offers best great performance at best economic price.
Impact Pro is a first device that combines modern robust design with most recent technologies
in metal detection field that enable to uncover deep hidden gold treasures and metals.
Impact Pro is a multi-frequency metal detector with 3 operating frequencies to enable searching
for different targets and metals like coins, relics, gold nuggets and treasures.
Impact Pro can also operate in all different terrains including rocky lands, wet beach sand, mineralized ground and so,
thanks to its built-in 12 search modes enabling detection of all types of targets.
Garrett ACE APEX
Garrett Ace Apex is a new innovative metal detector with new Garrett’s Multi-Flex technology a multi-frequency
feature introduced in Nokta Impact and Minelab Vanquish, but with best performance and sensitivity.
Multi-Flex technology give the prospector a wide variety in detection applications for different types of ferrous
or non-ferrous metals and detection of buried objects at different sizes in all terrain and soil types.
Garrett Ace Apex combines modern design with a large screen with excellent performance, excellent detection
depth on a wide variety of targets, plus a fast target recovery speed and a variety of practical uses
that suit all the needs of prospectors and treasure hunters.
Garrett Ace Apex is a metal detector that must be acquired by the prospector in order to discover
precious objects and hidden gold at a competitive price.
Gold Monster 1000
Gold Monster 1000 a simple easy to use gold detector device developed exclusively for natural gold nuggets detection in all terrains.
Gold Monster 1000 is the easiest gold detector to use, thanks to its simplicity and unique features like gold chance indicator
and automatic ground balance plus minimum controls need.
Despite of its simplicity, Gold Monster 1000 is effective device and includes latest advancement in natural gold detection
technology that offers high-end performance and reliable results.
Gold Monster 1000 includes enhanced ferrous/non-ferrous discrimination and works effectively in any type of soils
like salty soils better than any rival higher frequency metal detector, making it the most suitable device to maximize gold nuggets detection recovery.
Gold Monster 1000 combines super performance at a great price in one compact package,
and thus it is the perfect choice for any gold prospector in the world.
Pulse Induction (PI)
Pulse induction metal detectors are electronic devices that operate according to the pulse induction technology
which depends in turn on the principle of electromagnetic induction.
Unlike VLF technology, pulse induction metal detectors use one coil i.e. one electrical coil such as a transmitter
and receiver, or there may be two or even three coils working together for better performance and faster and accurate results.
The coming electric current in the coil is passed make a strong, short pulses of current through coils of wire.
Each pulse generates a short magnetic field. When the pulse is over, the polar magnetic field reflects and suddenly collapses
, causing a sharp electrical rise. This rise continues for a few microseconds (a millionth of a second)
and causes another current to pass through the coil.
This current is called the reflected pulse and is very short and lasts only about 30 microseconds.
Then another pulse is sent and the process repeats. A typical pulsed induction metal detector sends about 100 pulses per second,
but the number can vary greatly depending on the manufacturer and model, starting from twelve pulses per second to more than a thousand pulses per second.
If the metal detector is on top of a buried metal object, the pulse creates an opposite magnetic field in the object. When the magnetic field of the pulse collapses
causing the reflected pulse, the body’s magnetic field makes it take longer for the reflected pulse to disappear completely.
This process works something like an echo: if you scream in a room with a few hard surfaces, you may hear an echo too short, or you may not hear a sound at all;
But if I shout in a room with a lot of hard surfaces, the echo will last longer. In a metal detector with a pulse-induction technology, the magnetic fields of the target
bodies add an “echo” to the reflected pulse, making them last longer than they would have needed without them.
Example of Pulse Induction Metal Detectors
GARRETT ATX the most powerful natural gold detector with high sensitivity for detection of tiniest gold nuggets underground.
Garrett ATX uses a unique Pulse Induction technology that gives most accurate and reliable results
with extreme gold sensitivity to locate tiny gold nuggets in all hard terrain.
Garrett ATX is a versatile device can be used for many purposes and metal detection activities
like gold prospecting, relic hunting and coins shooting and so on.
Garrett ATX is a robust machine that give the prospector best performance in most hard terrains like rocky lands
and sandy soils thanks to its robust design and advanced features.
Pulse Dive is a set of two devices in one package including scuba metal detector and pin pointer.
Pulse Dive is a perfect choice for any professional prospector who work often to find gold or other metals
underwater like in lakes or rivers or oceans, it is also a must have tool for any diver who want to find hidden treasures underwater.
Pulse Dive scuba detector works using Pulse Induction technology which offer best performance and detection capabilities for different metal objects.
Lorenz Deep Max Z1 a most reliable metal detection device in the world,
It is probably one of the most sensitive and stable metal detecting devices of its kind presently available.
Lorenz Deep Max Z1 is most powerful device for detection of ferrous or non-ferrous metals underground,
thanks to its unique Pulse Induction system which is a result of many years of research and development.
Lorenz Deep Max Z1 includes a lot of useful features for metal detection like automatic ground balancing
facilities and easy operation via simple buttons.
Lorenz Deep Max Z1 works perfectly with great performance in all terrains and conditions and almost
unaffected by salt water, most types of mineralized grounds or temperature.