Metal detector (metal detector) is an electronic device that detects the presence of valuable things nearby. It is useful for detecting objects hidden inside objects or underground. How does a metal detector work and what is inside it?
What is it made of?
It often consists of a portable device with a sensor. If the device approaches a metal object, the tone in the headphones starts to change or the indicator arrow moves. Usually the device also gives an understanding of the distance to the object and depends on how deep the metal detector works. You can understand this by the changing tone in the headphones or by the indicator.
Another common type is the stationary version used to check prisons, courthouses and airports for weapons.
History of Creation
By the end of the 19th century, many scientists and engineers used their accumulated knowledge in the fieldtheories of electricity, trying to invent a machine capable of accurately giving out the necessary information. Using such a device to find ore-bearing rocks would give a huge advantage to any miner, for which it would be enough to explain to him how it works.
Early machines were underdeveloped, used too much power and only functioned under very limited conditions.
In 1874, Parisian inventor Gustave Trouvé developed a hand-held device for detecting and extracting metal objects such as bullets. Inspired by Trouvé, Alexander Graham Bell developed a similar device to try to detect a bullet in the chest of US President James Garfield in 1881. It worked correctly, but the attempt failed because Garfield's spring bed made adjustments.
The simplest form of a metal detector consists of a generator that creates an alternating current that passes through a coil of magnetic field. If a piece of electrically conductive object is near the coil, eddy currents will be induced in it, creating its own magnetic field.
Beginning of modern developments
The modern development of the metal detector began in the 1920s. Gerhard Fischer reasoned that if the radio beam could be distorted, then it should be possible to develop a machine that would detect metal using a search coil resonating at radio frequency.
In 1925, he applied for and received the first patent. Although Gerhard Fischer was the first to patentmetal detector, the first to apply was Shirl Herr, a businessman from Crawfordsville, Indiana. His application for a portable metal detector was filed in February 1924, but not patented until July 1928.
Herr assisted Italian leader Benito Mussolini in searching for items left in the galleys of Emperor Caligula at the bottom of Lake Nemi in Italy in August 1929. The invention was used on Admiral Richard Byrd's second Antarctic expedition in 1933 to discover objects left behind by earlier explorers.
Kosatsky's invention
The design invented by Kosatsky was widely used during the Second Battle of El Alamein, when 500 units of this device were sent to Field Marshal Montgomery to clear the minefields of the retreating Germans, and then used during the Allied invasion of Italy and Normandy.
Because the creation and improvement of the device was a wartime research operation, the fact that Kosatsky created the first practical metal detector was kept secret for more than 50 years.
Further development of the industry
Many manufacturers of these new devices have submitted their ideas to the market. White of Oregon Electronics began in the 1950s with a machine called the Oremaster Geiger Counter. Another leader in detector technology was Charles Garrett, who pioneered the BFO (Beat Frequency Oscillator) machine.
With the invention and development of the transistor in the 1950s and 1960s, metal detector manufacturers and designers developed lighter machinessmaller with improved circuitry, running on small batteries. Companies have sprung up across the United States and the UK to meet growing demand.
Modern top models are fully computerized and use integrated circuit technology, allowing the user to set sensitivity, discrimination, track speed, threshold volume, filters, and so on.
Invention of discriminators
The biggest technical change in the detectors was the development of the induction balance system. It included two coils that were electrically balanced. When metal got into their vicinity, they became unbalanced. This allowed the detectors to distinguish colors because each metal has a different phase response when exposed to alternating current.
Over time, detectors were developed that could selectively detect desirable metals while ignoring unwanted ones. Even with the discriminators, it was still difficult to avoid unwanted metals because some of them had similar phase characteristics, such as foil and gold, especially in alloy form.
Thus, improper adjustment of some detectors could increase the risk of confusing the valuable with the cheap. Another disadvantage of discriminators was that they reduced the sensitivity of the detector.
What other metal detection methods are there?
At the same time, the developers considered the possibilityusing a different metal detection method called pulse induction. Unlike the beat frequency generator or induction balancers, which used a uniform alternating current at a low frequency, the pulsed induction machine simply magnetized the ground with a relatively powerful instantaneous current through the search coil. In the absence of metal, the field decayed at the same rate. You could even measure the decay time.
These timing differences were minor, but advances in electronics made it possible to accurately measure them and determine the presence of metal at a reasonable distance. The new machines had one major advantage: they were largely immune to the effects of mineralization. The addition of computer control and digital signal processing further improved the pulse induction sensors.
Where else is a metal detector used?
Instruments were widely used in archeology in 1958. However, archaeologists have opposed their use by artifact seekers or marauders whose activities destroy archaeological sites.
The problem with their use in excavation sites by amateurs who find objects of archaeological interest is that the context in which the object was discovered is lost and a detailed survey of its surroundings is not carried out.
Hobby use
There are different types of metal detector hobbies. For example, many hobbyists are looking for valuable compounds such as gold, silver or copper. They are most often found inthe form of nuggets or flakes. But there are other kinds of hobbies.
Search for discarded or lost items. Most often, people lose jewelry, phones, cameras and other devices. This happens, for example, in parks where there is a large layer of fallen leaves. At what frequency does a metal detector work for these purposes? The most common indicator is the frequency of 7-8 kHz.
Searching for ancient artifacts is a hobby that requires more professional metal detectors, as well as significant experience in this matter. Coins, bullets, buttons, axes or buckles can be buried quite deep. In order not to damage them when digging, a person must know some rules. A frequency of 8.23 kHz works well for this.
Searching on the beach is quite common. Dropped a ring or a few coins on the beach and did not even notice, which is what treasure hunters use. After the bulk of the people leave the beach, they begin to search for these lost things. There is also a metal detector that works underwater, but you can wait for low tide, and then search with a conventional detector.
Joining numerous treasure hunt clubs is another hobby. Such clubs are located in the USA, Great Britain, Canada and many other countries. Here beginners can learn how to operate a metal detector and share their findings.
Homemade Assembly
With the development of technology, such a device can be assembled even at home. How does the "Pirate" metal detector work and how does it work?collect? Making homemade electronics is very dangerous. If you are not a professional, this is highly discouraged.
Basic and versatile assembly materials and tools:
- NE555 board (or similar KR1006VI1);
- transistors IRF750 or IRF740;
- K157UD2 microcircuit and transistor VS547;
- PEW wire 0.5;
- NPN transistors;
- soldering iron, wires, other tools.
How does the "Pirate" metal detector work? Just like any other. The only negative is the lack of discriminators, which means he will not be able to notice non-ferrous metal.
How to use it correctly?
If you have made your choice, you should know how to work with a metal detector. It does not matter at all whether it is homemade or not, the principle of operation is the same for everyone.
Let's analyze the operation of the device using the Garret ACE-250 metal detector as an example. It can be purchased for up to 20 thousand rubles, and it is an ideal choice for beginners. There is a more professional version (ACE-250 Pro) in the ACE-250 line, but it differs only in the frequency range.
How does a Garrett metal detector work? Since this version was created for beginners, the frequencies made it possible to search only for small objects at an average depth. It has several modes such as Ornaments, Relics, Coins, Any and Custom.
For beginners, the Custom mode will be useless, so it's betterwill use the first four options. From their name it is clear where and for what they are useful. It is quite easy to figure out how the Garrett metal detector works, because all the settings are made in advance.
For more professional searches, you can look at the following models:
- Garrett ACE 350;
- Minelab X-TERRA 505;
- Bounty Hunter Platinum PRO;
- Tesoro Cibola.
Security check
Not all metal detectors are small. A series of hijackings in 1972 brought technology to screen airline passengers in the United States. The Finnish company Outokumpu in the 1970s adapted mining metal detectors, still housed in a large cylindrical tube, to create a commercial walk-through security detector.
In 1995, systems such as the Metor-200 appeared, with the ability to indicate the approximate height of a metal object above the ground, which allowed security personnel to quickly determine the source of the signal. Small hand-held metal detectors are also used to more accurately identify weapons placed on a person's body and clothing.
