A metal detector (metal detector) is an electronic device that detects the presence of valuables nearby. It is useful for detecting objects hidden inside objects or underground. And how does the metal detector work and what is inside it?
What does it consist 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 movement of the arrow of the indicator appears. Typically, 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 stationary versions used to check for weapons in prisons, courthouses and airports.
History of creation
By the end of the 19th century, many scientists and engineers used their accumulated knowledge in the field of the theory of electricity, trying to invent a machine that could accurately provide the necessary information. Using such a device to search for ore-bearing rocks would give a huge advantage to any miner, for which it would be enough to explain to him the principle of work.
The early cars were unfinished, used too much energy, and functioned only in very limited conditions.
In 1874, Paris inventor Gustav Truve developed a hand-held device for detecting and retrieving metal objects such as bullets. Inspired by Truve, Alexander Graham Bell developed a similar device to try to locate a bullet in the chest of American President James Garfield in 1881. It worked correctly, but the attempt was unsuccessful because Garfield's spring bed made adjustments.
The simplest form of a metal detector consists of a generator that generates an alternating current that passes through a coil with a magnetic field. If a piece of an electrically conductive object is located next to the coil, eddy currents will be induced in it, which will create its own magnetic field.
The beginning of modern developments
The modern development of the metal detector began in the 1920s. Gerhard Fisher reasoned that if the radio beam could be distorted, then it should be possible to develop a machine that detects metal using a search coil resonating at the radio frequency.
In 1925, he applied for and received the first patent. Although Gerhard Fisher was the first to patent a metal detector, the first to file was Shirl Herr, a businessman from Crawfordsville, Indiana. His application for a portable metal detector was filed in February 1924, but was not patented until July 1928.
Herr assisted the Italian leader Benito Mussolini in finding items left in the galleys of Emperor Caligula at the bottom of Lake Nemi in Italy in August 1929. The invention was used in the second Antarctic expedition of Admiral Richard Byrd in 1933 to detect objects left by earlier researchers.
Kosatsky's invention
The design invented by Kosacki 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.
Since the creation and improvement of the device was a wartime research operation, the information 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 presented their ideas on the market. White of Oregon Electronics began in the 1950s with the creation of a machine called the Oremaster Geiger Counter. Another leader in detector technology was Charles Garrett, who first used the BFO (Beat Frequency Oscillator).
With the invention and development of the transistor in the 1950s and 1960s, manufacturers and designers of metal detectors developed lighter, smaller machines with improved circuitry that run on small batteries. Companies have sprung up throughout the United States and the United Kingdom 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.
The invention of discriminators
The biggest technical change in the detectors was the development of an induction balance system. It included two coils that were electrically balanced. When metal fell into their surroundings, they became unbalanced. This allowed the detectors to distinguish between color, because each metal has a different phase characteristic when exposed to alternating current.
Over time, detectors were developed that could selectively detect the desired metals, while ignoring the unwanted ones. Even with discriminators, it was still difficult to avoid unwanted metals, because some of them had similar phase characteristics, for example, foil and gold, especially in the form of an alloy.
Thus, improper tuning of some detectors could increase the risk of confusing valuable with 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 were considering the possibility of using another metal detection method called pulsed induction. Unlike a beat frequency generator or induction balancing machines that used uniform alternating current at a low frequency, a pulsed induction machine simply magnetized the earth with a relatively powerful instantaneous current through a search coil. In the absence of metal, the field decayed at the same rate. One could even measure the decay time.
These temporal differences were not significant, but the improvement in electronics made it possible to accurately measure them and determine the presence of metal at a reasonable distance. The new machines had one important advantage: they were largely immune to the effects of mineralization. The addition of computer control and digital signal processing has further improved pulse induction sensors.
Where else is a metal detector used?
Instruments were widely used in archeology in 1958. However, archaeologists opposed their use by artifact seekers or marauders, whose activities destroy archaeological sites.
The problem of their use in excavation sites by lovers who find objects of archaeological interest is that the context in which the object was discovered is lost and a detailed examination of its surroundings is not carried out.
Use as a hobby
There are various types of hobbies using a metal detector. For example, many amateurs search for valuable compounds such as gold, silver or copper. They are most often found in the form of nuggets or flakes. But there are other types 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 the detector work for these purposes? The most common indicator is the frequency of 7-8 kHz.
Finding artifacts of antiquity 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 deeply. In order not to damage them when digging up, a person must know some rules. The frequency of 8.23 kHz is well suited for this.
Searching on the beach is a fairly common occurrence. He dropped a ring or a few coins on the beach and did not even notice what treasure hunters use. After the bulk of people leave the beach, they begin to search for these lost things. There is also a metal detector working under water, but you can wait for the ebb, and then search with a conventional detector.
Joining numerous treasure hunter clubs is another hobby. Such clubs are located in the USA, Great Britain, Canada and many other countries. Here, beginners can learn how to work with a metal detector, as well as 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 to assemble it? Making home-made electronics is very dangerous. If you are not a professional, it is highly discouraged to do this.
Basic and universal materials and tools for assembly:
- NE555 board (or similar 10061);
- transistors IRF750 or IRF740;
- K157UD2 chip and transistor BC547;
- sew wire 0.5;
- NPN transistors;
- soldering iron, wires, other tools.
And how does the Pirate metal detector work? Just like any other. The only negative is the lack of discriminators, which means that he will not be able to notice non-ferrous metal.
How to use it?
If you have made a choice, you should know how to work properly with a metal detector. It doesn’t matter whether he is homemade or not, the principle of work 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 at a price of up to 20 thousand rubles, and it is an ideal choice for beginners. The ACE-250 line has a more professional version (ACE-250 Pro), but it differs only in the frequency range.
How does the Garrett metal detector work ? Since this version was created for beginners, the frequencies allowed to search only small objects at an average depth. It has several modes, such as "Jewelery", "Relics", "Coins", "Any" and Custom.
For beginners, the Custom mode will be useless, so it will be better to use the first four options. From their name it is clear where and why they are useful. It’s 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. As a result of a series of hijackings in 1972, the United States applied technology to screen airline passengers. The Finnish company Outokumpu in the 1970s adapted mining metal detectors, still housed in a large cylindrical pipe, to create a commercial end-to-end 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 signal source. Small hand-held metal detectors are also used to more accurately identify weapons placed on the body and clothing of a person.