Metal detectors are gadgets that are used for various purposes. These gadgets are the life of all detectorists as without them hunt is definitely not possible. A lot of famous and well-known companies have manufactured a diverse amount of metal detecting gadgets of different categories i.e. equipped with different technologies. Before, discussing the type of metal detectors, let’s have a look at its origin. How we all came to know about these amazing gadgets!
Origin Of Metal Detectors!
Well, it all started in 1881, when the United States president James A Garfield was shot by an assassin. In order to take the bullet out of his body and to save him, telephone inventor Alexander Graham Bell immediately, on the spot, made an electromagnetic device that would detect the bullet presence.
Well, graham called it the “induction balance”. He couldn’t save the president but he did invent a device that we now know as metal detectors. The induction balance device was actually based on an earlier invention made by a German physicist called, Heinrich Wilhelm Dove.
Well, as the year got by, a young German named Gerhard Fischer developed a portable metal detector called “Metalloscope” in 1925. His gadget then started to be sold commercially and with the passage of time, these metal detecting gadgets became more advanced, wrapped up with unique technologies. They are not only used for bullet detecting and demanding but can be used for treasure hunting activity as well.
Different Types Of Metal Detectors!
There are many different types of metal detectors which are
- Beat frequency oscillation metal detectors ( BFO)
- Very low-frequency metal detectors ( VLF)
- Pulse induction metal detectors ( PI)
- Industrial metal detectors
Beat Frequency Oscillation Metal Detectors:
Beat frequency metal detector is a very basic type of detector that’s very easy to understand and not to mention use. Well, this metal detector consists of 2 wire coils. One coil is present at the base and the other coil is present in the control box. The control box has a little receiver in it as well. Now, both these coil wires are connected to an oscillator that generates current (I).
The current flows through these coils and produces radio waves that are collected or received by the little receiver present in the control box. The receiver on receiving the radio waves starts producing audible tones or beats according to the difference between the two radio wave frequencies.
Now, when the search coil present at the base comes in contact with a metallic object, the magnetic field of the coil induces a magnetic field in the metallic object. This magnetic field of the object disrupts the frequency of the radio waves of the search coil.
When the receiver receives this frequency and matches it with the frequency of the coil in the control box, then the deviation between the two causes it to produce beats of different time and tone. Hence, we come to know about the existence of a metallic object.
Very Low-Frequency Metal Detectors:
Well, these types of metal detectors are still in use and are developed by many popular companies like Garrett and many others. They are the king of all metal detectors. Their working principle is easy to understand as well.
Like beat frequency oscillator metal detectors, they consist of 2 coils, an outer coil called the transmitter and an inner coil called the receiver. The receiver coil function is to receive the current generated by the transmitter coil and to amplify it. Well, the electric current in the transmitter coil generates a magnetic field around the coil both above and below.
Now, when the transmitter coil magnetic field comes into contact with a metallic object, it induces a magnetic field in it as well, as a result, the object’s magnetic field produces interference in the transmitter magnetic field.
This interference is received by the receiver coil and then sent to the control box whose audio control system then produces tones according to the interference and makes the detectorist aware of the presence of the metallic object.
Another interesting feature of this metal detector is that you can have an idea of the type of target metal by their magnetic fields as well as you can have an idea of their depth as well.
Some metal detectors are being invented that have specific systems that use this feature to tell the identity of the metal object as well as their depth. Some metals like iron and steel produce very strong and powerful magnetic fields.
Similarly, the closer the object is to the surface, the greater the magnetic field whereas the more it’s deep in the ground, the lesser the magnetic field.
Pulse Induction Metal Detectors:
So far, we have discussed 2 types of metal detectors both of which operate on two coils. One acts as a transmitter and the other acts as a receiver. However, pulse induction metal detectors act a little differently. It works on a single coil that acts as both a transmitter and a receiver.
It may also be operated by many coils acting like one. Anyhow, a strong electric current pulse is sent to the coil and the coil generates a magnetic field. When the pulse ends, an opposite polarity magnetic field is generated and then collapses producing a strong electrical spike.
This spike lasts for a few milliseconds and then allows another current to follow through the coil which is what we call a reflected pulse. Now, when the coil comes across a metallic object, the pulse in the coil generates the magnetic field of the coil, which induces a magnetic field in the opposite direction in the object.
When the pulse ends, the magnetic field of the coil collapses and generates a reflected pulse which takes longer to disappear because of the object’s magnetic field interference. The control box receives the reflected pulse and compares it with the expected length and when it detects the deviation, the audio signal system produces a sound that a metallic object has been discovered. This is how pulse induction detectors work and they are a lot more expensive than other detectors.
Industrial Metal Detectors:
Well, these metal detectors work on electromagnetic principles and are not used for treasure hunting. They are used to find concealed weapons that are most probably used by criminals. These detectors include the common door frame detectors and are used for providing security.
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