In July 1881, then-United States President James Garfield was injured in a shooting accident. Alexander Grahamble tried to find the location of the bullet with the help of a metal detector and the help of doctors, but unfortunately failed.
After some time, it became clear that Grahamble’s innovative method could work, but the reason his method failed was because the device’s waves overlapped with coiled metals like the bed on which James Garfield was placed! This event itself is an interesting historical point because the use of this new system for humanity for the first time was very exciting and interesting.
A metal detector is a device for finding metal objects hidden in the ground, wall, etc. The metal detector creates a magnetic field around its search disk.
When a metal object is placed in a magnetic field, the magnetic field strength changes and the metal detector detects the presence of metal around its disk by sensing and detecting these changes.
The higher the intensity of the magnetic field generated by the device, the greater the depth of metal detection. It should be noted that the depth of prospecting by a metal detector changes (becomes more or less) depending on the type of metal, the size and shape of the metal.
In other words, it can be said that metal detectors are electronic or mechanical devices that show sensitivity to a particular metal or all types of metals based on different physical laws, depending on the application, level of sensitivity, type of application and design, and the possibility of detecting metals buried in the soil or making other things possible.
Working with ordinary and semi-professional metal detectors is simple. When the device is turned on, we slowly search for the part of the coil in the desired area and move it forward and backward. When a device hovers over a metal, the device indicates its presence by sending an audio signal. Advanced metal detectors display the type of metal and the depth of presence of the metal through a small screen.
Most professional metal detectors are capable of determining the type of metal at a depth of 20 to 30 cm. Advanced metal detectors are also able to distinguish between the size of buried metal such as a small or large currency.
Underground treasure is the goal of many people who use metal detectors, but often find only essential metals underground. A metal detector can locate certain metals, but it cannot distinguish between precious metals and ordinary metals.
The metal detector works by means of a detector head (usually an electrical coil close to the surface of the earth). The magnetic field generated by this coil penetrates the soil, and if the field passes through iron, steel, or other special metals, it creates a weak current in the metal.
This current, in turn, produces a magnetic field that passes through the same or another coil in the metal detector’s head and generates a weak signal in that coil. Sensitive electronic components detect this signal and activate the light, hand, or alarm sound on the phone, indicating that a metal object has been found.
Metal detectors are also used to recognize and reject spoiled foods due to metal objects. Below, we will introduce this kind of industrial metal detectors.
Iron, steel or such metal objects propagate the magnetic field (from the detector) and create a weak electrical signal in the coil (around the magnet). These signals must be amplified in order to turn on the speaker.
The effect of moisture, groundwater and minerals on the work of metal detectors
In metal detectors with high operating frequency, these factors cause system malfunctions because at high frequencies, sensitivity to moisture and metals increases significantly. Metal detectors operating at very low frequencies have very good stability, accuracy and depth, and humidity has less impact on their performance.
The difference between institutional and recreational metal detectors
Institutional metal detectors are used to detect metal targets in the network of installations that have a control or inspection aspect.
The targets that are sought by this class of metal detectors are:
Valves (flange surrounding the valves in the absence of a valve)
Since this type of metal detector is used in cities and villages, and due to the presence of metal debris and the type of use, these systems have unique characteristics:
Remove the ground capacity effect
Remove the influence of moisture and minerals
Automatic or manual removal of metal debris
Ability to control sensitivity and depth of penetration
Detection depth more than 2 meters
In many cases, recreational metal detectors or other types of metal detectors show sensitivity to the smallest metals because they retain their sensitivity to moisture and metals, making the institutional user unable to use these devices for their intended purposes.
History of metal detectors and their applications
In the late nineteenth century, many scientists and engineers used their knowledge to invent a device capable of interacting with metals, and such a device can be considered a very useful and key tool in the search for mines.
German physicist Heinrich Wilhelm Dov invented the induction equilibrium system, which became the basis for the development of metal detectors today a hundred years later. The first devices were very primitive and were consuming a high battery and the penetration depth was very low.
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