The most recurrent issue of all that I am asked is about the depth that a certain team can reach ... or about the equipment necessary to reach a certain depth.
The current metal detectors do not reach very high depths ... nor is it foreseeable that they will be able to reach them in the future. This is not an obstacle for what, in specific circumstances and for specific targets, can reach much greater depths than normal.
Garrett ACE 200 Metal Detector with Waterproof Search Coil and Treasure Sound Headphone
Now ... What do we mean by normal?
Well, for a low-end detector, the normal is located in the range of 10 to 15 centimeters, for an average dexxRÒa, between 15 and 25 centimeters and for a high-end one we can be talking about between 25 and 35 centimeters. Always talking about land of medium and white mineralization the size of a coin.
This does not rule out that a certain team in very specific conditions can go deeper for a target of equal size.
As is evident, there are teams capable of going deeper ... but only for much larger targets. This type of equipment, either the so-called "two boxes" or the so-called "Impulses with large coils", can reach depths ranging from 2 to 10 meters (Some even more) , for targets able to offer a detection surface of one square meter or more.
Perhaps the fundamental difference between one and the other, besides the size of the detectable targets, lies in the level of identification that the target can make:
The equipment destined to the search of coins and lost objects usually provide a good volume of information to the user, while those destined to the search of large objects are limited to indicate the presence of one of these.
Why is this like this?
Well, there are several reasons and physical principles that explain this, as well as explain the tremendous difficulty of going further and increase the depth to which they are able to detect, but perhaps the most important are the penetration of different frequencies in the field and the principle of dissipation of energy.
PENETRATION OF THE DIFFERENT FREQUENCIES ON THE GROUND
Electromagnetic waves can travel through any medium, even through vacuum, but can move that does not mean that this displacement is equally optimal in any medium. In fact and speaking specifically in the displacement through solid bodies, how the ground we tread, its displacement is conditioned by the permeability of the ground at certain frequencies. This permeability is much higher, the lower the frequency that you have to travel through it. Low frequencies combine greater permeability at their lower "resolution", so extracting information from them is much more difficult than extracting it from high frequencies:
That is why in equipment designed to extract information, the highest possible frequencies are usually preferred, as is the case with aviation radars, which work in the megahertz range (Millions of cycles per second) , while detectors of metals are forced, to get a good penetration, to work in the range of kilohertz (Thousands of cycles per second) because of the better permeability of these frequencies in the field.
Currently there are on the market detectors that work with more than one frequency, even a few that work with a multitude of frequencies simultaneously. How each type of soil is more permeable to a given frequency than to all others, teams that use more than one frequency have the inestimable advantage of being able to reach deeper than others, based on, simply, the greater probability of that some of the frequencies they work with are more adequate to penetrate a concrete floor than the rest of them. On the other hand, equipment that uses only one frequency is subject to the penetration capacity that frequency has on a given floor.
PRINCIPLE OF DISSIPATION OF ENERGY
The radiated energy decreases with the square of the distance.
This means that the detection field emitted by your detector is reduced exponentially as it moves away from the emitting plate or antenna or, said much more simply, that the field strength at ten centimeters from the emitter plate is not from the double that to twenty centimeters, if not much greater.
To put a simile that makes this much more understandable, let's imagine a field with a power of 10,000 in origin. When decreasing the power with the square of the distance, that field at 10 cm will have a power of:
10,000 / (10 * 10) = 10,000 / 100 = 100
That same field, twenty centimeters away will have a power of:
10,000 / (20 * 20) = 10,000 / 400 = 25
Or, what is the same, a quarter of its value ten centimeters away. If we go ahead and see its value at thirty centimeters we realize what:
10,000 / (30 * 30) = 10,000 / 900 = 11.11
That is, scarcely more than a tenth of the power he had ten centimeters away.
What happens ALSO, and what is not usually taken into account when thinking about it, is that the distances, when making the detection are DUPLICAN, in such a way that the signal that the equipment emits 10,000 power, runs ten centimeters to reach the target and get there how 100 power. It is induced in the target and generates a signal that must travel again the ten centimeters to return to the detector ... so:
100 (10 * 10) = 100/100 = 1
That is to say:
It has been reduced to one ten thousandth part of the signal that our team issued !!!
... What is not (unfortunately: it is even worse) true at all, for several reasons:
• Not all the radiated energy reaches the target: Part is lost in other directions.
• Not all the energy that reaches the target creates a field in it: Part is consumed in the creation of that field.
• Not all the energy that the field has created is emitted when this is collapsed: Part is consumed in generating the emission.
• Not all the energy emitted by the target reaches the detector: Part is lost in other directions.
Consequently, the response is even more minimized.
We must also bear in mind that the signal suffers another series of wear when it is received and manipulated by the circuits of the equipment to extract information from it, in addition to that it can become so tenuous that it is lost with the background of radioelectric interference that is always present.
TO END
The depth to which a team is able to detect, as you can see, is not something simple to increase, since even large increases in the origin of the emission do not translate into appreciable increases in the received signal, and this is given in reason to the ability of a given target to generate a signal perceptible by the detector, rather than the ability of the detector to generate a signal capable of reaching the target.
A loose target, like a coin, has a limit on the amount of energy it can "manage" and on the "volume" of the signal it can then issue. That limit can not be transferred and, therefore, to "go beyond" it is necessary to improve more than the issuers, the receivers of the equipment.
That is why nowadays the microprocessed equipment is gaining advantage over the "conventional" electronics, since they allow a more complete analysis of the received signals.
Finally, I would advise you to distrust the ads that speak of impressive depths:
Remember that for a target located one meter deep from a signal of 1 the equipment would have to emit a signal 40,000 times greater ... and how "the energy is neither created nor destroyed, it only transforms" (and dissipate, I add) , the batteries that should equip such equipment would be more than big, and the antenna would have to be, to dissipate and emit that energy, of a size according to it.