Principles of magnetic field screening. Is there a material that reduces the magnetic field without the impact of the magnetic field itself? Which material does not miss the magnet

How to make two magnets next to each other, do not feel the presence of each other? What material must be placed between them to power lines magnetic field From one magnet would not reach the second magnet?

This question is not as trivial, as it may seem at first glance. We need to truly isolate two magnets. That is, that these two magnets can be turned to differently and move them to differently relative to each other and however, so that each of these magnets behave as if there is no other magnet nearby. Therefore, any tricks with the placement of a number of third magnet or ferromagnet, to create some particular configuration of magnetic fields with compensation for all magnetic fields at some single point, not pass on.

Diamagnetic ???

Sometimes it is mistaken that such an insulator of the magnetic field can serve diamagnetic. But it is not true. Diamagnetik really relaxes the magnetic field. But it weakens the magnetic field only in the thicker of the diamagnet itself, inside the diamagnet. Because of this, many mistakenly think that if one or both magnets climb in a piece of diamagnet, then, allegedly, their attraction or their repulsion will weaken.

But this is not a solution to the problem. First, the power lines of one magnet will still reach another magnet, that is, the magnetic field only decreases in the thickness of the diamagnet, but does not disappear at all. Secondly, if the magnets are closed in the thicker diamagnet, we cannot move them and turn them relative to each other.

And if you make a flat screen from the diamagnet, then this screen will skip the magnetic field through itself. And, behind this screen, the magnetic field will be exactly the same as if this diamagnetic screen would not be at all.

This suggests that even the magnets closed in the diamagnetic will not depend on the weakening of each other's magnetic field. In fact, because there is a stamped magnet, right in the volume of this magnet, the diamagnetic is simply absent. And once where there is a closed magnet, there is no diamagnet, it means that both closed magnets actually interact with each other exactly as if they were not closed in diamagnet. The diamagnet around these magnets is also useless, like a flat diamagnetic screen between magnets.

Perfect diamagnetic

We need such a material that, in general, did not pass through yourself the power lines of the magnetic field. It is necessary that the power lines of the magnetic field are pushed out of such a material. If the power lines of the magnetic field pass through the material, then, behind the screen from such a material, they completely restore all its strength. This follows from the law of conservation of the magnetic flux.

In diamagnet, the weakening of the external magnetic field occurs due to the induced internal magnetic field. This induced magnetic field creates circular cells of electrons inside atoms. When the external magnetic field is turned on, electrons in atoms should start moving around the power lines of the outer magnetic field. This is an induced circular movement of electrons in atoms and creates an additional magnetic field, which is always directed against an external magnetic field. Therefore, the total magnetic field in the thickness of the diamagnet becomes less than outside.

But the full compensation of the external field due to the induced indoor field does not occur. There is not enough circular strength in the atoms of the diamagnet to create exactly the same magnetic field as an external magnetic field. Therefore, the filament lines of the external magnetic field remain in the thicker of the diamagnet. The outer magnetic field, as it were, "breaks through" the material of the diamagnets through.

The only material that pushes the power lines of the magnetic field is a superconductor. In the superconductor, the external magnetic field burst such circular currents around the filament lines of the outer field, which create an oppositely directed magnetic field exactly equal to an external magnetic field. In this sense, the superconductor is the perfect diamagnet.

On the surface of the superconductor, the magnetic field strength vector is always directed along this surface along the surface tangent to the surface of the superconducting body. On the surface of the superconductor, the magnetic field vector does not have a component sent perpendicular to the surface of the superconductor. Therefore, the power lines of the magnetic field always enhance the superconducting body of any form.

Handling superconductor magnetic field lines

But this does not mean at all that if there is a superconducting screen between two magnets, it will solve the task. The fact is that the power lines of the magnetic field of the magnet will go to another magnet into the screen bypass from the superconductor. Therefore, from a flat superconducting screen will only attenuate the effect of magnets on each other.

This weakening of the interaction of two magnets will depend on how much the length of the power line has increased, which connects two magnets with each other. The larger the length of the connecting power lines, the less the interaction of two magnets with each other.

This is exactly the same effect as if you increase the distance between the magnets without any superconducting screen. If you increase the distance between the magnets, the lengths of the power lines of the magnetic field are also increasing.

It means that to increase the lengths of the power lines that connect two magnets into circulating the superconducting screen, you need to increase the size of this flat screen and in length and in width. This will lead to an increase in the length of the increasing power lines. And the greater the size of the flat screen compared to the calcination between the magnets, the interaction between the magnets becomes less.

The interaction between magnets completely disappears only when both sizes of the flat superconducting screen become infinite. This is an analogue of the situation when magnets spread to an infinitely large distance, and therefore the length of the magnetic field connecting their power lines has become infinite.

Theoretically, this, of course, completely solves the task. But in practice, we cannot make a superconducting flat screen of infinite sizes. I would like to have such a decision that can be carried out in practice in a laboratory or in production. (About the domestic conditions of speech no longer goes, because in everyday life it is impossible to make a superconductor.)

Separation of space superconductor

On the other, the flat screen of infinitely large sizes can be interpreted as a separator of the entire three-dimensional space into two parts that are not connected to each other. But the space into two parts can separate not only the flat screen of infinite sizes. Any closed surface divides the space also into two parts, on the volume inside the closed surface and the volume outside the closed surface. For example, any sphere divides the space into two parts: a bowl inside the sphere and everything outside.

Therefore, the superconducting sphere is the perfect magnetic field insulator. If you put a magnet into such a superconducting sphere, you never manage to detect any devices, whether there is no magnet or it is not there.

And, on the contrary, if you are placed inside such a sphere, then you will not have external magnetic fields. For example, the Earth's magnetic field cannot be detected within such a superconducting sphere with any devices. Inside such a superconducting sphere, it will be possible to detect only a magnetic field from those magnets that will also be inside this sphere.

In such a way that two magnets do not interact with each other, one of these magnets should be placed in the superconducting sphere, and the second leave the outside. Then the magnetic field of the first magnet will be fully concentrated within the sphere and will not be out of this sphere. Therefore, the second magnet will not feel the first. Similarly, the magnetic field of the second magnet will not be able to climb inside the superconducting sphere. And therefore, the first magnet will not feel the close presence of the second magnet.

Finally, both magnets can be activated and moved to each other. True, the first magnet is limited in its displacements by the radius of the superconducting sphere. But it only seems so. In fact, the interaction of two magnets depends only only on their relative location and their turns around the center of gravity of the corresponding magnet. Therefore, it is enough to place the center of gravity of the first magnet in the center of the sphere and there in the center of the sphere to place the origin of the coordinates. All possible location of the magnets will be determined only by all possible options The arrangements of the second magnet relative to the first magnet and their corners of turns around their mass centers.

Of course, instead of the sphere, you can take any other surface shape, for example, an ellipsoid or a surface in the form of a box, etc. If only she divided the space into two parts. That is, there should be no hole in this surface through which the power line can crawl, which connects the internal and outer magnets.

Consider the usual rod magnet: Magnet 1 relies on the surface of North pole up. Suspended distance Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y. Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e y Above it (supported from side to the side of the plastic tube) is a second, smaller rod magnet, Magnet 2, with North pole addressed down. Magnetic forces between them exceed gravity and hold Magnet 2 suspended. Consider some material, the Material-X which moves to the gap between the two magnets at the initial speed. V "Role \u003d" Presentation "STYLE \u003d" POSITION: RELATIVE; "\u003e v. V "Role \u003d" Presentation "STYLE \u003d" POSITION: RELATIVE; "\u003e V "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e v ,

Is there a material, material-x, which will reduce the distance Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y. Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e y between two magnets and go through the slot without changing speed V "Role \u003d" Presentation "STYLE \u003d" POSITION: RELATIVE; "\u003e v. V "Role \u003d" Presentation "STYLE \u003d" POSITION: RELATIVE; "\u003e V "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e v ?

Fan physics

such a strange question

Answers

Jojo.

The material you are looking for may be a superconductor. These materials have zero current resistance and, thus, can compensate for the penetrating power lines in the first layers of the material. This phenomenon is called the Mason Effect and is itself determining the superconducting state.

In your case, the plates between two magnets, it will definitely reduce Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y. Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e y ,

For speed:

Here are usually vortex currents induced by a magnetic field lead to the loss of power, defined as:

P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e p P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e = π P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e IN P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e p P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e d. P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e e. P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 6 K ρ D P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e , P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e sign equal P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e π P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 b p 2 d 2 f 2 6 k ρ d, "Role \u003d" Presentation "\u003e in P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e D P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e 2 P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e 6 P \u003d π 2 B P 2 D 2 F 2 6 K ρ D, "Role \u003d" Presentation "\u003e to P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e ρ P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e D P \u003d π 2 B P 2 D 2 F 2 6 K ρ d, "Role \u003d" Presentation "\u003e,

since, however, the superconductor has zero resistance and, thus, de facto

ρ \u003d ∞ "Role \u003d" Presentation "\u003e ρ = ∞ ρ \u003d ∞ "Role \u003d" Presentation "\u003e ρ \u003d ∞ "Role \u003d" Presentation "\u003e ρ ρ \u003d ∞ "Role \u003d" Presentation "\u003e sign equal ρ \u003d ∞ "Role \u003d" Presentation "\u003e ∞

no kinetic energy should be lost, and thus the speed will remain unchanged.

There is only one problem:

The superconductor can only exist at very low temperatures, so it may be impossible in the case of your machine ... you, at least need a cooling system working on liquid nitro to cool it.

In addition to superconductors, I do not see any possible material, because if the material is a conductor, then you always have losses due to vortex currents (thus reducing V "Role \u003d" Presentation "STYLE \u003d" POSITION: RELATIVE; "\u003e v. V "Role \u003d" Presentation "STYLE \u003d" POSITION: RELATIVE; "\u003e V "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e v) or the material is not a conductor (then Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y. Y "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e Y "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e y will not decrease).

adamDport.

This phenomenon can be observed in the car or somewhere in the experiment?

Jojo.

The case, however, is that when the superconductor enters the magnetic field, the power lines are deflected, which will be associated with the work ... Therefore, in fact, the entrance to the area between two magnets will cost some energy. If the plate leaves the area after, the energy will be won.

Lupurkus

There are materials with a very large magnetic permeability, for example, the so-called μ-metal. They are used to make screens that weaken the magnetic field of the Earth on the path of the electron beam in sensitive electron-optical devices.

Since your question combines two separate parts, I will share it to consider each of them individually.

1. Static case : Magnetic poles come closer to each other when the magnetic screening plate is installed between them?

Mu-materials do not "kill" the magnetic field between your magnetic poles, but only deflect its direction, directing part of it in a metal screen. It will strongly change the field strength. B "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e IN B "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e B "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e On the screen surface, almost overwhelming its parallel components. This leads to a decrease in magnetic pressure. P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e p \u003d. B. P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e 2 P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e 8 π. P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e μ P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e p \u003d b 2 8 π μ "Role \u003d" Presentation "style \u003d" position: relative; "\u003e sign equal p \u003d b 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: Relative; "\u003e P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e 2 P \u003d B 2 8 π μ "Role \u003d" Presentation "style \u003d" Position: relative; "\u003e 8 P \u003d B 2 8 π μ "ROLE \u003d" PRESENTATION "STYLE \u003d" POSITION: RELATIVE; "\u003e π p \u003d b 2 8 π μ "Role \u003d" Presentation "style \u003d" position: relative; "\u003e μ In the immediate vicinity of the screen surface. If this decrease in the magnetic field on the screen will significantly change the magnetic pressure on the site of magnets, forcing them to move? I'm afraid here is more detailed.

2. Plate movement : Is it possible that the speed of the shielding plate will not change?

Consider the next very simple and intuitive experiment: take the copper pipe and keep it vertically. Take a small magnet and let him fall into the pipe. Magnet drops: i) slow and ii) with uniform speed.

Your geometry can be made similar to the geometry of the falling pipe: Consider the column of magnets soaring each other, that is, with paired poles, NN and SS. Now take the "multifaceted" shield made of parallel sheets that are firmly held in place at the same distance from each other (for example, 2D-comb). This world imitates several falling pipes in parallel.

If you now hold the bar of magnets in the vertical direction and stretch through them a multifaceted force with a constant force (analogue of gravity), then you will reach a constant speed mode - by analogy with an experiment with a falling pipe.

This suggests that the magnets column or, more precisely, their magnetic field acts on the copper plates of a viscous environment:

M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e m. M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e p L A T E M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e v. M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e ˙ M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e = - γ M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e IN M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e V +. F. M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e p l l M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e M P L A T E V ˙ \u003d - γ b V + F p U L L "ROLE \u003d" PRESENTATION "\u003e M M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e P M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e L M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e T M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e E M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e V M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e ˙ m p l a t e v ˙ \u003d - γ b v + f p u l l "role \u003d" presentation "\u003e sign equal m p l a t e v ˙ \u003d - γ b v + f p u l l "Role \u003d" Presentation "\u003e - M P L A T E V ˙ \u003d - γ b V + F p U L L "ROLE \u003d" PRESENTATION "\u003e γ m p l a t e v ˙ \u003d - γ b v + f p u l l «Role \u003d" Presentation "\u003e M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e V M P L A T E V ˙ \u003d - γ B V + F P U L L "ROLE \u003d" PRESENTATION "\u003e + M P L A T E V ˙ \u003d - γ b V + F p U L L "ROLE \u003d" PRESENTATION "\u003e F M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e P M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e U M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e L M P L A T E V ˙ \u003d - γ b V + F P U L L "ROLE \u003d" PRESENTATION "\u003e L

Where γ b "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e γ γ b "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e γ b "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e IN γ b "Role \u003d" Presentation "STYLE \u003d" POSITION: Relative; "\u003e γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e γ γ b "Role \u003d" Presentation "STYLE \u003d" POSITION: relative; "\u003e in There will be an effective coefficient of friction due to the magnetic field perturbed by the presence of plates. After a while you will eventually reach the regime in which the friction force will compensate for your effort, and the speed will remain constant: V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e v \u003d. F. V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e p l l V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e γ V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e IN V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e v. V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e \u003d V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e F. V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e p V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e U. V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e L. V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e L. V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e γ V \u003d F p U L l γ b "Role \u003d" Presentation "Style \u003d" Position: relative; "\u003e IN ,

If this speed is equal to the speed that you have before you dragged the plates in the magnetic field, this is the question of how you control the force of attraction. Note : If there is no traction, the plate will be simply stopped by the magnetic brake effect. Thus, you must pull accordingly if you want to have a constant speed.

Screening of magnetic fields can be done by two methods:

Shielding with the help of ferromagnetic materials.

Shielding with vortex currents.

The first method is usually used when shielding permanent MPs and low frequency fields. The second method provides significant efficiency when shielding a MP high frequency. Because of the surface effect, the density of the vortex currents and the intensity of the alternating magnetic field as the exponential law falls into the metal:

The indicator of the decrease in the field and current, which is called the equivalent depth of penetration.

The smaller the penetration depth, the larger current flows in the surface layers of the screen, the greater the reverse MP created by it, which displaces the screen, occupied by the screen, the external field of the flood source. If the screen is made of non-magnetic material, then the shielding effect will depend only on the specific conductivity of the material and the frequency of the shielding field. If the screen is made of a ferromagnetic material, then, with other things being equal, the external field in it will indulge in it. d. s. Due to the larger concentration of magnetic power lines. With the same specific conductivity of the material, vortex currents will increase, which will lead to a smaller depth of penetration and for the better shielding effect.

When choosing the thickness and material of the screen, it is not necessary to proceed from the electrical properties of the material, but to be guided by considerations of mechanical strength, weight, stiffness, resistance against corrosion, convenience of docking individual parts and transitional contacts between them with low resistance, jobs soldering, welding and other things.

From the data of the table, it can be seen that for frequencies above 10 MHz copper and the more silver films with a thickness of about 0.1 mm gives a significant shielding effect. Therefore, at frequencies above 10 MHz, it is quite possible to use screens from a foil getyinaks or fiberglass. At high frequencies, steel gives a greater shielding effect than non-magnetic metals. However, it is worth considering that such screens can make significant losses in the shielded chains due to the large specific resistance and hysteresis phenomena. Therefore, such screens are applicable only in cases where you can not be considered with introductible losses. Also, for greater screening efficiency, the screen should have a smaller magnetic resistance than air, then the power lines of the magnetic field seek to pass through the walls of the screen and in a smaller number penetrate into space outside the screen. Such a screen is equally suitable for protection against the impact of the magnetic field and to protect the external space from the influence of the magnetic field created by the source inside the screen.

There are many steel grades and permalloe with different magnitudes of magnetic permeability, so for each material you need to calculate the magnitude of the penetration depth. The calculation is made by an approximate equation:

1) protection against an external magnetic field

The magnetic power lines of the outer magnetic field (the magnetic field induction line) will be mainly in the thickness of the screen walls, which has a small magnetic resistance compared to the resistance of the space inside the screen. As a result, the outer magnetic field of interference will not affect the operation of the electrical circuit.

2) Screening your own magnetic field

Such crawling is used if the task of protecting the external electrical circuits from the effects of the magnetic field created by the coil current is set. Inductance L, i.e. when it is required to practically localize the interference created by the inductance L, then such a task is solved using a magnetic screen, as schematically shown in the figure. Here, almost all the power lines of the inductor coil field will be closed through the thickness of the screen walls, without going beyond their limits due to the fact that the magnetic resistance of the screen is much less than the resistance of the surrounding space.

3) Double Screen

In a double magnetic screen, you can imagine that part of the magnetic power lines that will go beyond the walls of one screen, will be closed through the thickness of the second screen walls. Similarly, you can also imagine the action of a double magnetic screen during the localization of the magnetic interference created by the element of the electrical circuit inside the first (internal) screen: the bulk of magnetic power lines (magnetic scattering lines) will be closed through the walls of the outer screen. Of course, the thickness of the walls and the distance between them should be rationally chosen in double screens.

The overall shielding coefficient reaches the greatest value in cases where the wall thickness and gap between the screens increase is proportional to the distance from the center of the screen, and the size of the gap is the average geometric size of the walls of the walls of the screens adjacent to it. In this case, the shielding coefficient:

L \u003d 20LG (H / NE)

Production of double screens in accordance with this Recommendation is practically difficult from technological considerations. It is much more expedient to choose a distance between the shells adjacent to the airbap of screens, greater than the thickness of the first screen, approximately equal to the distance between the first screen surface and the edge of the shielded chain element (for example, iridulativity coils). The choice of one or another thickness of the magnetic screen walls cannot be made unambiguous. The rational wall thickness is determined. Screen material, interference frequency and a specified shielding coefficient. It is useful to consider the following.

1. With increasing the frequency of interference (the frequency of the variable magnetic field of interference), the magnetic permeability of the materials falls and causes a decrease in the shielding properties of these materials, since as the magnetic permeability decreases, the resistance of the screen rendered to the magnetic flux increases. As a rule, a decrease in magnetic permeability with an increase in frequency is most intensively in those magnetic materials that have the greatest initial magnetic permeability. For example, sheet electrical steel with a small initial magnetic permeability slightly changes the value of JX with an increase in frequency, and permalla, having large initial magnetic permeability values, is very sensitive to increasing the magnetic field frequency; Magnetic permeability drops sharply with the frequency.

2. In magnetic materials exposed to the high-frequency magnetic field of interference, the surface effect is noticeable, i.e., the magnetic flux to the surface of the screen walls, causing an increase in the magnetic resistance of the screen. Under such conditions it seems that it is almost useless to increase the thickness of the screen walls outside those values \u200b\u200bthat are occupied by the magnetic flux at a given frequency. Such a conclusion is incredible, for an increase in the wall thickness leads to a decrease in the magnetic resistance of the screen, even with the presence of a surface effect. At the same time, a change in magnetic permeability should be taken into account at the same time. Since the phenomenon of the surface effect in magnetic materials usually begins to affect more than a decrease in magnetic permeability in the low frequency area, the influence of both factors to choose from the thickness of the screen walls will be different on different ranges of magnetic interference frequencies. As a rule, a decrease in shielding properties with an increase in interference frequency is stronger in screens from materials with high initial magnetic permeability. The above features of magnetic materials give grounds for recommendations for the choice of materials and the thickness of the walls of magnetic screens. These recommendations may be reduced to the following:

A) screens from ordinary electrical (transformer) steel with low initial magnetic permeability, it can be used if necessary to provide small shielding coefficients (CE 10); Such screens provide almost unchanged shielding coefficient in a fairly wide frequency band, up to several tens of kilohertz; The thickness of such screens depends on the frequency of interference, and the lower the frequency, the greater the thickness of the screen is required; For example, at a magnetic field frequency of noise of 50-100 Hz, the thickness of the screen walls should be approximately 2 mm; If an increase in the shielding coefficient or a large screen thickness is required, it is advisable to apply several shielding layers (double or triple screens) less thickness;

B) screens from magnetic materials with high initial permeability (for example permallah) it is advisable to apply if necessary to provide a large shielding coefficient (CE\u003e Y) in a relatively narrow frequency band, with the thickness of each magnetic screen shell it is impractical to choose more than 0.3-0.4 mm; The shielding effect of such screens begins to fall significantly at frequencies, above several hundred or thousands of hertz, depending on the initial permeability of these materials.

All of the above-mentioned magnetic screens are true for weak magnetic interference fields. If the screen is close to powerful interference sources and arise in it magnetic threads with large magnetic induction, then, as you know, have to take into account the change in the magnetic dynamic permeability, depending on the induction; It is also necessary to consider losses in the thickness of the screen. Practically with such strong sources of magnetic interference fields, in which it would be necessary to reckon with their action on screens, are not found, with the exception of some special cases that do not provide for radio amateur practices and normal conditions for the operation of broadcasting devices.

Test

1. When magnetic shielding, the screen should:
1) have a smaller magnetic resistance than air
2) possess an equal air to the magnetic resistance
3) have a large magnetic resistance than air

2. When shielding a magnetic field Grounding the screen:
1) does not affect the screening efficiency
2) increases the effectiveness of magnetic shielding
3) reduces the efficiency of magnetic shielding

3. At low frequencies (<100кГц) эффективность магнитного экранирования зависит от:
a) screen thickness, b) magnetic permeability of material, c) distances between the screen and other magnetic pipelines.
1) is true only a and b
2) is true only b and in
3) is true only a and in
4) all options are correct

4. In magnetic shielding at low frequencies, uses:
1) Copper
2) aluminum
3) Permalla.

5. In magnetic shielding at high frequencies, uses:
1) Iron
2) Permalla
3) Copper

6. At high frequencies (\u003e 100kHz), the effectiveness of magnetic shielding does not depend on:
1) screen thickness

2) Magnetic Permeability Material
3) distances between the screen and other magnetic pipelines.

Used literature:

2. Semenenko, V. A. Information Security / V. A. Semenhenko - Moscow, 2008.

3. Yarochkin, V. I. Safety / V. I. Yarochkin - Moscow, 2000.

4. Demirchan, K. S. Theoretical basis Electrical Equipments III Tom / K. S. Demirchen S.-PP, 2003.

Two methods are used to shield the magnetic field:

Method of shunting;

Magnetic field method screen.

Consider each other from these methods.

Method of shunting the magnetic field screen.

The magnetic field shunt method is used to protect against a constant and slowly changing alternating magnetic field. Screens are made of ferromagnetic materials with high relative magnetic insight (steel, permalla). In the presence of a magnetic induction line, it is mainly in its walls (Figure 8.15), which have a small magnetic resistance compared to the airspace inside the screen. The screening quality depends on the magnetic permeability of the screen and the resistance of the magnetic pipeline, i.e. The thicker screen and the fewer seams, junctions, going across the direction of magnetic induction lines, the screening efficiency will be higher.

Method of displacement of the magnetic field screen.

The method of displacing the magnetic field screen is used to shield variables of high-frequency magnetic fields. In this case, screens from non-magnetic metals are used. Screening is based on induction phenomenon. Here the induction phenomenon is useful.

We put on the path of a uniform alternating magnetic field (Figure 8.16, a) copper cylinder. ED variables will be given in it, which, in turn, will create variables induction vortex currents (Foucault currents). The magnetic field of these currents (Figure 8.16, b) will be closed; Inside the cylinder, it will be directed towards the exciting field, and beyond its limits - to the same side as the exciting field. The resulting field (Figure 8.16, B) turns out to be weakened by the cylinder and reinforced outside it, i.e. The fields of the field occurred from the area occupied by the cylinder, in which its shielding effect is concluded, which will be the more efficient than the less the electrical resistance of the cylinder, i.e. The more vortex currents flowing along it.

Due to the surface effect ("skin effect), the density of the vortex currents and the strength of the alternating magnetic field as it deepends to the metal falls under the exponential law.

, (8.5)

where (8.6)

- indicator of the decrease in the field and current called equivalent penetration depth.

Here is the relative magnetic permeability of the material;

- Vacuum magnetic permeability, equal to 1.25 * 10 8 GN * cm -1;

- resistivity of the material, Ohm * cm;

- frequency Hz.

The value of the equivalent penetration depth is conveniently characterized by the shielding effect of vortex currents. The smaller x 0, the greater the magnetic field created by them, which is displaced from the space occupied by the screen, the external field of the flood source field.

For a non-magnetic material in formula (8.6) \u003d 1, the shielding effect is determined only and. And if the screen is made of ferromagnetic material?

With an equal effect, it will be better, since\u003e 1 (50..100) and x 0 will be less.

So, x 0 is the criterion of the shielding effect of vortex currents. It is of interest to estimate how many times the density of the current and the tension of the magnetic field becomes smaller at the depth of x 0 compared to the surface. To do this, in formula (8.5) we will substitute x \u003d x 0, then

where it can be seen that at the depths of X 0, the current density and the tension of the magnetic field are falling in a time, i.e. Prior to 1 / 2.72, which is 0.37 from density and tension on the surface. Since the weakening of the field is only in 2.72 times At depth x 0 not enough to characterize the shielding material, then two more values \u200b\u200bof the depth of penetration X 0.1 and x 0.01, characterizing the drop in the current density and the field voltage of 10 and 100 times from their values \u200b\u200bon the surface.

Express the values \u200b\u200bof x 0.1 and x 0.01 through the value of x 0, for this, the equation will be based on the base of the expression (8.5)

AND ,

deciding which we get

x 0.1 \u003d x 0 ln10 \u003d 2.3x 0; (8.7)

x 0.01 \u003d x 0 ln100 \u003d 4.6x 0

Based on formulas (8.6) and (8.7) for various shielding materials in the literature, the depths of penetration depths are given. The same data, for the purpose of visibility, we also give and we are in the form of Table 8.1.

From the table, it can be seen that for all high frequencies, starting from the range of medium waves, the screen from any metal with a thickness of 0.5..1,5 mm acts very efficiently. When choosing the thickness and material of the screen, it is not necessary to proceed from the electrical properties of the material, but to be guided considerations of mechanical strength, stiffness, resistance to corrosion, convenience of docking individual parts and the implementation between them transition contacts with low resistance, jobs soldering, welding, etc.

From the data table it follows that for frequencies more than 10 MHz copper film and especially from silver thickness less than 0.1 mm gives a significant shielding effect.. Therefore, at frequencies above 10 MHz, it is quite possible to use screens from a foil getynaks or other insulating material with copper or silver coated on it.

Steel can be used as screens, just need to remember that due to the high resistivity and phenomenon of the hysteresis, the screen can make significant losses in the shielding chains.

Filtration

Filtering is the main means of weakening the structural interference created in the power circuits and switching of the DC and AC. Disposed interference filters for this purpose make it possible to reduce conductive interference, both from external and internal sources. The filtration efficiency is determined by the filter injection:

dB

The following basic requirements are presented to the filter:

Ensuring the predetermined efficiency S in the required frequency range (taking into account the internal resistance and load of the electrical circuit);

Restriction of the permissible drop of constant or alternating voltage on the filter at a maximum load current;

Ensuring admissible nonlinear distortion of the supply voltage that determine the requirements for the linearity of the filter;

Constructive requirements - screening efficiency, minimal overall dimensions and weight, ensuring a normal thermal regime, resistance to mechanical and climatic influences, the manufacturability of the design of etc.;

Filter elements should be selected taking into account the rated currents and voltages of the electrical circuit, as well as the tensions caused by voltages and currents caused by the instability of the electrical mode and transition processes.

Capacitors. Apply as independent interference elements and as parallel links of filters. Constructive interference capacitors are divided into:

Bipolar types K50-6, K52-1B, it is, K53-1A;

Reference types KO, KO-E, KDO;

Controls of non-applicant type K73-21;

Passing coaxial types KTP-44, K10-44, K73-18, K53-17;

Condenser blocks;

The main characteristic of the interference capacitor is the dependence of its impedance from the frequency. To reduce interference in the frequency range, about 10 MHz, two-pole capacitors can be used, taking into account the low length of their conclusions. Supporting interference capacitors are applied to frequencies of 30-50 MHz. Symmetric passage capacitors are used in a two-wire chain to frequencies of about 100 MHz. Passing capacitors operate in a wide frequency range of about 1000 MHz.

Inductive elements. Applied as independent interference suppression elements and as sequential links of interference filters. Constructively most common chokes of special types:

Turns on the ferromagnetic core;

Canty.

The main characteristic of the interference choke is the dependence of its impedance from the frequency. At low frequencies, the use of magnetodielectric cores of MARODs of PP90 and PP250, made on the basis of M-Permooma, is recommended. To suppress interference in the circuits of equipment with currents up to 3A, it is recommended to use the type of type DM, with large nominal values \u200b\u200bof currents - chokes of the D200 series.

Filters. Ceramic passing filters of type B7, B14, B23 are designed to suppress interference in chains of constant, pulsating and alternating currents in the frequency range from 10 MHz to 10GHz. The designs of such filters are presented in Figure 8.17

Filters B7, B14, B23 injected in the frequency range 10..100 MHz increases from approximately 20..30 to 50..60 dB and in the frequency range over 100 MHz exceeds 50 dB.

Ceramic passing filters of type B23B are built on the basis of disk ceramic capacitors and loosening ferromagnetic chokes (Figure 8.18).

Besusless chokes are a tubular ferromagnetic core from ferrite 50 RF-2, dressed on the passing output. The inductance of the throttle is 0.08 ... 0.13 μH. The filter housing is made of Ceramic material UV-61 having high mechanical strength. The housing is metallized by a silver layer to ensure small transition resistance between the outdoor capacitor and the grounding threaded sleeve, with which the filter is fastened. The condenser on the outer perimeter is soldered to the filter housing., And internal - to the passing output. The sealing of the filter is ensured by the fill of the core of the case compound.

For filters B23B:

nominal containers of filters - from 0.01 to 6.8 μF,

rated voltage 50 and 250V,

rated current up to 20a,

Overall filter dimensions:

L \u003d 25mm, d \u003d 12mm

B23B filtered attenuation in the frequency range from 10 kHz to 10 MHz increases from approximately 30..50 to 60..0 dB and in the frequency range over 10 MHz exceeds 70 dB.

For onboard ES perspective, the use of special interference wires with ferronapplements having high magnetic permeability and large specific losses. So, in the Wiring of the PPE brand, the attenuation in the frequency range is 1 ... 1000 MHz increases from 6 to 128 dB / m.

Known the design of multi-heed connectors, in which each contact is installed by one P-shaped interference filter.

Overall dimensions of the built-in filter:

length 9.5 mm,

diameter 3.2 mm.

The filter attenuation in the 50-ohm chain is 20 dB at a frequency of 10 MHz and up to 80 dB at a frequency of 100 MHz.

Filtration of digital RES digital power circuits.

Pulse interference in power tires arising in the switching process of digital integrated circuits (CIS), as well as penetrating external paths, can lead to the appearance of failures in the operation of digital information processing devices.

Circuit-design methods are used to reduce the level of interference in power supply tires:

Reducing the inductance of tires "Power", taking into account the mutual magnetic connection of direct and reverse conductors;

Reducing the lengths of the "power" tires, which are common to currents for various cis;

Slowing down the fronts of pulse currents in the nutrition tires using interference capacitors;

The rational power chain topology on the printed circuit board.

An increase in the size of the cross-section of the conductors leads to a decrease in the own inductance of tires, and also reduces their active resistance. The latter is especially important in the case of the "Earth" tire, which is a reverse conductor for signaling chains. Therefore, in multilayer printed circuit boards, it is advisable to perform "power" tires in the form of conductive planes located in the adjacent layers (Figure 8.19).

Power supply tires used in print nodes on digital uses have large transverse dimensions compared to tires made in the form of printed conductors, and therefore less inductance and resistance. Additional advantages of mounted tires are:

Simplified tracing signal chains;

Increasing the rigidity of PP due to the creation of additional ribs that perform the role of limiters that protect the IP with hinged errega from mechanical damage during installation and configuration of the product (Figure 8.20).

High-tech is the "power supply" tires, made in printed method and fastening on PP vertically (Figure 6.12B).

Known designs of hinged tires installed under the Housing of the IP, which are located on the board with rows (Figure 8.22).

The constructed structures of the "power" tires provide a large circulatory capacity, which leads to a decrease in the wave resistance of the power line and, consequently, to reduce the level of pulse interference.

IP power wiring on PP should be carried out not sequentially (Figure 8.23a), and in parallel (Figure 8.23b)

It is necessary to use power wiring in the form of closed contours (Fig.8.23B). This design is approaching its electrical parameters to solid power planes. To protect against the influence of the external oxide magnetic field around the perimeter of the PP, an external closed circuit should be provided.

Ground

The grounding system is an electrical circuit that has a property to maintain a minimum potential, which is a reference level in a particular product. The grounding system in the ES should provide signal and power chains of the return, protect people and equipment from malfunctions in power supply circuits, remove static charges.

The following basic requirements are imposed on grounding systems:

1) minimization of the general impedance of the "Earth" tire;

2) the absence of closed grounding contours sensitive to magnetic fields.

The ES requires at least three separate grounding chains:

For signal circuits with low current and voltage;

For power chains with high levels Power consumption (power supplies, output Cascades ES, etc.)

For body chains (chassis, panels, screens and metallization).

Electrical chains in ES are grounded in the following ways: At one point and at several points closest to the reference point of the ground (Figure 8.24)

Accordingly, the grounding system can be called single-point and multipoint.

The largest level of interference occurs in a single-point grounding system with a common sequentially included "Earth" tire (Figure 8.24 a).

The further the grounding point is removed, the higher its potential. It should not be used for chains with a large variation of power consumed, since powerful fu creates large grounding currents that can affect the uninimed fu. If necessary, the most critical Fu should be connected as close as possible to the point of reference grounding.

Multipoint grounding system (Figure 8.24 c) should be used for high-frequency schemes (F≥10 MHz), connecting FU RES at points closest to the reference point of the ground.

For sensitive circuits, a floating ground circuit is used (Figure 8.25). Such a grounding system requires complete insulation of the circuit from the housing (high resistance and low capacity), otherwise It turns out to be ineffective. Solar elements or batteries can be used as power supply systems, and the signals must come and leave the circuit through transformers or optocouplers.

An example of the implementation of the considered grounding principles for the nine-legged digital drive on a magnetic tape is shown in Figure 8.26.

There are the following land tires: three signal, one power and one housing. The most susceptible to interference analog fu (nine read amplifiers) are grounded using two divided tires "Earth". Nine entry amplifiers working with large than read amplifiers, signal levels, as well as control and interface schemes with data transfer products are connected to the third Land Signal Tire. Three DC motors and their control schemes, relays and solenoids are connected to the power supply "Earth". The most susceptible control engine of the drive shaft is connected closer to others to the grounding point. The cabinet tire "Earth" serves to connect the housing and casing. The signal, power and cabinet tire "Earth" are connected together at one point in the source of the secondary power supply. It should be noted the expediency of the preparation of structural installation schemes in the design of the RES.