# Magnetic shielding question and answer

2021-02-03 619
How to stop the attraction between 2 magnets?

When shielding a magnet, an important consideration is that the magnet will be attracted to the shielding material. There is no magnetic shielding material that will not be attracted by magnets.

The shielding repulsion between two magnets is easy:
Use highly saturated alloys, such as Giron or MagnetShield. Just stack enough layers between the two magnets until the attractive force of the shielding layer balances the repulsive force between the magnets. The appropriate number of layers will depend on the strength of the magnets, the distance between the magnets, and the size and shape of the shield. A little experimentation can quickly get the correct result.

The shielding attraction between the two magnets requires that each magnet has its own shield. The shielding layer does not have to be in contact with its respective magnet, but must remain fixed in position relative to its magnet. Likewise, the appropriate number of layers will depend on the strength of the magnet, the distance between them, and the size and shape of the shield. Just add one layer at a time until the two magnets are separated from each other.

Finally, about shielding only one pole of the magnet:
Although this is technically impossible, it is possible to deform the lines of magnetic force around one pole of the magnet. Remember that magnetic field lines pass through the shield more easily than through air. Therefore, the shield acts as a "pipe" for certain magnetic field lines. They still have to travel from the N pole to the S pole of the magnet... but the path they follow can be manipulated. This means that if you "shield" one pole of a magnet, you are basically relocating where those magnetic field lines appear in the air. The effect is the same as bending the magnet itself into a different shape.

Why can't only use lead or copper or aluminum foil for magnetic shielding?
In the strictest sense, magnetic shielding is not a real shield at all. Unlike the way that lead shields block X-rays, magnetic shielding materials generate lower magnetic fields nearby by attracting magnetic field lines to themselves. The physical property that allows them to do this is called "permeability."

Unlike X-rays, sound, light, or bullets, magnetic field lines must travel from the north pole of the source and return to the south pole. Under normal circumstances, they will pass through air, and by definition, the permeability of air is "1". However, if there is a material with higher permeability nearby, the magnetic field lines (they are effective organisms) will travel along the path of least resistance (through the higher permeability material), leaving behind in the surrounding air. Lower the magnetic field.

The following is a comparison of permeability of some commonly used materials:

Air........... 1
Copper... 1
Aluminum... 1
Tin............. 1
Lead........ .. 1

Nickel...100
Commercial Rail... 200
Stainless steel....... 200
Magnetic shield..... 4000

*Such as anti-magnetic foil, anti-magnetic board and joint shield

Now, it is easier to see why magnetic shielding in the shape of a shell (sphere, box, tube, etc.) has a better shielding effect than a flat or partial shell. The radiation source in the shield will generate magnetic lines of force, which will pass through the air near the north pole until it reaches the shield. Then through the shield, they will appear in the air around the Antarctic and return to the source. Traveling through low permeability air outside the shield does not bring any efficiency advantages! (Please note that the picture on the right is a cross-sectional view of the tubular shield.)

Similarly, if the source of the magnetic field is outside the housing, the lines of magnetic force will pass through the material of the housing on the way back to the source and will never find more effective penetration into the air inside the housing. For these reasons, to close the source of the magnetic field or something you wish to protect from the magnetic field, shielding materials can be used most effectively, and usually the most economical!

Is there any material that can block the magnetic force? Does lead in particular block the magnetic field?

The magnetic field (the force caused by the magnetic field) cannot be blocked. That is, there is no magnetic insulator.

The main reason for this is related to one of Maxwell’s equations:

Del point B = 0,

This means that there are no magnetic monopoles. That is, when you can separate electric monopoles (positive and negative charges) so that the electric field never ends up with opposite charges, you cannot do this with magnetic poles. There are no magnetic monopoles. There is no such thing as "magnetic charge". All magnetic field lines must terminate at the opposite end. Therefore, they cannot be stopped-naturally a way must be found to return the magnetic field lines to the opposite pole.

However, the magnetic field can rewire around the object. This is a form of magnetic shielding. By surrounding an object with a material that can "conduct" magnetic flux better than the material around it, the magnetic field will tend to flow along the material and prevent the object from entering the interior. This allows the magnetic lines of force to end at opposite poles, but only provides them with a different path.

The permeability of lead is 1. This means that the performance of magnetic shielding is not better than that of air.

So the short answer:

No material can block the magnetic field
Lead has absolutely no effect on the magnetic field
If you want to block the magnetic force, the best way is to re-arrange the magnetic field lines (magnetic flux lines) around the objects that are sensitive to the magnetic field lines. This can be done by shielding the object in a material that has a much higher permeability than the surrounding material.
Respondent: Ted Pavlic, electrical engineering student at St. Louis University in Ohio.

The interesting observation is that despite the many analogies between electricity and magnetism, there is actually no magnetic "insulator." But, as a bunch of clever engineers, they came up with a solution to this problem....

...For example, in order to protect electronic equipment from external magnetic fields, engineers usually use a housing or housing made of a material with a high magnetic permeability, that is, the material will allow the internal The magnetic flux lines effectively concentrate the lines inside the material, and then "guide" them away from the internal precision electronic equipment.

From another perspective, it is sometimes necessary to transport magnetic parts and materials to the destination by airplane. The federal government has strict regulations on magnetic fields and aircraft instruments; for obvious reasons, the magnets on the aircraft must not interfere with the flight controller. Therefore, magnets are usually packaged “from beginning to end” so that their north poles are adjacent to other south poles, and thin steel plates or other iron-based materials are filled around the magnets to “shunt” the magnetic field and prevent it from penetrating outside the box.

Lead is not a ferromagnetic material, so it cannot shield or shunt magnetic fields.
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