The so-called demagnetization, in fact, does not disapp […]
The so-called demagnetization, in fact, does not disappear, but only changes the magnetic field distribution of the magnet through the magnetically conductive material.
Degaussing packaging is generally separated by iron sheet, and the six sides inside the box are fixed, then packed with pearl cotton, and then packed in a cardboard box. This can pass some airlines' security checks for some magnetically weak magnets. Some magnetic barrier materials sold in the market can also play a relatively good demagnetizing effect. Reassemble the powerful magnets to reduce the magnetism of the powerful magnets so that the powerful magnets can pass the security inspection of the airline and be brought on the aircraft.
The principle of magnetic isolation is to shield the magnetic field, which refers to a stable magnetic field or a low-frequency magnetic field. It mainly depends on the magnetic field circuit. If the box is made of a highly magnetically permeable material, the "magnetic lines" that would pass through the box are concentrated on the box material. Closed, the magnetic field lines leaking out of the box are greatly reduced. In order to achieve magnetic field shielding, the higher the magnetic permeability of the material, the better; the same material, the thicker the better; the same material and thickness, the more layered the better. In addition, the magnet should be placed in the center of the shielding box, so that the magnetic lines of force on one side are more concentrated and leak out more.
If you want to shield the high-frequency magnetic field, you need to use a method: use a highly conductive material such as metal, use the high-frequency magnetic field to form an alternating eddy current on it, and form an opposite magnetic field to cancel the original magnetic field. The magnetic field is superimposed, canceled outside the shield, and a new magnetic circuit is synthesized inside the shield. With regard to the second point, the material is magnetized. In a magnetic field, a magnetically permeable material is always magnetized. Except for hard magnetic materials, once the external magnetic field is removed, the magnetism is quickly eliminated. Therefore, if the shielding material is made of hard magnetic material and a new independent magnetic field is formed, the effect will be affected. This is why the shield can only use soft magnetic materials. (If you ask, since soft magnetic materials will also be magnetized in the magnetic field, how can they be shielded? This is because the soft magnetic materials are magnetized and the new magnetic field strength is completely based on the external original field strength. Change, and then according to the above-mentioned high-frequency magnetic field shielding principle, the "shielding" is realized by depletion. "Magnetic line" is an image saying, the essence is the superposition of the field.) Magnetic shielding in vacuum, because air is a paramagnetic substance, The magnetic permeability is slightly larger than that of vacuum, so theoretically the magnetic shielding effect in vacuum is better than in air, but the effect is minimal in engineering. Because the ratio of the relative magnetic permeability of the paramagnetic material and the diamagnetic material to the relative vacuum (that is, the relative magnetic permeability) is almost 1, the difference is at most a few thousandths; and the relative permeability of the magnetically permeable material (ferromagnetic material) There are hundreds or thousands of magnetic susceptibility, even over 100,000 or 100,000. Comparing the two, the existence of paramagnetic and diamagnetic substances is often ignored in engineering.