Circuit board manufacturer: magnetostatic shielding of shielding magnetic field materials

Circuit board manufacturer: magnetostatic shielding of shielding magnetic field materials

Circuit board manufacturer, circuit board design and PCBA processing manufacturer explain circuit board manufacturer: circuit board manufacturer: magnetostatic shielding of shielding magnetic field materials

The problem of field shielding is of both practical and theoretical significance. According to different conditions, electromagnetic field shielding can be divided into three cases: electrostatic shielding, magnetostatic shielding and electromagnetic shielding. These three cases have both qualitative differences and internal connections, which cannot be confused.

Magnetostatic shield

The static magnetic field is the magnetic field generated by a steady current or permanent magnet. Magnetostatic shield is made of high magnetic permeability μ A shielding cover is made of the ferromagnetic material to shield external magnetic field. It is similar to but different from electrostatic shielding.

The principle of magnetostatic shielding can be explained by the concept of magnetic circuit. If the ferromagnetic material is made into a circuit with a section as shown in Figure 7, most of the magnetic field in the external magnetic field is concentrated in the ferromagnetic circuit. This can be analyzed by taking the ferromagnetic material and the air in the cavity as the parallel magnetic circuit. Because the permeability of ferromagnetic materials is thousands of times greater than that of air, the magnetic resistance of the cavity is much greater than that of ferromagnetic materials. Most of the magnetic induction lines of the external magnetic field will pass through the ferromagnetic material wall, while the magnetic flux entering the cavity is very small. In this way, the cavity shielded by ferromagnetic materials basically has no external magnetic field, thus achieving the purpose of magnetostatic shielding. The higher the permeability of the material, the thicker the cylinder wall, and the more significant the shielding effect. Because ferromagnetic materials with high permeability such as soft iron, silicon steel and permalloy are commonly used as shielding layers, magnetostatic shielding is also called ferromagnetic shielding.

Circuit board manufacturer, circuit board design and PCBA processing manufacturer explain circuit board manufacturer: circuit board manufacturer: magnetostatic shielding of shielding magnetic field materials

Magnetostatic shielding is widely used in electronic devices. For example, the leakage flux generated by transformers or other coils will affect the movement of electrons and affect the focusing of electron beams in oscilloscope tubes or picture tubes. In order to improve the quality of instruments or products, magnetostatic shielding must be applied to the parts that generate magnetic flux leakage. In watches, a thin soft iron shell can play an antimagnetic role in the outer cover of the movement.

As pointed out earlier, the effect of electrostatic shielding is very good. This is because the conductivity of metal conductor is more than ten orders of magnitude larger than that of air, while the difference between the permeability of ferromagnetic material and air is only a few orders of magnitude, usually thousands of times larger. Therefore, magnetostatic shielding always has some magnetic leakage. In order to achieve better shielding effect, multi-layer shielding can be used to shield the residual magnetic flux leaked into the cavity again and again. Therefore, effective magnetic shielding is generally bulky. However, if we want to create an absolute "magnetostatic vacuum", we can use the Meissner effect of superconductors. That is to say, if a superconductor is placed in an external magnetic field, the magnetic induction B in its body will always be zero. Superconductors are completely diamagnetic and have the best magnetostatic shielding effect, but they cannot be widely used at present. Circuit board manufacturer, circuit board design, PCBA processing manufacturer explain circuit board manufacturer: circuit board manufacturer: magnetostatic shielding of shielding magnetic field materials.