Principle of Magnetic Beads

The main raw material of the magnetic beads is ferrite. Ferrite is a ferrimagnetic material of a cubic lattice structure. The ferrite material is iron-magnesium alloy or iron-nickel alloy. Its manufacturing process and mechanical properties are similar to those of ceramics, and the color is gray-black. One type of magnetic core often used in electromagnetic interference filters is a ferrite material. Many manufacturers provide ferrite materials specifically for electromagnetic interference suppression. This material is characterized by a very high frequency loss and a high magnetic permeability. It can be the smallest capacitance generated by the high-frequency high-resistance between the coil windings of the inductor.

The most important performance parameters for ferrite for suppressing electromagnetic interference are magnetic permeability μ and saturation magnetic flux density Bs. The magnetic permeability μ can be expressed as a complex number. The real part constitutes the inductance, and the imaginary part represents the loss, which increases as the frequency increases. Therefore, its equivalent circuit is a series circuit consisting of an inductor L and a resistor R, both L and R being a function of frequency. When a wire passes through such a ferrite core, the resulting impedance of the inductor increases in form as the frequency increases, but the mechanism is completely different at different frequencies.

In the low frequency range, the impedance is composed of the inductive reactance of the inductor. R is low at low frequencies, and the magnetic permeability of the core is high. Therefore, the inductance is large. L plays a major role, electromagnetic interference is reflected and suppressed. The loss of the core is small, and the whole device is a low-loss, high-Q inductor. This kind of inductance is easy to cause resonance. Therefore, in the low frequency range, the interference enhancement after the use of the ferrite bead may sometimes occur.

In the high frequency band, the impedance is composed of a resistance component. As the frequency increases, the magnetic permeability of the magnetic core decreases, resulting in a decrease in the inductance of the inductor, and a decrease in the inductive component. However, the loss of the core increases and the resistance component increases. This causes the total impedance to increase, and when the high frequency signal passes through the ferrite, the electromagnetic interference is absorbed and converted into heat energy to dissipate.

Ferrite suppression components are widely used in printed circuit boards, power lines, and data lines. High frequency interference can be filtered out by adding a ferrite suppression component to the input end of the power strip of the printed board. Ferrite magnetic rings or magnetic beads are designed to suppress high-frequency interference and spike interference on signal lines and power lines. They also have the ability to absorb electrostatic discharge pulse interference.


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