The principle of magnetic beads

The principle of magnetic beads

The main raw material of magnetic beads is ferrite. Ferrite is a ferrimagnetic material. The ferrite material is an iron-magnesium alloy or an iron-nickel alloy. Its manufacturing process and mechanical properties are similar to those of ceramics, and its color is gray-black. One type of core often used in EMI filters is ferrite material, and many manufacturers offer ferrite materials specifically for EMI suppression. This material is characterized by very large high-frequency loss and high magnetic permeability, which can minimize the capacitance generated between the coil windings of the inductor in the case of high frequency and high resistance. For ferrites used to suppress electromagnetic interference, the most important performance parameters are permeability μ and saturation magnetic flux density Bs. The permeability μ can be expressed as a complex number, with the real part constituting the inductance and the imaginary part representing losses, which increase with frequency. Therefore, its equivalent circuit is a series circuit consisting of an inductor L and a resistor R, both of which are functions of frequency. When a wire is passed through such a ferrite core, the impedance of the formed inductor increases in form with increasing frequency, but the mechanism is completely different at different frequencies. In the low frequency band, the impedance is composed of the inductive reactance of the inductor. At low frequencies, R is small, the magnetic permeability of the magnetic core is high, so the inductance is large, L plays a major role, and the electromagnetic interference is reflected and suppressed, and the magnetic The loss of the core is small, and the whole device is a low-loss, high-Q inductor, which is easy to cause resonance. Therefore, in the low frequency band, sometimes the phenomenon of increased interference after the use of ferrite beads may occur.

In the high frequency band, the impedance is composed of resistance components. As the frequency increases, the magnetic permeability of the magnetic core decreases, resulting in a decrease in the inductance of the inductance and a decrease in the inductive reactance component. However, at this time, the loss of the magnetic core increases, and the resistance component increases. , resulting in an increase in the total impedance, when high-frequency signals pass through the ferrite, the electromagnetic interference is absorbed and converted into heat and dissipated.

Ferrite suppression components are widely used on printed circuit boards, power lines, and data lines. If a ferrite suppression element is added to the inlet end of the power line of the printed board, high-frequency interference can be filtered out. Ferrite rings or beads are specially designed to suppress high frequency interference and spike interference on signal lines and power lines, and it also has the ability to absorb electrostatic discharge pulse interference.

The numerical value of the two components is proportional to the length of the magnetic bead, and the length of the magnetic bead has a significant influence on the suppression effect. The longer the length of the magnetic bead, the better the suppression effect.

As power supply filtering, inductors can be used. The circuit symbol of the magnetic bead is the inductance, but it can be seen from the model that the magnetic bead is used. In terms of circuit function, the magnetic bead and the inductance have the same principle, but the frequency characteristics are different. The magnetic bead is composed of oxygen magnets. The magnetic beads have a great hindering effect on high-frequency signals. The general specification is 100 ohms/100mmHZ, and its resistance is much smaller than the inductance at low frequencies. Magnetic beads are an anti-jamming component that has developed rapidly. It is cheap, easy to use, and has a remarkable effect of filtering out high-frequency noise.