The function of the magnetic bead is mainly to eliminate RF noise present in the transmission line structure, RF energy is an AC sine wave component superimposed on the DC transmission level, and the DC component is a useful signal that is needed. To eliminate this unwanted signal energy, a chip magnetic bead is used to act as a high-frequency resistor (attenuator).

Magnetic beads have high resistivity and permeability, equivalent to resistance and inductance in series, but the resistance value and inductance value vary with frequency. It has better high-frequency filtering characteristics than ordinary inductors, showing resistance at high frequencies, so it can maintain a high impedance in a wide frequency range, thereby improving the frequency modulation filtering effect.

Structural characteristics of magnetic beads:

1, when the current in the wire passes through, the ferrite has almost no impedance to the low frequency current, and the higher frequency current will have a large attenuation effect. In which the high-frequency current is dissipated as heat, the equivalent circuit is an inductor and a resistor in series, and the values of both components are proportional to the length of the magnetic bead.

There are many types of magnetic beads, and manufacturers should provide technical indicators, especially the curve of the impedance and frequency relationship of magnetic beads. Some magnetic beads have multiple holes, using a wire through the component impedance can increase (through the square of the number of magnetic beads), but the increased noise suppression ability at high frequencies can not be as much as expected, and the method of using more than a few magnetic beads in series will be better.

2, ferrite is a magnetic material, will produce magnetic saturation through the current is too large, and the magnetic permeability drops sharply. The high-current filter should use a specially designed magnetic bead on the structure, and pay attention to its heat dissipation measures. Ferrite magnetic beads can not only be used to filter high-frequency noise in power supply circuits (can be used for DC and AC output), but also can be widely used in other circuits, and its volume can be made very small.

Especially in digital circuits, because the pulse signal contains high frequency high-order harmonics, which is also the main source of high frequency radiation of the circuit, it can play the role of magnetic beads on this occasion. Ferrite beads are also widely used in noise filtering of signal cables.