The function of a magnetic bead is primarily to eliminate RF noise present in the structure of the transmission line. RF energy is the AC sine wave component superimposed on the DC transmission level, and the DC component is the desired useful signal. To eliminate this unwanted signal energy, a chip bead is used to play the role of a high-frequency resistor (attenuator).
Magnetic beads have high resistivity and permeability, equivalent to a resistor and inductor in series, but both the resistance and inductance values vary with frequency. It has better high-frequency filtering characteristics than ordinary inductors, and exhibits resistivity at high frequencies, so it can maintain a high impedance over a fairly wide frequency range, thus improving FM filtering.
Expanded Information
Structural Characteristics of Magnetic Beads:
1. When the current passes through the wire, the ferrite has little impedance to the low-frequency currents, while it produces a greater attenuation to the higher frequency currents. High frequency currents are dissipated in them as heat, and the equivalent circuit is an inductor and a resistor in series, with the values of both components proportional to the length of the magnetic bead.
There are many types of magnetic beads, and the manufacturer should provide a description of the specifications, especially the curve of the bead's impedance versus frequency. Some beads have multiple holes, with a wire through the component impedance can be increased (the square of the number of times through the bead), but the increased noise suppression at high frequencies is not likely to be as much as expected, and the use of a few more beads in series will be better.
2, ferrite is a magnetic material, through the current is too large and produce magnetic saturation, permeability drops sharply. High-current filtering should be used on the structure of specially designed beads, but also pay attention to its thermal measures. Ferrite beads are not only used in power supply circuits to filter out high-frequency noise (which can be used for both DC and AC outputs), but can also be used in a wide range of other circuits, and their size can be made very small.
Particularly in digital circuits, because the pulse signal contains a high frequency of high harmonics, but also the main source of high-frequency radiation in the circuit, so the role of magnetic beads can be played in such occasions. Ferrite beads are also widely used in signal cable noise filtering.
Baidu Encyclopedia - Magnetic Beads