Chip BeadThe main raw material is ferrite, which is a cubic lattice structure of ferrous magnetic material. The ferrite material is iron magnesium alloy or iron nickel alloy, and its manufacturing process and mechanical properties are similar to ceramics, with a color of gray black. A type of magnetic core commonly used in electromagnetic interference filters is ferrite material, and many manufacturers provide ferrite materials specifically for electromagnetic interference suppression. The characteristic of this material is that it has very high high-frequency losses and high permeability, which can minimize the capacitance generated between the coil windings of the inductor under high-frequency and high resistance conditions. Ferrite materials are usually used in high-frequency situations because they mainly exhibit inductive characteristics at low frequencies, resulting in minimal losses. At high frequencies, they mainly exhibit reactance characteristics and change with frequency. In practical applications, ferrite materials are used as high-frequency attenuators for RF circuits. In fact, ferrite can be effectively equivalent to the parallel connection of resistors and inductors. At low frequencies, the resistor is shorted by the inductor, and at high frequencies, the impedance of the inductor becomes quite high, so that all current passes through the resistor. Ferrite is a consumer device that converts high-frequency energy into thermal energy, which is determined by its resistance characteristics.

The most important performance parameters for ferrite used for suppressing electromagnetic interference are magnetic permeability and saturation magnetic flux density. The magnetic permeability can be expressed as a complex number, with the real part forming the inductance and the imaginary part representing the loss, which increases with frequency. Therefore, its equivalent circuit is a series circuit composed of inductance L and resistance R, both of which are functions of frequency. When the wire passes through this ferrite core, the inductance impedance formed increases formally with increasing frequency, but the mechanism is completely different at different frequencies. In the high-frequency range, impedance is mainly composed of resistance components. As the frequency increases, the magnetic permeability of the magnetic core decreases, resulting in a decrease in the inductance and inductance components of the inductance. 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, electromagnetic interference is absorbed and converted into heat energy for consumption. In the low frequency range, impedance is mainly composed of the inductance of the inductor. At low frequencies, R is very small, and the magnetic permeability of the magnetic core is high. Therefore, the inductance is large, and the inductance L plays the main role. Electromagnetic interference is suppressed by reflection, and at this time, the loss of the magnetic core is small. The entire device is a low loss, high-quality factor Q characteristic inductor, which is prone to resonance, Therefore, in the low frequency range, there may be an increase in interference caused by the use of ferrite magnetic beads.

There are many types of SMD magnetic beads, and manufacturers will provide technical specifications, especially the impedance frequency curve of the magnetic beads. Some magnetic beads have multiple holes, and passing a wire through them can increase the impedance of the component (the square of the number of times the magnetic beads are passed through). However, the increased noise suppression ability at high frequencies may not be as much as expected, and multiple magnetic beads can be connected in series.

It is worth noting that the energy of high-frequency noise is converted into thermal energy and dissipated through the coupling of ferrite magnetic moment and lattice, rather than introducing noise into the ground or blocking it back, as in the case of bypass capacitors. Therefore, when installing ferrite magnetic beads in a circuit, there is no need to set a grounding point for it. This is a prominent advantage of ferrite magnetic beads.