The main raw material of SMD magnetic beads is ferrite. Ferrite is a ferrite magnetic material with cubic lattice structure. Ferrite material is iron-magnesium alloy or iron-nickel alloy. Its manufacturing process, mechanical properties and ceramics Similar, the color is gray-black. One type of magnetic core often used in electromagnetic interference filters is ferrite materials, and many manufacturers provide ferrite materials specifically for electromagnetic interference suppression. The characteristic of this material is that the high frequency loss is very large and has a very high magnetic permeability. It can minimize the capacitance generated between the coil windings of the inductor under the condition of high frequency and high resistance. Ferrite materials are usually used in high-frequency situations, because at low frequencies they mainly exhibit inductive characteristics, making losses very small. At high frequencies, they mainly exhibit reactance characteristics and change with frequency. In practical applications, ferrite materials are used as high-frequency attenuators for radio frequency circuits. In fact, the ferrite can be effectively equivalent to the parallel connection of resistance and inductance. At low frequencies, the resistance is short-circuited by the inductance. At high frequencies, the impedance of the inductance becomes so high that all current flows through the resistance. Ferrite is a consumption device, high-frequency energy is converted into heat energy, which is determined by its resistance characteristics.
　　For ferrites for electromagnetic interference suppression, the most important performance parameters are permeability and saturation flux density. The permeability 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 composed of an inductor L and a resistor R, both of which are a function of frequency. When the wire passes through this ferrite core, the inductance impedance formed increases in form with increasing frequency, but the mechanism is completely different at different frequencies. In the high frequency band, the impedance is mainly composed of the resistance component. As the frequency increases, the magnetic permeability of the magnetic core decreases, resulting in a reduction in the inductance of the inductor and an inductive component. However, at this time, the loss of the magnetic core increases. The increase in the resistance component leads to an increase in the total impedance. When the high-frequency signal passes through the ferrite, the electromagnetic interference is absorbed and converted into heat and consumed. In the low frequency band, the impedance is mainly composed of the inductive reactance of the inductor. At low frequencies, R is small, and the magnetic permeability of the magnetic core is high, so the inductance is large, and the inductance L plays a major role. The electromagnetic interference is reflected and suppressed, and this When the loss of the magnetic core is small, the entire device is a low-loss, high-quality Q-characteristic inductance. This kind of inductance is likely to cause resonance. Therefore, in the low frequency band, interference may increase after using ferrite beads.
　　There are many types of SMD beads, and manufacturers will provide technical specifications, especially the curve of the relationship between the impedance and frequency of the beads. Some magnetic beads have multiple holes. Passing the wire through can increase the impedance of the element (the square of the number of times the magnetic beads are passed), but the increased noise suppression ability at high frequencies may not be as expected. A magnetic bead approach.
　　It is worth noting that the energy of high-frequency noise is converted into heat energy by coupling the ferrite magnetic moment and the lattice, and it is not to introduce noise or block it back, like a bypass capacitor. Therefore, when the ferrite bead is installed in the circuit, it is not necessary to provide a ground point for it. This is a prominent advantage of ferrite beads.