Principle of magnetic beads

- Aug 14, 2018-

The main material of magnetic beads is ferrite. Ferrite is a kind of ferrous magnetic material with cubic lattice structure. Ferrite material is ferromagnesium alloy or ferronickel alloy, its manufacturing technology and mechanical properties are similar to ceramics, color is gray black. Ferrite material is a kind of magnetic core commonly used in electromagnetic interference filters. Many manufacturers provide ferrite material specially for electromagnetic interference suppression. This material is characterized by high frequency loss and high magnetic conductivity, which can be the minimum capacitance between inductor winding and high frequency resistance. For the ferrite used to suppress electromagnetic interference, the most important performance parameters are the magnetic permeability dependence and the saturated flux density Bs. The magnetic conductivity is expressed as a complex number, the real part constitutes the inductance, and the imaginary part represents the loss, which increases with the increase of frequency. Therefore, its equivalent circuit is a series circuit composed of inductance L and resistance R, both L and R are functions of frequency. When the wire passes through the ferrite core, the inductance formed increases in form as the frequency increases, but the mechanism is completely different at different frequencies.

Made up of inductive impedance at low frequencies, impedance, low frequency when R is very small, the core permeability is higher, so the large inductance, L plays a main role, electromagnetic interference is reflected and suppressed, and then the core loss is small, the whole device is a characteristic of low loss, high Q inductance, the inductance is easy to cause resonance in low frequency band, therefore, may sometimes appear interference phenomenon of enhanced after using ferrite beads.


At high frequencies, impedance by resistance to composition, with increasing frequency, magnetic core permeability decrease, lead to the inductance of the inductance, inductance components But, at this time of the magnetic core loss increases, the resistance components increase, lead to the total impedance increases, when the high frequency signal through the ferrite, electromagnetic interference is absorbed into the form of heat energy wasted.