High-frequency optical module, to suppress EMI electromagnetic interference, there is an artifact called magnetic beads
Magnetic, generally we can guess, and electromagnetic induction, why is it called "beads"?
Because, at the earliest, these ferrite materials were made into loops on power lines or RF lines to suppress electromagnetic interference.
This kind of ferrite sleeve, as well as the method of wearing the tube, is very similar to the production of women's "pearl necklace", so it is called "bead", magnetic beads.
Inside the current optical module, the magnetic beads on the PCB are taken apart and still circled in a circle.
Magnetic beads and inductors have similarities in principle, and can suppress high-frequency noise. High-frequency alternating currents generate magnetic fields, and they generate electromagnetic induction, thereby suppressing the transmission of high-frequency signals.
It can pass through DC, and it is similarly circled in production.
What is the difference between them?
The material used for magnetic beads is ferrite, which is highlighted by an oxygen word, which was originally an oxide of iron. Nowadays, many metal oxides have been found to have the same characteristics, collectively referred to as ferrite.
Ferrite, compared with iron, has a larger magnetic flux. The same alternating electromagnetic field, ferrite can induce more magnetic fields.
For the optical module circuit, the external high-frequency alternating electromagnetic field is a kind of noise that needs to be filtered out. The ferrite is more sensitive to this induction and can be filtered more cleanly.
Ferrite, there is also an effect, the ferrite of the spinel structure has a gyromagnetic effect, the rotation of the magnetic field will generate eddy current, and the eddy current will release heat energy.
Ferrite, which absorbs high-frequency noise, generates gyromagnetic, increases eddy current loss, and is released in the form of heat.
Inductance, just store the energy of high-frequency noise, this energy will eventually be released to the circuit board in other forms, that is to catch a kind of noise, and then release a kind of noise.
Therefore, the choice of EMI is that the high-frequency impedance is larger, and no secondary noise is generated, and the ferrite bead is