The role of magnetic beads in solving EMI and EMC

    (magnetic beads), like inductors, is a common device used to solve EMI and EMC problems, and its main role is to suppress high-frequency conducted interference signals.

    (magnetic beads) can be equivalent to an inductor, but the equivalent inductor is different from the inductor coil, the biggest difference between (magnetic beads) and the inductor coil is that the inductor coil has a distributed capacitance. (magnetic bead), that is, the through-core inductor, is an inductor with a number of turns less than 1 turn. However, the distribution capacitance of the through-core inductor is several times to dozens of times smaller than that of the single-turn inductor, so the through-core inductor operates at a higher frequency than the single-turn inductor.

    The inductance of the core inductance is generally relatively small, about between a few micro heng to dozens of micro heng, the size of the inductance is related to the size and length of the wire in the core inductance, and the cross-sectional area of the (magnetic bead), but the biggest relationship with the (magnetic bead) inductance is also the relative permeability of the (magnetic bead).

    In addition, when the working frequency of the through-core inductor is very high, eddy currents will be generated in the body of the (magnetic bead), which is equivalent to the permeability of the through-core inductor to reduce, at this time, we generally use effective permeability. Effective permeability is the relative permeability of the (magnetic bead) at a certain operating frequency. However, since the operating frequency of the (magnetic beads) is only a range, the average magnetic permeability is used in practical applications.

    (magnetic beads) Another use is used to do electromagnetic shielding, its electromagnetic shielding effect is better than the shielding effect of the shielding line, which is generally not paid much attention to. The method of use is to let a pair of wires pass through the middle of the (magnetic bead), so when there is a current flowing from the double wire, the magnetic field generated will be mostly concentrated in the (magnetic bead) body, the magnetic field will not radiate out; Because the magnetic field will produce eddy currents in the (magnetic bead) body, the direction of the eddy current generation power line is opposite to the direction of the conductor surface power line, which can cancel each other, therefore, (magnetic bead) also has a shielding effect on the electric field, that is, (magnetic bead) has a strong shielding effect on the electromagnetic field in the conductor.

    The advantage of using (magnetic beads) for electromagnetic shielding is that (magnetic beads) do not need to be grounded, which can eliminate the trouble of grounding the shielding line. Using (magnetic beads) as electromagnetic shielding, for double wires, is also equivalent to connecting a common-mode suppression inductor in the line, which has a strong suppression effect on common-mode interference signals.