EMC Question of the Week: August 25, 2025
Which material property is primarily responsible for the loss in a high-frequency ferrite bead or ferrite core used for EMI suppression?
- complex permittivity
- complex permeability
- conductivity
- eddy currents
Answer
The best answer is “b.” The high-frequency loss in ferrite beads and cores designed for EMI suppression is primarily due to the hysteresis losses in the magnetic material. These losses are related to the complex permeability of the material, μ' + jμ". Specifically, the loss tangent, tan δ = tan ( μ"/μ') determines the percentage of stored energy that is lost with each cycle at a particular frequency.
The complex permittivity is a primary source of high-frequency loss in printed circuit board dielectrics, but it doesn't contribute significantly to the loss in a ferrite bead or core. The conductivity of the ferrite is low and contributes relatively little to the losses at the frequencies where the ferrite is designed to operate.
Finally, eddy currents are not the most significant source of loss in a ferrite and (more importantly) they are not a material property.
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