As electromagnetic and radio frequency energies interfere with low-level signals, people use ferrite cores, also known as ferrite beads, to dissipate high-frequency energies as minute levels of heat. Depending on the nature and frequency of the interference, ferrite cores will also re-direct the EMI/RFI signals back down the cable, away from the device that these signals may affect. In addition, ferrite is usually easy to mill, given its malleability. These factors, combined with low overall cost, make iron ferrite a natural choice for cores and beads.
Power cords are often the most susceptible to electromagnetic and radio frequency interference, given the fact that these cables directly connect with many feet of wire in the wall that often acts as an antenna. When the cords have ferrite beads clamped around them, this effectively reduces or eliminates the interference while not impeding the current flow in the cords.
HDMI and Digital Cables
Ferrite cores and beads effectively filter common mode noise, which is standard electromagnetic or radio frequency interference in digital applications. Since digital signals are differential in nature, with two identical signals offsetting noise on the line, ferrite cores and beads eliminate the EMI/RFI noise that differential signals may not eliminate. For long HDMI and digital cable runs where the wire passes through areas of strong interference, the combination is effective.
Long runs of unshielded and/or ungrounded low-level signal cables, such as RCA cables, benefit from clamp-on ferrite beads. Such cables have a tendency to act as antennas, with extreme examples having the ability to pick up radio stations. In situations where cable replacement is not feasible, ferrite cores placed on the cables will mitigate or eliminate this issue.
Computers have internal processors running at frequencies that dip into radio range. Each board within the computer's case oscillates, causing potentially significant amounts of interference. Although the design of the computer's case is to block these frequencies, the cables connected to these internal components must use ferrite cores or beads to prevent interference. In addition, unprotected wires will act as a local antenna for any oscillation frequencies the computer case failed to block. The ferrite cores typically connect at the ends of the computer cables to protect against this.