Ferrite bead

A ferrite bead at the end of a USB cable

A ferrite bead with its plastic shell removed

An rf inductor wound on a ferrite bead, and a pcb mount ferrite bead.

A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits. Ferrite beads employ the mechanism of high dissipation of high frequency currents in a ferrite to build high frequency noise suppression devices. Ferrite beads may also be called ferrite cores, ferrite rings, ferrite EMI filters, a ferrite choke or mistakenly as ferrous beads.^{[citation needed]}

Overview

Ferrite beads are inductors used as a passive low-pass filter. The geometry and electromagnetic properties of coiled wire over the ferrite bead result in a high impedance (resistance) for high-frequency signals, attenuating high frequency EMI/RFI electronic noise. The absorbed energy is converted to heat and dissipated by the ferrite, but only in extreme cases will the heat be noticeable.

Ferrite beads are one of the simplest and least expensive types of interference filters to install on preexisting electronic cabling. For a simple ferrite ring, the wire is simply wrapped around the core through the center typically 5 or 7 times. Clamp-on cores are also available, which can be attached without wrapping the wire at all.

Use with cell phone hands free wires

Ferrite beads may be used as a precautionary measure to limit cell phone radiation exposure. In 2005 Professor Lawrie Challis said clipping a ferrite bead onto hands-free kits stops the radio waves traveling up the wire and into the head^[1].

See also

• Balun
• Choke (electronics)
• Electromagnetic interference
• Ferrite (magnet)
• Ferrite (iron)
• Magnetic core
• Toroidal inductors and transformers
• Unintentional radiator

References

1. ^ "Bead 'slashes mobile radiation'". BBC News. 2005-01-25. http://news.bbc.co.uk/2/hi/health/4203077.stm. Retrieved 2009-03-17.

External links

• An explanation of the physics behind ferrite beads
• What are the bumps at the end of computer cables?
• Understanding Ferrite Bead Inductors, by Murata Manufacturing
• How to use ferrites for EMI suppression by Fair-Rite
• Tekzilla Daily Episode 13, short video podcast with explanation