Ferrite sleeves, also known as ferrite beads, are non-conductive components used in electrical circuits to suppress or filter high frequency electromagnetic interference noise. They prevent electromagnetic interference to and from a device.
If a device produces radio frequency energy, the conductive cable is used as an antenna to transmit the energy through the device. The ferrite sleeve or bead reduces the output of EMI from the device itself and prevents the cable from acting as an antenna for other sources of EMI, like household appliances.
Ferrite sleeves are commonly found on data cables and medical equipment and can be used on a wide range of other components. They may be built in to the equipment or be separate items that can be clamped on to a cable. You may see larger ones on computer monitor cables for example, while smaller ones can be used internally in electrical circuits, or printed circuit boards (PCBs) for example. Ferrite sleeves are often needed for regulatory compliance.