You see them all the time on your power cords. They may look like a little mini donuts or tubes close to one end of the power cord but what are they and why do we need them? Those are called ferrite beads and they are very useful in reducing electromagnet interference (EFI) and radio frequency (RFI). This can be important when you don’t want your machines to have any disruptions or interference of other kinds of signals. The beads can also be referred to by different names such as blocks, cores, rings, EMI filters and chokes.
Ferrite beads are a simple way in eliminating broadcast signals. It does the same thing as shielded wire but can be more cost effective as you can add it on at a later time and not have to buy a completely new cable or power cord. Cables can act like an antenna for broadcast signals so the ferrite will “choke” out the signal on the point that it is located on the cable. That’s why you see these beads on the ends. Once the signal is choked out the energy is turned into low heat with in the bead. Ferrite is a semi-magnetic substance made from iron oxide alloyed with other metals which makes in a great inductor.
There are two kinds of ferrite beads, molded and clip-on. The molded ferrite will have the wire through the bead when the cable is made. The clip-on will just attach to the outside of the preexisting cable in two pieces. If you remove the plastic coating on the outside of the ferrite you will just see this black metal cylinder.