Ferrite beads are a kind of electronic component which are used to restrain unwanted noise in the conducting wires. It has a hole in the center and is made of ferromagnetic element. It is a kind of electronic choke that acts as an effective shield to suppress noise that has higher frequency. It provides protection from interference coming from dual directions- one from a particular device and the other, to a particular device. Noise generating from high frequency circuits are generally ground leads, inter stage connections and power supply leads. If there is any unshielded conductor and active lead nearby, then they might facilitate the transference of energy from one to another. To prevent it, all that needs to be done is to place some ferrite Beads on this leads, so that they can totally block this exchange of energy. Its-best part is that it can be used on any existing circuit.
The cable on which the bead is used works like an antenna, through which electronic energy passes, ferrite bead here controls the flow of energy and helps to decrease EMI. On the other hand, if there is another source of EMI, it prevents action of the cable as a conductor of energy (antenna) and absorbs all the interferences into itself.
The amount of electrical resistance provided by the bead depends on the kind of material it is made of, the level of frequency and also the size of the bead. As the level of frequency gets higher, it also increases to show its resistance to electrical power in the form of low-level of reactance and as reactance is very low, so it has a very low chance of resonance that could disturb attenuation effect. The resistivity of the bead is directly connected to the length of it. They are available in different sizes- lengthy beads are applied to the external cables, whereas smaller ones are used inside electrical goods in circuits on conductors or around the pins of circuit board conductors.
You can add more beads to the same cable to enhance their power of resistance. As the magnetic field is contained within the bead, it works all the same whether it is touching the cable or not I not. The bead used in the inductors acts as a filter, in that it provides prevention from high pitch RFI or EMI electronic noise. The blocked energy is sent up on the cable or it gets disintegrated at the lower level in the form of heat. But if this heat oversteps the threshold of Curie point, then it will lose its magnetic quality and will be stripped off its power to block noises.
Ferrite Beads are generally small in size, so it enables only one turn through it. But the hole of the toroidal beads is bigger in size and it is used in cases where more turns are necessary to provide stronger impedance. The turn through the bead is counted by the time a cable passes through its center hole. Sometimes the level of impedance depends upon the turning pattern of the wire. The winding can be done clockwise, anticlockwise or in crisscrossed manner. This pattern is very important, as the pattern will show direct impact on the amount of impedance offered by the bead.