Ferrite beads and chokes both have impedance characteristics that can be employed as filters and safeguards to mitigate unwanted interference in electronic circuits. Random high frequency signals, also known as "noise" can cause other nearby circuits to malfunction.
An analogy for unwanted noise on top of the signal being at a party and trying to have an intimate conversation with someone you can not hear because everyone else around you is being too loud. The circuit through electromagnetic coupling, a circuit that has very sharp pulses can induce additional signals of the main signal in a nearby circuit, thereby becoming a source of noise that makes it almost impossible for the receiving circuit to interpret the main signal.
So what exactly are these things? A ferrite bead or choke is a non-resistant electronic member composed of ferromagnetic substances containing iron and trace amounts of nickel, zinc, or manganese oxides. Impedance characteristics of ferrite choke make it possible to deal with a high resistance to high frequency signals and low resistance to lower frequency signals. In this way the high frequency noise subdued, and the absorbed energy is converted to a very small amount of heat. The type of ferrite material used in the bead will determine the frequency range repression and the physical dimensions and shape of ferrite bead determine the amount of repression possible.
The beads themselves can be other than a dowel-type device that has a hole in the middle or something that looks like a blob of metal, which is really a multi-layer pearl used in surface mount applications. Electromagnetic interference (EMI) suppression beads, which are comparable with coils, designed to increase in transmission of signals with frequency until a resonance point. While a standard coil's wave propagation would begin to decline as the frequency continues to increase, the ferrite bead inductance flattened and serves as a perfect muffler for a wide frequency band.
A very basic use of ferrite chokes are on computer cables. You've probably seen these before, they look like a bump or a cylinder of wire. These bottles have snap-on ferrite beads to suppress the potential RF interference from the cables.
They can also be used in mobile phones. There is no agreement on whether the radiation from mobile phones will be detrimental to one's brain, and there are various devices available for sale as ferrite chokes or shields that are designed with the intent to suppress the radiation and interference from the phone. If your phone is placed near the speakers on your PC, you will actually hear this interaction of sound waves or interference.
Usually what happens is that you hear an annoying buzzing, which occurs because the cables on the speakers pick up the energy transfer from your mobile phone. Besides adding beads to your phone, you may also want to make snap-on beads on your speakers to curb disorder (unless you want two seconds alarm that your phone is about to ring).
Because today's circuits are faster and more of them packed in a circuit, it is highly desirable to employ ferrite beads and other techniques to suppress noise. Digital designers are thinking only of ones and zeros signals until they uncover nightmare of the sphere of analog, which is noisy circuit behavior or interference from power supplies or problems with grounding.
Besides protecting yourself from your own circuits, there are numerous "harden applications" where you need to protect circuits attenuate any noise caused by external sources. An example would be a strong transmitter as a mobile phone is accidentally operated on an aircraft, or a more focused attempt to jam a military use.
Ferrite bead and strangles are basic equipment which can serve as the first line of defense for RF and other noise damping suppresses applications. A company that produces pearls can give you the arcs in impedance vs. frequency for the beads they produce; typically their application engineers can help you choose the right type of pearl.
