Whether you are plugging in a laptop to a wall outlet for charging or are inserting a USB cable into a computer, you may have noticed the commonality of a large, nondescript cylinder that is located close to the connecting end of the cable. While you may not have thought much about the cylinder common to cables, it serves a very important role in connections and transfers. Known as ferrite cores, beads, or chokes, these cylinders are relied on for EMI management across a number of devices. While ferrite cores may play a diverse set of roles based on the application, this blog will be concerned with the operations of ferrite cores when they are specifically found on electronic cables.
As an element used for EMI protection, a ferrite core serves as a lowpass filter to guard a device. In a standard circuit, capacitors will operate as open when frequencies are low, while high frequencies will have them function as shorts. With consideration to Kirchoff’s voltage law, the total voltage of the loop will be equal to the sum of the drop across each component. It is important to know that both capacitors and inductors have a value known as capacitive reactance which is a counterpart to real number resistance. By adding resistance and reactance together as vectors, one will find the impedance value.