Answer: Ferrite Beads

That clunky cylinder of hard plastic on the end of many of the cables you’ll find around your home and office—USB cables, video cables, and so on—has a specific function. Inside the hard plastic casing is a chunk of ferrite-infused ceramic designed to suppress high-frequency noise. Essentially, the ferrite bead acts as a passive low-pass filter that both blocks energy from “outside” sources that could interfere with the cable’s function and absorbs energy the cable might emit that could interfere with nearby devices. The majority of energy is absorbed by the bead and then released as tiny amounts of heat into the surrounding air.

Why is it important to suppress high-frequency noise? The noise suppression serves two primary purposes. First, it prevents electrical noise generated within a device from interfering with other components—so, for example, interference from a computer doesn’t interfere with the performance of the monitor. Second, it prevents electrical and radio energy from leaking out and interfering with surrounding equipment like television sets and radios. Ferrite beads are one of the simplest (and certainly one of the cheapest) types of interference filters to install on existing cabling, if they are called for, since you can buy cheap snap-on models that clip right over existing cables.