Shielding

Shielding is wrapping a conductive (or magnetic) barrier around a circuit so electromagnetic fields can't get out — or in. Think of it as an umbrella for fields: the metal can over an oscillator, the braid woven around a cable, the silver-painted plastic enclosure of a laptop. When a wave hits the metal, some of it bounces straight off (reflection) and the rest is soaked up as tiny eddy currents in the metal (absorption), so very little makes it to the other side.

A shield only works if it's continuous and connected: every seam, slot and cable hole is a leak, because a slot longer than about a tenth of a wavelength radiates like the antenna you were trying to silence. That's why engineers obsess over gaskets, finger-stock, and grounding the shield — an ungrounded 'shield' can actually make emissions worse. Low-frequency magnetic fields are the hardest to block, needing thick high-permeability metal (like mu-metal) rather than ordinary copper or aluminium.