Tin foil hat radio with a metal bucket. The AM radio is completely inside a metal enclosure. This leads to a noticeable reduction in signal strength received by the AM radio. The efficiency of a metal enclosure in blocking electromagnetic radiation depends on the thickness of the foil, as dictated by the "skin depth" of the conductor for a particular wave frequency range of the radiation. For half-millimetre-thick aluminum foil, radiation above about 20 kHz (i.e., including both AM and FM bands) would be partially blocked, although aluminum foil is not sold in this thickness, so numerous layers of foil would be required
Foil (fencing) Olympics, although some organizations still fence competitively with non-electric swords. Foil have standardized, tapered, quadrangular (rectangular) blades that are made of tempered and annealed, low-carbon steel—or maraging steel as required for international competitions—and are designed to bend upon striking an opponent in order to prevent both injuries and breakage of the blade. The foil blade is no more than 90 cm in length with a blunted (or "foiled") tip, the maximum length of the assembled weapon is 110 cm, and the maximum weight is 500g; however, most competition foil are lighter, closer to 350g. The blade itself is subdivided into