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water is a good transparent absorber for RFwater is a good transparent absorber for RFPosted Nov 21, 2005 21:25 UTC (Mon) by stevenj (guest, #421)In reply to: A Better Tin-Foil Hat ? by MathFox Parent article: Richard Stallman's Tin-Foil Hat (Bruce Perens' Journal)
Light is a kind of electromagnetic wave, so you'll need to find a transparant material that reflects the (low frequency) radio waves, but allows (high frequency) light to pass through. These materials are available, but more expensive than tinfoil. At least for microwave (2.45GHz) RFID, which is used for the longest-range applications from what I'm reading, there is at least one very common and cheap material available that absorbs the RF but is optically transparent: water. At 2.45GHz, 3cm of water should be sufficient to attenuate the reflected RF power by over 98% according to the numbers here. If you use salt water then the absorption is even greater. Unfortunately, for longer wavelengths water may be impractical.
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