Radio waves bounce off metal, so it is impossible to read a radio frequency identification tag placed within a metal box. A passive ultrahigh-frequency (UHF) tag placed inside a wooden box might be readable, however. It would depend on how thick the wood was, whether the wood was wet (water absorbs radio waves in the UHF spectrum) and how close the reader antenna was to the box (if the antenna was closer, a greater amount of energy would likely reach the tag). There are active (battery-powered) RFID tags that broadcast a signal like a cell phone, and these would likely be readable even if the tag were inside a wooden box.
—Mark Roberti, Founder and Editor, RFID Journal
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