Already common in such gadgets as highway passes for paying tolls on the move, miniature radio-equipped circuit cards may ultimately become as widespread as bar codes. First, however, the cost of such radio frequency identification (RFID) tags must drop by a factor of 10 or more.
Engineers in Belgium have just developed an extraordinarily fast diode—a one-way valve for electric current—that could usher in RFID tags made of plastic rather than the more-expensive silicon of tags today.
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