More than 22 million visitors attended the Expo 2005 World's Fair in Aichi, Japan. Not one got in with a bogus ticket. The passes were practically impossible to forge because each harbored a tiny RFID (radio-frequency identification) chip - just 0.4 millimeter (mm) on a side and 0.06 mm thick - that transmitted a unique identification number via radio waves to a scanner at the gates.
Now Hitachi, the maker of that chip, is aiming even smaller. Last year it announced a working version of a chip only 0.05 mm on a side and 0.005 mm thick. Almost invisible, this prototype has one sixty-fourth the area yet incorporates the same functions as the one in the Expo tickets. Its minuteness, which will allow it to be embedded in ordinary sheets of paper, heralds an era in which almost anything can be discreetly tagged and read by a scanner that it need not touch.