Abstract: A tag has an integrated circuit (IC), electrode plates included in the IC, an electrically insulating film covering the electrode plates, antenna terminals each facing one of the electrode plates with the insulating film sandwiched between, antennas each being connected to one of the antenna terminals, and packings.

Abstract: In a transponder, power supply circuitry is connected to an antenna and a response circuit. DC power to be fed to the response circuit is generated out of an electromagnetic wave come in through the antenna. A rectifier diode has an n type and a p type semiconductor region and is adjusted such that a reverse resistance against a reverse current directed from the n type region toward the p type region is lower than a forward resistance against a forward current directed from the latter region to the former region. A voltage output from the antenna on the receipt of the electromagnetic wave is applied to the rectifier diode, thereby causing a reverse current to flow to the diode. The resulting DC voltage is used to feed power to the response circuit. Even when the electromagnetic wave received from an interrogator is weak, sufficient power can be surely fed to the response circuit.