Abstract: In an antenna 1a for reader/writer of an interrogator in a non-contact data carrier system comprising the interrogator and a transponder, the antenna for reader/writer of the interrogator comprises a transmitting antenna 2 for transmitting a signal to the transponder and a receiving antenna 3 for receiving a signal from the transponder, and the receiving antenna 3 is a loop coil located at a position where magnetic fields of opposite polarities are induced in the receiving antenna 3 by magnetic coupling between the receiving antenna 3 and the transmitting antenna 2 and where the magnetic fields of opposite polarities cancel out each other. Preferably, the transmitting antenna 2 is comprised of at least two loop coils 2a, 2b for generating magnetic fields of opposite polarities to each other.

Abstract: A battery-free non-contacting information card of a relatively simple arrangement which prevents an IC chip or the like from being destroyed by an excess voltage. This non-contacting information card includes a resonance circuit (3) for receiving a carrier signal (e.g., FSK signal) modulated on the basis of information supplied from a card reader/writer (2), an information processing systems (5), (6), (7) for obtaining information from the carrier signal and a rectifier systems (13) for obtaining a voltage by rectifying the carrier signal, wherein the non-contacting information card can be operated by the voltage obtained at the output side of the rectifier circuit (13). The resonance circuit (3) includes a variable capacitive element (3d).

Abstract: In a multiple loop antenna comprising a combination of a plurality of loop antennas, at least one factor among the diameter of each loop antenna, the number of turns thereof, the direction thereof, the effective permeability thereof, the relative values of electric currents of loop antennas and the phase difference of electric currents is controlled in such a way that the magnetic field intensity within the range extending from the multiple loop antenna to the distance of transmission wavelength of the multiple loop antenna decreases in inverse proportion to the n-th power (n>3) of the distance from the multiple loop antenna. This makes it possible to obtain a multiple loop antenna that has a high-intensity magnetic field within the predetermined communication zone but can steeply decrease the magnetic field intensity according to an increase in distance from the antenna and surely control the magnetic field intensity to be not greater than a stated value on the outside of the communication zone.

Abstract: A battery-free non-contacting information card of a relatively simple arrangement which prevents an IC chip or the like from being destroyed by an excess voltage. This non-contacting information card includes a resonance circuit (3) for receiving a carrier signal (e.g., FSK signal) modulated on the basis of information supplied from a card reader/writer (2), an information processing system (5), (6), (7) for obtaining information from the carrier signal and a rectifier system (13) for obtaining a voltage by rectifying the carrier signal, wherein the non-contacting information card can be operated by the voltage obtained at the output side of the rectifier circuit (13). The resonance circuit (3) includes a variable capacitive element (3d).