In conventional system (for example see reference 1), sensors or tags communicate with non-contact type IC cards in a magnetic field or electric field actuated by electric currents flowing in successive tiny loop antennas formed by coils.
In the conventional system, however, sometimes sensitivity is deteriorated due to a deviation of resonating frequency influenced by a dielectric substance, a magnetic substance or a metal around the system. In some cases when a load to the system is high, loaded Q is decreased, so that sensitivity is deteriorated. Usually communication status is aggravated, when magnetic field or electric field around the system is deteriorated due to an inversed current, a stoppage of magnetic path or a distortion of the magnetic field caused by metal around the system. The magnetic substance can maintain the magnetic path to some extent, but not sufficiently. Sometimes resonating frequency is deviated to a large extent due to interactions among loop antennas. Usually in such cases resonating frequencies shift toward a lower frequency side.    Cited reference 1: Japanese utility model registered No. 3121577