Abstract

Card and Card Reader contain a broadly m-shaped or twin looped antenna consisting of one or more thin conducting layers between plastic laminates wherein the middle branch 18 oscillates in anti-phase with the two outer branches 16 and 17 for proximity coupling applications, whereas all the said three branches oscillate in phase in distant read/write applications.The prevailingly capacitive positions 15, 13, 14 of the antenna can be utilised for card readers where it is preferred to draw a card through a slot into the interior of a sensor unit where the card may be tested, processed, or if need be, withdrawn. Capacitive transfer may be also useful in cases where the temporary clipping of the card to a piece of equipment will unite its data base to a digital system. The instructive component can best be utilized in informal proximity presentations of the card to a Reader area; and its electromagnetic manifestation can best be used in card identifications a distance of several meters.In order to avoid in proximity transactions a change of transfer efficiency due to subtle alterations in antenna attitudes relative to each other, or in the spacing from each other, or in other modifications of the environment affecting the radiation resistance of the antennas of the said units, this patent application also describes means for allowing the primary frequency of the oscillator source to fluctuate, and to be self-adapting to said random conditions.