The invention relates to a data store for use with capacitive reading and containing capacitive coupling electrodes which establish galvanic connection to data elements which are made up as impedances.

Pre-pay ents of goods and services, e.g. a certain amount of telephone use may take place by means of so-called 'debit' cards. These are portable and durable data stores which con¬ tain data of two types. One type is data which serves. o i- dentify the 'debit' card to the electronic reader, the other type is data which represents the value of the card and which must be changed according to the use. That is, these data ele¬ ments must be changed by the electronic reading station. It has been found expedient to use capacitive coupling to the data store which puts certain limits to the amount of energy that may be transferred to change one data element. In con¬ nection with the use of galvanic coupling it is well known to use the fusing of a conductor or the distruction of a di¬ electric; the former occurs using a high current, the latter with a high voltage. These methods have been used in the pro¬ gramming of semiconductor memories.

It is the purpose of the invention to provide a data store which contains data elements which give a definite indication of the condition of tha dataelement using capacitive coupling and which data elements are efficiently re-codeable. This is obtained by a data element according to the .invention which is characterized in that each impedance which constitutes a data element at least consists of a resistive link between the capacitive coupling electrodes.

In claim 2 a data store is indicated which gives a large va¬ riation following re-coding.

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In claim 3 a data store is indicated which is particularly adapted to the capacitive coupling.

In claim 4 there is indicated a data store which allows re- coding on several levels for each data element.

In claim 5 a procedure for re-coding is indicated.

In claim 6 a manner of manufacture of a data store is indi¬ cated.

In claim 7 a similar manner of manufacture of a data store accoridng to claim 4 is indicated.

In claim 8 a further expedient manner of manufacture is in¬ dicated.

In claim 9 a manner of manufacture is indicated which requi¬ res but one application of conductive material.

In claim 10 manner of manufacture of a data store according to the invention is indicated which is partucilarly adapted to the manufacture of a data store having a stiff carrying foil.

The invention is to be further described with reference to the drawings, in which ^"

Fig. 1 shows a data store according to the invention, and Fig. 2 shows details in a data store according to the inven¬ tion.

In Fig. 1 is shown a data store which consists of the capaci¬ tive electrodes (9) and (1) which communicate with correspon¬ ding electrodes in the apparatus which is adapted for reading and re-coding (changing) the data elements. The data store has a resistive connection between these electrodes as shown at (3) and in greater detail on Fig. 2. In Fig. 2c it 'is

shown that the resistive parts (3), (3'), and (3") are dif¬ ferent and that the two former are adapted for being de¬ stroyed when re-coding. Hence in a first re-coding operation one change may be introduced and in a second re-coding a se¬ cond change so that a data element which belongs to a certain position on the card may have more than two values. This is according to claim 4.

In data stores according to claims 4 and 7 the construction will be as shown on Fig. 1., having (8) as its upper edge, and an insulating covering that prevents corrosion and mecha¬ nical interference is required. In data stores which also have a capacitor in each data element the construction will be according to Fig. 1, having the upper part (above the line (8)) folded either forwards out of the plane of the paper and across the data element pattern, and in this case it is re¬ quired to supply it with an insulating covering before fold¬ ing, according to claim 8. In case the folding is performed backwards, then the insulation is established by the carry¬ ing foil (6) itself, but in that case the whole data store must subsequently be insulated on both sides, e.g. by casting in a resin or by lamination.

The data store may be advantageously manufactured by deposi¬ tion of a resitive material in a uniform thickness. In this case only the parameters length and width remain for control¬ ling the resistance and power capacity of the resistive con¬ nections (3), (3'), and (3"), however this is well known to the person skilled in the art and constitutes a simplifica¬ tion. The choice of the value of the resistor is partly con¬ trolled by the desired manner of changing; if the energy sup¬ plied has the character of a voltage, then the resistance must be small, but in case the energy has the character of a controlled current the resistance must be large, in order that sufficient energy shall be absorbed to obtain destruc¬ tion. In order that sufficient energy shall be absorbed it has been shown to be expedient to let the data elements of

the data store be part of resonant circuits as frequency de¬ termining elements in order that over-voltages or over-cur¬ rents occur at resonance.

As carrying foil (6) polyester, polyimides or similar materi¬ als well known in the electronics field have been shown to work well. However, there may be problems in cementing the two layers close to the fold (8) , in that certain of the in¬ sulating foils are stiff. As the two conducting areas marked "GROUND PLANE" are large, their juxtaposition alone will bring about such a coupling between the two layers that the part of the material having the greatest inner stresses follo¬ wing cementing, i.e. the material adjacent to the fold (8) , may be cut entirely away according to claim (10) .

It is obvious that in case the characteristics defined in claim 4 are combined with those of claim 2 many more possi¬ bilities of combination are obtained, in that there will then be a capacity with individual loss angles as a carrier of information in each data element.

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