A SURFACE-BOUND DIGITAL INFORMATION CAPACITIVE STORE AND PROCEDURE FOR READING AND RE-CODING THE SAME

Abstract: A surface-bound information store has its information coded in the form of capacitors of different values. The capacitors are constructed as conductive areas (2<n>) and (5) separated by a thin dielectric (3). The values of the capacitors are read capacitively by connection to reading electrodes and the application of a suitable signal. The values of the capacitors may be changed and thus the information store is re-coded. The change is obtained by the impression of a high-voltage pulse generating a high field strength in the dielectric (3) between conductive areas (2<n>) and (5) of a magnitude such that its properties are changed. Using a stiff supporting foil (D) the information store will be suitable for use as a 'debit card'. Any reading and re-coding are effected without relative movement, thus simplifying the reading and re-coding equipment.

Description: I i ASURFACE-BOUNDDIGITALINFORMATIONCAPACπTVESTOREANDPROCEDUREFOR: READINGANDRE-CODINGSAME The invention relates to a surface-bound information store and procedure for its reading and re-coding. Several kinds of surface-bound information store are well known, e.g. mag¬ netic, optical and conductive patterns. They may all be read when placed in a reading unit which is either stationary with respect to the informa¬ tions store or which • requires relative movement. Low cost is their common feature, however unauthorized changes in the information stored is not sufficiently difficult. Digital information stores based on a capacitive principle are well known, e.g. UK patent 1,037,633 which describes a con¬ struction based on a matrix of lines. In most cases galvanic connection to the information store is required, however US patent 3,604,900 describes a capacitive connection to a multilayer ' information store which incorpo¬ rates electronic circuitry. However no provision has been made for the au- thorized coding of the information store after encapsulation. German OS 26 00 289 in rather imprecise wording " describes a capacitive information store which has metal areas separated by a dielectric, the contents of the unit of information being expressed as the value of the capacitor formed, and coding being performed by destruction of the dielectric of the capa¬ citor by means of a high voltage applied capacitively to the unit capa¬ citor. None of the capacitive information stores having capacitive connec¬ tion known hitherto can be used in areas where there is limited power available for the reader and re-coding unit. It is the object of the invention to provide a digital, capacitive infor¬ mation store which has a low production cost, which is easy to read with low power consu tion of the reader apparatus, efficient to re-code by means of apparatus of low power consumption, and difficult to re-code for non-authorized persons. This is obtained according to the invention by letting the conductive areas of the unit capacitors only partially over¬ lap. Claim 2 specifies that one of the conductive areas may be common to seve¬ ral unit capacitors. Claim 3- specifies that a unit capacitor may have a weak link in the con¬ nection to the capacitor. * Claim 4 specifies that reading of a capacitor takes place by means of electrodes applied to one side of the information store only. Claim 5 specifies that re-coding of a unit capacitor takes place by means of a high-voltage pulse applied to electrodes disposed on one side of the information store only. Claim 6 specifies that re-coding of a unit capacitor in the case of its having a weak link takes place as according to claim 5, however the mecha¬ nism is different. The invention is to be described in detail in the following, supported by reference to the drawings, in which - Fig. 1 shows a plan view of 4 unit capacitors according to the inven¬ tion, and Fig. 2 shows a side view of the unit capacitors, and Fig. 3 shows plan and side view of a construction accoridng to claim 2, and Fig. 4 shows a plan view of unit capacitors according to claim 3, and Fig. 5 shows plan and side views of an embodiment of the invention ren¬ dering it particularly suitable for transactions in which the value of the information store as represented by the information coded, is to be depreciated during the transaction, and Fig. 6 shows the arrangement of electrodes (not to scale) to be used in connection with the procedures according to claims 4, 5, and 6, and Fig. 7 shows the basic construction of equipment to be connected to the electrodes shown in Fig. 6 in order to perform the procedure according to claim 4, and Fig. 8 shows the basic construction of equipment to be connected to the electrodes shown on Fig. 6 in order to perform the procedure. according to claims 5 and 6. Fig. 1 shows four capacitors out of a great number, the total of which constitute the information store. Capacitor (a) consists of a first con¬ ductive area * (1) which is separated from a second conductive area (2) by means of dielectric (3) which is seen in Fig. 2. The value of the capaci¬ tors is one. of two values, the capacitive store being digital. ' Since the distance between conductive areas is constant and provided the dielectric is also constant, the value of a unit capacitor is only dependent upon the overlap of the two areas. If due allowance is made for the reciprocal in¬ fluence between adjacent capacitors, these may be classified by value and establish certain information-carryirig discrete values. In connection with the description of the mode of operation of equipment as shown in Figs. 6 and 8 it will be seen that it may be expedient to have a certain area of information which cannot be re-coded. This is attained by placing certain capacitors at a distance from the surface which is greater than that of certain other capacitors. Fig. 3 shows a construction enabling the coding of a part information at the same horisontal line, i.e. information naturally belonging together ' with a view to further information processing. This is achieved by letting the first conductive layer of each capacitor be a continuous layer (5) separated from the other conductive layers by a thin dielectric (3). Using a continuous layer enables the use of an oxide coat on the surface of the continuous layer (5) as a dielectric, utilizing a technique which is well-known per se. Thus the advantage is obtained of a very thin and stable layer which does, however, have a well-defined breakdown field strength. Fig. 4 shows a construction entirely analogous to that of Fig. 3, how¬ ever a narrowing has been established in that part of the second conduc¬ tive area (8, 8', 8") which does not overlap the first conductive area (5). The use of this construction is explained when dealing with Fig. 8. Fig. 5 shows a construction analogous to that in Fig. 3, however using as an information store carrier stable insulator sheet (D). It is also shown how a varying degree of overlapping indicates whether the logical value ' corresponding to large overlap or '0' corresponding to small over¬ lap should be attached to that particular unit capacitor. It is demon- - URl strated that the part information defined by the conductive area (5) and the conductive areas (2 π ) indicates a binary number using n bit. Obvious¬ ly several degrees of overlapping may used so that the information reso¬ lution will depend on the discrimination ability of the equipment and on the uniformity of materials of the capacitors. In view of the mechanical reinforcement of the information store by means of the base (D) it may be handled, and cosidering the given re- coding possibilities it will be suitable for a so-called 'debit' card. A 'debit' card represents a value and may be used to obtain benefits, for instance the possibility of telephoning from public telephones- where it may represent a payment in line with coins. For each count pulse the value of the 'debit' card should be depreciated until the total number of count pulses has been used, upon which it should be rendered invalid. The information store embedded in a 'debit' card should have at least two functions, 1) part of the store should contain information enabling i- dentification of the card. The bit pattern of this part must not be changed as any change would render the card invalid, and 2) part of the store should contain information as to the instant value of the card. The bit pattern at this part of the information store will be changed as the card value decreases. The card may be made so as to have several se¬ parate tracks. Some tracks may contain information on the identity of the card, other tracks may contain information on the card value. Fig. 6 shows an arrangement of electrodes which may be used when measu¬ ring the pre-coded capacitors and when re-coding according to claims 4, 5, and 6. By its proximity each electrode is associated with only one of the conductive areas which constitute a capacitor. This, electrode (10) is associated with conductive area (1) and electrode (9) is associated with conductive area (2). There is also shown a different placement of electrode (10), namely on the other side of the information store (10'). This must be considered to be within the realm of the state of the art which has always prescribed a close relationship.between the two electro¬ des that constitute what may be termed coupling capacitors (C q ), (C- j ), and (relating to the state of the art as defined above) (C^'). As the electrodes are intended both for reading and for re-coding, as shown in the figure, it must be possible to connect them to various equipment ac- f O PI cording to the intended use. This has been shown by wire connections (11) to electrode (10) and (12) to electrode (9). Fig. 7 shows equipment to be connected to electrodes (9) and (10) to en¬ able reading of the embedded information-when the information store has been brought in proximity to the plane of the electrodes. A high frequen¬ cy voltage from generator (13) is applied to conductive area (2) through the coupling capacitor (C ) formed by part of the conductive area (2), insulator (4), and electrode (9) which may be termed the 'generator head'. The signal of conductive area (2) is transferred to conductive area (1) through the unit capacitor (C). From conductive area (1) the signal is transferred to electrode (10) through the coupling capacitor (C j ) formed by part of the conductive area (1), insulators (3) and (4), and the electrode (10) which may be termed the 'detector head'. From the detector head the signal is carried to an amplifier (14) (Fig. 7). The amplitude of the signal transmitted to the amplifier (14) depends on the values of the capacitors (C q ), (C), and (C^) which are effectively in series. If (C ) and (C d ) are considerably larger than (C) the amplitude of the signal transmitted will mainly be determined by the size-of the unit information capacitor (C). In case the capacitor (C) exceeds a cer¬ tain value, the output terminal (16) of a level detector (15) displays an output signal corresponding to logical '1'. Otherwise the output sig¬ nal will correspond to logical '0'. The level detector (15) may also be designed so that input signals within certain limits will correspond to logical '1', whereas input signals within certain other limits will cor¬ respond to logical '0'. Input signals outside these intervals will pro¬ duce an output signal at the other^soutput terminal (17) of the level de¬ tector (15), which signal may be used for controlling e.g. the rejection of the validity of the information. When used as a 'debit card" this may mean rejection due to invalidity. The reading of the information store may also be effected by interchanging the connection between generator (13), amplifier (14) and electrodes (9) and (10). The generator and de¬ tector heads may be oveable as one unit, a 'reader head' in order to associate with the appropriate area of the information store, or else the information store may be moved into a reader containing these heads in correct position. Pressure means may be applied from the side having a reinforcing base (D), ensuring sufficient mechanical contact. _ O PI The information encoded in the information store may be changed by chan¬ ging the physical properties of the dielectric (3) in the capacitor (C), thus changing its value so that reading as described above will produce a different signal at the level detector (15) output terminals. The pro¬ perties of dielectric (3) are changed by applying a high voltage between conductive areas (2) and (1) of capacitor (C). Equipment as shown in Fig. 8 is used for this, a high-voltage or combined high-voltage and high- frequency generator (e.g. a pulse generator) (18) being connected to e- lectrode (9) and a fixed voltage, possibly ground potential, to electrode (10). The high-tension generator (18) supplies a voltage pulse to conduc¬ tive area (2) thorough capacitor (C q ), and conductive area (1) may be considered to be connected to ground with respect to short voltage pul¬ ses through capacitor (C rf ). As capacitors (C Q ) and ( .) are assumed to be considerably larger than capacitor (C), the electrical field in the dielectric (3) will have the highest field strength in the area between the part of conductive areas (1) and (2) that constitute capacitor (C). At an adequately high field strenght which is simple to determine by the person skilled in the art the physical qualities of the dielectric will be changed so as to change the capacity and/or the insulation resistance between conductive areas (1) and (2). This change may then be read as de¬ scribed above. In the event that a configuration of conductive areas as shown in Fig. 4 is used, it will be possible to obtain a short current pulse in the nar¬ rowed part (8), (8'), (8"), and thus this may be fused. In this cast the electrode for reading and re-coding (9) should be placed adjacent to the part (7), (7'), (7") farthest away from conductive area (5), and similar conditions as to the relative values of the capacitors as above are assu¬ med to apply. The above description has been limited to small areas of an information store according to the invention. The example of the information store being used as a 'debit card' is an example of an application assuming a plane structure. However, the information store according to the in¬ vention is equally useful in connection-with singly curved surfaces (cy¬ linder surfaces, and if the radius of curvature is sufficiently larger than the extent of the individual capacitors, or if curved reading and re-coding electrodes are used, also doubly curved surfaces may use this •information store principle.

Claims: C L A I M S 1. ' A surface-bound digital information store having an insulating covering, in hwich the information is coded as a combination of discrete capacitors, each being made up of a first conductive area and a second conductive area separated by a dielectric, c h a r a c t e r i z e d i n that said first (1., 1', 1", ...) and said second (2, 2', 2", ...) conductive areas only partially overlap. 2. An information store according to claim 1, c h a r a c t e r i ¬ z e d i n that said first conductive area (5) is spread out in order to cooperate with a plurality of second conductive areas (2, 2', 2", ...). 3. An information store according to claim 1 or 2, c h a r a c t e ¬ r i z e d i n that each second conductive area consists of a part (6) at least partially overlapping said first conductive area, a part (7) which does not overlap, and an intermediate part (8) which has a reduced cross section as compared to said parts (6) and (7). 4. A procedure for the reading of a discrete unit of information in an information store according to claim 1 or 3, using the value of the capacitor as an indication of the contents of the unit of information, c h a r a c t e r i z e d i n that external electrodes (9) and (10) on the same side of the information store establish non-galvanic (capaci¬ tive) contact to the capacitor's first and second conductive areas. 5. A procedure for the re-coding of a discrete unit of information in an information store according to claim 1, c h a r a c t e r i z e d i n that external electrodes (9) and (10) on the same side of the infor¬ mation store establish non-galvanic (capacitive) contact to the capaci¬ tor's first and second conductive areas, whereupon a short high-voltage pulse is applied between said electrodes (9) and (10) in order to obtain a break-down of the dielectric (3) between conductive areas (1) and (2). 6. A procedure for the re-coding of a discrete unit of information in an information store according to claim 3, c h a r ac t e r i z e d i n that external electrodes (9) and (10) on the same side of the in- formation store establish non-galvanic (capacitive) contact to the ca- pacitor.'s first conductive area (5) and second conductive area (7), whereupon a short high-voltage pulse is applied between said electrodes in order to generate a current .(I) that destroys the part (8) having. a reduced cross section.

Inventors: MEYER PETER, MEYER, PETER
Applicants: GNT AUTOMATIC AS, GNT AUTOMATIC A/S
Application year: 1982
Main classification: G11C17
IPC codes: G06K19, G11C17