AU741616B2 - High-frequency identification means with passive electronic data storage medium - Google Patents

Description

HIGH FREQUENCY IDENTIFICATION MEDIUM WITH PASSIVE, ELECTRONIC DATA CARRIER The invention relates to a high frequency identification medium with a passive, electronic data carrier according to the preamble of claim 1, having a receiving antenna for receiving operating energy and for the contactless transmission of HF signals to an associated write and read station with a transmitting antenna, which has a carrier frequency of more than 1 MHz. High frequencies with a system clock or carrier frequency of over 1 MHz are necessary in order to be able to attain high communications and transmission efficiencies. An example for this is the Kaba AG Legic System.

As opposed to the situation with r.f. radio transmissions, where high efficiencies are sought in long range, with identification media a high transmission association in both directions is only necessary in close range, whereas in the long range the efficiency and also the corresponding losses are to be kept very small. This requires a very strong coupling of the two antennas, write and read station and identification medium, as well as a special configuration of the antennas.

In order with such passive identification media to pick up a good energy transmission with the receiving antenna and therefore so as to achieve a maximum range in the coupling region, use is made of receiving antennas with high inductance, i.e. with numerous turns, and only the inherent capacitance of the data carrier MI as the associated resonant circuit capacitance. However, with said known identification media there are still considerable limitations and problems. The tuning of the identification medium to the carrier frequency is only possible to a very limited extent. There is a nonconstancy of the receiver frequency. There are also strong influences on the receiver frequency. This leads to a reduced range and communications efficiency.

The problem of the invention is to provide an identification medium, which has significant improvements in connection with these problems. This problem is solved by an identification medium according to claim 1, with which much better transmission characteristics can be achieved.

Contrary to the entire development trend, there is not a maximum input yq1 ge at the identification medium or at the data carrier as a result of 2 high inductance antennas and instead the input voltage and inductance, i.e.

the number of turns of the antenna are reduced and correspondingly the total capacitance is greatly increased by introducing an additional, external capacitance Ce, which is higher than the internal capacitance Ci of the data carrier MI.

This leads to several advantages, whose combination leads to much better transmission characteristics: The receiver frequency of the identification medium can be set much better and more precisely to the carrier frequency.

The receiver frequency is substantially constant and less dependent on external influences.

This leads to a higher, constant range R of the communications and therefore to better communications efficiencies.

The dependent claims relate to advantageous further developments of the invention, which lead to further improvements ofthe transmission characteristics, as well as permitting a more universal use of such identification media. The invention is described in greater detail hereinafter relative to embodiments and the attached drawings, wherein show: Fig. 1 An inventive identification medium IM with external capacitance.

Fig. 2 An associated write and read station WR.

Fig. 3 Another example of an identification medium with coded communications.

Fig. 4 An example with twin antenna and associated, external capacitances.

Fig. 5 The communications characteristics as a function of the receiver frequency relative to the carrier frequency.

3 Fig. 6 The dependence of the receiver frequency on the coupling.

Fig. 7 The range R and solid angle W of the communications and the influence of the relative orientation of the antennas.

Fig. 8 An example of an identification medium in ISO card size with conducting paths as antenna.

Fig. 9 A small identification medium with ferrite antenna in the form of a bracelet.

Fig. 10 A small format key ring as an identification medium.

Figs. 1 and 3 show examples of inventive identification media IM and fig. 2 shows an associated write and read station WR. The diagrammatic representation of fig. 1 shows an identification medium IM with passive, electronic data carrier MI, which contains a processor 11, a control electronics 13 and a memory 12. A receiving antenna 15 with inductance L is used for receiving operating energy 20a and for the contactless transmission of HF signals to the associated read or write and read station WR. An external capacitance Ce is connected in parallel with the receiving antenna 15 and is higher than the internal capacitance Ci of the data carrier MI. The inductance L of the antenna and the external capacitance Ce are so tuned, that a natural frequency f of the identification medium is obtained, which corresponds to the carrier frequency fr. The carrier frequency fr is determined by the write and read station WR and its transmitting antenna 24.

The associated read station or write and read station WR according to fig. 2 generates the system clock, the carrier frequency fr, which is transmitted with the transmitting antenna 24 to the identification media IM. Both the energy 20a, which is required for operating the identification medium IM, and the data 20b are transmitted by the write and read station WR to the identification medium IM. In order to be able to achieve high communications efficiencies, the carrier frequency must be in the range above 1 MHz, preferably between 5 and 20 MHz and not above 30 MHz. This is inter alia linked with the fact that a very good transmission, i.e. a strong coupling must be 4 obtained in the close range, whereas in the long range a minimum power is to be emitted. With the indicated high frequency range, said near field range is between approximately 1 and 100 metres and therefore in a range which is important for identification media. A favourable carrier frequency is e.g.

in the ISM band of 13.56 MHz with which optimum transmission characteristics can be obtained for communications distances up to several metres.

Contrary to the general development direction, the inventive principle of deliberately reducing the inductance L of the receiving antenna 15 and increasing the given capacitance Ci of the identification medium by a higher, external additional capacitance Ce, leads to a significant improvement to the communications efficiency KL, despite a reduced input voltage, corresponding to the reduced inductance L at the receiving antenna This is illustrated in figs. 5 to 7. Fig. 5 illustrates the dependence of the communications efficiency KL on the coincidence of the carrier frequency fr of the write and read station and the transmitting antenna 24 with the natural frequency f of the identification medium and the receiving antenna The communications efficiencies (or communications capacity or characteristics) are e.g. the range R and solid angle W of the communication, as well as the angular range W2 of the relative position of the receiving antenna with respect to the field of the antenna 24 in which communication is possible.

As is apparent from fig. 5, the communications efficiency is very strongly dependent on the coincidence of carrier frequency fr and receiver frequency f, i.e. an optimum coupling is achieved in the case of coincidence of the two natural frequencies: f fr. With an increasing difference f fr, the communications efficiency drops very rapidly, so that even in the case of a divergence of a few per cent inadequate communications efficiencies KL are obtained.

This coincidence of the two antenna frequencies f and fr, i.e. the implementation of a natural frequency f of the identification medium, which corresponds to a given transmitter frequency fr of the write and read station WR, was hitherto scarcely possible for various reasons.

5 Fig. 6 shows the dependence of the natural frequency f on the antenna coupling AK or the spacing of the two antennas. The natural frequency fl of a known identification medium drops in a very pronounced manner with increased coupling AK, e.g. by 10%. However, the frequency response f2 of a novel antenna according to the invention shows a much smaller drop of e.g. only 1 to Thus, a permitted tolerance range Df of e.g. 2% can be much more readily achieved with the stable, novel antenna according to curve f2 than with the unstable, known antenna according to curve fl. Thus, the novel antenna leads to much higher communications efficiencies W, W2).

This is illustrated in fig. 7 with the field lines H of the transmitting antenna 24 of the write and read station WR and with an attainable range R and a maximum solid angle W within which communication with the identification medium IM is possible. This is additionally dependent on the relative position of the receiving antenna 15 in the field H. With increasing angle W2 between the antenna normal and the field direction H, the communications capacity drops. Much higher values of R, W, W2 are attained with the novel receiving antennas 15 according to the invention.

This is illustrated in the following comparison example for a carrier frequency fr of 13.56 MHz and identification media in the ISO format (cf.

fig. 8) for a known and a novel identification medium. In order that a natural frequency f fr is obtained in the coupling state, the natural frequencies of the identification media in the unloaded state must be set to the following values: For a known antenna fl 16.5 1.5 MHz For a novel antenna f2 13.6 0.3 MHz For the natural frequencies f of the identification media the following 2 relationship applies: (2Tr.f) .L.C 1.

This e.g. gives the following values: Known identification medium C Ci 16 pF L 6 pH 6 Number of turns N 5 to 6 Novel identification medium C Ci Ce 16 pF 100 to 300 pF L 1.2 to 0.5 pH Number of turns N 2 to 3 The strong dependence of the coupling AK of the known antennas according to curve fl in fig. 6 results from a strong dependence of the internal capacitance Ci of the data carrier MI on the coupling. This dependence is very significantly reduced with the relatively large, external capacitance Ce, which is independent of the coupling AK in the novel antenna according to curve f2 in fig. 6.

Preferably the stable, external capacitance Ce with high quality is chosen several times greater than the internal capacitance Ci,. e.g. 5 to 10 times.

This leads to a much higher quality factor Q fr/B (resonant frequency/band width) of the resonant circuit of the identification medium. Preferably the quality factor Q is at least The non-constancy or changes to the antenna frequency f in the known identification media result from different influences. These include a change to the internal capacitance Ci of the data carrier which, apart from the indicated dependence on the coupling intensity, is also influenced by ambient conditions, stray fields, conductors in the field, parasitic capacitances and ageing effects. Added to this is the high loss factor (poor quality) of the internal capacitance Ci, as well as relatively large production dispersions of the Ci values. All these influences and changes to the Ci values lead to corresponding changes to the natural frequency f in the known identification media.

In the inventive antenna, these influences are removed by the external, high quality capacitance Ce, stability or constancy, as well as the precisely defined, selectable capacitance values, at least to a very significant extent, so that there is a correspondingly constant, clearly defined and selectable frequency f, which leads to the indicated high communications efficiencies KL.

7 The inventive concept also leads to significant advantages with respect to the design and production of identification media. As the natural frequency f is much more precisely defined and is also measurable, it can also be much more accurately tuned to the carrier frequency fr. The setting of a desired nominal value for the natural frequency f is possible in a much simpler and more precise manner, because the additional, external capacitance Ce has a precisely defined, constant value, which can be randomly selected. Thus, also the relatively large dispersions of the Ci values during the manufacture of integrated circuits are compensated in a simple manner. In addition, e.g.

also with an antenna design (with regards size and number of antenna loops) by the choice of different, external capacitance values, it is easy to achieve corresponding different, desired natural frequency values f of the identification medium.

As there must be an integral number of antenna turns N and there is a given internal capacitance Ci of the data carrier MI, the implementation of a desired nominal value for the natural frequency f is very difficult and imprecise during production in the case of the known identification media.

Fig. 3 illustrates an example of an identification medium for coded communications. The data carrier MI, preferably constructed as an ASIC chip 16, here contains a support capacitor 17 for storing the received energy and for bridging transmission pauses or intervals, a voltage regulator 3, a clock processing means 4, a receiving demodulator 5, a transmitting modulator 6 and a coding and communications logic 7, as well as a writable EEPROM 12, which preferably has at least 256 bytes. An advantageous energy and data transmission between the write and read station WR and identification medium IM can be achieved by pulse modulation (pulse-pause modulation) from the write and read station WR to the identification medium IM and by load modulation in the opposite direction from IM to WR.

Such identification media with access and authorization functions are known for various installations and applications, e.g. as access cards for certain areas within a company (electronic keys), for time management, as access media for equipment, e.g. data installations, or as check card systems for obtaining services. The inventive identification media with much higher m 8 transmission efficiencies and capacities are therefore particularly suitable for applications having high demands with respect to functional reliability and data integrity, monitorability, prevention of misuse, etc. For this purpose use is made of a coded communication between identification medium IM and write and read station WR, e.g. in that the latter generates new initializing data for each identification process and transmits it to the identification medium IM, which is linked there with a fixed-stored encoding code 32 (in fig. 3) and is transmitted back in coded form to the write and read station, where said information is decoded and checked and then a synchronized communication takes place between WR and IM.

The identification medium can additionally be combined with a personal coding function, in order to satisfy particularly high security requirements. For this purpose e.g. a PIN code or biometric data codes can be used. Personal, biometric data are e.g. established from fingerprints or finger, hand or head geometry and compared with the corresponding code 33 stored in the data carrier MI (fig. 3) for personal identification and checking of an authorized carrier.

Another very important application, which is only made possible with identification media having a high communications capacity, is a higher data organization of the memory 12 of the data carrier MI and several independent applications can be written in a segmentable application data field ADF.

Thus, due to the higher communications efficiency of the inventive identification medium there is a virtual increase in its number of functions.

Fig. 4 shows another example of an identification medium with a receiving antenna constructed as a twin antenna with two loops 15.1 and 15.2. Here the first antenna loop 15.1 is used for receiving electromagnetic field energy 20a for supplying the data carrier and for receiving the data 20b of the write and read station WR. The second antenna loop 15.2 is used for transmitting data 20b to the write and read station WR. The antenna parts 15.1 and 15.2 correspond to the internal capacitances Cil and Ci2 of the data carrier MI. The external capacitances Cel and Ce2 connected in parallel to each antenna loop 15.1 and 15.2 are so dimensioned that the antenna frequencies of the two antenna loops are the same and for the same partial 9 inductances Ll, L2 this means: Cel Cil Ce2 Ci2.

Figs. 8a and b show as a particularly frequently used size or format an identification medium in ISO card size 28 (85 x 54 mm) with conducting paths 26 on a printed circuit board, here serving as a transmitting antenna The antenna loops can be integrated with the external capacitance Ce and with the data carrier MI on a carrier 29 (inlet) and consequently form a unit manufacturable in a particularly rational manner. The external capacitance Ce can e.g. be a ceramic capacitor having a very shallow construction of e.g.

0.3 to 0.5 mm thick and with a higher quality in the MHz frequency range.

Figs. 9 and 10 show examples of identification media with a small format the diameter DA of the receiving antenna 15 utilizing as completely as possible the space available, so that the antenna surface FA corresponds to almost the entire surface of the identification medium. With such small format identification media with antenna diameters of 30 mm and less, e.g.

only 10 mm, it is particularly difficult to obtain good communications characteristics and long ranges. As a result of the inventive combination with the additional, external capacitance Ce and the correspondingly reduced inductance L of the antenna 15 correspondingly fewer loop turns are required than hitherto and it is possible to operate with smaller antenna surfaces than hitherto. Thus, with small identification media such as keys, key rings, tokens, etc. it is possible to obtain roughly the same communications ranges as have been possible with the hitherto known relatively large ISO format cards, so that completely new applications arise.

Fig. 9 shows an example in which the receiving antenna is constituted by a ferrite antenna 19 with a bar-shaped ferrite and an electrical winding. In this example the identification medium is worn on a bracelet 36.

The small format identification medium of fig. 10 is a pendant 37, e.g. a key ring. However, this identification medium could also be combined with a key, e.g. on the key grip, or could be associated with a carrier in some other form. An example of a very small identification medium is constituted e.g. by rings, which can be fixed to the foot of homing pigeons for identifying individual pigeons during races.

10 For such small format identification media in accordance with figs. 9 and for a carrier frequency fr of 13.56 MHz, e.g. external capacitances Ce of to 150 pF are used and there is a corresponding reduction of the number of turns of the antenna loops e.g. to less than half.

According to a particularly advantageous further development of the invention, the carrier frequency fr on the transmission side is stabilized in the same way, the transmitting antenna 24 of the write and read station WR is made more independent of external, capacitive influences. Although the carrier frequency fr is in itself much more stable than the natural frequency f of the identification medium, through a further stabilization of the carrier frequency fr it is possible to further improve the communications characteristics KL in the same sense as for the identification medium and in particular the range R can be increased.

In principle, the carrier frequency fr is subject to the same influences as described hereinbefore, namely capacitive changes in the environment, e.g.

through the approach of the human body and metal objects, manufacturing tolerances, ageing of components, etc. The accurate setting of a desired nominal value for the carrier frequency fr has also hitherto involved a complicated tuning.

Through the application of the same principle to the transmitting antenna 24 as used for the receiving antenna 15, the indicated stabilization and improvements are achieved. As illustrated in fig. 2 as a variant, an additional capacitance Cz is connected in parallel to the transmitting antenna and its inductance is correspondingly reduced, so that the product L.C of the transmitting antena 24 remains constant. The additional capacitance Cz is preferably chosen higher than the existing back-up capacitance of the write and read station WR, relative to the base of the transmitting antenna (i.e.

without additional capacitance). The additional capacitance can advantageously be two to five times as high as the existing back-up capacitance.

This additional capacitance Cz comprises a standard component with a selectable, precisely defined and constant C values. Thus, a desired nominal value of the carrier frequency fr can be achieved on a serial basis in 11 simple manner and without complicated individual tuning operations.

A particularly advantageous and universally usable transmitting antenna 24 can be constructed as a foil antenna, e.g. as an antenna loop in the form of a wide conducting path on a plastic carrier (in much the same way as the much smaller antenna 15 in the example of fig. 8).

In exemplified manner with a single conducting path loop with a diameter of cm and a path width of 25 mm (appropriately round, oval, rectangular, etc.), it is possible to achieve ranges R of up to 1 m and more. Through a simple choice of the Cz value (as series components) it is possible to directly set any desired carrier frequency fr, without the hitherto necessary testing and tuning operations.

The following references are used in the present application: 3 4 6 7 11 12 13 15.1,15.2 16 17 19 24 26 28 29 Voltage regulator Clock processing means Receiving demodulator Transmitting modulator Coding and communications logic Processor Memory Control electronics Receiving antenna of IM Twin antenna ASIC chip Support capacitor Ferrite antenna HF communication Energy transmission Data transmission Transmitting antenna WR Conducting path on circuit board ISO card Carrier, inlet 12 Small format 32 Coding 33 Personal, biometric coding function 36 Bracelet 37 Pendant IM Identification medium MI Electronic data carrier WR Read or write and read station fr Carrier frequency, system clock of WR f Frequency of IM Q=fr/B Quality factor of IM H Field line direction KL Communication efficiency, capacity, characteristics R Communications range W Solid angle for communication W2 Angle between field direction H and antenna normal DA Diameter of transmitting antenna FA Surface of antenna AK Antenna coupling (distance) Df Tolerance range f fr N Number of turns L Inductance Ce External capacitance Ci Internal capacitance Cz Additional capacitance with respect to 24 ADF Application data field

Claims (15)

1. High frequency identification medium IM with passive electronic data carrier MI, which contains a processor, a control electronics and a memory, as well as with a receiving antenna with inductance L for receiving operation energy and for the remote contactless transmission of HF signals to an associated write and read station with a transmitting antenna, with a carrier frequency fr of at least 1 MHz, said carrier frequency being determined by the transmitting antenna; characterized in that an additional external, constant capacitance Ce is connected in parallel to the receiving *o antenna, and the capacitance Ce is higher than the entire .15 internal capacitance Ci of the data carrier MI; whereby the inductance L of the receiving antenna is correspondingly reduced, so that the natural frequency f of the identification medium corresponds to the carrier o frequency fr.

2. Identification medium according to claim 1, characterized in that the carrier frequency fr is determined by the transmitting antenna of the write and read station WR and that the frequency f, as well as the external capacitance Ce and inductance L of the receiving antenna of the identification medium IM is determined by the following relationship: (27.f) 2 .L.(Ci+Ce) 1, with fr f 3%.

3. Identification medium according to claim 1, characterized in that the data carrier MI has a support capacitor for storing the energy received, a voltage regulator, a clock processing means, a receiving demodulator, a transmitting modulator, a coding and communications logic and an EEPROM. H:\Shonal\Keep\Speci\P32529 HIGH-FREQUENCY IDENTIFICATION MEANS 18/10/01 13a

4. Identification medium according to claim 1, characterized in that the data carrier is constructed as an ASIC chip with an EEPROM with at least 256 bytes.

5. Identification medium according to claim 1, characterized in that the carrier frequency fr is between 1 and 30 MHz, preferably between 5 and 20 MHz.

6. Identification medium according to claim 1, characterized in that the carrier frequency fr corresponds to the ISM band of 13.56 MHz. *o 022*: o S.0 H:\Shonal\Keep\Speci\P32529 HIGH-FREQUENCY IDENTIFICATION MEANS 18/10/01

14- 7. Identification medium according to claim 1, characterized in that the external capacitance Ce is at least fives times as high as the internal capacitance Ci of the data carrier MI. 8. Identification medium according to claim 1, characterized in that the external capacitance Ce is between 100 and 300 pF. 9. Identification medium according to claim 1, characterized in that the quality factor Q fr/B (resonant frequency/band width) of the IM resonant circuit is at least Identification medium according to claim i, characterized in that the external capacitance Ce comprises a ceramic capacitor with a maximum thick- ness of 0.5 mm. 11. Identification medium according to claim 1, characterized in that the receiving antenna (15) is formed as a conducting path (26) on a printed circuit board. 12. Identification medium according to claim 1, characterized in that the antenna loops (15) correspond to the ISO card format (28). 13. Identification medium according to claim 1, characterized in that the antenna loops (15) are integrated with the external capacitance Ce and the data carrier MI on a carrier (29) (inlet). 14. Identification medium according to claim 1, characterized in that, in the case of small format identification media the diameter of the receiving antenna (15) is max 3 cm. Identification medium according to claim i, characterized in that the receiving antenna is constructed as a twin antenna (15.1, 15.2) with in each case an external capacitance (Gel, Ce2) with a centre tap, one antenna loop being used for the reception of energy (20a) and data and the other antenna loop for transmitting data.

16. Identification medium according to claim I, characterized in that the receiving antenna is constructed as a ferrite antenna (19) with a bar-shaped ferrite and electrical winding.

17. Identification medium according to claim I, characterized in that the data transmission from the write and read station WR to the identification medium IM takes place by pulse modulation and in the opposite direction by load modulation.

18. Identification medium according to claim I, characterized in that the communication (20) between the write and read station WR and identification medium IM is coded (32).

19. Identification medium according to claim 18, characterized in that the memory (12) has a segmentable application data field ADF for several independent applications. Identification medium according to claim 18, characterized in that the data carrier MI contains an additional personal coding function such as a PIN code or a biometric data code.

21. Identification medium according to claim 1 with associated write and read station, characterized in that the write and read station WR has a transmitt- ing antenna with which is connected in parallel an additional capacit- ance Cz.

22. Identification medium according to claim 21, characterized in that the additional capacitance Cz is at least as large as the back-up capacitance of the write and read station WR, relative to the base of the transmitting antenna (24) without additional capacitance Cz.

23. Identification medium according to claim 21, characterized in that the additional capacitance Cz is two to five times as large as the back-up capacitance of the write and read station WR, relative to the base of the transmitting antenna (24) without additional capacitance Cz. 16

24. Identification medium according to claim 21, characterized in that the transmitting antenna is constructed as a foil antenna and preferably only has one antenna loop. High frequency identification medium substantially as herein described with reference to and as illustrated by the accompanying drawings. Dated this 18 th day of October 2001 KABA SCHLIESSSYSTEME AG o.. By their Patent Attorneys •00 15 GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 9 ooooo: H:\Shonal\Keep\Speci\P32529 HIGH-FREQUENCY IDENTIFICATION MEANS 18/10/01