Title of Invention	METHOD AND SYSTEM FOR OPTIMIZED READING OF A RADIO FREQUENCY COMMUNICATION TRANSPONDER WITH THE AID OF A PASSIVE RESONANT CIRCUIT
Abstract	Method and system for optimized reading of a radio frequency communication transponder with the aid of a passive resonant circuit. The invention relates to a method of reading RF transponders disposed in one and the same magnetic interrogation field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit (17) during reading. The method is distinguished in that the passive antenna (21) of the resonant circuit is associated with at least one transponder antenna (3, 13-16), and the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association M corresponds to one of the frequencies of the emission side bands of the transponder (3, 13-16) to be read. The invention also relates to the system corresponding to the method, a transponder structure and an object containing the transponder, in particular a travel document.

Title of Invention

METHOD AND SYSTEM FOR OPTIMIZED READING OF A RADIO FREQUENCY COMMUNICATION TRANSPONDER WITH THE AID OF A PASSIVE RESONANT CIRCUIT

Abstract

Method and system for optimized reading of a radio frequency communication transponder with the aid of a passive resonant circuit. The invention relates to a method of reading RF transponders disposed in one and the same magnetic interrogation field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit (17) during reading. The method is distinguished in that the passive antenna (21) of the resonant circuit is associated with at least one transponder antenna (3, 13-16), and the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association M corresponds to one of the frequencies of the emission side bands of the transponder (3, 13-16) to be read. The invention also relates to the system corresponding to the method, a transponder structure and an object containing the transponder, in particular a travel document.

Full Text	Method and system for optimized reading of a radio frequency communication transponder with the aid of a passive resonant circuit. The invention relates to the field of methods and systems for reading RF radio frequency transponders and the structure of such radio frequency transponders. More particularly, the invention relates to an improvement in the reading and/or the communications between a transponder liable to be surrounded by several transponders and a reader provided for this purpose. The invention more particularly aims at an application of such methods and systems to the contactless reading of electronic travel documents such as electronic passports and electronic visas in the form of transponders positioned together. In particular, such documents and visas are compliant with ICAO "International Civil Aviation Organization" specification and the IS07IEC 14443 standard. The travel documents such as the electronic passports and/or the electronic visas are composed on the one hand of a paper document whereon information relative to the holder of said document is noted and on the other hand a contactless electronic chip which also contains secured information relative to the same holder. The unsolved problem arises as soon as the travel document of the electronic passport type must also include several electronic visas. As a matter of fact, because of the variable principles used by such contactless electronic chips, the increase in the number of electronic visas in the document makes the simultaneous reading more and more difficult when and as their number increases, which can even make the operation thereof impossible as soon as the number is greater than 4 or 5 visas. The need expressed as regards electronic travel documents is that said document may contain a maximum of contactless electronic visas which are simultaneously operated when they are submitted to a magnetic field from a contactless reader. The reader and the travel documents must be compliant with the ISO/IEC 14443 standard. The specifications of contactless electronic visa or visas request that on the one hand each visa consumes as little as possible magnetic field from the contactless reader and interacts therewith as little as possible and on the other hand that each one causes a variation of said magnetic field which is compatible with the specifications imposed by the ISO/IEC 14443 standard during the phases of responses from the visa to the reader. The contactless technology resulting from the ISO/IEC 14443 standard describes the mechanisms making it possible to implement the anti-collision principles between contactless products. Such principles provide logical mechanisms which make it possible to retrieve a contactless product among several others when they are submitted to the same magnetic field. The condition required for a correct operation of such principle is that the reader supplies all the products existing in the field it generates and that it detects them all. More particularly, the contactless anti-collision mechanism is limited by the consumption and the magnetic load induced by the sum of several contactless transponders. This limits the number of electronic visas which can be read in or out of an electronic passport. In addition, the ISO/IEC 14443 standard contains a specification imposing that the contactless products be operated in a range of magnetic field between 1.5 A/m and 7.5 A/m. This specification makes it possible for contactless products to be operated from a magnetic field of at least 1.5 A/m. A standard compliant reader can thus generate only a 1.5 A/m field in the presence of the travel document while being conformable with the standard. The ISO/IEC 14443 standard also imposes the minimum amplitude of the response of the contactless product so that the reader can detect it. Such minimum amplitude is worth at least 30/H1*2 (or 18.6mV), with H amplitude of the magnetic field. Such value is defined from the amplitude of the side bands generated because of the amplitude modulation of the reader magnetic field, with the frequency of 13.56MHz by the contactless product at the rate of the sub-carrier thereof, rated at 847Khz. If these conditions are complied with, the contact reader complying with the standard should be capable of receiving the data from the contactless chip. The present state of the art makes it possible to comply with all such conditions whenever a maximum number of a few electronic visas are positioned in the travel document. At present, 5 visas seem to be a maximum as regards the curve of the transponders response (Figure 3 retrieved from the official document N1088 from ISO/IEC JTC1/SC17/WG8). The inventor noted that if more than five contactless products which are individually standard compliant are used, when they are grouped in the same travel document, because of the electromagnetic coupling together, the assembly, is no longer compliant with the ISO/IEC 14443 standard. The conformable contactless reader is no longer capable of supplying them or detecting them. This limitation to five as regards the number of transponders is considered by the inventor as being potentially a disadvantage in the development of an electronic passport and also in a general way for the reading of several transponders positioned together whatever the considered application. Thus the inventor has considered improving in a general way the contactless communication of a certain number of transponders for a constant power of the reader. As regards the known prior art making it possible to improve the communication between the transponders and a reader, the patents FR 2 777 141 or US 6172608 are known. Such patents make it possible to have a second oscillating circuit which can be tuned on a frequency which is close to (or equal to) the electromagnetic field, so that the modulation of the field performed by the transponder is better detected by the antenna of the reader. Such documents more particularly teach the utilization of a passive resonant circuit for increasing the communication distance between the reader and the transponder while keeping a correct operation and without increasing the emission power of the reader. On the other hand, the document FR 2 812 482-A1 is known, which uses a collective antenna which is closed to amplify the communication from the reader with several transponders positioned on the same support. The multiplicity of the transponders on a support corresponds to the problem of increasing the storage memory available on the support. The transponders have a more reduced format than the passive antenna because of the manufacturing cost. This document does not teach the optimization of the number of legible transponders for a constant electromagnetic field power. In addition, the arrangement of a closed passive collective antenna associated with several transponders having more reduced dimensions than the passive antenna seems not to be operational, as exposed in the present document in the present state of the art of the person skilled in the art. The invention more particularly relates to the solving of the above-mentioned drawbacks. It more generally aims at improving the reading of transponders, such improvements being intended to lead to the increase in the number of transponders which can be read together in a determined electromagnetic field, whatever the dimension thereof. It also aims at providing the optimization of the number of transponders which can be read together for the application to an electronic passport, in compliance with specifications of the ICAO and ISO/IEC14443, in particular. New transponders characteristics are supplied for this purpose. According to a first aspect, the invention aims at a method for the contactless reading RF transponders positioned in one and the same magnetic interrogation field, wherein a magnetic coupling of the transponders is ensured with a passive resonant circuit during reading. The method is characterised in that the passive antenna of the resonant circuit is associated with at least one transponder antenna, and the passive resonant is tuned in such a way that the resonant frequency resulting from the association corresponds to one of the frequencies of the emission side bands of the transponder to be read. Such provisions make it possible to favor the amplitude of the transponder return signal. According to a particular embodiment, the association of the passive antenna of the resonant circuit with at least one antenna of the transponder is made negligible and the passive resonant circuit is tuned to a resonant frequency corresponding to one of the frequencies of the emission side bands on the transponder to be read. Such provisions make it possible to further simplify the reading method while favoring the amplitude of the return signal delivered by the chip of the antenna module or transponder. The invention also relates to a system for reading at least one RF transponder, said system including a reader able to emit an interrogation field on at least one transponder and to collect a response from the transponder, a passive resonant circuit for performing a magnetic coupling with at least one transponder during the reading. The system is characterised in that the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association of the resonant circuit with at least one transponder corresponds to one of the frequencies of the emission side bands of the transponder to be read. Another aspect of the invention relates to a support object containing at least one main transponder, at least one secondary transponder and one passive resonant circuit associated with at least a main transponder. The object can be distinguished in that the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association of the resonant circuit with the main transponder at least corresponds to one of the frequencies of the emission side bands of the secondary transponder. Another aspect of the invention relates to a support object containing at least one transponder and a passive resonant circuit associated with at least the transponder. It can be differentiated in that the passive resonant circuit is tuned to a resonant frequency corresponding to one of the frequencies of the emission side bands of the transponder. Another aspect of the invention relates to a transponder including a flat antenna on a support defining an outer turn; the transponder is characterised in that: - the surface outside the outer turn is greater than a 15 x 15mm surface and smaller than a surface of approximately 30 x 30mm, - the antenna includes approximately between 13 and 18 turns, - the tuning frequency is between 15 and 18 MHz, - a quality factor is above 30. Another aspect of the invention relates to a travel document including several pages between two covers and a plurality of transponders between the pages, with each transponder being contained in a plane support distinct from the pages or covers, but having substantially the same format of a page, with the transponder having the above characteristics. According to an advantageous provision making it possible to have less interference or coupling between the transponders, the latter are positioned in the support in various positions and particularly in a random way. Other characteristics and advantages of the invention will appear upon reading the following description given as a non limitative example and by referring to the appended drawings wherein: - Figure 1 illustrates an electronic passport reading system according to the prior art; - Figure 2 illustrates an electronic passport and the various visas of the prior art; Figure 3 illustrates response curves in response to the number of transponders of the prior art; - Figure 4 illustrates a section in Figure 5 along A-A; - Figure 5 illustrates a transponder reading system complying with one embodiment of the invention; - Figure 6 illustrates an area for the possible dimensions of the passive antenna according to one embodiment; - Figure 7 illustrates a travel document which is compliant with an embodiment of the invention; - Figure 8 illustrates a travel document reading system complying with the preceding Figure; - Figure 9 illustrates a schematic view of the reading system of the preceding Figure; - Figure 10 illustrates a reading configuration for transponders using an association of the passive resonant circuit with a main transponder; - Figure 11 illustrates a transponder according to one embodiment of the invention; Figures 12, 13 illustrate the transponder packaging according to another embodiment of the invention. In Figure 1, an existing system 1 for reading electronics passport and electronic visas in the form of transponders of the radio frequency (RF) type includes a reader able to emit an interrogation field via an emitting antenna 2 and to collect a response from the transponder submitted to this field. The passport 3 (PICIO) and each visa 4 (PCI1- PICI5) include the same type of transponders, i.e. an electronic circuit (5a, 5b) of the RF-ID (radio frequency identification) type connected to an antenna (4a-4b). In Figure 2, the passport transponder is buried in the cover 6 of a passport 7 and each electronic visa transponder is buried in a sheet 8. In Figure 3, a diagram of voltage response curve (10) of a transponder with a ID1 format (the format of present passports) has a peak beyond 35 volts whereas the voltage response of 5 transponders PICI positioned together is close to 5 volts. Beyond 5 transponders, the voltage dramatically drops and it is no longer possible to detect and to read more than 5 transponders having a frequency of 13.56MHz. Generally speaking, within the frame of the present description, transponder means any identification electronic circuit using detection or a communication using an electromagnetic field. More particularly, electromagnetic fields are concerned and they include a coil connected to a condenser and where an integrated circuit or any other electronic components can be found. The transponders more particularly include an electronic component such as an integrated circuit chip connected to an antenna. They can be inserted into, or associated with any type of support. They may, for example, have the shape of adhesive electronic labels, contactless card; they can be buried in a packaging, the cover of a document, a sheet or any other thing, etc. Transponders are used in various economics fields such as bank (electronic purse), communications, transport, identity (e-passport, ID card). More particularly as regards identity, identifying a person through a radio frequency communication with a contactless portable electronic object of the RFID type, is known. In a general way, reader means within the scope of the following description, an emitter/receiver device provided with one antenna which creates an electromagnetic field at a given frequency. The antenna of the device also makes it possible to modulate the electromagnetic field and to measure variations in the electromagnetic field. The antenna of the device also makes it possible to modulate the electromagnetic field and to measure the variations in the electromagnetic field. The reader antenna is generally composed of one or several coils. The reader-transponder system is operated in a more or less complex way according to the type of the transponder used. The general operation principle consists in emitting an electromagnetic field with a given frequency. When one transponder goes within the electromagnetic field, it is supplied and it reacts. The reaction of the transponder causes the variation of an electromagnetic field which is detected by the reader. For the simplest systems, the transponder being for example composed of one coil and one condenser, the assembly is an oscillating circuit tuned on the frequency of the electromagnetic field. The presence of the transponder in the field makes the oscillating circuit resonate and causes a modification of the field which can be detected by the reader. Such systems which are very simple are currently used as anti-theft devices in department stores. As regards the most complex systems, the transponder includes for example an integrated circuit connected to a coil, the coil and the integrated circuit forming among other things a tuned resonant circuit. The presence of the transponder in the electromagnetic field supplies the integrated circuit which modulates the electromagnetic field to have the reader detect the presence thereof. Then, a dialog can take place between the transponder and the reader through the modulation of the electromagnetic field. In Figures 4 and 5, a reading system allows improvements in the reading of several transponders 13- 16 by implementing during the reading, a magnetic coupling of the transponders with a passive resonant circuit 17. The reading system 12 includes the emission- reception antenna 18 buried in a support 19 and the passive resonant circuit 17 is performed on a plane support 20 for example a paper sheet, and includes an open antenna 21 the ends of which are connected to plates 22, 23 of a capacitor. The antenna is in fact a double face device made by screen printing with a conductive ink; on the inner face the capacitor plate 24 is opposite two terminal plates 22, 23 connected to the turns. The passive circuit is positioned in the above example of the reader antenna, for example placed or glued on a support plane close to the radio frequency antenna of the reader. According to one implementation system, the passive antenna of the resonant circuit is associated, at least during the reading, with at least one transponder antenna. Association means a physical bringing together of their positions so as to obtain a magnetic coupling therebetween with or without a common support. According to one step on the method, the passive resonant circuit is tuned to a resonant frequency so that the resonant frequency resulting from the association with at least one transponder antenna corresponds to one of the frequencies of the emission side bands of the transponder to be read. The advantage consists in favoring the detection, by the reader, of the variations in the field caused by the transponders when they respond. Preferably, the transponders are designed or configured so as to be neglected in the association with the passive resonant circuit, each more particularly by drawing less magnetic field and/or by interfering less with the other transponder antennas. The transponders, for this purpose, have a reduced format as compared to the antenna of the passive resonant circuit. In the example, the transponder is one or several of the transponders 13-16 with the small dimension to be read as compared to the antenna. The reduced format of the transponders is for example less than 1/10°, even 1/5°, the format of the passive resonant circuit antenna. The advantage consists in allowing the supply of as many transponders as possible with the same field density. Thus, in the example above, as this association is negligible in so far as there is no significant influence of small transponders on the resonant frequency resulting from the association, the resonant circuit is tuned to a frequency corresponding to one of the frequencies of the emission side band of the transponder to be read. The emission side bands are generated by any other transponder submitted to an interrogation magnetic field that the transponder modulates more particularly in amplitude, during its response. The side bands exist for other principles of modulations of the communication between a reader and a transponder, more particularly the phase modulation and frequency modulation. In the example, an amplitude modulation of a sine-wave signal having a 13.56MHZ frequency by a 847Khz modulating signal corresponding to the sub- carrier generated by the transponder creates, from a spectral point of view, a signal with two side bands located at 13.56MHz +/-847KHz or 12.71 and 14.4MHz respectively. Other side bands as other than those hereabove are also generated but with less energy. In order to favor as much as possible the detection by the reader and reach the minimum level of retro-modulated field defined by the ISO/IEC 14443 standard the resonance frequency of the passive resonant circuit is selected at 14.4MHz, i.e. 13.56MHz +847KHZ. Other examples of association will be subsequently illustrated. According to another implement, at least one format F of the transponder antenna and one transponder response having a behavior or characteristics corresponding to this format are determined and then the passive resonant circuit is configured in such a way as to obtain the behavior of the characteristics corresponding to such format for each transponder. The passive antenna has thus been voluntarily defined in an area Z (Fig. 6) between two rectangles 25, 26 centered on each other and in the IDl format described in the ISO/IEC 14443 standard, respectively 81mm x 49mm and 64mm x 34 mm. The advantage consists in obtaining a response from small transponders having the same characteristics as the big ones while allowing a reading of more transponders with a constant interrogation field. This makes it possible to meet the specifications of the ICAO in order to allow the reading to a greater number of transponders, and a travel document 27 (Fig. 7) of the e-passport or e-Visa is manufactured and includes the passive antenna (or passive resonant circuit 17 composed of one or several conductive tracks) more particularly in the cover of the passport. This travel document can shelter one or several transponder or transponders 13 to 16, each taking the part of the local field induced by the passive resonant circuit submitted to the field of the reader plus the part of the field which is radiated by the antenna of the reader about the surface of the antenna module or modules 13-16. Figures 8 and 9 illustrate the system for reading the travel document. It includes, as above, a reading support 19 containing an emitting and receiving antenna 18 connected to means 28 for processing and operating the signal received. The resonant circuit 17 is here fixed under the reading support. The advantage is to have a common circuit at the level of the reader for all the passports whereas in the example in Figure 7, each document including such resonant circuit, it is not indispensable to have it at the reading level. In the example, conformably with the provisions of ICAO, the amplitude of the magnetic field H of the reader is determined at a value above or equal to 1.5 A/m and the amplitude of the transponder response to a value above or equal to 30/H1'2. The travel document includes a large dimensioned transponder 3 for example ID1 and several transponders 13-16 of smaller dimensions such as electronic visas. The antenna modules 13-16 are not necessarily positioned on the same plane as those on which the passive antenna is positioned. In Figure 8, the passive resonant circuit 17 is positioned out of the travel document. It is associated with the reading system by being fixed under the reading support. However, it could be positioned close to it, more particularly close to or stuck onto the reading support. The passive resonant circuit can have the shape of a label stuck on the document more particularly with an adhesive. It can be integrated in the document more particularly in one of the pages or the covers thereof. The transponders to be read (13-16, 3) are in the travel document 27B. In such a document, reduced dimensions, so-called secondary transponders, and large dimensions, so-called main transponders can be found. In this case, as indicated while referring to Figure 10 described infra, it is recommended to tune the passive resonant circuit while considering the association with the main circuit. The energy and coupling balance of such a solution cannot be compared with the balance obtained by ID1 dimension transponders which are compatible with ISO/IEC14443. Each antenna-module is separately perceived by the reader as having a format and thus an action on the magnetic field of the reader which corresponds to that of the passive antenna which is itself in compliance with the standard ID1 for the travel documents. The geometric and electric characteristics, on the one hand, of the passive resonant circuit and the antenna-module preferably corresponding to the following description, on the other hand, exist. As regards the reader and also the test devices such as those described in the test methods for contactless products: ISO/IEC 10373-6, the travel document including several electronic visas must be considered as only one contactless product. The following preferable principles aiming at making a passive resonant circuit to be included in the travel document of the electronic passport type are the results thereof. The passive resonant circuit must be such that the couple thereof with the reader causes an effect complying with the contactless card equipped with a IDl format antenna. It must cause a low load on the electromagnetic field generated by the reader. Such load must correspond to that caused by the reference PICC, appendix D of the ISO/IEC 10373-6 standard adjusted on 6Volt for Hmin. The loading induced by the transponder corresponds to an ID1 antenna tuned on 13.56Mhz and including a resistive part of 1.8kQ and the continuous voltage of which is the result of an interrogation field of less than 6V at the load terminals. This results in the resonant circuit having the following geometric characteristics. As described hereabove, the passive antenna has thus been voluntarily defined in a zone Z between two rectangles 25, 26 centered on each other and on the ID1 format described in the ISO/IEC 14443 standard, respectively 81mm x 49mm and 64mm x 34mm (Fig. 6). In order not to limit too much the field generated by the contactless reader, the quality factor on the passive resonant circuit is voluntarily limited to a value of less than 30. The optimum quality coefficient of such resonant circuit for meeting the conditions described hereabove is between 10 and 20. The optimum value of the quality factor of the passive resonant circuit is 20. This allows drawing technologies for an antenna with a strong electric resistance such as screen printing using silver ink or carbon ink. Because of the necessity for an overvoltage factor, the passive resonant circuit must be composed of an antenna composed of several terms and connected to a capacitor. The passive resonant circuit must supply to the electromagnetically coupled antenna-modules, the additional energy which they require because of their small coupling surfaces with the reader. The passive resonant circuit mu3t generate an additional local field as a complement to that delivered by the reader which supplies the antenna modules. On the other hand (Fig. 11) the transponder 13 can be made in the form of an antenna module complying with the chip card technology. It includes a flat antenna 29 on an isolating support 30 (dielectric film) in a plane and is connected to an integrated circuit chip 31. The chip may include a protective coating resin 32 or not. The assembly may have a global thickness of less than 1mm. The antenna 29 is preferably made of a metal wire or copper etching so as to have a good quality factor. The transponder will advantageously have a reasonable size for example 25mm in length, 15mm in width and include an antenna of about fifteen turns for example between 13 and 18 turns. The number of turns will slightly depend on the selected chip. Each turn for example made of copper has for example a width of the order of 50 to 300um with a spacing between two contiguous turns of the order of 50 to 200um. A compromise or optimization between the surface ratio is still to be reached. A module-antenna having too small a surface for example of less than 10mm by 10mm would require a very accurate positioning with respect to the passive resonance circuit in order to allow a correct operation which a priori excludes the devices based on antennas directly made on the surface of the chip. A contrario, a module-antenna having dimensions above 30mm by 30mm would consume too much magnetic field and would be too coupled to the other modules having an antenna to allow the operation of several integrated circuit chips or electronic visas. The ideal solution is a resonance frequency of transponders amounting to 17MHz. Considering the geometry of the transponders, the resonance frequency and the number of the turns, the number of the passive resonance circuit turns is optimum for 4 turns. The surface of the capacitor plates is so calculated as to make the frequency tuning, as mentioned hereabove. In Figure 10, the passive resonant circuit 17 is associated with a transponder having an antenna, the dimensions of which can be compared to those of the passive circuit. The importance thereof is such that it must be considered within the tuning in frequency of the passive resonant circuit. As a matter of fact, the resultant resonance frequency of two circuits is defined by the following relation: where k: the coupling coefficient between the transponders (equal to 1 if the coupling is the maximum one) fres.2: resonance frequency resulting from the association of two transponders having the same resonance frequency "fres". This could be for example the ID1 format transponder such as presently positioned in the cover of the electronic passport of the prior art or one of the electronic visas in the ID1 format as in Figure 2. The passive resonant circuit is so tuned that the resonance frequency resulting from the association M corresponds to one of the frequencies of the emission side bands of the transponder to be read. The two associated elements can be grouped together in the same support, for example a cover 6A of the travel document. Due to the extension of this principle, the association may concern several transponders so long as the number thereof gives them a non-negligible importance. According to an advantageous provision illustrated in Figures 12 and 13, each electronic visa is positioned in a support 33, 34, for example a sheet which is substantially of the same format as the document or slightly smaller. In the application to the passport, the support is in the IDl format or slightly smaller. The important thing is not leaving the choice to the user when it is applied into the document. This transponder support 33 must be placed in the document or stuck onto a page more particularly using a self-adhesive coating. The transponder 13 is positioned in a random position inside the support upon the manufacturing of the visa more particularly through lamination. In Figure 12, it is positioned along the left side edge 35 whereas it is positioned along the right side edge 36 in Figure 13. Thus, when both sheets are superimposed, the transponders get less coupled together. An embodiment of the transponders must include, for this purpose, a step and means for the random or varied position of the transponder on the surface of a transporter support sheet for example during the lamination of sheet sandwiching the transponder. Thus, when it is copied in the travel document, it is distributed also in a random way with respect to the other transponders. The result is that the labels are all different as regards the magnetic point of view and they can be more easily operated even though they are superimposed. Thus, thanks to the invention, it is possible to make the application of an electronic Visa with a more important number of electronic visas possible. The preferred characteristics, as mentioned hereabove, make it possible to read up to 15 transponders complying with the ICAO specifications. The reading method can implement an anti- collision mechanism or protocol of a known type more particularly the one described in the standard. The mechanism can be triggered by the reader processing means. According to another aspect, the invention makes it possible to produce an electronic travel document. This document is supposed to include a plurality of transponders complying with constraints or specifications more particularly resulting from the standard (ICAO) which impose at least one ID1 format of transponder antenna, a minimum amplitude of the magnetic field H for the reading and a minimum amplitude for the response from the transponders. According to this other aspect, the transponder is made with an antenna format smaller than the IDl format and said transponder is so arranged with a passive resonant circuit and a capacitor and a passive antenna with an ID1 format, so that the transponder is seen by the reader as a ID1 format transponder. The travel document according to the invention may include several pages and a plurality of transponders between the pages, with each transponder being contained in a plane support separate from the pages but substantially having the format of a page of the document. This document can easily be read by all the transponders in so far as the transponders are positioned in the supports in various positions. Consequently, the invention is also characterised by an assembly or a set of transponders, more particularly for electronic visas, in that each transponder is positioned in a sheet (33, 34) having a bigger format than the format and in that the transponders are positioned in the sheets (33, 34) in various positions from one sheet to another. Although the invention has mainly been described in relation with a travel document, it can be applied to any object supporting a passive resonant circuit associated to at least one transponder such as for example an electronic label, a chip card including a module-antenna associated with a passive resonant circuit the antenna of which has the dimensions of the contactless chip ID1. Such objects are preferably portable devices such as a chip card or a cell phone. The passive antenna can be included in the body of the chip card, more particularly about the module antenna inserted in a standard cavity of the chip card. The passive antenna together with the resonant circuit can also be integrated in the reader. CLAIMS 1. A method for reading RF transponders disposed in one and the same magnetic interrogation field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit (17) during reading, characterised in that the passive antenna (21) of the resonant circuit is associated with at least one transponder antenna (3, 13-16), and the passive resonant circuit is tuned in such a way that the resonance frequency resulting from the association M corresponds to one of the frequencies of the emission side bands of the transponder (3, 13-16) to be read. 2. A method according to the preceding claim, wherein the association of the passive antenna (21) of the passive resonant circuit with at least one transponder antenna (3) is made negligible and the passive resonant circuit (17) is tuned to a resonance frequency corresponding to one of the frequencies of the emission side bands of the transponder to be read. 3. A reading method according to the preceding claim, characterised in that the method further includes a step during which: - the transponders (13-16) are so configured as to be negligible in the association with the passive resonant circuit (17), by each drawing less magnetic field and/or by interfering less with the other antennas of the transponder. 4. A reading method according to the preceding claim, - wherein at least one antenna format F and one response from a transponder having a behavior corresponding to such format are determined , - the passive resonant circuit is so configured as to obtain a behavior corresponding to such a format for each transponder. 5. A reading method according to claim 4, characterised in that the passive antenna is defined between two rectangles respectively 81mm x 49mm, and 64mm x 34mm. 6. A reading method according to one of claims 1 or 2, characterised in that the side bands are respectively selected approximately at 13.56 MHz ± 847Khz or respectively 12.71 and 14.4 MHz, the interrogation frequency being 13.56MHz rated at 847Khz. 7. A reading method according to claim 5, characterised in that the antenna of the passive resonant circuit (17) includes between 3 and 6 turns. 8. A reading method according to one of the preceding claims, characterised in that the passive resonant circuit (17) has a quality factor with a value of less than 30. 9. A reading method according to one of the preceding claims, characterised in that the transponder has a reduced format and has an antenna, the surface inside the outer turn of which is greater than a 15 x 15mm surface and smaller than a surface of approximately 30 x 30mm. 11. A reading method according to the preceding claim, characterised in that the transponder antenna includes 13 to 18 turns. 12. A reading method according to the preceding claim, characterised in that the tuning frequency is between 15 and 18 MHz. 13. A reading method according to the preceding claim, characterised in that the transponder has a quality factor above 30. 14. A reading method according to the preceding claim, characterised in that each transponder (13, 14) is positioned in a support in a random position, with the support allowing several positions of the transponder which are shifted with respect to each other. 15. A reading system (12) with at least one RF transponder, with said system including - one reader (18, 19, 28) able to emit an interrogation field on at least one transponder (13, 14) and to collect a response from the transponder, - a passive resonant circuit (17) to perform a magnetic coupling with at least one transponder during the reading, characterised in that the passive resonant circuit (17) is tuned in such a way that the resonant frequency resulting from the association (M) of the resonant circuit with at least one transponder (3, 13) corresponds to one of the frequencies of the emission side bands of the transponder to be read. 16. A supporting object containing at least one main transponder, one secondary transponder and an associated passive resonant circuit associated with at least the main transponder, characterised in that the passive resonant circuit (17) is tuned in such a way that the resonant frequency resulting from the association (M) of the resonant circuit with at least the main transponder (3) corresponds with one of the frequencies of the emission side bands of the secondary transponder (13). 17. A supporting object containing at least one transponder and one passive resonant circuit associated with at least one transponder, characterised in that the passive resonant circuit (17) is tuned to a resonance frequency corresponding to one of the frequencies of the emission side bands of the transponder. 18. A transponder including a flat antenna on a support defining an outer turn, characterised in that: - the surface inside the outer turn is greater than a 15 x 15mm surface and smaller than or equal to a surface of approximately 30 x 30mm, - the antenna includes about 13 to 18 turns, - the tuning frequency is between 15 and 18 MHz, - a quality factor is above 30. 19. A travel document (27) including several pages between two covers and a plurality of transponders (13-16) between the pages, each transponder being contained in a plane support (33, 34) separate from the pages or covers but having substantially the format of a page, characterised in that the transponders are configured as in the preceding claim. 20. A travel document according to the preceding claim, characterised in that the transponders are positioned in the supports (33, 34) in various positions. 21. An assembly of transponders according to claim 18, with each transponder being positioned in a sheet (33, 34) having a greater format than the latter, characterised in that the transponders are positioned in the supports (33, 34) in various positions from one sheet to another. Method and system for optimized reading of a radio frequency communication transponder with the aid of a passive resonant circuit. The invention relates to a method of reading RF transponders disposed in one and the same magnetic interrogation field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit (17) during reading. The method is distinguished in that the passive antenna (21) of the resonant circuit is associated with at least one transponder antenna (3, 13-16), and the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association M corresponds to one of the frequencies of the emission side bands of the transponder (3, 13-16) to be read. The invention also relates to the system corresponding to the method, a transponder structure and an object containing the transponder, in particular a travel document.

Full Text

Method and system for optimized reading of a
radio frequency communication transponder with the aid
of a passive resonant circuit.
The invention relates to the field of methods and
systems for reading RF radio frequency transponders and
the structure of such radio frequency transponders.
More particularly, the invention relates to an
improvement in the reading and/or the communications
between a transponder liable to be surrounded by
several transponders and a reader provided for this
purpose. The invention more particularly aims at an
application of such methods and systems to the
contactless reading of electronic travel documents such
as electronic passports and electronic visas in the
form of transponders positioned together. In
particular, such documents and visas are compliant with
ICAO "International Civil Aviation Organization"
specification and the IS07IEC 14443 standard.
The travel documents such as the electronic
passports and/or the electronic visas are composed on
the one hand of a paper document whereon information
relative to the holder of said document is noted and on
the other hand a contactless electronic chip which also
contains secured information relative to the same
holder.
The unsolved problem arises as soon as the travel
document of the electronic passport type must also
include several electronic visas.
As a matter of fact, because of the variable
principles used by such contactless electronic chips,
the increase in the number of electronic visas in the

document makes the simultaneous reading more and more
difficult when and as their number increases, which can
even make the operation thereof impossible as soon as
the number is greater than 4 or 5 visas.
The need expressed as regards electronic travel
documents is that said document may contain a maximum
of contactless electronic visas which are
simultaneously operated when they are submitted to a
magnetic field from a contactless reader. The reader
and the travel documents must be compliant with the
ISO/IEC 14443 standard.
The specifications of contactless electronic visa
or visas request that on the one hand each visa
consumes as little as possible magnetic field from the
contactless reader and interacts therewith as little as
possible and on the other hand that each one causes a
variation of said magnetic field which is compatible
with the specifications imposed by the ISO/IEC 14443
standard during the phases of responses from the visa
to the reader.
The contactless technology resulting from the
ISO/IEC 14443 standard describes the mechanisms making
it possible to implement the anti-collision principles
between contactless products. Such principles provide
logical mechanisms which make it possible to retrieve a
contactless product among several others when they are
submitted to the same magnetic field. The condition
required for a correct operation of such principle is
that the reader supplies all the products existing in
the field it generates and that it detects them all.
More particularly, the contactless anti-collision
mechanism is limited by the consumption and the

magnetic load induced by the sum of several contactless
transponders. This limits the number of electronic
visas which can be read in or out of an electronic
passport.
In addition, the ISO/IEC 14443 standard contains
a specification imposing that the contactless products
be operated in a range of magnetic field between 1.5
A/m and 7.5 A/m. This specification makes it possible
for contactless products to be operated from a magnetic
field of at least 1.5 A/m.
A standard compliant reader can thus generate
only a 1.5 A/m field in the presence of the travel
document while being conformable with the standard.
The ISO/IEC 14443 standard also imposes the minimum
amplitude of the response of the contactless product so
that the reader can detect it.
Such minimum amplitude is worth at least 30/H1*2
(or 18.6mV), with H amplitude of the magnetic field.
Such value is defined from the amplitude of the side
bands generated because of the amplitude modulation of
the reader magnetic field, with the frequency of
13.56MHz by the contactless product at the rate of the
sub-carrier thereof, rated at 847Khz.
If these conditions are complied with, the
contact reader complying with the standard should be
capable of receiving the data from the contactless
chip.
The present state of the art makes it possible to
comply with all such conditions whenever a maximum
number of a few electronic visas are positioned in the
travel document. At present, 5 visas seem to be a
maximum as regards the curve of the transponders

response (Figure 3 retrieved from the official document
N1088 from ISO/IEC JTC1/SC17/WG8).
The inventor noted that if more than five
contactless products which are individually standard
compliant are used, when they are grouped in the same
travel document, because of the electromagnetic
coupling together, the assembly, is no longer compliant
with the ISO/IEC 14443 standard. The conformable
contactless reader is no longer capable of supplying
them or detecting them.
This limitation to five as regards the number of
transponders is considered by the inventor as being
potentially a disadvantage in the development of an
electronic passport and also in a general way for the
reading of several transponders positioned together
whatever the considered application.
Thus the inventor has considered improving in a
general way the contactless communication of a certain
number of transponders for a constant power of the
reader.
As regards the known prior art making it possible
to improve the communication between the transponders
and a reader, the patents FR 2 777 141 or US 6172608
are known.
Such patents make it possible to have a second
oscillating circuit which can be tuned on a frequency
which is close to (or equal to) the electromagnetic
field, so that the modulation of the field performed by
the transponder is better detected by the antenna of
the reader. Such documents more particularly teach the
utilization of a passive resonant circuit for
increasing the communication distance between the

reader and the transponder while keeping a correct
operation and without increasing the emission power of
the reader.
On the other hand, the document FR 2 812 482-A1
is known, which uses a collective antenna which is
closed to amplify the communication from the reader
with several transponders positioned on the same
support. The multiplicity of the transponders on a
support corresponds to the problem of increasing the
storage memory available on the support. The
transponders have a more reduced format than the
passive antenna because of the manufacturing cost.
This document does not teach the optimization of the
number of legible transponders for a constant
electromagnetic field power.
In addition, the arrangement of a closed passive
collective antenna associated with several transponders
having more reduced dimensions than the passive antenna
seems not to be operational, as exposed in the present
document in the present state of the art of the person
skilled in the art.
The invention more particularly relates to the
solving of the above-mentioned drawbacks.
It more generally aims at improving the reading
of transponders, such improvements being intended to
lead to the increase in the number of transponders
which can be read together in a determined
electromagnetic field, whatever the dimension thereof.
It also aims at providing the optimization of the
number of transponders which can be read together for
the application to an electronic passport, in
compliance with specifications of the ICAO and

ISO/IEC14443, in particular. New transponders
characteristics are supplied for this purpose.
According to a first aspect, the invention aims
at a method for the contactless reading RF transponders
positioned in one and the same magnetic interrogation
field, wherein a magnetic coupling of the transponders
is ensured with a passive resonant circuit during
reading.
The method is characterised in that the passive
antenna of the resonant circuit is associated with at
least one transponder antenna, and the passive resonant
is tuned in such a way that the resonant frequency
resulting from the association corresponds to one of
the frequencies of the emission side bands of the
transponder to be read.
Such provisions make it possible to favor the
amplitude of the transponder return signal.
According to a particular embodiment, the
association of the passive antenna of the resonant
circuit with at least one antenna of the transponder is
made negligible and the passive resonant circuit is
tuned to a resonant frequency corresponding to one of
the frequencies of the emission side bands on the
transponder to be read.
Such provisions make it possible to further
simplify the reading method while favoring the
amplitude of the return signal delivered by the chip of
the antenna module or transponder.
The invention also relates to a system for
reading at least one RF transponder, said system
including a reader able to emit an interrogation field
on at least one transponder and to collect a response

from the transponder, a passive resonant circuit for
performing a magnetic coupling with at least one
transponder during the reading.
The system is characterised in that the passive
resonant circuit is tuned in such a way that the
resonant frequency resulting from the association of
the resonant circuit with at least one transponder
corresponds to one of the frequencies of the emission
side bands of the transponder to be read.
Another aspect of the invention relates to a
support object containing at least one main
transponder, at least one secondary transponder and one
passive resonant circuit associated with at least a
main transponder.
The object can be distinguished in that the
passive resonant circuit is tuned in such a way that
the resonant frequency resulting from the association
of the resonant circuit with the main transponder at
least corresponds to one of the frequencies of the
emission side bands of the secondary transponder.
Another aspect of the invention relates to a
support object containing at least one transponder and
a passive resonant circuit associated with at least the
transponder. It can be differentiated in that the
passive resonant circuit is tuned to a resonant
frequency corresponding to one of the frequencies of
the emission side bands of the transponder.
Another aspect of the invention relates to a
transponder including a flat antenna on a support
defining an outer turn;
the transponder is characterised in that:

- the surface outside the outer turn is greater
than a 15 x 15mm surface and smaller than a surface of
approximately 30 x 30mm,
- the antenna includes approximately between 13
and 18 turns,

- the tuning frequency is between 15 and 18 MHz,
- a quality factor is above 30.
Another aspect of the invention relates to a
travel document including several pages between two
covers and a plurality of transponders between the
pages, with each transponder being contained in a plane
support distinct from the pages or covers, but having
substantially the same format of a page, with the
transponder having the above characteristics.
According to an advantageous provision making it
possible to have less interference or coupling between
the transponders, the latter are positioned in the
support in various positions and particularly in a
random way.
Other characteristics and advantages of the
invention will appear upon reading the following
description given as a non limitative example and by
referring to the appended drawings wherein:
- Figure 1 illustrates an electronic passport
reading system according to the prior art;
- Figure 2 illustrates an electronic passport and
the various visas of the prior art;
Figure 3 illustrates response curves in
response to the number of transponders of the prior
art;
- Figure 4 illustrates a section in Figure 5
along A-A;

- Figure 5 illustrates a transponder reading
system complying with one embodiment of the invention;
- Figure 6 illustrates an area for the possible
dimensions of the passive antenna according to one
embodiment;
- Figure 7 illustrates a travel document which is
compliant with an embodiment of the invention;
- Figure 8 illustrates a travel document reading
system complying with the preceding Figure;
- Figure 9 illustrates a schematic view of the
reading system of the preceding Figure;
- Figure 10 illustrates a reading configuration
for transponders using an association of the passive
resonant circuit with a main transponder;
- Figure 11 illustrates a transponder according
to one embodiment of the invention;
Figures 12, 13 illustrate the transponder
packaging according to another embodiment of the
invention.
In Figure 1, an existing system 1 for reading
electronics passport and electronic visas in the form
of transponders of the radio frequency (RF) type
includes a reader able to emit an interrogation field
via an emitting antenna 2 and to collect a response
from the transponder submitted to this field.
The passport 3 (PICIO) and each visa 4 (PCI1-
PICI5) include the same type of transponders, i.e. an
electronic circuit (5a, 5b) of the RF-ID (radio
frequency identification) type connected to an antenna
(4a-4b).

In Figure 2, the passport transponder is buried
in the cover 6 of a passport 7 and each electronic visa
transponder is buried in a sheet 8.
In Figure 3, a diagram of voltage response curve
(10) of a transponder with a ID1 format (the format of
present passports) has a peak beyond 35 volts whereas
the voltage response of 5 transponders PICI positioned
together is close to 5 volts. Beyond 5 transponders,
the voltage dramatically drops and it is no longer
possible to detect and to read more than 5 transponders
having a frequency of 13.56MHz.
Generally speaking, within the frame of the
present description, transponder means any
identification electronic circuit using detection or a
communication using an electromagnetic field. More
particularly, electromagnetic fields are concerned and
they include a coil connected to a condenser and where
an integrated circuit or any other electronic
components can be found.
The transponders more particularly include an
electronic component such as an integrated circuit chip
connected to an antenna. They can be inserted into, or
associated with any type of support. They may, for
example, have the shape of adhesive electronic labels,
contactless card; they can be buried in a packaging,
the cover of a document, a sheet or any other thing,
etc.
Transponders are used in various economics fields
such as bank (electronic purse), communications,
transport, identity (e-passport, ID card). More
particularly as regards identity, identifying a person
through a radio frequency communication with a

contactless portable electronic object of the RFID
type, is known.
In a general way, reader means within the scope
of the following description, an emitter/receiver
device provided with one antenna which creates an
electromagnetic field at a given frequency. The
antenna of the device also makes it possible to
modulate the electromagnetic field and to measure
variations in the electromagnetic field. The antenna
of the device also makes it possible to modulate the
electromagnetic field and to measure the variations in
the electromagnetic field. The reader antenna is
generally composed of one or several coils.
The reader-transponder system is operated in a
more or less complex way according to the type of the
transponder used. The general operation principle
consists in emitting an electromagnetic field with a
given frequency. When one transponder goes within the
electromagnetic field, it is supplied and it reacts.
The reaction of the transponder causes the variation of
an electromagnetic field which is detected by the
reader.
For the simplest systems, the transponder being
for example composed of one coil and one condenser, the
assembly is an oscillating circuit tuned on the
frequency of the electromagnetic field. The presence
of the transponder in the field makes the oscillating
circuit resonate and causes a modification of the field
which can be detected by the reader. Such systems
which are very simple are currently used as anti-theft
devices in department stores.

As regards the most complex systems, the
transponder includes for example an integrated circuit
connected to a coil, the coil and the integrated
circuit forming among other things a tuned resonant
circuit. The presence of the transponder in the
electromagnetic field supplies the integrated circuit
which modulates the electromagnetic field to have the
reader detect the presence thereof. Then, a dialog can
take place between the transponder and the reader
through the modulation of the electromagnetic field.
In Figures 4 and 5, a reading system allows
improvements in the reading of several transponders 13-
16 by implementing during the reading, a magnetic
coupling of the transponders with a passive resonant
circuit 17.
The reading system 12 includes the emission-
reception antenna 18 buried in a support 19 and the
passive resonant circuit 17 is performed on a plane
support 20 for example a paper sheet, and includes an
open antenna 21 the ends of which are connected to
plates 22, 23 of a capacitor. The antenna is in fact a
double face device made by screen printing with a
conductive ink; on the inner face the capacitor plate
24 is opposite two terminal plates 22, 23 connected to
the turns.
The passive circuit is positioned in the above
example of the reader antenna, for example placed or
glued on a support plane close to the radio frequency
antenna of the reader.
According to one implementation system, the
passive antenna of the resonant circuit is associated,
at least during the reading, with at least one

transponder antenna. Association means a physical
bringing together of their positions so as to obtain a
magnetic coupling therebetween with or without a common
support.
According to one step on the method, the passive
resonant circuit is tuned to a resonant frequency so
that the resonant frequency resulting from the
association with at least one transponder antenna
corresponds to one of the frequencies of the emission
side bands of the transponder to be read.
The advantage consists in favoring the detection,
by the reader, of the variations in the field caused by
the transponders when they respond.
Preferably, the transponders are designed or
configured so as to be neglected in the association
with the passive resonant circuit, each more
particularly by drawing less magnetic field and/or by
interfering less with the other transponder antennas.
The transponders, for this purpose, have a reduced
format as compared to the antenna of the passive
resonant circuit. In the example, the transponder is
one or several of the transponders 13-16 with the small
dimension to be read as compared to the antenna. The
reduced format of the transponders is for example less
than 1/10°, even 1/5°, the format of the passive
resonant circuit antenna.
The advantage consists in allowing the supply of
as many transponders as possible with the same field
density.
Thus, in the example above, as this association
is negligible in so far as there is no significant
influence of small transponders on the resonant

frequency resulting from the association, the resonant
circuit is tuned to a frequency corresponding to one of
the frequencies of the emission side band of the
transponder to be read.
The emission side bands are generated by any
other transponder submitted to an interrogation
magnetic field that the transponder modulates more
particularly in amplitude, during its response.
The side bands exist for other principles of
modulations of the communication between a reader and a
transponder, more particularly the phase modulation and
frequency modulation.
In the example, an amplitude modulation of a
sine-wave signal having a 13.56MHZ frequency by a
847Khz modulating signal corresponding to the sub-
carrier generated by the transponder creates, from a
spectral point of view, a signal with two side bands
located at 13.56MHz +/-847KHz or 12.71 and 14.4MHz
respectively.
Other side bands as other than those hereabove
are also generated but with less energy.
In order to favor as much as possible the
detection by the reader and reach the minimum level of
retro-modulated field defined by the ISO/IEC 14443
standard the resonance frequency of the passive
resonant circuit is selected at 14.4MHz, i.e. 13.56MHz
+847KHZ.
Other examples of association will be
subsequently illustrated.
According to another implement, at least one
format F of the transponder antenna and one transponder
response having a behavior or characteristics

corresponding to this format are determined and then
the passive resonant circuit is configured in such a
way as to obtain the behavior of the characteristics
corresponding to such format for each transponder.
The passive antenna has thus been voluntarily
defined in an area Z (Fig. 6) between two rectangles
25, 26 centered on each other and in the IDl format
described in the ISO/IEC 14443 standard, respectively
81mm x 49mm and 64mm x 34 mm.
The advantage consists in obtaining a response
from small transponders having the same characteristics
as the big ones while allowing a reading of more
transponders with a constant interrogation field.
This makes it possible to meet the specifications
of the ICAO in order to allow the reading to a greater
number of transponders, and a travel document 27 (Fig.
7) of the e-passport or e-Visa is manufactured and
includes the passive antenna (or passive resonant
circuit 17 composed of one or several conductive
tracks) more particularly in the cover of the passport.
This travel document can shelter one or several
transponder or transponders 13 to 16, each taking the
part of the local field induced by the passive resonant
circuit submitted to the field of the reader plus the
part of the field which is radiated by the antenna of
the reader about the surface of the antenna module or
modules 13-16.
Figures 8 and 9 illustrate the system for reading
the travel document. It includes, as above, a reading
support 19 containing an emitting and receiving antenna
18 connected to means 28 for processing and operating
the signal received.

The resonant circuit 17 is here fixed under the
reading support. The advantage is to have a common
circuit at the level of the reader for all the
passports whereas in the example in Figure 7, each
document including such resonant circuit, it is not
indispensable to have it at the reading level.
In the example, conformably with the provisions
of ICAO, the amplitude of the magnetic field H of the
reader is determined at a value above or equal to 1.5
A/m and the amplitude of the transponder response to a
value above or equal to 30/H1'2.
The travel document includes a large dimensioned
transponder 3 for example ID1 and several transponders
13-16 of smaller dimensions such as electronic visas.
The antenna modules 13-16 are not necessarily
positioned on the same plane as those on which the
passive antenna is positioned.
In Figure 8, the passive resonant circuit 17 is
positioned out of the travel document. It is
associated with the reading system by being fixed under
the reading support.
However, it could be positioned close to it, more
particularly close to or stuck onto the reading
support.
The passive resonant circuit can have the shape
of a label stuck on the document more particularly with
an adhesive. It can be integrated in the document more
particularly in one of the pages or the covers thereof.
The transponders to be read (13-16, 3) are in the
travel document 27B. In such a document, reduced
dimensions, so-called secondary transponders, and large
dimensions, so-called main transponders can be found.

In this case, as indicated while referring to Figure 10
described infra, it is recommended to tune the passive
resonant circuit while considering the association with
the main circuit.
The energy and coupling balance of such a
solution cannot be compared with the balance obtained
by ID1 dimension transponders which are compatible with
ISO/IEC14443. Each antenna-module is separately
perceived by the reader as having a format and thus an
action on the magnetic field of the reader which
corresponds to that of the passive antenna which is
itself in compliance with the standard ID1 for the
travel documents.
The geometric and electric characteristics, on
the one hand, of the passive resonant circuit and the
antenna-module preferably corresponding to the
following description, on the other hand, exist.
As regards the reader and also the test devices
such as those described in the test methods for
contactless products: ISO/IEC 10373-6, the travel
document including several electronic visas must be
considered as only one contactless product.
The following preferable principles aiming at
making a passive resonant circuit to be included in the
travel document of the electronic passport type are the
results thereof.
The passive resonant circuit must be such that
the couple thereof with the reader causes an effect
complying with the contactless card equipped with a IDl
format antenna.
It must cause a low load on the electromagnetic
field generated by the reader. Such load must

correspond to that caused by the reference PICC,
appendix D of the ISO/IEC 10373-6 standard adjusted on
6Volt for Hmin. The loading induced by the transponder
corresponds to an ID1 antenna tuned on 13.56Mhz and
including a resistive part of 1.8kQ and the continuous
voltage of which is the result of an interrogation
field of less than 6V at the load terminals.
This results in the resonant circuit having the
following geometric characteristics.
As described hereabove, the passive antenna has
thus been voluntarily defined in a zone Z between two
rectangles 25, 26 centered on each other and on the ID1
format described in the ISO/IEC 14443 standard,
respectively 81mm x 49mm and 64mm x 34mm (Fig. 6).
In order not to limit too much the field
generated by the contactless reader, the quality factor
on the passive resonant circuit is voluntarily limited
to a value of less than 30.
The optimum quality coefficient of such resonant
circuit for meeting the conditions described hereabove
is between 10 and 20. The optimum value of the quality
factor of the passive resonant circuit is 20. This
allows drawing technologies for an antenna with a
strong electric resistance such as screen printing
using silver ink or carbon ink. Because of the
necessity for an overvoltage factor, the passive
resonant circuit must be composed of an antenna
composed of several terms and connected to a capacitor.
The passive resonant circuit must supply to the
electromagnetically coupled antenna-modules, the
additional energy which they require because of their
small coupling surfaces with the reader. The passive

resonant circuit mu3t generate an additional local
field as a complement to that delivered by the reader
which supplies the antenna modules.
On the other hand (Fig. 11) the transponder 13
can be made in the form of an antenna module complying
with the chip card technology. It includes a flat
antenna 29 on an isolating support 30 (dielectric film)
in a plane and is connected to an integrated circuit
chip 31. The chip may include a protective coating
resin 32 or not. The assembly may have a global
thickness of less than 1mm.
The antenna 29 is preferably made of a metal wire
or copper etching so as to have a good quality factor.
The transponder will advantageously have a
reasonable size for example 25mm in length, 15mm in
width and include an antenna of about fifteen turns for
example between 13 and 18 turns. The number of turns
will slightly depend on the selected chip.
Each turn for example made of copper has for
example a width of the order of 50 to 300um with a
spacing between two contiguous turns of the order of 50
to 200um.
A compromise or optimization between the surface
ratio is still to be reached. A module-antenna having
too small a surface for example of less than 10mm by
10mm would require a very accurate positioning with
respect to the passive resonance circuit in order to
allow a correct operation which a priori excludes the
devices based on antennas directly made on the surface
of the chip.
A contrario, a module-antenna having dimensions
above 30mm by 30mm would consume too much magnetic

field and would be too coupled to the other modules
having an antenna to allow the operation of several
integrated circuit chips or electronic visas.
The ideal solution is a resonance frequency of
transponders amounting to 17MHz.
Considering the geometry of the transponders, the
resonance frequency and the number of the turns, the
number of the passive resonance circuit turns is
optimum for 4 turns. The surface of the capacitor
plates is so calculated as to make the frequency
tuning, as mentioned hereabove.
In Figure 10, the passive resonant circuit 17 is
associated with a transponder having an antenna, the
dimensions of which can be compared to those of the
passive circuit. The importance thereof is such that
it must be considered within the tuning in frequency of
the passive resonant circuit.
As a matter of fact, the resultant resonance
frequency of two circuits is defined by the following
relation:
where k: the coupling coefficient between the
transponders (equal to 1 if the coupling is the maximum
one)
fres.2: resonance frequency resulting from the
association of two transponders having the same
resonance frequency "fres".
This could be for example the ID1 format
transponder such as presently positioned in the cover
of the electronic passport of the prior art or one of
the electronic visas in the ID1 format as in Figure 2.

The passive resonant circuit is so tuned that the
resonance frequency resulting from the association M
corresponds to one of the frequencies of the emission
side bands of the transponder to be read.
The two associated elements can be grouped
together in the same support, for example a cover 6A of
the travel document.
Due to the extension of this principle, the
association may concern several transponders so long as
the number thereof gives them a non-negligible
importance.
According to an advantageous provision
illustrated in Figures 12 and 13, each electronic visa
is positioned in a support 33, 34, for example a sheet
which is substantially of the same format as the
document or slightly smaller. In the application to
the passport, the support is in the IDl format or
slightly smaller. The important thing is not leaving
the choice to the user when it is applied into the
document.
This transponder support 33 must be placed in the
document or stuck onto a page more particularly using a
self-adhesive coating.
The transponder 13 is positioned in a random
position inside the support upon the manufacturing of
the visa more particularly through lamination. In
Figure 12, it is positioned along the left side edge 35
whereas it is positioned along the right side edge 36
in Figure 13. Thus, when both sheets are superimposed,
the transponders get less coupled together.
An embodiment of the transponders must include,
for this purpose, a step and means for the random or

varied position of the transponder on the surface of a
transporter support sheet for example during the
lamination of sheet sandwiching the transponder.
Thus, when it is copied in the travel document,
it is distributed also in a random way with respect to
the other transponders. The result is that the labels
are all different as regards the magnetic point of view
and they can be more easily operated even though they
are superimposed.
Thus, thanks to the invention, it is possible to
make the application of an electronic Visa with a more
important number of electronic visas possible. The
preferred characteristics, as mentioned hereabove, make
it possible to read up to 15 transponders complying
with the ICAO specifications.
The reading method can implement an anti-
collision mechanism or protocol of a known type more
particularly the one described in the standard. The
mechanism can be triggered by the reader processing
means.
According to another aspect, the invention makes
it possible to produce an electronic travel document.
This document is supposed to include a plurality of
transponders complying with constraints or
specifications more particularly resulting from the
standard (ICAO) which impose at least one ID1 format of
transponder antenna, a minimum amplitude of the
magnetic field H for the reading and a minimum
amplitude for the response from the transponders.
According to this other aspect, the transponder
is made with an antenna format smaller than the IDl
format and said transponder is so arranged with a

passive resonant circuit and a capacitor and a passive
antenna with an ID1 format, so that the transponder is
seen by the reader as a ID1 format transponder.
The travel document according to the invention
may include several pages and a plurality of
transponders between the pages, with each transponder
being contained in a plane support separate from the
pages but substantially having the format of a page of
the document.
This document can easily be read by all the
transponders in so far as the transponders are
positioned in the supports in various positions.
Consequently, the invention is also characterised
by an assembly or a set of transponders, more
particularly for electronic visas, in that each
transponder is positioned in a sheet (33, 34) having a
bigger format than the format and in that the
transponders are positioned in the sheets (33, 34) in
various positions from one sheet to another.
Although the invention has mainly been described
in relation with a travel document, it can be applied
to any object supporting a passive resonant circuit
associated to at least one transponder such as for
example an electronic label, a chip card including a
module-antenna associated with a passive resonant
circuit the antenna of which has the dimensions of the
contactless chip ID1.
Such objects are preferably portable devices such
as a chip card or a cell phone.
The passive antenna can be included in the body
of the chip card, more particularly about the module
antenna inserted in a standard cavity of the chip card.

The passive antenna together with the resonant circuit
can also be integrated in the reader.

CLAIMS
1. A method for reading RF transponders disposed
in one and the same magnetic interrogation field, in
which a magnetic coupling of the transponders is
ensured with a passive resonant circuit (17) during
reading,
characterised in that the passive antenna (21) of
the resonant circuit is associated with at least one
transponder antenna (3, 13-16), and the passive
resonant circuit is tuned in such a way that the
resonance frequency resulting from the association M
corresponds to one of the frequencies of the emission
side bands of the transponder (3, 13-16) to be read.
2. A method according to the preceding claim,
wherein the association of the passive antenna (21) of
the passive resonant circuit with at least one
transponder antenna (3) is made negligible and the
passive resonant circuit (17) is tuned to a resonance
frequency corresponding to one of the frequencies of
the emission side bands of the transponder to be read.
3. A reading method according to the preceding
claim, characterised in that the method further
includes a step during which:
- the transponders (13-16) are so configured as
to be negligible in the association with the passive
resonant circuit (17), by each drawing less magnetic
field and/or by interfering less with the other
antennas of the transponder.
4. A reading method according to the preceding
claim,

- wherein at least one antenna format F and one
response from a transponder having a behavior
corresponding to such format are determined ,
- the passive resonant circuit is so configured
as to obtain a behavior corresponding to such a format
for each transponder.
5. A reading method according to claim 4,
characterised in that the passive antenna is defined
between two rectangles respectively 81mm x 49mm, and
64mm x 34mm.
6. A reading method according to one of claims 1
or 2, characterised in that the side bands are
respectively selected approximately at 13.56 MHz ±
847Khz or respectively 12.71 and 14.4 MHz, the
interrogation frequency being 13.56MHz rated at 847Khz.
7. A reading method according to claim 5,
characterised in that the antenna of the passive
resonant circuit (17) includes between 3 and 6 turns.
8. A reading method according to one of the
preceding claims, characterised in that the passive
resonant circuit (17) has a quality factor with a value
of less than 30.
9. A reading method according to one of the
preceding claims, characterised in that the transponder
has a reduced format and has an antenna, the surface
inside the outer turn of which is greater than a 15 x
15mm surface and smaller than a surface of
approximately 30 x 30mm.
11. A reading method according to the preceding
claim, characterised in that the transponder antenna
includes 13 to 18 turns.

12. A reading method according to the preceding
claim, characterised in that the tuning frequency is
between 15 and 18 MHz.
13. A reading method according to the preceding
claim, characterised in that the transponder has a
quality factor above 30.
14. A reading method according to the preceding
claim, characterised in that each transponder (13, 14)
is positioned in a support in a random position, with
the support allowing several positions of the
transponder which are shifted with respect to each
other.
15. A reading system (12) with at least one RF
transponder, with said system including
- one reader (18, 19, 28) able to emit an
interrogation field on at least one transponder (13,
14) and to collect a response from the transponder,
- a passive resonant circuit (17) to perform a
magnetic coupling with at least one transponder during
the reading,
characterised in that the passive resonant
circuit (17) is tuned in such a way that the resonant
frequency resulting from the association (M) of the
resonant circuit with at least one transponder (3, 13)
corresponds to one of the frequencies of the emission
side bands of the transponder to be read.
16. A supporting object containing at least one
main transponder, one secondary transponder and an
associated passive resonant circuit associated with at
least the main transponder,
characterised in that the passive resonant
circuit (17) is tuned in such a way that the resonant

frequency resulting from the association (M) of the
resonant circuit with at least the main transponder (3)
corresponds with one of the frequencies of the emission
side bands of the secondary transponder (13).
17. A supporting object containing at least one
transponder and one passive resonant circuit associated
with at least one transponder,
characterised in that the passive resonant
circuit (17) is tuned to a resonance frequency
corresponding to one of the frequencies of the emission
side bands of the transponder.
18. A transponder including a flat antenna on a
support defining an outer turn, characterised in that:
- the surface inside the outer turn is greater
than a 15 x 15mm surface and smaller than or equal to a
surface of approximately 30 x 30mm,
- the antenna includes about 13 to 18 turns,
- the tuning frequency is between 15 and 18 MHz,
- a quality factor is above 30.
19. A travel document (27) including several
pages between two covers and a plurality of
transponders (13-16) between the pages, each
transponder being contained in a plane support (33, 34)
separate from the pages or covers but having
substantially the format of a page, characterised in
that the transponders are configured as in the
preceding claim.
20. A travel document according to the preceding
claim, characterised in that the transponders are
positioned in the supports (33, 34) in various
positions.

21. An assembly of transponders according to
claim 18, with each transponder being positioned in a
sheet (33, 34) having a greater format than the latter,
characterised in that the transponders are positioned
in the supports (33, 34) in various positions from one
sheet to another.

Method and system for optimized reading of a radio frequency communication transponder with the aid of a passive
resonant circuit. The invention relates to a method of reading RF transponders disposed in one and the same magnetic interrogation
field, in which a magnetic coupling of the transponders is ensured with a passive resonant circuit (17) during reading. The method
is distinguished in that the passive antenna (21) of the resonant circuit is associated with at least one transponder antenna (3, 13-16),
and the passive resonant circuit is tuned in such a way that the resonant frequency resulting from the association M corresponds to
one of the frequencies of the emission side bands of the transponder (3, 13-16) to be read. The invention also relates to the system
corresponding to the method, a transponder structure and an object containing the transponder, in particular a travel document.

Documents:

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Patent Number

268740

Indian Patent Application Number

1034/KOLNP/2009

PG Journal Number

38/2015

Publication Date

18-Sep-2015

Grant Date

15-Sep-2015

Date of Filing

18-Mar-2009

Name of Patentee

GEMALTO S.A.

Applicant Address

6, RUE DE LA VERRERIE, 92190 MEUDON

Inventors:

#	Inventor's Name	Inventor's Address
1	CARUANA, JEAN-PAUL	LES JARDINS DE TOSCANE, BAT. E2, 89, CHEMIN JOSEPH AIGUIER, F-13009 MARSEILLE

PCT International Classification Number

G06K 19/077

PCT International Application Number

PCT/EP2006/066252

PCT International Filing date

2006-09-11

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA