WO2012009776A1 - Magnetic coupling antenna and system for exchanging data comprising the same - Google Patents

Magnetic coupling antenna and system for exchanging data comprising the same Download PDF

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Publication number
WO2012009776A1
WO2012009776A1 PCT/BR2011/000238 BR2011000238W WO2012009776A1 WO 2012009776 A1 WO2012009776 A1 WO 2012009776A1 BR 2011000238 W BR2011000238 W BR 2011000238W WO 2012009776 A1 WO2012009776 A1 WO 2012009776A1
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WIPO (PCT)
Prior art keywords
coil
antenna
coils
protective
coupling
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PCT/BR2011/000238
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French (fr)
Inventor
Jorge De Albuquerque Lambert
Original Assignee
Jorge De Albuquerque Lambert
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Priority to BRPI1002245-7A priority Critical patent/BRPI1002245A2/en
Priority to BRPI1002245-7 priority
Application filed by Jorge De Albuquerque Lambert filed Critical Jorge De Albuquerque Lambert
Publication of WO2012009776A1 publication Critical patent/WO2012009776A1/en

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00Details of, or arrangements associated with, antennas
    • H01Q1/12Supports; Mounting means
    • H01Q1/22Supports; Mounting means by structural association with other equipment or articles
    • H01Q1/2208Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
    • H01Q1/2225Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q7/00Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

The present invention refers to an antenna (7, 13, 14, 15, 16, 17, 18, 19), designed to be safe against unauthorized excitation and communication, with no mobile parts. Said antenna is suitable for application on radiofrequency identification (RFID) systems, including transponders and readers, wherein the problem to protect data and the integrity of the transponders at the air (RF) interface level is crucial. The antenna includes protective coils, especially suitable to proximity coupling smart-cards operating on the range of High Frequencies (HF) when is required to limit the reading range to about two centimeters. The antenna might be assembled in electronic documents, as identification cards, commercial cards and Mechanical Readable Travel Documents, providing protection at hardware level and also being compatibility with standard readers.

Description

Title: "MAGNETIC COUPLING ANTENNA AND SYSTEM FOR EXCHANGING DATA COMPRISING THE SAME".

The present invention refers to an antenna which is designed to be safe against unauthorized excitation and communication, without mobile parts, cost effective, for application on (but not limited to) radiofrequency identification (RFID) systems, including transponders and readers, where it is necessary to protect the information (e.g. privacy, integrity and/or authenticity) stored or exchanged and the transponders integrity.

The antenna is especially suitable to proximity coupling smart- cards operating on the range of High Frequencies (HF) when is required to reduce the reading range to about two centimeters, without the need of changing the reader circuitry and maintaining the compatibility between reader and standard transponders (loop antennas).

BACKGROUND OF THE INVENTION

The advantages of proximity coupling RFID systems (e.g.

ISO/IEC 14443) are described in different references (e.g. K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication; ISO/IEC 14443-1-09 - Identification cards, Contactless integrated circuit cards, Proximity cards - Part 1 : Physical characteristics; and ISO/IEC 14443- 2-02 - Identification Cards, Contactless Integrated Circuit(s) Cards, Proximity Cards - Part 2: Radio Frequency Power and Signal Interface).

The standard reading distances for these systems are up to 10 cm (as described by K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, chapter 9), and the theoretical limit is about 40 cm (as described by K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, section 8.1.2.3.1).

Regarding contact-based smart-cards systems, most of the advantages of RFID systems are related to time of operation and maintenance (as described by K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication). On the other hand, the main disadvantage of RFID systems is the vulnerability of said systems to attacks over the air (RF) interface (as described by K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, chapter 8). Said vulnerability occurs because the power supply to the data-carrying device and the data exchange between the transponder and the reader are achieved by magnetic and electromagnetic fields, with no galvanic contacts. If the exchanged data contain private and important information or if large scale financial frauds can be mounted by cloning or modifying data on transponders, the vulnerability problem becomes critical.

To solve this problem, cryptography is widely employed in order to achieve access control and data protection at the logical level, as can be found on several applications (e.g. MRTD - Mechanical Readable Travel Document - standardization by International Civil Aviation Organization) and other applications mentioned by K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, chapters 8, 9 and 13). However, some attacks are not related with cryptography.

Four classes of attacks will be defined based on the necessary conditions that should be satisfied to mount an attack. Therefore, to prevent attacks of each class, it is sufficient to guarantee that said necessary condition will not be satisfied.

Class I: the attacker needs to induce enough electrical voltage at the terminals of the RFID chip in the transponder without the authorization of the owner;

Class II: the attacker needs that the system uses an anti-collision function;

Class III: the attacker needs to intercept the communication between reader and transponder;

Class IV: the attacker needs to induce some electrical voltage at the terminals of the RFID reader antenna.

According to this classification, skimming, extended-range attacks and intentional damage of the transponder by overvoltage induction belong to class I; DNS attacks exploiting anti-collision procedures belong to class II; eavesdropping belongs to class III and jamming the reader belongs to class IV. Further information might be found in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, chapter 8, and the referenced articles.

Applications like identification and commercial systems are using proximity coupling standard systems (ISO 14443) with cryptographic security procedures.

In this regard, the documents BR05122872 A and US 2007/0069858 A1 , refer to the use of switched or detachable antennas to prevent class I attacks against proximity coupling smart-cards at the hardware level. The switching mechanism may be electro-mechanical or optoelectronic. The electro-mechanical switches has mobile parts which are undesirable in smart-cards for many reasons, including rapidly decaying reliability of the transponder due to mechanical deterioration and presence of dirty, which is a prohibitive disadvantage. The optoelectronic device has two inconvenient aspects: the switch demands an additional circuitry in the transponder to include a photo sensor and the housing of the transponder must provide a window allowing the light to reach the sensor (as described in BR0512287-2 A). These characteristics increase the costs of production of the transponder and the complexity of the circuitry, contributing to decrease the MTBF (Mean Time Between Failures) of the device.

Since the vulnerability to class I attacks at the RF level remains a problem without a commercially attractive solution for the transponder itself, the most popular manner to prevent these attacks is electromagnetic shielding. Electromagnetic shielding can be achieved by interposing an electrically conductive surface (Faraday cage), a resonant circuit or some RF absorbing material in the path of the magnetic flow lines, in order to "block" (strongly attenuate) the magnetic field across the antenna, compromising the power supply to the transponder (e.g. US 7,719,425 B2, US 6, 121 , 544 A, US 2006/0044206 A1 , BR0512287-2 and RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, chapter 8). Several products, mainly protective sleeves and wallets, are available on the market, as can be found at www.smartcardfocus.com, RFID blocking (accessed on February 14th, 201 1 ). However, this type of protection is not so efficient at lower frequencies and has limited efficiency if the attacker has means to properly increase the power of the reader. Moreover, the electromagnetic shielding is an external solution. In fact, shielding is an independent protective solution which can be used without considering the design of the antenna.

From the state of the art in RFID proximity coupling, the standard ISO/IEC 14443 antennas, operating at 13.56 MHz, are the main reference for the present invention. The inductive coupling of proximity cards, described in ISO/IEC 14443. Figures 1 and 2 show some aspects that are relevant for the complete understanding of the state-of-the art.

Inductive proximity coupling RFID cards as described in ISO/IEC 14443 standard are composed basically by a loop antenna connected to the RFID CHIP, both housed in a non-magnetic insulated body, typically a plastic card.

To increase the range of the smart-card up to 10 cm, the antenna is designed as large as possible. In practice, ISO 14443 cards are similar to the one shown in figure 1 , which illustrates a three-six turns loop antenna (magnetic coupler) 1 connected to the RFID CHIP 2, both embedded in a plastic body 3 (housing). The ID-1 format (85.72 x 54.03 x 0.76 mm ± tolerances) is adopted for the card and it is familiar from credit cards and telephone cards (as described by K. Finkenzeller in RFID Handbook: Fundamentals and Applications in Contactless Smart Cards, Radio Frequency Identification and Near-Field Communication, chapter 2; and ISO/IEC 7810). According to ISO/IEC 14443-1 , the PICC may have the shape of a card compliant with ISO/IEC 7810 or ISO/IEC 15457-1 , or an object of any other dimension. The standard defines a Class 1 PICC, for which the coupling antenna (1 ) should have the shape and location as shown in figure 1 , provided that the inner rectangle dimensions are at least 64 mm x 34 mm. If the PICC dimensions are not compliant with ISO/IEC 7810 or ISO/IEC 15457-1 , the dimensions of the PICC antenna shall not exceed 86 mm x 54 mm x 3 mm.

The frequency of the operating field is 13.56 MHz (± 7 kHz) and the reader's RF interface must supply power to the transponder and exchange data.

Inside the reading zone (5) defined by the manufacturer of the

PCD, the magnitude of the unmodulated operating field H shall be between 1.5 A/m (rms) and 7.5 A/m (rms). Also, the PICC operating in a normal manner should function normally when exposed to H = 12 A/m (rms). Therefore, a standard PICC operates in a normal manner when the magnetic field H across the loop is greater than 1.5 A/m and lower than 12 A/m (rms).

A typical reading zone (5) of an ISO 14443 PCD, considering a standard transponder coupler (1 ) parallel to PCD's coupler (4), is shown in figure 2 (superior and frontal views). The ISO/IEC 14443 practical limit of the reading distance (r) is about 6 to 10 cm. By reciprocity, a standard stand- alone (portable) reader could activate the transponder from any point of the reading zone(5). This reading distance (r) is enough to execute any class I attack against proximity cards in the pocket or in the wallet of the victim, especially in a crowded place and if the attacker properly increases the magnitude of the reader current /' (and H).

To physically (at the RF layer) prevent class I attacks against a transponder, it is necessary to reduce the "reading zone" of the transponder, making the limit of the reading range regarding that transponder very short (about 2 cm), independently of the power and sensibility of the reader.

OBJECTIVES OF THE INVENTION

One objective of the present invention is to provide an antenna comprising a conductive path forming the coils of the antenna, at least one first coupling coil encircling an area of the antenna, at least one first protective coil having an opposed winding direction relative to the coupling coil, wherein said at least one first protective coil encircles another area of the antenna, and wherein the sum of the products of the number of turns of each protective coil and its corresponding encircled area is equal to the sum of the products of the number of turns of each coupling coil and its corresponding encircled area.

It is also an object of the present invention to provide a system for exchanging data in a radiofrequency identification system comprising said magnetic inductive coupling planar antenna, a RFID integrated circuit connected to said antenna, a RFID reader with a magnetic coupler, unlocking means having at least one magnetic shield blocking the magnetic fields of the protective coils of said antenna which are detected by the RFID reader.

BRIEF DESCRIPTION OF THE INVENTION

The objectives of the invention are achieved by means of an antenna which comprises a conductive path forming the coils of the antenna, at least one first coupling coil encircling an area of the antenna, at least one first protective coil having an opposed winding direction relative to the coupling coil, wherein said at least one first protective coil encircles another area of the antenna, and wherein the sum of the products of the number of turns of each protective coil and its corresponding encircled area is equal to the sum of the products of the number of turns of each coupling coil and its corresponding encircled area.

In a first embodiment of the invention, the antenna comprises a second protective coil, wherein: the protective coils have the same winding direction; the three coils are disposed in line such that the coupling coil is disposed in the center.

In another embodiment, the antenna comprises a second coupling coil and a second protective coil wherein: the protective coils have the same winding direction; the coupling coils have the same winding direction; the four coils are disposed in line such that the coupling coils are disposed in the center and are separated by a gap; and the first coupling coil is adjacent to the first protective coil and the second coupling coil is adjacent to the second protective coil.

The antenna might alternatively comprises a second coupling coil and a second protective coil, wherein the protective coils have the same winding direction; the coupling coils have the same winding direction; and the four coils are adjacent and disposed in line.

In a different embodiment, the antenna might comprises a second coupling coil and a second protective coil, wherein the protective coils have the same winding direction, the coupling coils have the same winding direction, the first protective coil and the first coupling coil are disposed in line; the second coupling coil and the second protective coil are disposed in line; the first coupling coil and the second coupling coil are disposed parallel to the first coupling coil and the second protective coil.

In an alternative embodiment, the antenna comprises a second coupling coil, a third coupling coil, a second protective coil and a third protective coil, wherein the protective coils have the same winding direction and the coupling coils have the same winding direction, wherein the six coils are disposed adjacently and in line.

Otherwise, the antenna might comprise a second coupling coil, a third coupling coil, a second protective coil and a third protective coil, wherein the protective coils have the same winding direction and the coupling coils have same winding direction, wherein the first protective coil, the first coupling coil and the second protective coil are disposed in line; the second coupling coil, the third protective coil and the third coupling coil are disposed in line; and the first protective coil, the first coupling coils and the second protective coil are disposed parallel to the second coupling coil, the third protective coil and the third coupling coil.

The objectives of the invention are also achieved by means of a system for exchanging data in a radiofrequency identification system which comprises a magnetic inductive coupling planar antenna, a RFID integrated circuit connected to said antenna; a RFID reader with a magnetic coupler; unlocking means having at least one magnetic shield in order to block the magnetic fields across the protective coils of said antenna which are detected by the RFID reader.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail based on examples of embodiments depicted in the drawings. The figures show:

Figure 1 shows a typical ID-1 format ISO/IEC 14443 standard proximity card;

Figure 2 shows the superior and frontal views of magnetic flow lines and typical reading zone for ISO 14443 standard couplers, considering standardized PICC and PCD couplers parallel to each other;

Figure 3 shows an antenna comprising three coils (GS3) and the outline of the ID-1 plastic body;

Figure 4 shows a protected smart-card (GSAFECARD3 - GSC3); Figure 5 shows the magnetic flow lines at the GS3 antenna;

Figure 6 defines the outline sides and the adjacent sides of the coils of an antenna;

Figure 7 shows an alternative embodiment of a three-coil antenna (GS3-T);

Figure 8 shows a two-coil antenna (GS2);

Figure 9 shows a four-coil antenna (GS4);

Figure 10 shows a four-coil antenna (GS4-A) with the coils in line;

Figure 11 shows a four-coil antenna (GS4-B) with the coils disposed in two rows and two columns;

Figure 12 shows a six-coil antenna (GS6-A) with the coils in line; Figure 13 shows a six-coil antenna (GS6-B) with the coils disposed in two rows and three columns;

Figure 14 shows the superior and frontal views of magnetic flow lines from the standard coupler of Figure 2 coupling a GS3 antenna and the reduced reading range;

Figure 15 shows the superior view of the magnetic flow lines across the three-coil transponder with three different types of PCD couplers;

Figure 16 is the superior view of the magnetic flow lines across the three-coil antenna GS3, employing two shields (not shown) to block the protective coils;

Figure 17 shows the superior and frontal views of a larger reader coupler and the three-coil transponder coupler positioned to operate in the coupling method 2 (with magnetic shields);

Figure 18 shows the superior view of the transponder coupler GS3 and reader coupler properly positioned to operate in coupling method 3 (CM3 - with one magnetic shield);

Figure 19 is the superior view of an adhesive tag with two shields fixed on the reader (not shown) and positioned on the path of the magnetic flow lines induced by the reader across the GS3 protective coils;

Figure 20 is the superior view of an adhesive tag with one magnetic shield fixed on the reader (not shown) on the right relative position to allow CM3 with a GS3 coupler;

Figure 21 is analogous to Figure 19, considering a transponder assembled with a GS4-A antenna;

Figure 22 is analogous to Figure 20, considering a transponder assembled with a GS4-A antenna;

Figure 23 is analogous to Figures 19 and 21 , considering a transponder assembled with a GS4-B antenna;

Figure 24 is analogous to Figures 20 and 22, considering a transponder assembled with a GS4-B antenna;

Figure 25 shows the regions of weaker magnetic flow due to the rectangular form of a PCD coupler (corner effect);

Figure 26 shows a magnetic coupling condition using the coupler shown in Figure 25 and a six-coil GS6-B coupler in CM1 ;

Figure 27 shows a magnetic coupling condition using the coupler shown in Figure 25 and a three-coil GS3-T coupler in CM1 ;

Figure 28 shows a magnetic coupling condition using the coupler shown in Figures 18-24 and a three-coil GS3-T coupler in CM1 ; Figure 29 shows the superior view of an indicative tag or label to be fixed together with two magnetic shields on the reader's surface;

Figure 30 shows the assembling of the indicative tag and the magnetic shields to the reader's surface in perspective;

Figure 31 shows the superior and the frontal views of the key- card (unlocking card) to be used together with a GSAFECARD3 (GSC3);

Figure 32 shows the assembling of the key-card (unlocking card);

Figure 33 shows an alternative embodiment of the four-coil antenna (GS4-R);

Figure 34 shows an alternative embodiment of the four-coil antenna (GS4-C) with chamfered external corners;

Figure 35 shows the first layer of a two-layer GS2 antenna;

Figure 36 shows the second layer of GS2 antenna depicted in

Figure 35;

Figure 37 shows the first layer of a two-layer GS3-T antenna;

Figure 38 shows the second layer first layer of the two-layer GS3-T antenna depicted in Figure 37;

Figure 39 shows the first layer of a two-layer GS4-B antenna;

Figure 40 shows the second layer first layer of the two-layer GS4-B antenna depicted in Figure 39;

Figure 41 shows the first layer of a two-layer GS6-B antenna; and

Figure 42 shows the second layer of the two-layer GS6-B antenna depicted in Figure 41.

DETAILED DESCRIPTION OF THE INVENTION

The present invention refers to an antenna comprising one conductive path forming the coils of the antenna, said conductive path defining a set of C coupling coils (C being a positive number) having the same winding direction and dimensioned to perform magnetic coupling in non-magnetic medium. Said antenna further comprises a set of P protective coils (P be being a positive number) having the winding direction opposed to the winding direction of the coupling coils. Each protective coil is disposed adjacently to at least one coupling coil and is dimensioned to cancel the voltage induced on the respective coupling coil when the antenna is placed in a homogeneous time- variant magnetic field.

The coupling coils and the protective coils will be identified by even and odd indexes, respectively.

The antenna is designed such that the overall sum of the products of the number of turns (N1, N2, N3,... ) of each coil by the respective vector area (S1, S2, S3, ... ) is nearly zero, i.e., less than a neglectible value Z. Considering only the coupling coils, said sum (Sj x Nj) is greater than a working value W. The area vectors Sj (j = 1 , 2, 3, ... ) are oriented according to the winding direction such that opposed winding directions implies in opposed signals (+ or -). Sj denotes the magnitude of vector Sj. Note that the references N1, N2, N3, ... refer to the number of turns of the respective coils C1 . C2. C3, ...

The values of Z and W depend on the system considered. More particularly, if the system is compliant with ISO/IEC 14443, the values adopted for Z and Ware 350 mm2 and 650 mm2, respectively.

It should be considered that , is the normal component of the magnetic flux across the area Sj, Bj is the density of ,, H, is the respective time-variant magnetic field strength and μ0 is the magnetic permeability of the non-magnetic medium (= air = vacuum). So, the voltage magnitude Vj induced on each coil is given by the expression

Vj = Nj dOydt = Nj d[f(8 dS/)]/dt = μ0Λ//'■ d[f(Hy dS/)]/dt. Equation (1 )

Since the coils are connected in series, the overall voltage V on terminals T1 and T2 is given by the equation

V =∑/=i ,2,3...(c+p) (Vj). Equation (2)

In order to activate the IC (e.g., an ISO 14443 standard CHIP) connected to the terminals T1 and T2, the overall voltage V must be greater than the operation voltage.

The equivalent area SE encircled by the antenna is defined by the general equation 3: SE = {N2 x S2) + (N4 x S4) + (N6 x S6) +.. + (N2xC x S2xc) +

+ (N1 x Si) + (N3 x S3) + (N5 x S5) +... + (N2xp-i x S2xP-i) * 0. Equation (3)

The equation 3 implies that the magnitude of the electrical voltage V at the terminals T1 and T2 of the multi-coil antenna (and CHIP) is strongly dependent on the magnitudes of s across the sections S and also on the geometry of the magnetic flow lines. If B is roughly uniform along the antenna, as observed when the source is a relatively large loop antenna or the regions are not close enough to the source, equation 3 ensures that the voltage V will be lower than the non-activation voltage. To this end, considering, for example, the magnitudes involved in ISO/IEC 14443 standard systems, the antenna should be designed such that SE < 350 mm2.

Assuming that it is not possible to change the design of the PCD coupler, the antenna should be designed according to equation 3 and should supply the operating power to the ISO 14443 IC in at least one of the three following coupling methods, depending on the dimensions of the reader antenna.

Coupling method 1 (CM1 ): at least one of the dimensions of the PCD coupler is short enough to meet the size restrictions imposed to the transponder housing (e.g. , ID-1 card format). This method uses this geometric convenience and no shield is needed.

Coupling method 2 (CM2): the PCD coupler dimensions are too large to meet the size restrictions imposed to the transponder housing or the model of the antenna is such that it is not possible to design a transponder for operation on CM1 . This method uses magnetic shielding (blocking) at all the protective coils.

Coupling method 3 (CM3): This method is a combination of CM1 and CM2. In this method, some protective coils are blocked by magnetic shielding and at least one protective coil uses geometric convenience to enforce the magnetic coupling achieved by the coupling coils.

A first embodiment of the antenna 7 is shown in figure 3. In this embodiment, the antenna 7 comprises three coils and is named GS3. Said antenna comprises one central coupling coil C2 and two lateral protective coils C1 , C3 (i.e., C = 1 and P = 2).

Figure 3 depicts the three-coil antenna 7 (GS3). The arrows indicate the directions of winding. In figure 4, the antenna 7 is connected to an RFID CHIP 8, both embedded in a plastic housing 9 (e.g., ID-1 format card).

Figure 5 depict how the magnetic flow lines should satisfy the condition to achieve the CM1 with the three-coil GS3 antenna 7 and a standard PCD.

As shown in figure 6, the outline sides 10 of the coils C1 , C2 and C3 refer to the segments of the perimeter of each coil that also represent the external outline of the antenna and cannot be adjacent to other coil. The sides 1 1 , 12 are the adjacent sides. To make the protection of the protective coils C1 , C3 more effective, the protective coils are designed and disposed to maximize the portion of its perimeter which is adjacent to coupling coil(s). To this end, if the sides of a protective coil are not equally sized, the size adjacent 12 of the protected coupling coil will be at least the larger size of the protective coil.

It should be noticed that figure 7 illustrates an alternative embodiment of the three-coil antenna named GS3-T 13 wherein the coils are triangular and the larger side of each protective coil is adjacent to the coupling coil. This embodiment is convenient for the coupling method CM1 when the radius of the PCD coupler is short enough to create the corner effect, independently from the size of the PCD, as shown in figures 27 and 28.

Figure 8 depicts the second embodiment of this invention wherein the antenna 14 is a two-coil (C = P = 1 ) antenna, which is called GS2. In the GS2 antenna 14, one of the coils is the coupler coil C2 and the other one is the protective coil C1 , with opposed winding directions from each other. Figure 8 also depicts the winding direction indicated by the arrows.

As shown in figure 8, the parameter a1 stands for the average length of coil C1 (considering the outer and the inner turns) and the parameter b1 is the average height of coil C1 (considering the outer and the inner turns), such that the product a1 x b1 is the average area S1 encircled by the N1 turns of C1. The same explanation holds for the coil C2. The RFID CHIP 8 might be an ISO 14443 IC.

Figure 9 depicts a third embodiment of this invention wherein the antenna 16 is a four-coil (C = P = 2) antenna and the four coils C1 , C2, C4, C3 are disposed in the same one row such that C1 is adjacent to C2 and C4 is adjacent to C3. The antenna further comprises a gap between the pair C1 C2 and the pair C4C3. In this embodiment, the antenna works as a GS3, where the coupling coil was broken in two parts C2 and C4.

Figure 9 also presents the direction of winding (indicated by arrows and current /) and the direction of the associated magnetic field B across the coils. Analogously to the GS3 antenna 4, the central coils of the GS4 antenna 15 are the coupling coils (C2, C4) and the side coils are the protective coils (C1 , C3). As shown in figure 9, the distance D should match one of the dimensions of the reader antenna in order to achieve the coupling method CM1 , analogously to the illustration in figures 14 and 15 (replacing the antenna 7 GS3 by the antenna 15 GS4).

Figure 10 depicts a fourth embodiment of this invention wherein the antenna 16 (GS4-A) is a four-coil (C = P = 2) antenna and the four coils C1 , C2, C3, C4 are disposed in line. Figure 10 shows the winding direction indicated by the arrows and the number of turns of each coil indicated by N1 , N2, N3, and N4.

It should be noticed that the parameter a1 stand for the average length of coil C1 (considering the outer and the inner turns) and the parameter b1 is the stands for the average height of coil C1 (considering the outer and the inner turns), such that the product a1 x b1 is the average area encircled by the N1 turns of C1. The same explanation holds for the four coils and for the embodiments shown in figures 1 1 , 12 and 13.

Figure 1 1 depict the fifth embodiment of this invention wherein the antenna (GS4-B) 17 is a four-coil (C = P = 2) coupler and the coils are disposed in two rows and two columns.

Figure 12 depicts the sixth embodiment of this invention wherein the antenna (GS6-A) 18 is a six-coil (C = P = 3) coupler and the coils are adjacent and disposed in one row.

Figure 13 depicts the seventh embodiment of this invention wherein the antenna (GS6-B) 19 is a six-coil (C = P = 3) coupler and the coils are adjacent and disposed in two rows and three columns. This embodiment may be convenient for the coupling method CM1 , as shown in figure 26.

Figure 14 and figure 15 depict how the magnetic flow lines should satisfy the condition to achieve the coupling method CM1 with the three-coil GS3 antenna 7 and a standard PCD. It should be noticed that the length of the rectangle defined by the coupling coil C2 must be specified to precisely fit one of the dimensions of the reader coupler, as shown in figure 14, or with some tolerance, as shown in figure 15. In figure 14, the reading zone 21 is reduced such that the reading range is represented by r2. The reading zone 21 is defined considering the position of the central axe 20 of the antenna 7 and the couplers 4 and 7 in parallel planes.

The magnetic flow lines through the coupling coil C2 have opposed direction relative to the flow lines across the protective coils C1 , C3 as well as the coupling coil C2 winding direction is opposed to the protective coils C1 , C3 winding directions. So, if the coupling method CM1 is chosen, the voltage induced in protective coils C1 , C3 will also contribute to increase the overall voltage V at the terminals T1 , T2 of the antenna. Therefore, in this particular situation, the protective coils C1 , C3 also work as coupling coils.

Figure 15 presents the three-coil GS3 antenna 7 in three different situations (A, B, and C). In cases A and B, the reader couplers 22 and 23 are larger than the coupler 4. In A and B, the contribution from the outer coils C1 , C3 is expected to be weaker than in the situation of figure 14. In fact, in the situations A, B, and C shown in figure 15, with the increasing size of the reader coupler 22, 23, 24 the positive contribution from the outer coils C1 , C3 is expected to be increasingly weaker. Case C illustrates the expected tolerance regarding the size relationship between the GS3 antenna 7 and PCD reader 24 in order to achieve the coupling method CM1 (coupling without shielding). In case C, each protective coil will be divided in two magnetically opposed halves, and the induced voltage on each protective coil will be zero. No contribution from the outer protective coils C1 , C3 will come for the coupling. Beyond this limit, the protective coils will contribute negatively to the energy on the GS3 antenna 7.

Independently from the coupling method adopted, in order to show where to properly place the transponder for reading, some instruction must be provided (or adapted) on the PCD's housing surface.

For the coupling method CM1 , the PCD is not electromagnetically affected (e.g., compatibility with ISO/IEC 14443 transponders).

For the coupling method CM2, it is assumed that the dimensions of the considered PCD coupler 26 is larger than the transponder coupler 7 and it may be necessary to "block" the magnetic field lines across the protective coils to achieve the condition shown in figures 16 and 17. Said condition can be achieved interposing an electrically conductive surface or mesh 25, 29 in the path of the magnetic flow lines, providing an electromagnetic shield for that area (Faraday's cage).

In Figure 7, the reader coupler 26 and the multi-coil transponder coupler 7 are positioned to operate in the coupling method CM2. The magnetic flow lines at the protective coils regions are properly blocked by two shields 25. For several reasons (e.g., if the reader coupler is not too large), it might be convenient to use the coupling method CM3. Figure 18 presents the coupling method CM3 in a situation analogous to that shown in figure 17 employing one shield 25 and a convenient position of the transponder coupler 7 relative to the reader coupler 26 to achieve the coupling method CM3.

As can be seen in figure 18, the PCD integrated circuit 30 is connected to the terminals of each coupler. If a protective antenna 7 is to be used instead of standard couplers, the connection to the antenna may include a resonant capacitor connected in series between one of the terminals of the antenna and one of the terminals of the RFID IC.

An electromagnetic absorbing material or a closed circuit resonant to the operating frequency also can be used to achieve magnetic shielding.

The shield(s) 25, 18 shall be properly disposed on the PCD housing with some instruction in order to show the user where to properly place the transponder for reading.

Figures 19 to 24 present the superior views of the relative position of the instruction tag 28 considering the reader coupler 26 on the PCD 40.

In figures 19, 21 and 23, the tag 28 and the two magnetic shields 25, 29 must be dimensioned to match size and position of the protective coils of the corresponding embodiment of the protective antenna in order to operate in the coupling method CM2.

With reference to figures 18, 20, 22, and 24, it is depicted the coupling method CM3, an alternative way of achieving coupling which employs only one shield 25, 29 and comprises a smaller area of the reading surface of the PCD. In this coupling method CM3, one of the protective coils is shielded and the other contributes to the overall voltage V induced on the antenna 4, similar to the coupling method CM1. If the antenna has more than three coils, more than one protective coil may be blocked and one or more may be used to enforce the magnetic coupling taking advantage of some specifically convenient geometry.

Figures 19 and 20 consider that the antenna is the GS3 antenna.

Figures 21 and 22 consider that the antenna is the GS4-A antenna.

Figures 23 and 24 consider that the antenna is the GS4-B antenna.

The magnetic shields 25, 29 should be in or under the tag 13 or even under the surface of the reader, providing that the transponder can be placed close enough to the reader coupler 26, both properly positioned to meet the coupling methods CM2 or CM3 conditions.

Notice that figures 19 and 20 illustrate labeling and magnetic shielding for a GS3 coupler 4. Figures 21 and 22, analogously, refer to the use of a GS4-A coupler; and figures 23 and 24 refer to the use of a GS4-B coupler.

Figure 29 shows a superior view of the tag or label to be fixed on the surface of the reader 40 (which has the coupler 26 inside) in order to fix the shields 25 and indicate to the user where to place the card for reading.

Figure 30 shows a perspective view of the assembling of the tag 28 and the magnetic shields 25 on the reader surface on PCD housing 40. For most of the current PCD available on the market and assembled with large antennas, it is not expected that placing the small shields 25 or 29 on the PCD housing surface will affect the operation with of the PCD with standard transponders (e.g. ISO/IEC 14443).

If the owner of the RFID system wants to supply protected transponders only for some applications, some services or some clients, keeping the readers untouched, an unlocking-card 31 , as shown in figures 31 and 32, may be manufactured and supplied together with the safe transponder, in the same housing format (e.g., ID-1), said unlocking-card 32 having the proper shields inside.

Figure 32 shows the assembling of the unlocking card 31 , showing its component parts, i.e., two external plastic plates 31A dimensioned according to the size of the safe-card, two magnetic shields 25 and one central layer 30B (which is also a plastic plate), having two recesses to place the shields 25.

The safe transponder will operate as a standard transponder only when positioned for reading together with the unlocking-card 31. The unlocking card can also be used for achieve the coupling method CM3, but in this case the transponder should be placed on the right position indicated on the standard reader, as in figures 20, 22, 24, without shields on the reader. It should be noticed that, in order to prevent skimming, the unlocking-card 31 shall not be disposed in the same location of the protected transponder.

Figures 25 and 26 show the corner effect if the radius of the corner of a reader coupler 4 is short enough, the magnetic-flow across the regions 41 diagonally located outside the coupler are relatively weak. Consider figure 24. Due to the corner effect, the magnetic-flow across the region which is blocked by the shield 29 is naturally weaker than the magnetic-flow across the other three quadrants of the tag, especially when compared to the quadrant of the tag which is "inside" the reader antenna 26. As a consequence, for a transponder employing a GS4-B antenna or the antennas GS4-R 32, GS4-C, and GS4-E 36, it is expected that said shield 29 is not really necessary and said transponder may be readable at that location (or at other corners) without any shielding (performing the coupling method CM1 ).

The corner effect is also exploited in the situation of the coupling method CM1 illustrated in figure 26. Figure 26 shows the coupling method CM1 employing a standard coupler and a GS6-B antenna.

Figures 27 and 28 show the coupling method CM1 employing a standard coupler and a transponder employing a GS3-T 13 antenna. In both cases, due to the corner effect, the fields on the diagonal region outside the corners were assumed to be neglectible. The design of the coupler 13 takes into consideration the corner effect and does not have a fourth coil to encircle the region of weaker fields when the magnetic coupling occurs on the corner of the reader coupler by the coupling method CM1. Notice that the transponder employing 13 may also be used in the coupling method CM2, as well.

The chosen coupling method may strongly affect the antenna's inductance, resonant frequency and performance at the reading position and shall be taken into account to properly specify the parameters of the coupler.

One of the main advantages of the proposed antenna is the possibility of using a transponder as an ID-1 (or smaller) format card and operate with an ISO 14443 standard compatible PCD.

The remarkable difference from conventional loop couplers is that, because the magnetic flow lines spread rapidly with the distance from its source (reader), if the transponder is not close enough to the reader, the component of the magnetic flow lines across adjacent coils will have roughly the same direction and will cancel each other. The form and the adjacency of coupling coils and protective coils are designed to minimize the distances between opposed oriented area elements, increasing the coupling coefficient and the magnitude of its related mutual inductance. If the power of the reader is increased in order to skim said transponder, the magnetic flux density increases accordingly, but the flow lines geometry, which is a function of the antenna's geometry (including size), remains roughly the same. Hence, if the couplers are not close enough to each other, increasing the power of the reader will make the positive and negative voltages induced on adjacent coils of the transponder grow together, cancelling each other.

A resource used by attackers to increase the reading distance to a RFID transponder (proximity card) is to use a reader with a larger loop antenna. However, this strategy is useless with multi-coil antennas since larger loop antennas tend to spread even more the magnetic flow-lines (producing a more uniform magnetic flow).

It should be noticed that the reading range for the coupling methods CM1 , CM2 or CM3 is strongly dependant on the size and relative position of the coils. If the protective antenna is dimensioned to fit in an ID-1 format card, it is not expected that an operation occurs when the couplers are more than two centimeters far from each other.

By the exposed reasons, an effective class I attack against a transponder having a multi-coil antenna is much more difficult to achieve than it would be on a standard ISO 14443 PICC.

Moreover, the reduced reading region ensures that only one transponder may be positioned for reading at a given time. As a consequence, anti-collision procedures may be disabled, making class II attacks also impossible to achieve.

The presented antennas have another interesting property. Since the sum∑_/=i ,2,3 [Nj x Sj] is equal to zero, even without using any ferrite core, when the multi-coil antenna is assembled in the source of the magnetic flow (reader), the major portion of magnetic flow lines will be confined into the limits of the coils, and the magnetic flow density outside these limits tends to decay much more radically with the distance than it would decay if a standard loop antenna were used. Analogous confining effect is expected when such a transponder answers to the reader. Therefore, a RFID system with the described antenna is much less vulnerable to class III attacks and, by reciprocity, class IV attacks. Furthermore, these RFID devices are more suitable to use in environments where EMC (Electromagnetic Compatibility) is required.

If the reader and transponder are assembled with properly matched multi-coil antennas, a more efficient inductive coupling is possible, considering that many flow lines are encircled by two coils on each coupler, increasing the mutual inductance between the couplers.

More particularly, figure 4 shows a protected smart-card, named GSAFECARD3 (GSC3), assembled with an antenna 4, an ISO/IEC 14443 standard RFID CHIP 8, both embedded in a plastic housing 7 (e.g., ID-1 format).

Figures 3, 8, 9, 10, 1 1 , and 12 show the parameters of different embodiments of the antenna. The parameter Nj is the number of turns of the j-th coil Cj. For roughly rectangular coils, the dimensions aj and bj (j = 1 , 2, 3,... P+C) are the average lengths and heights of the rectangles defined by the respective coils, such that for the -th coil the absolute value of the internal area can be approximated by the product Sj = aj x bj, each turn. If the coils are not rectangular, as in the antennas 13, 32 and 33 (see figures 7, 33 and 34), the areas Sj should be calculated properly. The parameter e is the distance between the axis of two adjacent conductors, R is the radius of the corners, X and Yare the coordinates of the IC position referred to the low-left corner of the antenna and may assume negative values, if the IC is required outside the coils. The distance between terminals and depends on the CHIP layout.

Table 1 presents a summary of the specifications for eight different practical configurations of the antenna. Notice that said parameters are not restrictive or exhaustive. They should be applied to transponders employing the ISO/IEC 14443 standard IC's (e-g- MIFARE® family) and operating at HF 13.56 MHz in the coupling methods CM1 , CM2 and CM3.

The conductive paths are dimensioned to be manufactured by a wire embedding machine, with enameled copper wire AWG 36-AWG 40 and the separation e between the axis of two adjacent wires should be from 0.25 mm to 1 mm.

Table 1 - Design Parameters of the Antennas (wired constructions)

GS2 GS3 GS3T GS4 GS4A GS4B GS6A GS6B

(Fig.8) (Fig.3) (Fig.7) (Fig.9) (Fig.10) (Fig.11) (Fig.12) (Fig.13)

N1 3-11 3-11 3-9 3-10 3-10 3-10 3-10 3-10

N2 3-11 3-10 3-9 3 - 10 3-10 3-10 3-10 3-10

N3 0 3-11 3-9 3-10 3-10 3-10 3-10 3-10

N4 0 0 0 3-10 3-10 3-10 3-10 3-10

N5 0 0 0 0 0 0 3-10 3-10

N6 0 0 0 0 0 0 3-10 3-10 a1 8-35 8-25 0 8-15 6-15 8-35 10-20 10-25 a2 8-35 8-55 0 8-15 6-15 8-35 10-20 10-55 a3 0 8-25 0 8-15 6-15 8-35 10-20 10-25 a4 0 0 0 8-15 6-15 8-35 10-20 a1 a5 0 0 0 0 0 0 10-20 a2 a6 0 0 0 0 0 0 10-20 a3

0 10- b1 10 10-75 10-75 8-24 22-47 8-24

47

b2 75 10-75 0 9-45 10-75 8-24 22-47 8-24

0 10- b3 0 10-75 10-75 8-24 22-47 8-24

47

b4 0 0 0 9-45 10-75 8-24 22-47 8-24 b5 0 0 0 0 0 0 22-47 8-24 b6 0 0 0 0 0 0 22-47 8-24

0 30-

D 0 0 0 0 0 0

60

L1 0 0 15-45 0 0 0 0 0 L2 0 0 15-45 0 0 0 0 0 L3 0 0 25-45 0 0 0 0 0 a 0 0 30°-50° 0 0 0 0 0 β 0 0 80°- 120° 0 0 0 0 0 r 0 0 90°-130° 0 0 0 0 0 On table 1 , parameters N1 to N6 are numbers of turns for respective coils (C1 to C6), and may not be an integer. A non-integer turn may be achieved by reducing the size of the inner turn of a given coil.

The dimensions, in millimeters, have ± 0.2 mm of tolerance for all dimensions greater than 1 mm and ± 0.05 mm for dimensions less than 1 mm.

It should be considered that the protective coils are odd numbered and the coupling coils are even. Thus, the parameters on table 1 might be defined as

SE = (N2 x S2) + (N4 x S4) + (N6 x S6) +... + (N2C x S2C) +

+ (N1 x Si) + (N3 x S3) + (N5 x S5) +... + (Λ/2ρ-ί x S2p-i) < 350 mm2

Equation (4) and, if the coupling method CM1 is intended,

(N2 x S2) + (N4 x S4) + (N6 x Se) +... + {N2C x S2C) > 1000 mm2 Equation (5)

The housing material might be an ABS in ISO/IEC 7810 ID-1 standard format. If a short card is required, shorter construction are allowed, provided that a 3 mm margin around the antenna-chip set be left for mechanical assembling.

In general, the radii of the corners should be from 0.5 mm to 3 mm. However, for outer corners, may be convenient to chamfer or define greater radii, which are limited only by the size of the given coil. If this is adopted, the average section Sj of the respective coil may not be well approximated by aj x bj and should be calculated accordingly.

Figures 33 and 34 present two antennas 32 (GS4-R) and 33 (GS4-C), respectively, similar to the one shown in figure 1 1 . In these alternative embodiments, the external corners of the antenna 33, 34 are circular and chamfered, respectively.

In a particular embodiment, the GS4-R antenna comprises the following parameters: the lengths and heights defined for the coils (C1 , C2, C3, C4) are a = 23.6 mm and b = 23.6 mm, respectively. The distance between the terminals (T1 , T2) is dT = 6.5 mm and the separation between the axis of two adjacent wires is e = 0. 5 mm. Also, in a particular embodiment of the GS4-C antenna 33 shown in figure 34, the lengths and heights defined for the coils (C1 , C2, C3, C4) are a = 28.6 mm and b = 23.6 mm, respectively. The auxiliary distances are da = 13.84 mm and db = 10.55 mm. The distance between the terminals (T1 , T2) is dT = 6.5 mm and the separation between the axis of two adjacent wires is e = 0. 5 mm.

Figures 35 to 42 present designs of conductive paths in two layers to manufacture the antennas GS2, GS3-T, GS4-B and GS6-B by screening, etching, or by any method of metallic deposition. The points 38 are reference points for the relative position of the two layers A (layer 1) and B (layers 2), which might be superimposed separated by an insulating nonmagnetic material. For the galvanic continuity of the antennas, the point 39 in layer A must be connected (welded) to the correspondent point 39 in layer B. The RFID IC will be connected to the open terminals, analogously to the wired embodiments GS2 14, GS3-T 13, GS4-B 17, GS6-B 19, respectively (as shown in figures 8, 7, 1 , 13).

If the design of the antenna is intended to an etching, printing or metallic deposition multi-layer manufacturing process, as shown in figures 35 to 42, the cross-section of the conductive track should have, for example, 0.035 mm to 0.2 mm (height) x 0.3 mm to 1.2 mm (length) and the separation between tracks should be 0.5 mm to 1.5 mm. For each required design, the specifications might be defined in such a way that the electrical characteristics are enough compatible to the wired embodiments GS2 14, GS3-T 13, GS4-B 17, GS6-B 19 (as shown in figures 8, 7, 11 , 13). The dimensions of the coils might follow the same values specified for the wired constructions (table 1) and the number of turns of each coil is from 3 to 6.

Therefore, it should be understood that the objectives of the present invention are part of some of the preferred embodiments and examples of situations that could occur, the real scope of the object of the invention being defined in the claims.

Claims

1. A magnetic inductive coupling planar antenna (7, 13, 14, 15, 16, 17, 18, 19) comprising:
a conductive path forming the coils of the antenna; and at least one first coupling coil (C2) encircling an area (S2) of the antenna;
characterized by further comprising:
at least one first protective coil (C1) having an opposed winding direction relative to the coupling coil (C2);
wherein said at least one first protective coil (C1) encircles another area (S1) of the antenna; and
wherein the sum of the products of the number of turns of each protective coil and its corresponding encircled area is equal to the sum of the products of the number of turns of each coupling coil and its corresponding encircled area.
2. The antenna according to claim 1 , characterized in that the larger side of said at least one first protective coil (C1) is adjacent to said coupling coil (C2).
3. The antenna according to claim 1 , characterized by further comprising a second protective coil (C3), wherein:
the protective coils (C1 , C3) have the same winding direction; and
the three coils (C1 , C2, C3) are disposed in line such that the coupling coil (C2) is disposed between the protective coils (C1 , C3). .
4. The antenna according to claim 1 , characterized by further comprising a second coupling coil (C4) and a second protective coil (C3), wherein:
the protective coils (C1 , C3) have the same winding direction; the coupling coils (C2, C4) have the same winding direction;
the four coils (C1 , C2, C4, C3) are disposed in line such that the coupling coils (C2, C4) are disposed in the center and are separated by a gap; and the first coupling coil (C2) is adjacent to the first protective coil (C1) and the second coupling coil (C4) is adjacent to the second protective coil (C3).
5. The antenna according to claim 1 , characterized by further comprising a second coupling coil (C4) and a second protective coil (C3), wherein:
the protective coils (C1 , C3) have the same winding direction; the coupling coils (C2,C4) have the same winding direction; and the four coils (C1 , C2, C3, C4) are adjacent and disposed in line.
6. The antenna according to claim 1 , characterized by further comprising a second coupling coil (C4) and a second protective coil (C3), wherein:
the protective coils (C1 , C3) have the same winding direction, the coupling coils (C2, C4) have the same winding direction, the first protective coil (C1) and the first coupling coil (C2) are disposed in line;
the second coupling coil (C4) and the second protective coil (C3) are disposed in line; and
the coils C1C4 and C2C3 are disposed in parallel.
7. The antenna according to claim 1 , characterized by further comprising a second coupling coil (C4), a third coupling coil (C6), a second protective coil (C3) and a third protective coil (C5), wherein the protective coils (C1 , C3, C5) have the same winding direction and the coupling coils (C2, C4, C6) have the same winding direction, wherein:
the six coils (C1 , C2, C3, C4, C5, C6) are disposed adjacently and in line.
8. The antenna according to claim 1 , characterized by further comprising a second coupling coil (C4), a third coupling coil (C6), a second protective coil (C3) and a third protective coil (C5), wherein the protective coils (C1 , C3, C5) have the same winding direction and the coupling coils (C2, C4, C6) have same winding, wherein:
the first protective coil (C1), the first coupling coil (C2) and the second protective coil (C3) are disposed in line;
the second coupling coil (C4), the third protective coil (C5) and the third coupling coil C6 are disposed in line; and
the coils C1C2C3 and C4C5C6 are disposed in parallel.
9. The antenna according to any of claims 1 to 8, characterized in that the conductive path is made by etching, printing, screening or any metal deposition technique on a non-magnetic two-layers insulating foil.
10. A system for exchanging data in a radiofrequency identification system characterized by comprising:
the antenna (7, 13, 14, 15, 16, 17, 18, 19) according to any of claims 1 to 9;
a RFID integrated circuit connected to said antenna; a RFID reader (30) with a magnetic coupler (4, 22, 23, 24, 26); unlocking means (28, 31) having at least one magnetic shield (25, 29) blocking the magnetic fields through the protective coils of said antenna which is detected by the RFID reader.
11. System according to claim 10, characterized in that said antenna is assembled in a transponder.
12. System according to claim 11 , characterized in that said transponder is assembled in a smart-card.
13. System according to claim 11 , characterized in that said transponder is assembled as a security document inlay.
14. System according to claim 13, characterized in that said transponder is assembled in a mechanical readable travel document (MRTD).
15. System according to claim 10, characterized in that the unlocking means are a tag (28, 25).
16. System according to claim 10, characterized in that the unlocking means is a card (31).
18. System according to claim 10, characterized in that said unlocking means are assembled in said RFID reader.
18. System according to claim 10, characterized in that said antenna is assembled in a PCD reader.
19. System according to claim 10, characterized in that the antenna is connected to the RFID integrated circuit (2, 8, 30) by means of a capacitor which is serial with said antenna.
PCT/BR2011/000238 2010-07-23 2011-07-22 Magnetic coupling antenna and system for exchanging data comprising the same WO2012009776A1 (en)

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BRPI1002245-7A BRPI1002245A2 (en) 2010-07-23 2010-07-23 self-protected antenna with application to (but not limited to) RFID electronic documents intrinsically protected against clandestine activation
BRPI1002245-7 2010-07-23

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EP3599574A1 (en) * 2018-07-27 2020-01-29 STMicroelectronics Design and Application s.r.o. Antenna and system for rf communications

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