Smart card with radio frequency antennas

Abstract

Smart card with radio frequency antennas. The invention relates to a smart card (CD1) comprising a card body (6) including a metallic layer (8), an RF chip (4), and a first RF antenna (ANT1) disposed in a recess (14) and connected to the chip. The metallic layer has two regions (R1, R2), the first region (R1) entirely containing the recess (14). A first slot (F1) connects the recess (14) to an edge of the first region (R1), and a second slot (F2) opens onto an edge of the layer (8) or into the recess (14) and terminates in the second region (R2). Two other RF antennas (ANT2, ANT3) allow coupling with the first antenna (ANT1). They each have at least one turn opposite the first slot (F1) and at least two turns opposite the second slot (F2). Figure for the abridged version: Fig. 10.

Description

Title of the invention: Smart card with radio frequency antennas technical field

[0001] The invention relates to the field of smart cards and more particularly to metallic smart cards capable of operating in contactless mode. Prior art

[0002] The use of smart cards (or microcircuit cards) is now widespread in everyday life. Such cards are used, for example, as bank cards, loyalty cards, access cards, etc., and can take various forms depending on their respective uses. Smart cards can be designed to perform various types of functions, including carrying out transactions, such as banking transactions (payment transactions, transfers, etc.), authentication transactions, etc.

[0003] As is known, a smart card generally comprises a card body equipped with an electronic chip configured to exchange signals with the outside world and perform various functions depending on the intended use of the card. To this end, smart cards are equipped with communication means enabling interaction with the outside world, typically with an NFC reader or external reader.

[0004] Traditionally, a smart card is designed to cooperate with an external reader by means of external contacts accessible on the surface of the card. An external reader can thus position appropriate contact pins on the external contacts of the card in order to establish contact communication.

[0005] More recently, contactless smart cards have experienced increasing growth due to the speed and simplicity of contactless transactions. To achieve this, contactless cards incorporate a radio frequency (RF) antenna that allows the exchange of RF signals with an external NFC reader (for example, using NFC, or Near Field Communication). This RF antenna is generally composed of a plurality of conductive loops extending into the body of the card.

[0006] The structure and appearance of smart cards can vary depending on the case. Metallic smart cards, in particular, are experiencing growing interest due to their attractive aesthetic appearance (metallic reflections, brushed surface effect, etc.), the high-quality impression they can provide (the substantial weight of the metal, high-end aesthetics), and the prestigious connotation they confer on their users. Particularly because of their significant weight and the high-quality impression they produce, these cards are preferred by certain users. to serve as a social marker and differentiating element.

[0007] However, it has been observed that the presence of metal in the body of a smart card poses major difficulties when the card incorporates an RF antenna to operate in contactless mode. The metal acts as electromagnetic shielding and blocks or interferes with the RF signals exchanged by the RF antenna with the outside world. The metal present in the card body can thus disrupt contactless communication between a smart card and an external NFC reader and hinder, for example, the completion of a contactless transaction (payment or otherwise).

[0008] The problem arises particularly when the card is moved in the plane away from the center of the NFC reader. This is very common in the HF NFC RFID environment, for example during a payment when the user brings their card close to the point-of-sale reader in an off-center position.

[0009] Figure 16 illustrates, for example, an operational volume within which the card must be operational to comply with a standard defined by the international body EMVCO. Those skilled in the art may refer to the document "EMV Contactless Specifications for Payment Systems, Book D: EMV Contactless Communication Protocol Specification. Version 2.6, March 2016." One of the objectives of EMVCo is to ensure the interoperability and compatibility of smart cards and card readers under specified operational conditions.

[0010] This operational volume is defined by dimensions Si, S2, Db D2 recalled on [Fig.16].

[0011] This figure also represents the projection of 9 volume points onto a plane. For example, point 6 illustrates a situation in which the center of the card is offset by 25 mm from the center of the NFC reader.

[0012] In the current state of the art, metallic smart cards do not function satisfactorily throughout the EMVCo operational volume, in particular for the card positions corresponding to point 6.

[0013] There is therefore a need for high-performance metallic smart cards (of the RFID type, for example) that are simple to manufacture and capable of cooperating effectively in contactless mode with an external NFC reader, regardless of the card's position relative to the reader, under specific operating conditions. Description of the invention

[0014] For this purpose, the present invention relates to a smart card comprising a smart card comprising a card body of generally rectangular shape formed at least in part by a metallic layer comprising a recessed area; - an RF chip; - a first RF antenna positioned in or opposite the recessed area, said first RF antenna being electrically connected to the RF chip; said metallic layer being constituted by a first region and a second region entirely delimited by a straight line parallel to a short side of the map, the first region entirely containing the hollowed-out area and its surface being smaller than that of the second region, - a first slot connecting the recessed area to a peripheral edge of the first region; - a second slot opening either onto a peripheral edge of the metallic layer or into the recessed area, the second slot ending with a closed part in the second region; - a second RF antenna electrically isolated from the metallic layer and the first RF antenna and configured to allow coupling with the first antenna, the second antenna having at least one turn opposite the first slot; - a third RF antenna electrically isolated from the metallic layer, the first RF antenna and the second RF antenna and configured to allow coupling with the first antenna, the third antenna having at least one turn opposite the second slot.

[0015] The invention thus provides a high-performance metallic smart card (of the RFID type for example) and simple to manufacture, capable of cooperating effectively in contactless mode with an external NFC reader, regardless of the position and orientation of the card with respect to the external NFC reader.

[0016] Very advantageously, the metallic layer therefore comprises at least two slots, a first slot being located in the first region, the second slot being located in the second region.

[0017] Preferably, the first slot opens onto a small side of the smart card, as close as possible to the recessed area.

[0018] Preferably, the second metal slot opens into the cavity and terminates in an area of ​​the card located between the cavity and the center of the smart card.

[0019] Each of these slots allows the magnetic field generated by a card reader to pass through the metallic layer, which generates an induced current in the turns of the second antenna located opposite the first slot and an induced current in the turns of the third antenna located opposite the second slot.

[0020] This configuration also allows the turns of the second antenna located opposite the first slot and the turns of the third antenna located opposite the second slot, to collect an image current induced by a current flowing on the metallic layer locally at the level of these slots due to the magnetic field generated by the smart card reader.

[0021] As detailed below, due to the continuity of the eddy currents, the two currents collected by these turns of the second antenna, namely that induced directly by the electromagnetic field passing through the first slit and that image of a local eddy current circulating on the metallic layer, accumulate in phase.

[0022] Similarly, the two currents collected by these turns of the third antenna, namely that induced directly by the electromagnetic field passing through the second slit and that image of a local eddy current circulating on the metallic layer, accumulate in phase.

[0023] This configuration allows efficient coupling between the two antennas, regardless of the operating conditions of the card.

[0024] In one embodiment, the second RF antenna comprises: - a first antenna section extending opposite a peripheral area of ​​the metallic layer, with at least one turn of said first antenna section extending opposite the first slot, - a second antenna part, electrically connected to the first part of the second antenna, and extending opposite the recessed area to allow coupling with the first antenna; the first part of the second antenna being configured to collect an image current induced by first eddy currents flowing on an edge in the metallic layer when the smart card is subjected to an electromagnetic field under smart card operating conditions.

[0025] The third RF antenna comprises: - a first antenna section arranged at least partly opposite the second region of the metallic layer, with at least one turn of said first antenna section extending opposite the second slot, - a second antenna part electrically connected to the first part of the third antenna, and extending opposite the recessed area to allow coupling with the first antenna; the first part of the third antenna being configured to collect an image current induced by eddy currents flowing in the second region of the metallic layer when the smart card is subjected to an electromagnetic field under so-called adverse operating conditions corresponding to only a part of said operating conditions.

[0026] The routing of the second and third antennas is configured so that the current flows in the same direction in: - the first part of the second antenna; - the second part of the second antenna; - the first part of the third antenna; and in - the second part of the third antenna.

[0027] In particular, when the hollow area (or cavity) is relatively far from the field of maximum intensity, the operating conditions may be unfavorable.

[0028] The first part of the second antenna is arranged opposite a peripheral area of ​​the metallic layer, preferably according to a substantially rectangular routing which follows the contour along the four sides of the smart card, particularly in the first region of the card in the vicinity of the recess area.

[0029] Normally, regardless of the operating conditions of the card, the magnetic field of the card reader generates a loop of an eddy current which circulates along the edge of the card and which induces an image current capable of being collected by this first part of the second antenna.

[0030] The first part of the second antenna advantageously allows the energy of a main loop of eddy currents flowing along the peripheral edge of the metallic layer to be recovered when the entire surface of the card is exposed to a uniform magnetic field generated by the antenna of a reader of said card, in particular when is centered with respect to the antenna of the smart card reader.

[0031] The first part of the third antenna makes it possible to efficiently recover the energy of the eddy currents circulating on the smart card when the smart card is used under less favorable conditions, the card being off-center with respect to the card reader antenna.

[0032] Indeed, when the card is off-center with respect to the reader's antenna so that the recessed area and the first antenna move away from the center of the reader's antenna, the main loop of the eddy current is found mainly confined in the second region of the metallic layer, then opposite the magnetic field of maximum intensity.

[0033] In one embodiment, the second region comprises a privileged area for exploiting eddy currents, one or more turns of the third antenna being located opposite the second slot at the level of this privileged area.

[0034] In one embodiment, the privileged area for exploiting eddy currents is a disk centered on said card and whose radius corresponds to the radius of an operational volume of said card.

[0035] This embodiment ensures that, regardless of the operating conditions of the smart card, the second metal layer slot is itself located in this operational area and that a main eddy current loop circulates on the edge of this slot.

[0036] In one embodiment, the smart card conforms to the EMVCo standard, the eddy current operating area is a disk with a radius of 25mm centered on said card.

[0037] When the smart card is subjected to a magnetic field, the combined action: (i) of the image current carried from the first part of the second antenna and / or the first part of the third antenna on the one hand, and (i) of a current induced in the second part of the second antenna and / or in the second part of the third antenna by the magnetic field received through the metallic layer on the other hand, allows maximizing the amount of energy collected in the second RF antenna and / or in the third RF antenna from the magnetic field, and thus ensuring efficient magnetic coupling between the first RF antenna and the second and / or third RF antenna, which allows maximum energy to be delivered to the RF chip connected to the first RF antenna.

[0038] During operation, under the influence of the magnetic field to which the smart card is subjected, the RF chip is thus able to use the second and / or third RF antenna coupled with the first RF antenna to communicate with an external NFC reader (in particular to exchange RF signals in transmission and / or reception with the NFC reader). When a user presents the smart card to the NFC reader, under certain operating conditions, contactless communication can thus be established between the NFC reader and the smart card, regardless of the latter's orientation relative to the NFC reader. Indeed, eddy currents are generated in the metallic layer regardless of the smart card's orientation relative to the NFC reader.Similarly, regardless of which side of the smart card is presented to the NFC reader, the second part of the second antenna and the second part of the third antenna are capable of collecting a current component induced by the magnetic field at the recessed area.

[0039] According to a particular embodiment, the second and third RF antennas are configured so that their second parts extend exclusively in relation to the recess area.

[0040] According to a particular embodiment, the first RF antenna is arranged opposite the recessed area so that the recessed area is interposed between the first antenna on the one hand and the second and third RF antennas on the other hand to allow magnetic coupling between the first antenna and the second and third antennas.

[0041] According to a particular embodiment, the second and third RF antennas are electrically isolated from the metallic layer and the first RF antenna by an insulating layer interposed between the second and third RF antennas on the one hand, and the metallic layer and the recessed area on the other hand.

[0042] According to a particular embodiment, the smart card further comprises an electronic module including the RF chip, said electronic module being provided in or opposite the recessed area.

[0043] According to a particular embodiment, the first and second parts of the second RF antenna are connected in parallel with a first capacitive component.

[0044] According to a particular embodiment, the first and second parts of the third RF antenna are connected in parallel with a second capacitive component, independent of the first capacitive component.

[0045] According to a particular embodiment, magnetic coupling enables the RF chip to establish contactless communication with the outside of the smart card using the second and / or third RF antenna coupled to the first RF antenna.

[0046] In one embodiment, the metallic layer is at least partially, preferably entirely, covered by a coating that is more conductive than the metallic layer, for example, copper, silver, or gold. The thickness of the coating is preferably greater than the skin thickness of said coating.

[0047] For example, the conductivity of the coating is greater than 3.5x107 S / m.

[0048] The invention also relates to a method for manufacturing a smart card of generally rectangular shape from a card body formed at least in part by a metallic layer, said metallic layer comprising a recessed area, the metallic layer being constituted by a first region and a second region entirely delimited by a straight line parallel to a short side of the card, the first region entirely containing the recessed area and its surface being smaller than that of the second region, a first slot in the metallic layer connecting the recessed area to a peripheral edge of the metallic layer of the first region and a second slot in the metallic layer opening either onto a peripheral edge of the metallic layer or into the recessed area, the second slot terminating with a closed portion in the second region, the method comprising: - formation on or in the card body of a first RF antenna in or opposite the area of ​​the metal layer recess; - assembly of an RF chip with the board body such that the RF chip is electrically connected to the first RF antenna; and - formation on or in the card body of a second RF antenna such that the second RF antenna is electrically isolated from the metal layer and the first RF antenna, the second antenna being configured to allow coupling with the first antenna, the second antenna having at least one turn located opposite the first slot; - Formation on or within the board body of a third RF antenna such that the third RF antenna is electrically isolated from the metal layer, the first RF antenna, and the second RF antenna, the third antenna being configured for to allow coupling with the first antenna, the third antenna having at least one turn located opposite the second slot. Brief description of the drawings

[0049] Other features and advantages of the present invention will become apparent from the description below, with reference to the accompanying drawings which illustrate non-limiting examples of embodiments. In the figures:

[0050] [Fig-1] Figure [Fig.1] schematically represents a smart card cooperating with a NFC reader, according to at least one particular embodiment of the invention;

[0051] [Fig.2] The [Fig.2] is a top (or bottom) view of a metallic layer of a smart card according to at least one particular embodiment of the invention;

[0052] [Fig.3] The [Fig.3] is an exploded cross-sectional view schematically representing the structure of a smart card according to at least one particular embodiment of the invention;

[0053] [Fig.4] The [Fig.4] is a detailed cross-sectional view of a portion of a smart card, according to at least one particular embodiment of the invention;

[0054] [Fig.5] The [Fig.5] illustrates an exploitable zone of eddy currents on a metallic layer;

[0055] [Fig.6] The [Fig.6] represents a smart card centered with respect to the source of an incident magnetic field;

[0056] [Fig.7] The [Fig.7] represents a smart card decentred with respect to the source of an incident magnetic field;

[0057] [Fig.8A] Fig.8A represents a first example of a metallic layer that can be used in particular modes of implementation of the invention;

[0058] [Fig.8B] The [Fig.8B] represents a second example of a metallic layer that can be used in particular embodiments of the invention;

[0059] [Fig.8C] Fig.8C represents a third example of a metallic layer that can be used in particular embodiments of the invention;

[0060] [Fig.8D] The [Fig.8D] represents a fourth example of a metallic layer that can be used in particular embodiments of the invention;

[0061] [Fig.9] Fig.9 illustrates the circulation of eddy currents and the circulation of image currents on the smart card in a particular embodiment of the invention;

[0062] [Fig. 10] The [Fig. 10] represents an example of an arrangement of an antenna and a metallic layer that can be implemented in a smart card according to a particular embodiment of the invention;

[0063] [Fig. 11] The [Fig. 11] represents a smart card conforming to a particular mode of the invention;

[0064] [Fig. 12] The [Fig. 12] represents a smart card conforming to another particular mode of the invention;

[0065] [Fig. 13] The [Fig. 13] illustrates the operation of the smart card of the [Fig. 11];

[0066] [Fig. 14] Fig. 14 represents another smart card conforming to a particular mode of the invention;

[0067] [Fig. 15] Figure 15 represents in diagram form the steps of a manufacturing process for a smart card of the invention, according to at least one particular embodiment; and

[0068] [Fig. 16] The [Fig. 16] already described represents operational conditions of a smart card defined by the international organization EMVCo. Description of the implementation methods

[0069] As previously stated, the invention relates to metallic smart cards configured to operate in contactless mode, and also relates to the manufacture of such smart cards. In this document, a "metallic smart card" means a smart card comprising a metal or a combination (alloy) of metals, for example in the form of a metallic layer or a plurality of metallic layers.

[0070] As previously mentioned, a contactless smart card is inherently configured to communicate wirelessly with external devices, particularly with an external NFC reader. To this end, a contactless smart card incorporates a radio frequency (RF) antenna to exchange (receive and / or transmit) RF signals with an external NFC reader. Such a smart card may also be capable of operating in contact mode, using external contacts provided for this purpose on the card's surface: these are referred to as "dual" cards (or cards with a dual communication interface), as these cards are thus capable of operating in both contactless and contact modes.

[0071] There is currently strong user demand for metallic smart cards, particularly for the reasons mentioned above (aesthetic appeal, high-quality printing, prestige, etc.). It is especially desirable to produce smart cards in which the majority (or a significant portion) of the card body is made of metal, or at least in which the card body includes a metallic plate (or metallic layer), in order to achieve a certain uniformity and quality in the visual and aesthetic appearance of the card.

[0072] However, when a contactless smart card has a metallic layer and an RF antenna disposed on or near one of the faces of the metallic layer, it has been observed that this metallic layer disrupts contactless communication between the RF antenna and the outside, particularly when the metallic layer is The metallic layer acts as an electromagnetic barrier between the RF antenna and the external NFC reader with which the smart card attempts to communicate. Therefore, depending on the card's position and orientation relative to the reader, a contactless transaction between a metallic smart card and an external NFC reader may or may not be possible. In some cases, a transaction is possible if the smart card is presented so that the antenna is facing the NFC reader (without the metallic layer interposed), but RF communication is disrupted, or even impossible, if the metallic layer forms an electromagnetic barrier between the card's RF antenna and the NFC reader (the metallic plate acts as an electromagnetic barrier between the RF chip and the NFC reader).However, for RF communication to occur between a metallic smart card and an external NFC reader, the card generally needs to contain ferrite to limit electromagnetic interference from the metallic part. Without ferrite, even when correctly oriented relative to an external NFC reader, proper RF communication between the card and the NFC reader is generally impossible, making any transaction impossible (or at least very difficult).

[0073] The invention aims to overcome, in particular, the drawbacks and problems mentioned above. To this end, the invention relates to a smart card comprising a metallic layer and a specific antenna structure comprising three RF antennas, namely a first RF antenna electrically connected to an RF chip of the card, and two RF antennas each extending partially alongside the metallic layer to collect an image current induced by eddy currents flowing in the metallic layer when the card is subjected to an electromagnetic field. Each of these two RF antennas includes a portion configured to allow magnetic coupling of this antenna with the first RF antenna.To achieve this, the metallic layer includes a recessed area. The first RF antenna is positioned within or adjacent to this recessed area, and a portion of each of the two other RF antennas is positioned adjacent to the recessed area to allow magnetic coupling with the first RF antenna. By establishing such coupling through the recessed area, the card's RF chip can then use the second RF antenna to communicate wirelessly with the outside world. At least two slots are also provided in the metallic layer, each to facilitate magnetic coupling of at least one of the two other antennas with the first RF antenna, regardless of the card's operating conditions.

[0074] To this end, the present invention relates to a smart card comprising a card chip comprising a card body of generally rectangular shape formed at least in part by a metallic layer comprising a recessed area, an RF chip, a first RF antenna disposed in or opposite the recessed area, said first RF antenna being electrically connected to the RF chip, the metallic layer consisting of a first region and a second region entirely delimited by a straight line parallel to a short side of the card, the first region entirely containing the recessed area and its area being smaller than that of the second region, a first slot connecting the recessed area to a peripheral edge of the first region, a second slot opening either onto a peripheral edge of the metallic layer or into the recessed area, the second slot terminating with a closed portion in the second region;a second RF antenna electrically isolated from the metallic layer and the first RF antenna and configured to allow coupling with the first antenna, the second antenna having at least one turn opposite the first slot and a third RF antenna electrically isolated from the metallic layer, the first RF antenna, and the second RF antenna and configured to allow coupling with the first antenna, the third antenna having at least one turn opposite the second slot. ;

[0075] The invention also relates to a method for manufacturing such smart cards. Particular embodiments, as well as other aspects of the invention, are described in more detail below.

[0076] In the present description, examples of implementations of the invention are described in relation to a "dual" type smart card, that is, a card with a dual communication interface, capable of communicating both in contact mode (via external contacts) and in contactless mode (via an RF antenna structure). It should be noted, however, that the invention can be applied more generally to any smart card configured to communicate in contactless mode, regardless of whether or not it also has the capacity to operate in contact mode.

[0077] Furthermore, in the following examples, the smart card is considered to be a bank card, such as a payment card. This smart card may conform to ISO 7816 and may operate according to the EMV standard, although neither of these aspects is mandatory for implementing the invention. More generally, the invention applies to any metallic smart card configured to implement a contactless transaction, including EMV cards or smart cards using another transaction standard, for example, the NFC standard (according to, for example, ISO 14443-2, ISO 10373-6, "EMV Contactless Certification"), NFC Forum standard. In general, the smart card of the invention can be configured to carry out any type of transaction, such as banking transactions (payment, transfer, debit transactions, etc.), authentication transactions, etc.

[0078] Unless otherwise indicated, common or similar elements in several figures bear the same reference signs and have identical or similar characteristics, so that these common or similar elements are generally not described again for the sake of simplicity.

[0079] The terms "first(s)", "second(s)", etc. are used in this document by arbitrary convention to allow identification and distinction of different elements (such as keys, devices, etc.) implemented in the embodiments described below.

[0080] Figure 1 shows a metallic CD1 smart card configured to communicate in contactless mode with the outside world, for example with an external NFC reader. The CD1 smart card comprises an RF chip 4, a card body 6, and three RF antennas, namely a first RF antenna ANT1, a second RF antenna ANT2, and a third RF antenna ANT3. The RF chip 4 and the three RF antennas ANT1, ANT2, and ANT3 are positioned on or within the card body 6.

[0081] The card body 6 is formed at least in part (or comprises) a metallic layer 8. This metallic layer 8 may be made of a single metal, such as stainless steel or aluminum, for example, or of an alloy of several different metals. The metallic layer 8 may comprise a plurality of metallic sublayers. According to a particular example, the card body 6, and more generally the CD1 smart card, is ferrite-free, which simplifies the manufacture of the card while ensuring symmetrical operation of both sides of the card.

[0082] The smart card is generally rectangular in shape (with slightly rounded corners). In the examples considered here, the card body 6 is in the ID1 format of a credit card, although other shapes are possible to implement the invention.

[0083] The RF chip 4 is an electronic chip configured to establish contactless communication with the external NFC reader using the ANT1 RF antenna and, depending on the operating conditions, at least one of the ANT2 or ANT3 antennas, as described below. To achieve this, the RF chip 4 is electronically connected to the first RF antenna, ANT1, but each of the ANT2 and ANT3 RF antennas is electrically isolated from the RF chip 4 and the first RF antenna, ANT1. The ANT2 and ANT3 antennas are also electrically isolated from each other.

[0084] The ANT1 antenna is at least partially aligned with a portion of the ANT2 antenna and with at least a portion of the ANT3 antenna to allow, depending on the operating conditions, magnetic induction coupling between the first ANT1 antenna and at least one of the two ANT2 and ANT3 antennas, and thus allow to the RF chip 4 to use the second RF antenna ANT2 and / or the third RF antenna ANT3 to establish contactless communication Cl with the external NFC reader, as described in more detail below.

[0085] The RF chip 4 may include, for example, a microcontroller (or a processor) configured to establish contactless communication with the outside of the smart card CD1 (with the external NFC reader in this example) using the first and second RF antennas ANT1, ANT2 (and / or the first and third RF antennas ANT1, ANT3) coupled together by magnetic induction.

[0086] By way of illustration, [Fig.2] represents only the metallic layer 8 according to one embodiment.

[0087] In this example, the metal layer 8 includes a recess 14 opening onto a peripheral edge (or contour) 8a of the metal layer 8. The recess 14 is a through-opening (or zone) formed in the metal layer 8 to allow the positioning of the first RF antenna ANT1 with a portion of the second RF antenna ANT2 as described below. The shape and dimensions of this recess 14 can be adapted as needed. For example, the recess 14 formed in the metal layer 8 is rectangular.

[0088] In the present application, and as represented in [Fig.2], the metallic layer is considered to consist of two regions RI, R2 delimited by a straight line LIM parallel to a short side of the card, the first region RI containing entirely the recess area 14 and its surface being smaller than that of the second region R2.

[0089] In the embodiment shown in [Fig.2], the line LIM is tangent to the recess area 14 on its side closest to the center of the smart card.

[0090] In the example shown in [Fig.2], the metallic layer 8 includes a first slot Fl which connects or joins a peripheral edge 8a of the first RI region with the recessed area 14. In other words, the recessed area 14 emerges (or opens) onto the peripheral edge 8a via this first slot FL. This first slot Fl is characterized by a distance dl separating two opposite peripheral edges of the metallic layer 8, the value of this distance dl being able to vary depending on the case.

[0091] The position of the recessed area 14 in the metallic layer 8 can vary depending on the case. According to the particular example shown in [Fig.2], the recessed area 14 is positioned in the vicinity of a peripheral edge 8a of the metallic layer 8, which makes it possible to ensure efficient magnetic coupling FL1 between the RF antennas ANT1 and ANT2, as explained in more detail below.

[0092] Other implementations are possible, however, in which, for example, the recessed area 14 is positioned at the center (or substantially at the center) of the metallic layer 8, it being understood that this recessed area 14 is always configured to open onto (or be connected to) a peripheral edge 8a of the metallic layer 8 via a first slot Fl.

[0093] This recessed area 14 corresponds approximately to the module's reception area, this reception area being specified by the standards so that terminals can connect the contacts of a module 2 described below.

[0094] In one embodiment, the conductive turns of the first RF antenna ANT1 extend in the form of a winding around the RF chip 4 in the recess area 14. This arrangement allows the RF chip 4 to be positioned as close as possible to the first RF antenna ANT1 and thus to limit the manufacturing complexity of the smart card CD1, in particular the electrical connection between the RF chip 4 and the first antenna ANT1.

[0095] We now consider particular embodiments in which the metallic layer 8 includes a recessed area 14 according to the configuration illustrated in [Fig.2],

[0096] In particular, [Fig. 3] schematically represents an exploded cross-sectional view of the CD1 smart card and [Fig.4] schematically represents a detailed cross-sectional view of the CD1 smart card, according to at least one particular embodiment.

[0097] As shown in [Fig. 3], the RF chip 4 is considered to be contained (or embedded) in an electronic module 2, the latter being inserted into the card body 6. The electronic module 2 is, for example, positioned in a cavity 5 formed on the upper surface of the card body 6. To this end, the recess 14 comprises an electrically insulating material 9 in which the cavity 5 is formed to accommodate the electronic module 2. Thus, the RF chip 4 is positioned in the recess 14 (or, alternatively, opposite and above the recess 14). It should be noted, however, that various arrangements of the RF chip 4 are possible. In particular, variants are possible in which the RF chip 4 is not located in, or opposite, the recess 14.

[0098] According to one embodiment, the RF chip 4 (with or without the electronic module 2) is positioned on (or opposite) the metallic layer 8. For this purpose, an insulating material can be disposed between the RF chip 4 and the metallic layer to ensure electrical insulation.

[0099] In the example of [Fig.3], the electronic module 2 has on its su face The external CTI contacts (or contact areas) are configured to allow contact communication between the RF chip 4 and an external NFC reader designed for this purpose (e.g., with the NFC reader). More specifically, the electronic module 2 may include a printed circuit board (PCB) comprising the external CTI contacts on its upper surface and the lower surface RF chip 4. The external CRI contacts are metallic areas designed to accommodate connection pins of an external NFC reader. These external CRI contacts may conform to ISO 7816, although other examples are possible. The electronic module 2 is arranged in the smart card CD1 so that its external CRI contacts are accessible from the top surface of the card body 6 to allow the RF chip 4 to communicate by contact with an external NFC reader.

[0100] As already indicated, embodiments are also possible without such external CTL contacts. In addition, the integration of the RF chip 4 into the electronic module 2 as shown in the figures is not mandatory, other arrangements of the RF chip 4 being possible without such a module.

[0101] In the example of [Fig. 3], the RF chip 4 is located in the recess 14. According to one embodiment, the first RF antenna ANT1 is located outside the recess 14, namely opposite the recess 14 (aligned above it). The recess 14 is thus interposed between the first RF antenna ANT1 on the one hand and the second and third RF antennas ANT2 and ANT3 on the other hand to allow magnetic induction coupling CL1 between said first antenna ANT1 and at least one of said second and third antennas ANT2, ANT3.

[0102] The RF chip 4, and more generally the electronic module 2, can be arranged in the insulating layer 9 (commonly called the "inlay"). This configuration makes it easier to mount the RF chip 4 and the first RF antenna ANT1 in the card body 6.

[0103] As shown in [Fig.4], the card body 6 comprises at least one external insulating layer 12 provided on the lower face 10b of the insulating layer 10 so as to cover and protect the second and third RF antennas ANT2, ANT3. At least one protective insulating layer may also be provided, if necessary, on the upper face of the card body.

[0104] Each of the RF antennas ANT1, ANT2, ANT3 comprises at least one electrically conductive turn to allow RF signal exchange between the smart card CD1 and the outside. The RF antennas ANT1, ANT2, and ANT3 can each be made, for example, of an electrically conductive track, wire, or member forming one or more conductive turns. In this case, the first, second, and third RF antennas ANT1, ANT2, ANT3 are considered to each comprise a plurality of conductive turns. Various manufacturing techniques (wire, deposition, etching) that are well known per se can be used to produce these RF antennas. The physical characteristics (shape / size of the intersection, antenna length, number of turns, material, etc.) of the RF antennas ANT1, ANT2 and ANT3 can be adapted on a case-by-case basis in order to enable wireless communications at the desired frequencies (or frequency ranges).

[0105] More specifically, as shown in [Fig.3], the first RF antenna ANT1 comprises a plurality of electrically conductive turns - called "first" conductive turns - arranged in the recess area 14. In this particular case, the size of the RF antenna ANT1 is therefore limited insofar as its first conductive turns are contained in the recess area.

[0106] Furthermore, the second RF antenna ANT2 and the third RF antenna ANT3 are electrically isolated from the metal layer 8 and the first RF antenna ANT1. The second and third RD antennas ANT2, ANT3 are electrically isolated from each other.

[0107] This insulation can be achieved in various ways. For example, if the second and third antennas ANT2, ANT3 are produced by etching, an insulating layer (a "solder mask") can be placed between the second and third antennas ANT2, ANT3 and the metal layer 8 to prevent a short circuit and oxidation of the second antenna. According to another example, the second and third antennas ANT2, ANT3 can each consist of a conductive wire surrounded by an insulating plastic sheath.

[0108] By way of example, the card body 6 is considered to comprise an electrically insulating layer 10 (commonly called an "inlay," meaning "inner layer") interposed between the second RF antenna ANT2 on the one hand, and the metallic layer 8 and the recessed area 14 on the other. The insulating layer 10 is located, in particular, at the interface between the second antenna ANT2 and the insulating material 9 in which the first RF antenna ANT1 extends.

[0109] Figure 9 illustrates the circulation of the different currents on the map in an example of an embodiment: - IMP represents a peripheral eddy current whose main loop circulates around the periphery of the card when it is centered with the reader; - IA2 is an image current induced by this peripheral eddy current and circulating in the second antenna ANT2. It is routed to the level of the recess area 14; - IMI represents an internal eddy current whose main loop circulates in the second region of the map when it is off-center relative to the reader; - IA3 is an image current induced by this internal eddy current and circulating in the second antenna ANT3. It is routed to the level of the recess 14 area.

[0110] IA2 and IA3 circulate in the same direction.

[0111] As illustrated in [Fig. 10] in particular, the second RF antenna ANT2 is considered to comprise two antenna parts, namely a first antenna part ANT2a, and a second antenna part ANT2b electrically connected to each other.

[0112] Similarly, the third RF antenna ANT3 comprises two antenna parts, namely a first antenna part ANT3a, and a second antenna part ANT3b electrically connected to each other.

[0113] More specifically, the first parts ANT2a and ANT3a of the second and third RF antennas ANT2, ANT3 comprise a plurality of electrically conductive turns, which extend opposite (or in opposition to) the metal layer 8 to collect an image current induced by eddy currents flowing in the metal layer 8 when the latter is subjected to an incident magnetic field.

[0114] More specifically, and as explained in detail below: (i) the first part ANT2a of the second antenna ANT2 is arranged to efficiently collect eddy currents flowing in the metallic layer when the smart card CD1 is centered with respect to the NFC reader antenna; (ii) the first part ANT3a of the third ANT3 antenna is arranged to efficiently collect eddy currents flowing in the metallic layer when the CD1 smart card is in an off-center position relative to the NFC reader antenna).

[0115] In this document, the card will be considered to be centered with respect to the NFC reader antenna when the entire surface of the card is exposed to a magnetic field generated by the NFC reader antenna, uniform and of maximum intensity over the surface of the card.

[0116] In the embodiment of [Fig. 3], at the level of the recess zone 14, the ANT2b turns of the second antenna ANT2 surround the ANT3b turns of the third antenna ANT3. Alternatively, the ANT3b turns of the third antenna ANT3 surround the ANT2b turns of the second antenna ANT2. Alternatively, the ANT2b and ANT3b turns are not in the same plane.

[0117] As shown in [Fig. 4], in at least one embodiment, the RF chip 4 is electrically connected to the first RF antenna ANT1. In the example considered here, the electrical connection is made via connection pads (or ranges) 16a and 16b of the electronic module 2, these pads being connected respectively to connection pads (or ranges) 18a and 18b provided for this purpose in the recess area 14 (in the insulating material 9 in this example). The connection pads 18a and 18b are in turn connected respectively to the two ends of the first RF antenna ANT1. Other ways of connecting the RF chip 4 to the first RF antenna ANT1 are, however, conceivable.

[0118] Various configurations of the second and third RF antennas ANT2, ANT3 are possible. According to a preferred embodiment, the second part ANT2b of the second antenna ANT2 and the second part ANT3b of the third antenna ANT3 extend exclusively in relation to the recess area 14. In other words, these antenna parts ANT2b, ANT3b, formed of a plurality of conductive turns, are arranged in relation to the recess area 14 so that they do not extend in relation to the metallic layer 8. In particular, these antenna parts ANT2b, ANT3b do not overlap (or do not cover) the metallic layer 8 at the periphery of the recess area 14, which makes it possible to optimize the flux of the magnetic field to which these second antenna parts ANT2b, ANT3b as well as the first RF antenna ANT1 are subjected.Although it is not desirable for a portion of the second part ANT2b, ANT3b of the second antenna ANT2 or the third antenna ANT3 to extend in relation to the metallic layer 8, a certain tolerance may be accepted in some cases.

[0119] Fig. 5 illustrates in hatched form, for a particular embodiment of the invention, a privileged ZC zone for exploiting eddy currents that circulate on the metallic layer 8 when the smart card is exposed to a magnetic field under determined conditions, this privileged ZC zone being included in the R2 region of the metallic layer 8.

[0120] This [Fig.5] is placed, for illustrative purposes only, in the particular context of the operational conditions defined by the international organization EMVCo and recalled previously with reference to [Fig. 16].

[0121] In a known way, when a metallic surface is subjected to a magnetic field, this magnetic field induces eddy currents on this surface which circulate in a closed loop, the dominant loops being such that they maximize the surface area of ​​these loops with respect to the magnetic field of maximum intensity.

[0122] Thus, when a metallic layer is subjected to a uniform magnetic field over the entire surface of the card, the dominant loop of the eddy currents induced by the incident magnetic field follows the contour of the card.

[0123] On the other hand, assuming that the reader has a circular antenna and that it produces a uniform magnetic field, as soon as the metallic surface is no longer entirely opposite a uniform field, the dominant loop no longer follows the contours of the card, but maximizes the surface of this loop in direct line of sight with the magnetic field of maximum intensity.

[0124] In other words, as a first approximation, the dominant loop delimits the projection of this field onto the surface of the map.

[0125] In one embodiment of the invention, the privileged zone ZC for exploiting eddy currents can be an area of ​​the map surface that is subjected to a uniform magnetic field of maximum intensity regardless of the operating conditions of the card.

[0126] For example, in [Fig.5] a smart card in ID1 format (length L of 85.6mm and a width 1 of 54.0mm) is shown, C the center of the card, subsequently assimilated to the center of the metallic layer 8, and an eddy current exploitability zone ZC constituted by a disk of center C and radius r of 2.5 cm.

[0127] The inventors have determined that regardless of the position of the center C of the card in the operational volume defined by the EMVCo body, such a privileged exploitable zone ZC (disk of radius 25mm at the center of the card) is entirely contained within an electromagnetic field generated by the NFC reader antenna of sufficient intensity for eddy currents circulating in this zone to be exploited by the invention.

[0128] In [Fig.6], a magnetic field is delimited by a CHR circle of maximum intensity generated by an NFC reader. This figure assumes a perfectly circular and rotationally symmetrical NFC reader antenna.

[0129] In this figure the center C of the smart card CD1 is located at the center of the circle CHR.

[0130] In [Fig.7], the smart card CD1 is shown, the center C of the smart card CP being offset by 25 mm from the center of the CHR circle; this offset of 25 mm corresponds to the maximum offset of the card in the operational volume defined by EMVCo (point 6 of [Fig. 16]).

[0131] The inventors have observed that the eddy current exploitability zone ZC shown in [Fig.7] (25mm radius disk centered on the card) lies entirely within the maximum intensity CHR field of the NFC reader, in particular for the maximum offset (point 6) of the card in the operational volume defined by EMVCo, and therefore for any position of the card in the determined operating conditions.

[0132] The invention can be used in contexts other than that of the EMVCo standard.

[0133] In general, the ZC zone of exploitability of eddy currents used in the invention can be defined so that this ZC zone lies entirely within a magnetic field of maximum intensity, regardless of the position of the card under predetermined operating conditions.

[0134] Figures 8A to 8D show, in four examples, a metallic layer 8 comprising: (i) a recessed area 14 connected by a first slot Fl to the edge 8a corresponding to the shorter side of the metallic layer 8 closest to the recessed area; and (ii) a slot F2, notable in that it opens either onto an edge of the metallic layer 8 or into the recessed area 14 and in that it has an end closed located in the second region R2 of the metallic layer, and in the examples of figures 8A to 8C more precisely in a privileged zone ZC of exploitability of eddy currents.

[0135] In these figures 8A to 8D, the symbol FL1 represents the direction of the NFC reader's magnetic field. This magnetic field generates eddy current loops on the metallic layer 8.

[0136] For the sake of simplicity, in figures 8B to 8D corresponding to the off-center use of the card, only two loops Bl, B2 of the internal eddy current IMI of [Fig.9] have been represented, of which a dominant loop Bl.

[0137] Eddy currents form in closed loops over the entire metallic surface having an incident magnetic field from the reader. The direction of the eddy currents in these loops is opposite in phase with respect to the magnetic field that created them, i.e. a clockwise direction for the example of the incident magnetic field of [Fig.9].

[0138] In the four examples, the slots Fl and F2 are arranged in this way to allow the passage of the magnetic field generated by a smart card reader and to be traversed by an eddy current circulating on the metallic layer 8.

[0139] These slots F2 allow the eddy currents to be directed so that they are in phase with the magnetic flux from the terminal around the slot, and so that the eddy currents around the slot do not oppose this magnetic flux.

[0140] Since the turns of the ANT2 and ANT3 antennas are all in planes parallel to that of the metallic layer carrying the eddy current loops, a conduction current will be induced by image effect in these conducting wires forming the antenna turns and, consequently, in opposite phase to the eddy currents to which they exhibit the image effect. These image currents induced in the different turns of ANT2 and ANT3 are therefore in phase with the magnetic field of the NFC reader.

[0141] In [Fig. 10] in addition to the metallic layer 8, two antennas ANT2, ANT3 (second and third antennas in the sense of the invention) are shown, implemented on a plastic layer not shown.

[0142] The second antenna ANT2 (respectively the third antenna ANT3) comprises a first part ANT2a (respectively ANT3a) and a second part ANT2b (respectively ANT3b).

[0143] The second antenna ANT2a and the third antenna ANT3 are configured so that the current flows in the same direction in the first ANT2a, ANT3a and second ANT2b, ANT3b parts of the second and third antennas ANT2, ANT3.

[0144] In the embodiment of [Fig. 10], the first part ANT2a of the second antenna ANT2 is the outermost part. It is arranged opposite the metallic layer 8 and extends along the four edges of the metallic layer 8. It has at least one turn that overlaps the first slot Fl.

[0145] In the embodiment of [Fig. 10], the first part ANT3a of the third antenna ANT3 is notable in that it is arranged opposite the second region R2 of the metal layer 8 and has at least one turn opposite the second slot F2.

[0146] Thus, at least one turn of the third ANT3 antenna is able to capture an image current induced by a current flowing in a main loop of an eddy current generated by an incident magnetic field under the operating conditions of the smart card, when this loop is located in the second region R2.

[0147] In the embodiment of [Fig. 10], the second part ANT2b, ANT3b of each of the second and third antennas ANT2, ANT3 does not overlap with the metallic layer 8 but overlaps with at least part of the recessed area 14.

[0148] Figure 11 represents a CD1 smart card according to an embodiment of the invention. It includes in particular a first ANT1 antenna electrically connected to an RF chip, a second ANT2 antenna, a third ANT3 antenna and a metallic layer 8.

[0149] The metallic layer 8 having a recessed area 14 or cavity whose size is at least equal to the size of the dielectric substrate which accommodates the first antenna ANT1, the first antenna ANT1 being disposed in or opposite the recessed area, such that the first antenna ANT1 does not overlap the metallic layer 8.

[0150] In an embodiment of [Fig. 1 1], the first antenna ANT1 is implemented on the substrate carrying a contact plate. Alternatively, the first antenna ANT1 can be hosted by another dielectric substrate placed in the recess area 14 and connected to the contact plate module, carrying the RF chip, by an ACF connection.

[0151] In the embodiment of [Fig. 11], the recessed area 14 opens onto a peripheral edge 8a of the metal layer. To this end, the recessed area is connected to the peripheral edge 8a of the metal layer by a first slot Fl which extends from the recessed area towards the edge 8a of the metal layer 8.

[0152] In the embodiment of [Fig. 11], a second slot F2 extends from the recessed area 14 towards the interior (or central area) of the metal layer. This second slot is closed and its end is located in the second region R2.

[0153] In the embodiment described here, the second and third antennas ANT2, ANT3 are electrically isolated from the metal layer 8 by means of a dielectric insulation layer.

[0154] As illustrated [Fig.10], the first part ANT2a of the second antenna ANT2 is the most peripheral part. It is arranged opposite the metal layer 8 and extends along the four edges of the metal layer 8. It overlaps the slot Fl.

[0155] As illustrated [Fig.10], the first part ANT3a of the third antenna ANT3 is arranged opposite the metal layer 8 and less than one turn overlaps the slot F2 in the second region R2.

[0156] As illustrated in [Fig. 10], the second part ANT2b (respectively ANT3b) of the second antenna ANT2 (respectively of the third antenna ANT3) terminates the second antenna ANT2 (respectively the third antenna ANT3). It does not overlap with the metallic layer 8 but it overlaps with at least part of the recessed area 14.

[0157] As described in detail below, the second part ANT2b of the second antenna ANT2 and / or the second part ANT3b of the third antenna ANT3 provide inductive coupling between the second and / or third antenna ANT2, ANT3 and the first antenna ANT1 depending on the operating conditions.

[0158] In the embodiment described here, the CD1 board includes a capacitive element CPI connected in parallel to the second antenna ANT2 and a capacitive element CP2 connected in parallel to the third antenna ANT3. In the embodiment described here, the capacitive elements CPI and CP2 are parallel-plate capacitors. Other implementations may be used. The capacitive element CPI and / or the capacitive element CP2 may be implemented as a discrete capacitive component.

[0159] In the example described here, the capacitive components CPI, CP2 are arranged in the insulating layer 10 or on the lower face 10b of this insulating layer 10. Once the magnetic coupling CL1 is established, the RF antennas ANT1 and ANT2 (respectively ANT1 and ANT3) are connected in parallel with the capacitive component CPI (respectively CP2). The capacitive component CPI (respectively CP2) thus forms with the RF antennas ANT1 and ANT2 (respectively ANT1 and ANT3) an RLC circuit allowing the resonant frequency of the second RF antenna ANT2 (respectively of the third antenna ANT3) to be adapted so that it is for example equal to 13.56 MHz, which allows contactless communication of the RFID type with an RFID reader (for example according to the ISO 14443 / ISO 10373 standard, in particular the current version ISO / IEC 10373-6:2020 or any of the earlier versions, or any later version).

[0160] The capacitive component CPI or CP2 may be of the interdigital type and comprises two opposing sets of intertwined conducting fingers, although other capacitor forms are possible (parallel plate capacitor, discrete surface-mounted capacitor, parallel-wire capacitor, etc.).

[0161] For example, the first capacitive component CPI (respectively the second capacitive component CP2) is connected with one end of the first part ANT2a (respectively ANT3a) of the second antenna ANT2 (respectively the third antenna ANT3) and with one end of the second part ANT2b (respectively ANT3b) of the second antenna ANT2 (respectively the third antenna ANT3).

[0162] In the embodiment of [Fig. 11], the capacitive elements CPI and CP2 connected in parallel respectively to the second antenna ANT2 and the third antenna ANT3 are on the same side of the recess area 14.

[0163] In the embodiment of [Fig. 12], the capacitive elements CPI and CP2 are on either side of the recess area 14.

[0164] The examples of slots F2 shown in Figures 8 are only non-limiting examples. Any slot opening either into the cavity 14 or onto an edge of the card and ending with a closed end in the second region R2, preferably in a privileged ZC zone of eddy current exploitation, can be used in the context of the invention.

[0165] Fig. 13 illustrates the operation of the smart card of Fig. 12 when it is centered with respect to the NFC reader antenna, in other words when the surface of the card is exposed to a uniform magnetic field FL1 generated by the reader.

[0166] Under the influence of the magnetic field FL1, IMP (peripheral) and / or IMI (internal) eddy currents are generated in the metallic layer 8 according to the operating conditions of the board. These eddy currents circulate as closed current loops on the surface of the metallic layer 8. These eddy currents form on the metallic layer 8 in closed loops in a direction such that they create a magnetic field opposite to the incident magnetic field.

[0167] In the example of [Fig. 13], the eddy currents flow in a clockwise direction.

[0168] Assuming that the entire surface of the card is exposed to a uniform magnetic field and as in the case illustrated in [Fig. 13], the dominant loop of the IMP eddy currents follows the peripheral contour of the metallic layer 8.

[0169] In a manner known to those skilled in the art, eddy currents, flowing in a clockwise direction, induce an image current I2a which flows in the first part of the ANT2 antenna in a counterclockwise direction.

[0170] As shown in [Fig. 13], IMP denotes eddy currents – called first eddy currents – corresponding to dominant loops circulating on the surface of the metallic layer 8 in the vicinity of the peripheral contour of said metallic layer 8. Ilb denotes eddy currents – called second eddy currents Foucault - corresponding to secondary loops circulating on the surface of the metallic layer 8 in the vicinity of the peripheral contour of the hollowing zone 14.

[0171] Since the eddy currents circulate in closed loops, the eddy currents Ilb are in fact the continuation of the eddy currents IMP in the vicinity of the peripheral contour of the recessed area 14. As can be seen from [Fig. 13], the second eddy currents Ilb circulate, in the vicinity of the second part of the antenna ANT2b, in a direction of rotation (or direction of circulation) opposite to that of the first eddy currents IMP circulating in the vicinity of the peripheral contour of the metallic layer 8. By way of example, it is considered that the first and second eddy currents IMP, Ilb circulate in the clockwise and counterclockwise directions respectively, an inverse configuration being possible however depending on the orientation of the magnetic field FL1 considered.The opposite direction circulation of the eddy currents IMP and Ilb results in particular from the continuity of the eddy currents mentioned above, as well as from the presence of the recess zone 14 which is connected in this example by the connecting slot Fl to the peripheral contour 8a of the metallic layer 8.

[0172] Consequently, the current IA2 flowing in the second RF antenna ANT2 is an induced current resulting from two components, namely: an image current I2a induced by the first eddy currents IMP flowing on the surface of the metallic layer 8 in the vicinity of the first antenna part ANT2a; and a current I2b which is induced directly in the second antenna part ANT2b by the incident magnetic field FL1 through the recess area 14 (IA2 = I2a + I2b). The very structure of the CD1 smart card is designed to lead to this dual contribution of the induced currents I2a and I2b in order to collect in the second RF antenna the largest possible overall induced current IA2.

[0173] More specifically, the first antenna part ANT2a extending opposite the metallic layer 8 collects an image current I2a induced by the first eddy currents IMP circulating on the surface of the metallic layer 8 under the effect of the magnetic field FL1 when the smart card CD1 is centered with the NFC reader antenna.

[0174] These first eddy currents IMP correspond to dominant loops circulating on the surface of the metallic layer 8 in the vicinity of the turns of the first antenna part ANT2a. As already indicated, the first part of the second antenna ANT2a can preferably extend towards a peripheral zone (or band) of the metallic layer 8 to collect a maximum of energy generated by the dominant loops of the eddy currents. The first eddy currents IMP circulating in the vicinity of the first part ANT2a of the second antenna ANT2 (in this example at the periphery of the metallic layer 8) produce an effect that opposes the incident magnetic field FL1. The induced current I2a collected in the turns of the first part of the ANT2a antenna is itself a reaction effect to the first eddy currents.

[0175] The image current I2a induced by the first eddy currents IMP is carried by electrical conduction to the second part ANT2b of the second antenna ANT2, due to the electrical continuity between the first and second antenna parts ANT2a, ANT2b which are connected together.

[0176] As illustrated in [Fig. 13], the image current IA2 flows in the same direction of rotation (or same direction of circulation) in the turns of the first and second antenna parts ANT2a, ANT2b, namely in the counterclockwise direction in this example. However, due to the presence in the metallic layer 8 of the recess 14 connected via the connecting slot Fl to the peripheral edge 8a, the second eddy currents Ilb (secondary loops) circulate in the vicinity of the recess 14, on the surface of the metallic layer 8, in a direction of rotation (or direction of flow) opposite to that of the first eddy currents IMP circulating at the periphery of the metallic layer 8. For example, the second eddy currents Ilb circulate here counterclockwise while the first eddy currents IMP circulate clockwise. Therefore, the second eddy currents Ilb circulating at the periphery of the recess 14 do not oppose the magnetic field passing through the slot and contribute to amplifying the image current a circulating in the turns of the third antenna section ANT2c.

[0177] Moreover, the effect of the second slot F2 is to push the dominant eddy current loop towards the first part ANT3a of the third antenna ANT3, which increases the energy coupling between the eddy currents of the metal layer 8 and the third antenna in the vicinity of the second slot F2.

[0178] As already mentioned, the second antenna part ANT2b also collects in its turns a current I2b which is directly induced by the incident magnetic field FL1 captured at the recess 14 area by the second antenna part ANT2c. In this example, the magnetic field FL1 is directed from the upper face of the chip CD1 to its lower face. Therefore, the current component I2b induced in the second antenna part ANT2b also flows counterclockwise and thus adds to the image current I2a. Since the two current components I2a and I2b flow in the same direction (in-phase components) in the second antenna ANT2, they combine to contribute to the generation of the overall induced current IA2 flowing in the second antenna ANT2.

[0179] The overall current I2A flowing in the second antenna part ANT2b in turn induces a magnetic field causing magnetic coupling CL1 between the first RF antenna ANT1 and the second RF antenna part ANT2b, and therefore a fortiori between the first RF antenna ANT1 and the second RF antenna ANT2. The combined action The image current I2a carried from the first antenna part ANT2a on the one hand, and the current I2b induced by the magnetic field FL1 at the level of the recess area 14 in the third antenna part ANT2c on the other hand, makes it possible to maximize the amount of energy collected in the second RF antenna ANT2 from the magnetic field FL1, and thus to guarantee a high-performance magnetic coupling CL1 between the two RF antennas ANT1, ANT2, which makes it possible to deliver a maximum of energy to the RF chip 4 connected to the first RF antenna ANT1.

[0180] The second antenna part ANT2b thus contributes to amplifying energy harvesting because it also includes an electric current component directly induced by the incident magnetic field of the NFC reader. The fact that the current flows in the same direction in both parts of the ANT2 antenna increases the energy transfer (harvested both by eddy currents on the surface of the metallic layer 8 combined with that harvested directly induced by the incident magnetic flux through the cavity area 14) by coupling to the first antenna ANT1 and therefore to the RF chip 4.

[0181] In an absolutely equivalent manner, the second part ANT3b of the third antenna ANT3 also contributes to amplifying energy harvesting because it also includes, in the same way, an electric current component directly induced by the incident magnetic field of the NFC reader. The fact that the current flows in the same direction in both parts of the ANT3 antenna increases the energy transfer (harvested both by the internal eddy currents IMI on the surface of the metallic layer 8 combined with that harvested directly induced by the incident magnetic flux through the cavity area 14) by coupling to the first antenna ANT1 and thus to the RF chip 4.

[0182] Returning to [Fig.8A] for example, when the CD1 card is off-center with respect to the NFC reader, the dominant loop B1 of the IMI eddy currents circulates in the second region R2 clockwise in a closed loop along the edges 8b, 8c, 8d of the metallic layer 8, this loop passing through the metallic layer from edge 8d to edge 8b along a path which maximizes the area of ​​this loop in direct line of sight with the magnetic field of maximum intensity.

[0183] As shown with reference to [Fig. 10], the first part ANT3a of the third antenna ANT3 is arranged so that at least one of its turns overlaps the slot F2 in the second region F2, preferably in a privileged area ZC of exploitability of the eddy currents ZC.

[0184] The ANT3a antenna is thus able to capture an image current induced by a current flowing in the dominant loop B1 of the eddy current induced by the magnetic field when the card is off-center, the dominant loop B1 being deflected by the slot F2, opposite at least one turn of the ANT3a part.

[0185] In operation, under the effect of the magnetic field FL1 to which the smart card CD1 is subjected, the RF chip 4 is thus able to use the second RF antenna ANT2 and / or the third antenna ANT3, one, the other or both of these antennas ANT2, ANT3 being able to be coupled with the first RF antenna ANT1 to communicate with the external NFC reader (in particular to exchange RF signals in transmission and / or reception with the NFC reader) regardless of the position of the card relative to the NFC reader in determined operating conditions.

[0186] When a user presents the CD1 smart card in the vicinity of the NFC reader, contactless communication can thus be established between the NFC reader and the CD1 smart card, regardless of the position and orientation of the latter with respect to the NFC reader, the current induced by the dominant loops of the eddy currents being collected either by the second antenna ANT2, or by the third antenna ANT3 depending on whether the card is centered or offset with respect to the reader, within the limits of the operating conditions of the card.

[0187] As already indicated, various arrangements of the CD1 smart card can be envisaged, particularly with regard to the shape configuration, dimensions, position, etc. of the recess area 14 and the slots Fl and F2.

[0188] Figure 14 illustrates another smart card according to the invention. In this embodiment, the second slot F2 opens onto an edge opposite to the edge 8a into which the first slot FL opens.

[0189] As detailed previously, the CHR circle represents the contour delimiting the region / zone of maximum intensity of the NFC reader's magnetic field, in the plane of the card, where the field can be considered approximately uniform.

[0190] Fig. 14 illustrates a situation in which the NFC card is placed offset from the center of the CHR circle, so that the recess area 14, the second parts of antennas ANT2b and ANT3b are outside this region of maximum magnetic field.

[0191] The slot F2 opens onto an edge of the card and terminates with a closed part in the second region R2 of the metallic layer.

[0192] This slot F2 is thus arranged to deflect the dominant loops of the eddy current towards the eddy current exploitation zone ZC opposite which extends at least one turn of the first part ANT3a of the third antenna ANT.

[0193] In the embodiment described here, the depth of the slot F2 along the longitudinal dimension of the smart card is chosen to be at least equal to or close to the distance of the adjacent turns of the first part ANT3 of the ANT3 antenna from the edge of the metallic layer on which the slot F2 opens.

[0194] Furthermore, and as shown in the detail area of ​​[Fig. 14], the slot F2 It also allows the incident magnetic field from the reader to pass through the metallic layer 8 while remaining in phase with the electric current induced in the turns of the ANT3a antenna. As explained previously, the current in the third ANT3 antenna has the following components: (i) a first component corresponding to the image current captured by the third antenna ANT3a; and (ii) a second component created by magnetic induction through the opening of slot F2 in the portion of the antenna wires of the third antenna ANT3 that overlap slot F2.

[0195] Figure 15 schematically represents a method for manufacturing one of the CD1 smart cards described above, according to at least one particular embodiment. During a supply step S2, a card body 6 comprising a metallic layer 8 as previously described is formed (or supplied). In particular, this card body 6 is formed at least in part by a metallic layer 8, this metallic layer 8 comprising a recessed area 14.

[0196] The metallic layer 8 is considered to consist of a first region RI and a second region R2 entirely delimited by a straight line LIM parallel to a short side of the CD1 card, the first region RI entirely containing the recess area 14, its surface being smaller than that of the second region R2.

[0197] The metal layer has a first slot Fl which connects the recessed area to a peripheral edge 8a of the metal layer and a second slot F2 opening either onto a peripheral edge of the metal layer or into the recessed area 14, the second slot F2 ending with a closed part the second region R2.

[0198] During a formation step S4, a first RF antenna ANT1 is formed (or assembled) on or in the card body 6 in or opposite the recess area 14 of the metal layer 8, as already described.

[0199] During an S6 assembly step, an RF chip 4 is assembled with the card body 6 so that the RF chip 4 is electrically connected to the first RF antenna, as previously described.

[0200] In one embodiment, an insulating layer (solder mask) is formed to isolate the first antenna ANT1 from the second and third antennas ANT2 and ANT3 formed during steps S8 and S10. During a formation step S8, a second RF antenna ANT2 is formed (or assembled) on or in the board body 6 such that the second RF antenna ANT2 is electrically isolated from the metal layer 8 and the first RF antenna ANT1, as already described. In particular, the formation step S8 is carried out such that the second RF antenna is intended to allow coupling with the first antenna, the second antenna having at minus one turn located opposite the first slot Fl. The second antenna ANT2 is for example formed in an insulating sheath to isolate it from the third antenna ANT3 formed in step S10.

[0201] During a formation step S10, a third RF antenna ANT3 is formed (or assembled) on or in the board body 6 such that the third RF antenna ANT2 is electrically isolated from the metal layer 8, the first RF antenna ANT1, and the second RF antenna ANT2, as already described. The third antenna ANT3 is, for example, formed in an insulating sheath to isolate it from the second antenna ANT2.

[0202] In particular, the S10 formation step is carried out so that the third RF antenna is intended to allow coupling with the first antenna, the third antenna having at least one turn located opposite the second slot F2.

[0203] A person skilled in the art will understand that the embodiments and variants described above are merely non-limiting examples of implementation of the invention. In particular, a person skilled in the art may consider any adaptation or combination of the embodiments and variants described above in order to meet a very specific need in accordance with the claims set forth below.

[0204] In one embodiment, the metallic layer 8 is at least partially covered by a coating that is more conductive than the metallic layer. Preferably, it is entirely covered by this conductive coating, but when a coating is used, it is at least present in the circulation zone of the main eddy current loops.

[0205] The coating has, for example, a conductivity greater than 3.5 x 0.7 S / m. It can, for example, be made of copper, silver or gold.

Claims

1. Demands Smart card including: - a rectangular card body formed at least in part by a metallic layer (8) comprising a recessed area; - an RF chip; - a first RF antenna positioned in or opposite the recess area and electrically connected to the RF chip; said metallic layer being constituted by a first region and a second region delimited by a straight line (LIM) parallel to a short side of the card, the first region containing the recess area (14), - a first slot (Fl) connecting the recess area to a peripheral edge of the first region (RI); - a second slot (F2) opening either onto a peripheral edge of the metallic layer (8) or into the recessed area, the second slot terminating in a closed portion in the second region; and - a third RF antenna (ANT3) electrically isolated from the metallic layer, the first RF antenna, and the second RF antenna and configured to allow coupling with the first antenna, the third antenna (ANT3) having at least one turn located opposite said second slot (F2), the smart card being characterized in that: It includes a second RF antenna (ANT2) electrically isolated from the metallic layer and the first RF antenna and configured to allow coupling with the first antenna, the second antenna comprising: - at least one turn located opposite the first slot (Fl), - a first antenna part (ANT2a) extending opposite a peripheral area of ​​the metallic layer (8), at least one turn of said first antenna part (ANT2a) extending opposite the first slot (Fl); - a second antenna part (ANT2b), electrically connected to the first antenna part (ANT2a), and extending opposite the recessed area (14) to allow coupling with the first antenna (ANT1); the first antenna part (AT2a) is configured to collect an image current (I2a) induced by first eddy currents (a) flowing on an edge in the metallic layer (8) when the board at chip is subjected to an electromagnetic field under smart card operating conditions (CD1); the third RF antenna (ANT3) comprises: - a first antenna part (ANT3a) arranged at least in part opposite the second region (R2) of the metallic layer (8), at least one turn of said first antenna part (ANT3a) extending opposite the second slot (F2), - a second antenna part (ANT3b), electrically connected to the first antenna part (ANT3a), and extending opposite the recess area (14) to allow coupling with the first antenna (ANT1);(ii) the first part of the third antenna (ANT3a) being configured to collect an image current (I2a) induced by eddy currents (a) flowing in the second region (R2) of the metallic layer (8) when the smart card is subjected to an electromagnetic field under so-called adverse operating conditions corresponding to only a part of said operating conditions, - a routing of the second and third antennas being configured so that the current flow flows in the same direction in: - the first part of the second antenna; - the second part of the second antenna; - the first part of the third antenna; and in - the second part of the third antenna.;

2. Smart card according to claim 1, wherein the second adverse operating conditions are conditions in which the card is off-center with respect to an antenna of a device generating said electromagnetic field.

3. Smart card according to any one of claims 1 to 2, wherein said second region (R2) comprises a privileged area (ZC) for eddy current exploitation, said second antenna (ANT2) being located opposite the second slot (F2) at the level of said privileged area (ZC).

4. Smart card according to claim 3, characterized in that said privileged zone (ZC) for eddy current operation is a zone on the surface of the card which is subjected to a uniform magnetic field of maximum intensity regardless of the operating conditions of the card.

5. Smart card according to claims 3 or 4, characterized in that said privileged zone (CZ) for eddy current exploitation is a disk centered on said card and whose radius corresponds to the radius of an operational volume of said card.

6. Smart card according to any one of claims 5, characterized in that the smart card is in accordance with the EMVCo standard, said privileged area (ZC) for eddy current operation being a disk with a radius of 25 mm centered on said card.

7. Smart card according to any one of claims 1 to 6 characterized in that the metallic layer (8) is at least partially covered by a coating (70) more conductive than the metallic layer.

8. Smart card according to claim 7 characterized in that the metallic layer (8) is entirely covered by said coating.

9. Smart card according to claim 7 or 8, characterized in that the thickness of the coating is greater than the skin thickness of said coating.

10. Smart card according to any one of claims 7 to 9, characterized in that the conductivity of said coating (70) is greater than 3.5x07S / m.

11. Smart card according to any one of claims 7 to 10, characterized in that said coating (70) is made of copper, silver, or

12. or. Method of manufacturing a smart card (CD1) of generally rectangular shape from a card body (6) formed at least in part by a metallic layer (8), said metallic layer comprising a recessed area (14), said metallic layer (8) being constituted by a first region (RI) and a second region (R2) entirely delimited by a straight line (LIM) parallel to a short side of the card (CD1), the first region (RI) entirely containing the recessed area (14) and its surface being smaller than that of the second region (R2), a first slot (F1) of the metallic layer connecting the recessed area (14) to a peripheral edge (8a) of the first region (RI) and a second slot (F2) of the metallic layer opening either onto a peripheral edge of the metallic layer (8) or into the recessed area (14), the second slot (F2) terminating with a closed portion in the second region (R2),The process includes: - forming a first RF antenna on or within the circuit board body, (ATI) in or opposite the recessed area of ​​the metallic layer; - Assembling an RF chip (4) with the card body such that the RF chip (4) is electrically connected to the first RF antenna; - Forming on or within the card body a third RF antenna (ANT3) such that the third RF antenna is electrically isolated from the metal layer, the first RF antenna, and the second RF antenna, the third antenna being configured to allow coupling with the first antenna, the third antenna having at least one turn located opposite the second slot, the method being characterized in that it comprises a step of - Formation on or within the board body of a second RF antenna (AT2) such that the second RF antenna is electrically isolated from the metal layer and the first RF antenna, the second antenna being configured to allow coupling with the first antenna, the second antenna comprising: - at least one turn located opposite the first slot; and - a first antenna part (ANT2a) extending opposite a peripheral area of ​​the metallic layer (8), at least one turn of said first antenna part (ANT2a) extending opposite the first slot (Fl); - a second antenna part (ANT2b), electrically connected to the first antenna part (ANT2a), and extending opposite the recessed area (14) to allow coupling with the first antenna (ANT1); the first antenna part (AT2a) being configured to collect an image current (I2a) induced by first eddy currents (a) flowing on an edge in the metallic layer (8) when the smart card is subjected to an electromagnetic field under smart card operating conditions (CD1); the third RF antenna (ANT3) comprising: - a first antenna part (ANT3a) arranged at least partly opposite the second region (R2) of the metallic layer (8), at least one turn of said first antenna part (ANT3a) extending opposite the second slot (F2), - a second antenna section (ANT3b), electrically connected to the first antenna section (ANT3a), and extending opposite the recessed area (14) to allow coupling with the first antenna (ANT1); (ii) the first part of the third antenna (ANT3a) being configured to collect an image current (I2a) induced by eddy currents (a) flowing in the second region (R2) of the metallic layer (8) when the smart card is subjected to an electromagnetic field under so-called adverse operating conditions corresponding to only a part of said operating conditions, - a routing of the second and third antennas being configured so that the current flow flows in the same direction in: - the first part of the second antenna; - the second part of the second antenna; - the first part of the third antenna; and in - the second part of the third antenna.

Images