Smart card with radio frequency antennas

Abstract

Smart card with radio frequency antennas. The invention relates to a smart card (CD1, CD2) comprising a card body (6) including a metallic layer (8) at least partially covered by a coating (70) more conductive than the metallic layer, an RF chip (4), a first RF antenna (ANT1) disposed in a recessed area (14) and connected to the chip. The metallic layer includes at least one RF antenna portion (ANT2, ANT2) electrically isolated from the metallic layer and the first RF antenna and configured to collect an image current (I2a) induced by first eddy currents (I1a) circulating at least on the coating (70) of the metallic layer and to allow coupling with the first antenna. Fig. 9.

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 NFC reader by means of external contacts accessible on the surface of the card. An external NFC 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 printing they can provide (the considerable weight of the metal, high-end aesthetics), and the prestigious connotation associated with them for their users. This is due in particular to their significant weight and the printing Because of the high quality they convey, these cards are preferred by some users 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] 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

[0009] To this end, 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, the metallic layer being at least partially covered by a coating more conductive than the metallic layer; - 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; - at least one RF antenna portion electrically isolated from the metallic layer and the first RF antenna and configured to collect an image current induced by first eddy currents flowing over the coating and enable coupling with the first antenna.

[0010] Said at least one part of RF antenna is thus arranged to collect an image current induced by first eddy currents and circulating on the coating of the metallic layer.

[0011] A person skilled in the art will understand that since the conductive coating is never perfect, said at least part of the antenna also collects the image current induced by eddy currents circulating in the thickness of this coating, or even in the metallic layer itself if the thickness of the coating is less than its skin effect.

[0012] In one embodiment, the thickness of the coating is greater than the skin thickness, at the frequency of use, of said coating.

[0013] The skin thickness 'ô' is given approximately by the formula: 1

[0014] being the frequency of the signal in Hz, 'q' the permeability of said coating, 'o' the electrical conductivity of the coating in S / m and ô is in meters.

[0015] In one embodiment, the metallic layer is entirely covered with said coating.

[0016] This embodiment is the simplest to implement, but a person skilled in the art will understand that it is not absolutely necessary, the conductive coating having to be present at least in the areas of the map corresponding to the areas of circulation of the dominant eddy currents.

[0017] Consequently, said at least one antenna part may also collect an image current induced by eddy currents flowing over parts of the metallic layer not covered by the coating.

[0018] In one embodiment, the conductivity of said coating is greater than 3.5x07S / m.

[0019] In one embodiment, the coating is made of copper, silver or gold.

[0020] In one embodiment, the eddy currents are produced under the effect of a magnetic field to which the smart card is subjected.

[0021] In one embodiment, said at least one RF antenna part is electrically isolated from the metal layer and the first RF antenna by an insulating layer interposed between said at least one RF antenna part on the one hand, and the metal layer and the recessed area on the other hand.

[0022] According to one embodiment, the smart card further comprises an electronic module including the RF chip, said electronic module being provided in or opposite the recessed area.

[0023] According to one embodiment, magnetic coupling enables the RF chip to establish contactless communication with the outside of the smart card by using said at least one RF antenna portion coupled to the first RF antenna.

[0024] According to one embodiment, the first and second antenna parts of the second RF antenna are connected in parallel with a capacitive component.

[0025] According to one embodiment, the first RF antenna is arranged opposite the recessed area so that the recessed area is intercalated between the first and second RF antennas to allow said magnetic coupling between said first and second antennas.

[0026] In a first embodiment, the recessed area opens onto a peripheral edge of the metallic layer, said at least one antenna part being a second antenna comprising: (i) a first antenna portion extending opposite a portion of the metallic layer covered by said coating to collect said image current; and (ii) a second antenna part, electrically connected to the first antenna part, and extending opposite the recessed area to permit said magnetic coupling.

[0027] This first embodiment of 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 terminal, regardless of the orientation of the card with respect to the external terminal.

[0028] When the smart card is subjected to a magnetic field, the combined action of the image current carried from the first antenna part on the one hand, and of a current induced in the second antenna part by the magnetic field at the level of the recess area on the other hand, makes it possible to maximize the amount of energy collected in the second RF antenna from the magnetic field, and thus to guarantee efficient magnetic coupling between the two RF antennas, which makes it possible to deliver a maximum of energy to the RF chip connected to the first RF antenna.

[0029] In 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 RF antenna coupled with the first RF antenna to communicate with an external terminal (in particular to exchange RF signals in transmission and / or reception with the terminal). When a user presents the smart card near the terminal, contactless communication can thus be established between the terminal and the smart card, regardless of the latter's orientation relative to the terminal. Indeed, eddy currents are generated on the coating of the metallic layer regardless of the smart card's orientation relative to the terminal. Similarly, regardless of which side of the smart card is presented to the terminal, the second antenna element is able to collect a current component induced by the magnetic field at the recessed area.

[0030] In one embodiment, the second RF antenna is configured so that the first antenna part extends in relation to a peripheral area of ​​the metallic layer covered by the coating.

[0031] In one embodiment, the metal layer includes a slot connecting the recessed area to the peripheral edge of the metal layer (corresponds to rev 4 of the first file).

[0032] According to one embodiment, the recessed area extends to the peripheral edge of the metallic layer.

[0033] According to one embodiment, the second RF antenna is configured so that the second antenna part extends exclusively in relation to the recess area.

[0034] The inventors detected that prior art metallic smart cards encountered a problem, particularly when the card is moved in the plane off-center from the NFC reader. This is very common in the RFID HF NFC environment, for example during a payment when the user approaches their card off-center from the point-of-sale reader.

[0035] Figure 23 illustrates, for example, an operational volume in the whole of which the The card must be operational to comply with a standard defined by the international organization EMVCO. Those skilled in the art can refer to the document "EMV Contactless Specifications for Payment Systems, Book D: EMV Contactless Communication Protocol Specification. Version 2.6, March 2016." One of EMVCo's objectives is to ensure the interoperability and compatibility of smart cards and card readers under specific operating conditions.

[0036] This operational volume is defined by dimensions SI, S2, Dl, D2 recalled on the [Fig.23].

[0037] 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.

[0038] 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.

[0039] To further improve the operation of the smart card according to the invention, in a second embodiment of the invention, said metallic layer is 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 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 section in the second region; and - said at least one part of the antenna is a second antenna comprising at least one turn opposite the first slot and at least one turn opposite the second slot.

[0040] 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.

[0041] 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.

[0042] Preferably, the first slot opens onto a small side of the smart card, as close as possible to the recessed area.

[0043] 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.

[0044] 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 these slots.

[0045] This configuration also allows each of the turns of the second antenna mentioned above to collect an image current induced by a current flowing on the metallic layer locally at the slots due to the magnetic flux generated by the smart card reader.

[0046] When the metallic layer is not entirely covered with coating, the latter must at least be present in the areas of circulation of the dominant currents, and in particular along the peripheral edges of the card and along the two slots.

[0047] As detailed below, due to the continuity of the eddy currents, the two currents collected by these antenna turns, namely that induced directly by the electromagnetic field passing through a slit and that image of a local eddy current circulating on the metallic layer, accumulate.

[0048] This configuration allows efficient coupling between the two antennas, regardless of the operating conditions of the card.

[0049] In one mode of this second embodiment, the second RF antenna comprises: - a first antenna section extending opposite a peripheral area of ​​the metallic layer covered by said coating, with at least one turn of said first antenna section extending opposite the first slot, - a second antenna part connected to the first antenna part and arranged at least partly opposite a part of the second region of the metallic layer covered by said coating, at least one turn of said second antenna part extending opposite the second slot (F2), - a third antenna part, electrically connected to the second antenna part, and extending opposite the recessed area to allow coupling with the first antenna; (i) the first antenna part 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; (ii) the second antenna part being configured to collect an image current induced by eddy currents circulating in the second region of the layer metallic 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.

[0050] In particular, when the hollow area (or cavity) is relatively far from the field of maximum intensity, the operating conditions may be unfavorable.

[0051] The first antenna part is arranged opposite a peripheral area of ​​the metallic layer covered by said coating, 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.

[0052] 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.

[0053] 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.

[0054] The second part of the second antenna makes it possible to efficiently recover the energy of the eddy currents circulating the coating of the smart card when the smart card is used in less favorable conditions, the card being off-center with respect to the antenna of the card reader.

[0055] 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.

[0056] In one embodiment, the second region comprises a privileged area for exploiting eddy currents, this privileged area being entirely covered by said coating, the part of the loop of the second antenna being located opposite the second slot at the level of this privileged area.

[0057] 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.

[0058] This embodiment ensures that, regardless of the operating conditions of the smart card, the second metal layer slot is located itself in this operational zone and that a main loop of the eddy current flows on the edge of this slit.

[0059] 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.

[0060] When the smart card is subjected to a magnetic field, the combined action of the image current routed from the first part and / or the second part of the second antenna on the one hand, and of a current induced in the second part and / or the third part of the second antenna by the magnetic field received through the metallic layer on the other hand, makes it possible to maximize the amount of energy collected in the second RF antenna from the magnetic field, and thus to ensure efficient magnetic coupling between the two RF antennas, which makes it possible to deliver a maximum of energy to the RF chip connected to the first RF antenna.

[0061] 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 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 third antenna part of the second antenna is capable of collecting a current component induced by the magnetic field at the recessed area.

[0062] According to a particular embodiment, the second RF antenna is configured so that the third antenna part extends exclusively in relation to the recess area.

[0063] According to a particular embodiment, the first and third antenna parts of the second RF antenna are connected in parallel with a capacitive component.

[0064] The invention also relates to a method for manufacturing a smart card from a card body formed at least in part by a metallic layer comprising a recessed area, the method comprising: - cover at least partially, preferably entirely, the metallic layer with a coating that is more conductive than the metallic layer; - 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 at least one part of an RF antenna electrically isolated from the metal layer and the first RF antenna and configured to collect an image current induced by first eddy currents flowing at least on the coating of the metal layer and allow coupling with the first antenna.

[0065] In one embodiment, the recessed area opens onto a peripheral edge of the metallic layer, said at least one antenna part being a second RF antenna comprising: (i) a first antenna portion extending opposite the metallic layer to collect an image current induced by first eddy currents circulating at least on the coating of the metallic layer; and (ii) a second antenna part, electrically connected to the first antenna part and extending opposite the recess area to allow magnetic coupling between the first RF antenna and the second RF antenna.

[0066] In another embodiment of the manufacturing process, the card body is generally rectangular in shape, the metal layer consists 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 recess area and its surface being smaller than that of the second region, a first slot in the metal layer connecting the recess area to a peripheral edge of the first region and a second slot in the metal layer opening either onto a peripheral edge of the metal layer or into the recess area, the second slot ending with a closed part in the second region, - said at least one antenna part being a second antenna comprising at least one turn located opposite the first slot and at least one turn located opposite the second slot. Brief description of the drawings

[0067] 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:

[0068] [Fig.1] Fig.1 schematically represents a smart card cooperating with a terminal, according to at least one embodiment of a first variant of the invention;

[0069] [Fig.2] The [Fig.2] is a top (or bottom) view of a metallic layer constituting part of a smart card according to at least one particular embodiment of this first variant of embodiment;

[0070] [Fig.3] The [Fig.3] is a top (or bottom) view of a metallic layer constituting part of a smart card according to at least one particular embodiment of this first variant of embodiment;

[0071] [Fig.4A] The [Fig.4A] is an exploded cross-sectional view schematically representing the structure of a smart card according to at least one embodiment of this first variant of embodiment;

[0072] [Fig.4B] The [Fig.4B] is an exploded cross-sectional view schematically representing the structure of a smart card according to at least one embodiment of this first variant of embodiment;

[0073] [Fig.5] The [Fig.5] is a detailed cross-sectional view of a smart card, and more particularly of a portion of the card comprising a recessed area, according to at least one particular embodiment of this first variant of the embodiment;

[0074] [Fig.6] The [Fig.6] is a bottom view schematically representing a smart card according to at least one particular embodiment of this first variant of embodiment;

[0075] [Fig.7] The [Fig.7] is a bottom view schematically representing the operation of a smart card according to at least one particular embodiment of this first variant of embodiment;

[0076] [Fig.8] The [Fig.8] is a bottom view schematically representing the operation of a smart card according to at least one particular embodiment of this first variant of embodiment;

[0077] [Fig.9] Fig.9 represents in the form of a diagram the steps of a manufacturing process for a smart card of the invention, according to at least one particular embodiment of this first variant of the embodiment.

[0078] [Fig. 10] The [Fig. 10] schematically represents a smart card cooperating with an NFC reader, according to at least one particular embodiment of a second variant of the invention;

[0079] [Fig. 11] The [Fig. 11] is a top (or bottom) view of a metallic layer of a smart card according to at least one particular embodiment of the invention;

[0080] [Fig.12A] The [Fig.12A] is an exploded cross-sectional view schematically representing the structure of a smart card according to at least one particular embodiment of the invention;

[0081] [Fig.l2B] The [Fig.l2B] is an exploded cross-sectional view schematically representing the structure of a smart card according to at least one particular embodiment of the invention;

[0082] [Fig. 13] The [Fig. 13] is a detailed cross-sectional view of a portion of a smart card, according to at least one particular embodiment of the invention;

[0083] [Fig. 14] The [Fig. 14] illustrates an exploitable zone of eddy currents on a metallic layer;

[0084] [Fig. 15] The [Fig. 15] represents a smart card centered with respect to the source of an incident magnetic field;

[0085] [Fig. 16] The [Fig. 16] represents a smart card decentred with respect to the source of an incident magnetic field;

[0086] [Fig.17A] The [Fig.17A] represents a first example of a metallic layer that can be used in particular modes of implementation of the invention;

[0087] [Fig.17B] The [Fig.17B] represents a second example of a metallic layer that can be used in particular embodiments of the invention;

[0088] [Fig.17C] The [Fig.17C] represents a third example of a metallic layer that can be used in particular embodiments of the invention;

[0089] [Fig.17D] Fig.17D represents a fourth example of a metallic layer that can be used in particular embodiments of the invention;

[0090] [Fig. 18] The [Fig. 18] 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;

[0091] [Fig. 19] The [Fig. 19] represents a smart card conforming to a particular mode of the invention;

[0092] [Fig.20] The [Fig.20] illustrates the operation of the smart card of the [Fig. 10];

[0093] [Fig. 21] Fig. 21 represents another smart card conforming to a particular mode of the invention;

[0094] [Fig. 22] Figure 22 represents, in diagram form, the steps of a process manufacturing a smart card of the invention, according to at least one particular embodiment; and

[0095] [Fig.23] The [Fig.23] already described represents operational conditions of a smart card defined by the international organization EMVCo. Description of the implementation methods

[0096] The present application claims priority from French patent applications No. FR2113850 filed on 17 / 12 / 2021 and FR2214390 filed on 23 / 12 / 2022.

[0097] 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.

[0098] As previously mentioned, a contactless smart card is inherently configured to communicate wirelessly with the outside world, more specifically 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 then 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.

[0099] 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.

[0100] However, when a contactless smart card has a metallic layer and an RF antenna located 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 world, particularly when the metallic layer is located between the RF antenna and the external NFC reader with which the smart card attempts to communicate, due to the electromagnetic shielding induced by the metallic layer. Thus, depending on the position and orientation of the card relative to the reader, it may or may not be possible to complete a contactless transaction between a metallic smart card and an external NFC reader.In some cases, a transaction is possible if the smart card is presented with the antenna facing the NFC reader (without the metallic layer interposed between them). However, 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). For RF communication to occur between a metallic smart card and an external NFC reader, the card generally needs to contain ferrite to mitigate electromagnetic interference from the metallic portion. Without ferrite, even with the metallic smart card correctly oriented relative to an external NFC reader, proper RF communication between the card and the reader is generally not possible. the NFC reader, thereby making any transaction impossible (or at least difficult).

[0101] 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 card body formed at least in part by a metallic layer including a recessed area, the metallic layer being at least partially covered by a coating more conductive than the metallic layer, an RF chip, a first RF antenna disposed in or opposite the recessed area and electrically connected to the RF chip, at least one RF antenna portion electrically isolated from the metallic layer and from the first RF antenna and configured to collect an image current induced by first eddy currents circulating at least on the coating in the metallic layer and to allow coupling with the first antenna.

[0102] 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.

[0103] 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.

[0104] 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, for example, to ISO 14443-2, ISO 10373-6, "EMV Contactless Certification"). In general, the smart card of the invention can be configured to perform any type of transaction, such as banking transactions (payment, transfer, debit transactions, etc.), authentication transactions, and so on.

[0105] Unless otherwise indicated, elements common or similar to several figures bear the same reference numerals and have identical characteristics or analogous, so that these common or analogous elements are generally not described again for the sake of simplicity.

[0106] 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.

[0107] Particular embodiments of a CD1 smart card conforming to a first variant of the invention are now described with reference to Figures 1-6.

[0108] As shown in [Fig. 1] according to certain particular embodiments, the metallic smart card CD1 is configured to communicate in contactless mode with the outside world, for example with an external terminal (or reader) T1. To this end, the smart card CD1 comprises an RF chip 4, a card body 6, and two RF antennas (or at least two RF antennas), namely a first RF antenna ANT1 and a second RF antenna ANT2. The RF chip 4 and the two RF antennas ANT1 and ANT2 are positioned on or within the card body 6.

[0109] 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.

[0110] The metallic layer 8 is covered at least partially with a coating 70 that is more conductive than the layer 8, for example copper, silver or gold.

[0111] In the examples considered here, the card body 6 is in the ID1 format of a credit card, although other forms are possible to implement the invention.

[0112] The RF chip 4 is an electronic chip configured to establish contactless communication Cl with the external terminal Tl using the RF antennas ANT1 and ANT2, as described below. To achieve this, the RF chip 4 is electronically connected to the first RF antenna ANT1, but the second RF antenna ANT2 is electrically isolated from the RF chip 4 and the first RF antenna ANT1. The antennas ANT1 and ANT2 are partially facing each other to allow magnetic coupling between these two antennas and thus enable the RF chip 4 to use the second RF antenna ANT2 to establish contactless communication Cl with the external terminal Tl, as described in more detail below.

[0113] Various implementations of the CD1 smart card, including the metal layer 8, the coating 70 and the RF antennas ANT1 and ANT2, are possible, as shown in Figures 2-8.

[0114] By way of illustration, Figures 2 and 3 show only the metallic layer 8 according to two different embodiments. In both examples, the metallic layer 8 is entirely covered by the coating 70 and includes a recessed area 14 opening onto a peripheral edge (or contour) 8a of the metallic layer 8. The recessed area 14 is a through-opening (or zone) formed in the metallic 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 recessed area 14 can be adapted as appropriate. By way of example, the recessed area 14 formed in the metallic layer 8 is rectangular.

[0115] More specifically, in the example shown in [Fig. 2], the metallic layer 8 includes a connecting opening (or zone) 20 that connects the peripheral edge 8a with the recessed zone 14. This connecting opening 20 itself constitutes a peripheral recessed zone that can, for example, take the form of a slot. In other words, the recessed zone 14 emerges (or opens) onto the peripheral edge 8a via this connecting opening 20. This connecting zone 20 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 as the case may be.

[0116] Thus, according to the example shown in [Fig. 3], the distance dl of the joining zone 20 separating two opposite peripheral edges of the metal layer 8 is identical to the height (or length) of the recess zone 14 itself. The joining zone 20 thus forms in the metal layer 8 a second recess zone which extends in line with the first recess zone 14. The recess zone 14 thus forms with the joining zone 20 a notch in the metal layer 8. In other words, the recess zone 14 extends in this example to the peripheral edge 8a of the metal layer 8 (without the formation of a slot or anything else being necessary).

[0117] The position of the recessed area 14 in the metal layer 8 can vary depending on the specific case. According to the particular examples shown in Figures 2-3, the recessed area 14 is positioned in the vicinity of a peripheral edge 8a of the metal layer 8, which ensures efficient magnetic coupling FL1 between the RF antennas ANT1 and ANT2, as explained in more detail below. Other implementations are, however, possible, in which, for example, the recessed area 14 is positioned at the center (or substantially at the center) of the metal 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 metal layer 8 via a connecting area 20.

[0118] The advantage of forming such a recessed area 14 in the metallic layer 8 will become clearer in the following description. We now consider particular embodiments with reference to Figures 4A-7 in which the metallic layer 8 includes a recessed area 14 according to the configuration illustrated in [Fig. 2].

[0119] In particular, figures 4A and 4B schematically represent an exploded cross-sectional view of the CD1 smart card according to two embodiments, in which the coating is respectively only in the peripheral area of ​​the metallic layer or over its entire surface.

[0120] Fig. 5 schematically represents a detailed cross-sectional view of the CD1 smart card, according to at least one particular embodiment.

[0121] Figures 6 and 7 are schematic bottom views of the CD1 smart card viewed from its underside, i.e., from the viewpoint of an OBI observer shown in [Fig. 5], so as to allow visualization of the second antenna ANT2. To facilitate understanding of the figures, neither the first RF antenna ANT1 nor the electronic module 2 are shown in Figures 6-7.

[0122] Figure 7 illustrates more particularly the CD1 smart card in operation, as described later.

[0123] As shown in Figures 4A-7, 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.

[0124] According to one embodiment, the RF chip 4 (with or without the electronic module 2) is positioned on (or opposite) the metal layer 8. For this purpose, an insulating material can be disposed between the RF chip 4 and the metal layer to ensure electrical insulation.

[0125] According to the examples considered in Figures 4A-7, the electronic module 2 has external CTI contacts (or contact areas) on its upper surface configured to allow contact communication between the RF chip 4 and an external terminal provided for this purpose (for example, with terminal T1). More particularly, the electronic module 2 may include a printed circuit board (or PCB) having the contacts on its upper surface External CTI contacts and, on its underside, the RF chip 4. External CRI contacts are metallic areas designed to accommodate connection pins of an external terminal. These external CTI 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 CTI 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 terminal.

[0126] 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.

[0127] As already indicated with reference to [Fig.1], the CD1 smart card includes two RF antennas, denoted ANT1 and ANT2, which are positioned in or on the card body 8. Each of the RF antennas ANT1, ANT2 includes at least one electrically conductive turn so as to allow exchanges of RF signals between the CD1 smart card and the outside.

[0128] The RF antennas ANT1 and ANT2 can each be made, for example, of a track, wire, or electrically conductive member forming one or more conductive turns. In this case, the first and second RF antennas ANT1 and ANT2 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 and ANT2 can be adapted on a case-by-case basis, in particular to allow wireless communication at the desired frequencies (or frequency ranges).

[0129] More specifically, as shown in Figures 4A-7, the first RF antenna ANT1 comprises a plurality of electrically conductive turns—referred to as the “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 within the recess area. Alternatively, the first RF antenna ANT1 can be arranged not within the recess area 14 itself, but opposite (above) this recess area 14.

[0130] Furthermore, the second RF antenna ANT2 is electrically isolated from the metallic layer 8 and from the first RF antenna ANT1.

[0131] This insulation can be achieved in various ways. For example, if the second antenna ANT2 is produced by etching, an insulating layer (in English, a "solder mask") can be placed between the second antenna ANT2 and the metal layer 8 to prevent a short circuit and oxidation of the second antenna. According to another example, the second ANT2 antenna can be made of a conductive wire surrounded by an insulating plastic sheath.

[0132] Furthermore, the second RF antenna ANT2 comprises two antenna parts, namely a first antenna part AT2a and a second antenna part AT2b, which are electrically connected to each other. In this particular example, this second RF antenna AT2 is formed in the insulating layer 10 or optionally on the lower face 10b of the insulating layer 10.

[0133] More specifically, the first antenna part AT2a comprises a plurality of electrically conductive turns, called "second" conductive turns, which extend opposite (or in opposition to) a part of the metallic layer 8 covered with coating 70 to collect in particular an image current I2a induced by eddy currents II - hereafter called "first" eddy currents - circulating at least on this coating, possibly in its thickness, possibly in the metallic layer 8 if the skin effect of the coating 70 is less than its thickness.

[0134] In the embodiment of [Fig.4A], the coating 70 is present only on a peripheral edge of the metallic layer 8.

[0135] In the embodiment of [Fig.4B], the coating 70 covers the entire metallic layer 8.

[0136] As described below with reference to [Fig. 7], eddy currents are produced under the influence of a magnetic field FL1 to which the smart card is subjected. Such a magnetic field is generated in this example ([Fig. 1]) by an external terminal T1 with which the smart card CD1 cooperates in contactless mode. When the smart card CD1 is exposed to the magnetic field FL1, eddy currents flow in the form of current loops (primary and secondary loops) at least on the coating 70 of the metallic layer 8. The phenomenon of eddy current formation is known to those skilled in the art and will therefore not be described in detail in this document.

[0137] Various configurations of the first antenna portion AT2a are possible to accomplish the collection of the aforementioned image current I2a. As illustrated in Figures 6-7, in this example, the first antenna portion AT2a (and more precisely the second conducting turns that compose it) is considered to extend along a peripheral area of ​​the metal layer 8 (i.e., in the vicinity of the peripheral contour of the metal layer 8). This peripheral area encircles the recess 14 formed in the metal layer 8. This configuration aims to allow the first antenna portion AT2a to collect a maximum of energy in the form of the image current induced I2a by the dominant loops of the eddy currents generated on the surface of the coating 70 of the metal layer 8 under the effect of a magnetic field FL1 to which the chip CD1 is subjected. In other words, thanks to this particular configuration, the first eddy currents II (from which the image current 12 collected in the first part of the AT2a antenna is produced) correspond to dominant loops of eddy currents circulating at least on the coating of the metallic layer 8 in response to the magnetic field FL1. Other configurations of the second conductive turns of the first part of the AT2a antenna are, however, conceivable.

[0138] Thus, according to a particular example, the first antenna part AT2a interlocks (or encircles, or surrounds) the second part AT2b and the first RF antenna ANT1. Thus, in the case, for example, where the smart card CD1 has a classic bank card format (ID1 format), the first antenna part AT2a can be arranged along the peripheral contour of the metal layer 8 (preferably as close as possible to the physical edge of the metal layer 8), this peripheral contour being covered with the coating 70, while adopting this spatial interlocking configuration.The gap between the first antenna element AT2a and the peripheral edge of the metal layer 8 can be greater than or equal to a minimum gap that depends on the antenna technology used (for example, the minimum gap is set at approximately 500 µm if the first antenna element AT2a is manufactured using a PCB (Printed Card Board) technique, or at approximately 2 mm, or even approximately 3 mm, if the first antenna element AT2a is manufactured using a wire technology). The maximum gap between the first antenna element AT2a and the peripheral edge of the metal layer 8 can also be adjusted on a case-by-case basis, insofar as the first antenna element AT2a encircles the second element AT2b and the first RF antenna ANT1.

[0139] According to a particular example, the card body 6 is in the ID1 format of a credit card and the first antenna part AT2a comprises second conductive turns which are also substantially in IDL format

[0140] Furthermore, the second antenna portion AT2b comprises a plurality of electrically conductive turns, referred to as "third" conductive turns. The second antenna portion AT2b is electrically connected to the first antenna portion AT2a and extends opposite the recessed area 14 to allow for CL1 coupling ([Fig. 5]) by magnetic induction (magnetic coupling) between the first RF antenna ANT1 and the second RF antenna AT2.

[0141] Indeed, the metallic layer 8 extends into the card body 6 so as to form an electromagnetic shield (or electromagnetic barrier) between the two faces of the smart card DV1. Thus, the second antenna part AT2b is electromagnetically isolated by the metallic layer 8 from the upper face of the smart card CD1 and from the external environment in the vicinity of this upper face. This excludes the first RF antenna ANT1, which may, if applicable Being positioned within the recess 14, this recess 14 is devoid of electrically conductive material, which allows the second antenna element AT2b to couple electromagnetically with the first RF antenna ANT1 through said recess 14 ([Fig. 5]), without the metallic layer 8 being able to obstruct this coupling. This also allows direct energy coupling from the incident magnetic field of terminal T1 and the second antenna element AT2b, which generates a current component I2b as described below with reference in particular to Figures 7-8.

[0142] To establish effective magnetic coupling CL1, the second antenna section AT2b is preferably positioned opposite, at least partially, the first RF antenna ANT1. Generally, the second antenna section AT2b is at least aligned with, or opposite, the recess area 14 so that magnetic coupling CL1 can be established. However, a slight offset between the first turns of the first RF antenna ANT1 and the third turns of the second antenna section AT2b is acceptable, provided that the recess area 9 still allows for magnetic coupling CL1.

[0143] Once magnetic coupling CL1 is established between the RF antennas ANT1 and ANT2 under the influence of a magnetic field FL1 to which the smart card CD1 is subjected, the RF chip 4 can then use the second RF antenna ANT2, coupled to the first RF antenna ANT1, to communicate in contactless mode with the outside world, namely with the external terminal T1 in this example ([Fig. 1]). The operation of the smart card CD1 and in particular of its RF antennas is described in more detail later.

[0144] The RF chip 4 may include, for example, a microcontroller (or a processor) configured to establish contactless communication Cl with the outside of the smart card CD1 (with the external terminal Tl in this example) using the first and second RF antennas ANT1, ANT2 coupled together by magnetic induction.

[0145] In general, the first antenna part AT2a of the second RF antenna ANT2 occupies a larger area than the second antenna part AT2b since the latter is positioned opposite the recess area 14.

[0146] As already indicated, the RF chip 4 is disposed in the recess area 14 in the example shown in Figures 4A-7. According to one variant, the first RF antenna ANT1 is disposed outside the recess area 14, namely opposite the recess area 14 (in alignment above it), so that the recess area 14 is intercalated between the first and second RF antennas ANT1 and ANT2 to allow CL1 coupling by magnetic induction between said first and second antennas ANT1 and ANT2.

[0147] As shown in Figures 4A-5, the RF chip 4 is electrically connected to the first RF antenna ANT1. In the example considered here, the electrical connection Connection is ensured via connection pads (or pads) 16a and 16b on the electronic module 2, these pads being connected respectively to connection pads (or pads) 18a and 18b provided for this purpose in the recessed 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, possible.

[0148] Various configurations of the second RF antenna ANT2 are possible. According to a preferred embodiment, the second antenna part AT2b extends exclusively opposite the recessed area 14. In other words, this second antenna part AT2b, formed of a plurality of third conducting turns, is arranged opposite the recessed area 14 so that it does not extend opposite the metallic layer 8. In particular, the second antenna part AT2b does not overlap (or cover) the metallic layer 8 at the periphery of the recessed area 14, which optimizes the magnetic field flux to which the second antenna part AT2b and the first RF antenna ANT1 are subjected. Although it is not desirable for a portion of the second part of the AT2b antenna to extend in relation to the metallic layer 8, some tolerance may be accepted in certain cases.

[0149] As shown in Figures 1, 4, and 5, the RF chip 4 (and optionally the electronic module 2) can be aligned or centered with respect to the recess 4. Thus, in the examples considered, the conductive turns of the first RF antenna ANT1 extend as a winding around the RF chip 4 in the recess 14. This arrangement allows the RF chip 4 to be positioned as close as possible to the first RF antenna ANT1 and thus limits the manufacturing complexity of the smart card CD1. As already mentioned, however, other implementations are possible where the RF chip 4 is not positioned in, or even opposite, the recess 14.

[0150] 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.

[0151] As shown in [Fig. 6], the smart card CD1 may further include a capacitive component CPI electrically connected to the second RF antenna ANT2. In the examples considered here, the capacitive component CPI is disposed in the insulating layer 10 or on the lower face 10b of this insulating layer 10. Once magnetic coupling CL1 is established, the RF antennas ANT1 and ANT2 are connected in parallel with the capacitive component CPI. This capacitive component CPI thus forms, with the RF antennas ANT1 and ANT2, an RLC circuit for frequency matching. resonance of the second RF antenna ANT2 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 ISO14443 / ISO 10373, in particular the current version ISO / IEC 10373-6:2020 or any of the earlier versions, or any later version).

[0152] In the examples shown in Figures 6-7, the CPI capacitive component is of the interdigital type and comprises two opposing sets of intertwined conductive fingers, although other capacitor forms are possible (parallel-plate capacitor, discrete surface-mount capacitor, parallel-lead capacitor, etc.). It should be noted that the "interdigital" CPI capacitor (with intertwined conductive fingers arranged face to face) is schematically represented in Figures 6-7 (and in [Fig. 8] described below) and is not necessarily the most suitable implementation of the CPI capacitance in the CD1 smart card. For example, the CPI capacitance might be implemented as a parallel-plate capacitor on either side of the insulating layer 10 or as a discrete surface-mount capacitor.

[0153] As shown in Figures 6-7, for example, a first end 30a of the second antenna part AT2b is considered to be connected via a first connection CX1 to the capacitive component CPI, and a second end 30b of the second antenna part AT2b is connected via a second connection CX2 to a first end of the first antenna part AT2a. Furthermore, the capacitive component CPI is connected via a third connection CX3 to a second end of the first antenna part AT2a.

[0154] The RF chip 4 is thus configured to communicate in contactless mode using the second RF antenna ANT2 when the latter is magnetically coupled with the first RF antenna ANT1. In addition, the RF chip 4 can, if necessary, communicate in contact mode with the outside via the external CTI contacts, although variants without such external contacts are possible.

[0155] As shown in Figures 4-7, the card body 6 may further comprise at least one external insulating layer 12 formed on the underside 10b of the insulating layer 10 so as to cover and protect the second RF antenna ANT2. The first and second antenna parts AT2a and AT2b are thus interposed between the internal insulating layer 10 and the external insulating layer 12 in this particular example. At least one protective insulating layer may also be formed, if necessary, on the upper side of the card body.

[0156] The CD1 smart card as described previously with reference to Figures 1-2 and 4-6 is now described in operation with reference to [Fig. 7], according to at least one particular embodiment. It is always assumed here that the metallic layer 8 has a configuration as illustrated in [Fig.2] although variants are possible.

[0157] It is assumed that the smart card CD1 is positioned within range of (in the vicinity of) the external terminal Tl so as to be exposed to the magnetic field FL1 emanating from the terminal Tl. Under the effect of the magnetic field FL1 to which the smart card CD1 is subjected, eddy currents – generally denoted II – are generated in the metallic layer 8. These eddy currents II circulate as current loops on the surface of the metallic layer 8. According to a well-known physical phenomenon, dominant and secondary eddy current loops are thus generated on the surface of the metallic layer 8 in reaction to the magnetic field FL1.

[0158] As shown in [Fig. 7], lia denotes eddy currents – called first eddy currents – corresponding to dominant loops circulating on the surface of the coating 70 of the metallic layer 8 in the vicinity of the peripheral contour of said metallic layer 8. 11b denotes eddy currents – called second eddy currents – corresponding to secondary loops circulating on the surface of the coating 70 of the metallic layer 8 in the vicinity of the peripheral contour of the recessed zone 14. Since the eddy currents circulate in closed loops, the eddy currents 11b are in fact the continuation of the eddy currents lia in the vicinity of the peripheral contour of the recessed zone 14. As can be seen from [Fig. 7], lia denotes eddy currents – called first eddy currents – corresponding to dominant loops circulating on the surface of the coating 70 of the metallic layer 8 in the vicinity of the peripheral contour of the recessed zone 14.[7] The second eddy currents Ilb circulate, in the vicinity of the second antenna part AT2b, in a direction of rotation (or direction of circulation) opposite to that of the first eddy currents lia circulating on the coating 70 in the vicinity of the peripheral contour of the metallic layer 8. As an example, in this case, the first and second eddy currents lia, Ilb are considered to circulate in clockwise and counterclockwise directions respectively, although a reverse configuration is possible depending on the orientation of the magnetic field FL1 considered. The opposite-direction circulation of the eddy currents lia and Ilb results in particular from the continuity of the eddy currents mentioned above, as well as from the presence of the recessed area 14 which is connected in this example by the connecting slot 20 to the peripheral contour 8a of the metallic layer 8.

[0159] As explained in more detail below, the current 12 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 II flowing on the coating 70 of the metallic layer 8 in the vicinity of the first antenna part AT2a; and a current I2b which is induced directly in the second antenna part AT2b by the incident magnetic field FL1 through the recessed area 14 (12 = I2a + I2b). The very structure of the chip card CD1 is designed to conduct to this double contribution of the induced currents I2a and I2b to collect in the second RF antenna an overall induced current 12 as large as possible.

[0160] More specifically, the first antenna portion AT2a, extending opposite the coating 70 of the metallic layer 8, collects an image current I2a induced by the first eddy currents lia circulating on this coating under the influence of the magnetic field FL1 ([Fig. 7]). These first eddy currents lia correspond to dominant loops circulating on the surface of the metallic layer 8 in the vicinity of the turns of the first antenna portion AT2a. As already mentioned, the first antenna portion AT2a can preferably extend opposite a peripheral area (or band) of the metallic layer 8 covered by the coating 70 in order to collect a maximum of energy generated by the dominant loops of the eddy currents. The first eddy currents lia circulating in the vicinity of the first antenna portion ANTla (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 AT2a antenna is itself a reaction effect to the first eddy currents lia. .

[0161] Thus, the image current I2a induced by the first eddy currents lia is carried by electrical conduction to the second antenna section AT2b, due to the electrical continuity between the first and second antenna sections AT2a and AT2b, which are connected together. The image current I2a thus flows in the turns of the second antenna section AT2b positioned opposite the recessed area 14. As illustrated in [Fig. 7], the image current I2a flows in the same direction of rotation (or same direction of flow) in the turns of the first antenna section AT2a and in those of the second antenna section AT2b, namely counterclockwise in this example.However, due to the presence in the metallic layer 8 of the recess 14 connected via the connecting slot 20 to the peripheral edge 8a, the second eddy currents I1b (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 I2a circulating at the periphery of the metallic layer 8. For example, the second eddy currents I1b circulate here counterclockwise while the first eddy currents I1a circulate clockwise. Also, the second eddy currents I1b circulating at the periphery of the recess 4 contribute to amplifying the image current I1a circulating in the turns of the second antenna part AT2b.

[0162] As already indicated, the second antenna part AT2b further collects in its turns a current I2b which is induced directly by the incident magnetic field FL1 captured at the level of the recess area 14 by the second antenna part AT2b. In this example, the magnetic field FL1 is directed from the top of the chip CD1 to its bottom. Therefore, the current component I2b induced in the second antenna element AT2b also flows counterclockwise and thus adds to the image current I2a. Since both current components I2a and I2b flow in the same direction (in phase) in the second antenna ANT2, they combine to contribute to the overall induced current I2 flowing in the second antenna ANT2.

[0163] The overall current 12 flowing in the second antenna part AT2b in turn induces a magnetic field causing magnetic coupling CL1 between the first RF antenna ANT1 and the second RF antenna part AT2b, and therefore a fortiori between the first RF antenna ANT1 and the second RF antenna ANT2. The combined action of the image current I2a routed from the first antenna part AT2a on the one hand, and the current I2b induced by the magnetic field FL1 at the recess area 14 in the second antenna part AT2b on the other hand, maximizes the amount of energy collected in the second RF antenna ANT2 from the magnetic field FL1, and thus ensures efficient magnetic coupling CL1 between the two RF antennas ANT1 and ANT2, which allows maximum energy to be delivered to the RF chip 4 connected to the first RF antenna ANT1

[0164] 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 coupled with the first RF antenna ANT1 to communicate with the external terminal Tl (in particular to exchange RF signals in transmission and / or reception with the terminal Tl).When a user presents the smart card CD1 in the vicinity of the terminal Tl, a contactless communication can thus be established between the terminal Tl and the smart card CD1, regardless of the orientation of the latter with respect to the terminal TL. Indeed, the eddy currents II (and in particular the first eddy currents II) are generated in the metallic layer 8 regardless of the orientation of the smart card CD1 relative to the terminal TL. Similarly, regardless of which side of the smart card CD1 is presented in front of the terminal Tl, the second part of the antenna AT2b of the second antenna ANT2 is able to collect the current component I2b induced by the magnetic field FL1 at the level of the recess area 14.

[0165] As already indicated, various arrangements of the CD1 smart card can be envisaged, particularly with regard to the shape, dimensions, position, etc., configuration of the recessed area 14 and the connecting opening 20 connecting the recessed area 14 to the peripheral edge 8a of the metallic layer 8 (Figures 2-7). Thus, [Fig. 8] is a bottom view schematically representing the operation of a CD1 smart card according to at least one embodiment. In particular, when this card is subjected to a magnetic field FL1 emanating, for example, from an external terminal Tl ([Fig.1]). In the example of [Fig.8], the metal layer 8 is configured as illustrated in [Fig.3], such that the connection area 20 forms a second recess in the metal layer 8, extending from the first recess 14. The recess 14 thus forms, together with the connection area 20, a notch in the metal layer 8. In other words, the recess 14 extends in this example to the peripheral edge 8a of the metal layer 8 (without the formation of a slot or anything else being necessary).

[0166] The above description relating to the arrangement and operation of the CD1 smart card with reference to Figures 1-7 applies analogously to the CD1 smart card beyond [Fig.8].

[0167] Fig. 9 schematically represents a manufacturing process for one of the CD1 smart cards described above, according to at least one particular embodiment. The above description of the CD1 smart card according to various embodiments with reference to Figures 1-8 applies by analogy to the manufacturing process illustrated in [Fig.9].

[0168] During a supply step S2, a card body 6 comprising a metal layer 8 as previously described is formed (or supplied). In particular, this card body 6 is formed at least in part by a metal layer 8, this metal layer 8 comprising a recessed area 14 opening onto a peripheral edge 8a of the metal layer, as already described.

[0169] 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.

[0170] 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.

[0171] 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 comprises: - a first AT2a antenna section extending opposite the metallic layer to collect an image current I2a induced by initial eddy currents lia circulating in the metallic layer; and - a second AT2b antenna section, electrically connected to the first AT2a antenna section, and extending towards the area a recess to allow FL1 coupling by magnetic induction between the first RF antenna and the second RF antenna.

[0172] Figure 10 represents a CD2 smart card according to a second embodiment of the invention.

[0173] The CD2 smart card is generally rectangular in shape (with slightly rounded corners).

[0174] As shown in [Fig. 11], in this second embodiment, 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.

[0175] In the embodiment shown in [Fig.1 1], the line LIM is tangent to the recess area 14 on its side closest to the center of the smart card.

[0176] In the example shown in [Fig. 11], the metallic layer 8 includes a first slot Fl which connects or joins a peripheral edge 8a of the first region RI with the recess area 14.

[0177] We now consider particular embodiments in which the metallic layer 8 includes a recessed area 14 according to the configuration illustrated in [Fig.11].

[0178] In particular, Figures 12A and 12B schematically represent an exploded cross-sectional view of the CD2 smart card and [Fig. 13] schematically represents a detailed cross-sectional view of the CD2 smart card, according to at least one particular embodiment.

[0179] In the embodiment shown in Figures 12A, 12B and 13, the card body 6 includes at least one external insulating layer 12 provided on the underside 10b of the insulating layer 10 so as to cover and protect the second RF antenna ANT2.

[0180] As illustrated in [Fig. 18], and for ease of description, the second RF antenna ANT2 is considered to comprise at least three antenna parts, namely a first antenna part ANT2a, a second antenna part ANT2b, and a third antenna part ANT2c which are electrically connected to each other.

[0181] More specifically, the first and second antenna parts ANT2a and ANT2b comprise a plurality of electrically conductive turns, which extend opposite (or in opposition to) the metallic layer 8 covered with coating 70 to collect an image current induced by eddy currents II flowing in the metallic layer 8 when the latter is subjected to an incident magnetic field.

[0182] In the embodiment of [Fig. 12A], the coating 70 completely covers the metallic layer 8.

[0183] In the embodiment of [Fig. 12B], the coating 70 only covers the periphery of the metallic layer 8.

[0184] More specifically and as explained in detail below, the first antenna part ANT2a (respectively the second antenna part ANT2b) is arranged to efficiently collect the eddy currents flowing on the coating 70 of the metallic layer when the smart card CD2 is centered with respect to the NFC reader antenna (respectively in a position off-center with respect to the NFC reader antenna).

[0185] 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 uniform magnetic field of maximum intensity generated by the NFC reader antenna.

[0186] Various configurations of the second RF antenna ANT2 are possible. According to a preferred embodiment, the third antenna part ANT2c extends exclusively opposite the recessed area 14. In other words, this third antenna part ANT2c, formed of a plurality of conductive turns, is arranged opposite the recessed area 14 so that it does not extend opposite the metallic layer 8. In particular, the third antenna part ANT2c does not overlap (or cover) the metallic layer 8 at the periphery of the recessed area 14, which optimizes the magnetic field flux to which the third antenna part ANT2b and the first RF antenna ANT1 are subjected. Although it is not desirable for a portion of the third part of the ANT2c antenna to extend in relation to the metallic layer 8, some tolerance may be accepted in certain cases.

[0187] Fig. 14 illustrates in hatched form, for a particular embodiment of the invention, a privileged ZC zone for exploiting eddy currents that circulate on the coating 70 of the metallic layer 8 when the smart card is exposed to a magnetic field under determined conditions, this privileged ZC zone entirely covered by the coating 70 being included in the R2 region of the metallic layer 8.

[0188] 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.23].

[0189] Assuming that the reader has a circular antenna and 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 area of ​​this loop in direct line of sight with the magnetic field of maximum intensity.

[0190] In other words, as a first approximation, the dominant loop delimits the projection of this field onto the surface of the map.

[0191] In one embodiment of the invention, the privileged area ZC for eddy current exploitation can be an area of ​​the surface of the card which is subjected to a uniform magnetic field of maximum intensity regardless of the operating conditions of the card.

[0192] For example, in [Fig. 14] 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 consisting of a disk with center C and radius r of 2.5 cm.

[0193] 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.

[0194] In [Fig. 15], a CHR circle delimits a magnetic field of maximum intensity generated by an NFC reader. This figure assumes a perfectly circular and rotationally symmetrical NFC reader antenna.

[0195] In this figure the center C of the CD2 smart card is located at the center of the circle CHR.

[0196] In [Fig. 16], the smart card CD2 is shown, the center C of the smart card CP is offset by 25 mm from the center of the CHR circle; this 25 mm offset corresponds to the maximum offset of the card within the operational volume defined by EMVCo (point 6 of [Fig. 23]). In the embodiment of [Fig. 16], the coating 70 covers the entire metallic layer 8.

[0197] Figures 17A to 17D show, in four examples, a metallic layer 8 covered at least in the privileged zone ZC by the coating 70 and comprising: (i) a recess zone 14 connected by a first slot Fl to the edge 8a corresponding to the small side of the metallic layer 8 closest to the recess zone; and (ii) a slot F2, notable in that it opens either onto an edge of the metallic layer 8 covered with coating 70, or into the recess zone 14 and in that it has a closed end located in the second region R2 of the metallic layer covered with coating 70, and in the examples of figures 17A to 17C more precisely in a privileged zone ZC of exploitability of eddy currents.

[0198] In [Fig. 17A], the metallic coating is present only on the periphery of the metallic layer 8 and in the privileged zone ZC.

[0199] In figures 17B, 17C and 17D, the metallic layer 8 is completely covered with coating 70.

[0200] In these figures 17A to 17D, the symbol FL1 represents the direction of the magnetic field of the NFC reader. This magnetic field generates eddy current loops on the coating 70 of the metallic layer 8. For simplicity, only two loops Bl, B2 have been shown, of which one loop is dominant Bl.

[0201] In the four examples, the slots Fl and F2 are arranged thus to allow the passage of the magnetic field generated by a smart card reader and to be traversed by a current image of a current flowing in a loop of an eddy current flowing on the metallic layer 8.

[0202] 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.

[0203] In [Fig. 18] in addition to the metallic layer 8, an ANT2 antenna (second antenna in the sense of the invention) ANT2 implemented on a plastic layer not shown is represented.

[0204] In this figure, this antenna is represented in three parts, hereinafter referred to as the first antenna part ANT2a, the second antenna part ANT2b and the third antenna part ANT2c.

[0205] The ANT2 antenna is configured so that the current flows in the same direction in the first, second and third antenna parts ANT2a, ANT2b, ANT2c.

[0206] In the embodiment of [Fig. 18], the first antenna part ANT2a is the most peripheral part. It is arranged opposite a part of the metal layer 8 covered with coating 70 and extends along the four edges of the metal layer 8. It has at least one turn that overlaps the first slot Fl.

[0207] In the embodiment of [Fig. 18], the second antenna part ANT2b is connected to the first antenna part ANT2a. The second antenna part ANT2b is notable in that it is arranged opposite the second region R2 of the metal layer 8, which is covered with coating 70, and that it has at least one turn opposite the second slot.

[0208] Thus, at least one turn of the ANT2b 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.

[0209] In the embodiment of [Fig. 18], the third antenna part ANT2c terminates the second antenna ANT2. It is the part of the ANT2 antenna that does not does not overlap with the metallic layer 8 but overlaps with at least part of the recessed area 14.

[0210] Figure 19 represents a CD2 smart card according to an embodiment of the invention. In the embodiment described herein, the CD2 card comprises a CPI capacitive element connected in parallel to the second antenna ANT2.

[0211] The examples of slots F2 shown in Figures 17 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.

[0212] Fig. 20 illustrates the operation of the smart card of Fig. 19 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.

[0213] Under the effect of the magnetic field FL1, eddy currents - generally denoted II - are generated on the coating 70 of the metallic layer 8. These eddy currents II circulate in the form of closed current loops on the surface of the metallic layer 8. These eddy currents form on the coating 70 of the metallic layer 8 in closed loops in a direction such that they create a magnetic field opposite to the incident magnetic field.

[0214] In the example of [Fig.20], the eddy currents flow in the direction of clockwise hands.

[0215] Assuming that the entire surface of the card is exposed to a uniform magnetic field and as in the case illustrated in [Fig.20], the dominant loop B1 of the eddy currents follows the peripheral contour of the metallic layer 8 covered with coating 70. For illustrative purposes only, two other secondary loops B2 and B3 are shown.

[0216] 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.

[0217] As shown in [Fig.20], we note lia of eddy currents - called first eddy currents - corresponding to dominant loops circulating on the surface of the coating 70 of the metallic layer 8 in the vicinity of the peripheral contour of said metallic layer 8. We note 11b of eddy currents - called second eddy currents - corresponding to secondary loops circulating on the surface of the coating 70 of the metallic layer 8 in the vicinity of the peripheral contour of the recess zone 14.

[0218] Since eddy currents circulate in closed loops, eddy currents IIb are in fact the continuation of eddy currents lia in the vicinity of the peripheral contour of the recessed area 14. As shown in [Fig. 20], the second eddy currents Ilb circulate, in the vicinity of the second antenna section ANT2b, in a direction of rotation (or direction of circulation) opposite to that of the first eddy currents Ia circulating in the vicinity of the peripheral contour of the metallic layer 8. For example, in this case, the first and second eddy currents Ia and Ilb are considered to circulate clockwise and counterclockwise, respectively, although a reverse configuration is possible depending on the orientation of the magnetic field FL1. The opposite-direction circulation of the eddy currents Ia and Ilb results in particular from the continuity of the eddy currents mentioned above, as well as from the presence of the recessed area 14, which in this example is connected by the connecting slot Fl to the peripheral contour 8a of the metallic layer 8.

[0219] Consequently, the current 12 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 II 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 third antenna part ANT2c by the incident magnetic field FL1 through the recessed area 14 (12 = I2a + I2b). The very structure of the CD2 chip 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 12.

[0220] More specifically, the first antenna part ANT2a extending opposite the coating 70 of the metallic layer 8 collects an image current I2a induced by the first eddy currents lia circulating on the surface of the metallic layer 8 under the effect of the magnetic field FL1 when the smart card CD2 is centered with the NFC reader antenna.

[0221] These first eddy currents lia correspond to dominant loops circulating on the surface of the coating 70 of the metallic layer 8 in the vicinity of the turns of the first antenna part ANT2a. As already mentioned, the first antenna part ANT2a can preferably extend towards a peripheral area (or band) of the metallic layer 8 covered by the coating 70 in order to collect a maximum of energy generated by the dominant loops of the eddy currents. The first eddy currents lia circulating in the vicinity of the first antenna part ANTla (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 antenna part ANT2a is itself a reaction effect to the first eddy currents lia.

[0222] Thus, the image current I2a induced by the first eddy currents lia is carried by electrical conduction to the third antenna part ANT2c, due to the electrical continuity between the first, second and third antenna parts ANT2a, ANT2b, ANT2c which are connected together.

[0223] The image current I2a thus circulates in the turns of the third part of the antenna ANT2c positioned opposite the recess area 14.

[0224] As illustrated in [Fig. 20], the image current I2a flows in the same direction of rotation (or same direction of flow) in the turns of the first, second, and third antenna sections ANT2a, ANT2b, and ANT2c, namely counterclockwise in this example. However, due to the presence in the metal layer 8 of the recess 14 connected via the connecting slot Fl to the peripheral edge 8a, the second eddy currents Ilb (secondary loops) flow in the vicinity of the recess 14, on the surface of the metal layer 8 covered with coating 70, in a direction of rotation (or direction of flow) opposite to that of the first eddy currents I2a flowing around the periphery of the metal layer 8. By way of example, the second eddy currents Ilb flow here counterclockwise while the first eddy currents Ila flow clockwise.Also, the second eddy currents Ilb circulating around the periphery of the recessed area 14 do not oppose the magnetic field passing through the slit and contribute to amplifying the image current lia circulating in the turns of the third part of the ANT2c antenna.

[0225] Furthermore, the effect of the second slot F2 is to push the dominant eddy current loop towards the second part ANT2b of the second antenna ANT2, which increases the energy coupling between the eddy currents of the coating 70 of the metallic layer 8 and the second antenna part ANT2b in the vicinity of the second slot F2.

[0226] As already mentioned, the third antenna element ANT2c also collects in its turns a current I2b which is directly induced by the incident magnetic field FL1 captured at the recess 14 by the third antenna element ANT2c. In this example, the magnetic field FL1 is directed from the upper face of the chip CD2 to its lower face. Therefore, the current component I2b induced in the second antenna element 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 12 flowing in the second antenna ANT2.

[0227] The overall current 12 flowing in the third antenna part ANT2c in turn induces a magnetic field causing a magnetic coupling CL1 between the first RF antenna ANT1 and the third RF antenna part ANT2c, and therefore a fortiori between the first RF antenna ANT1 and the second RF antenna ANT2. The combined action of the image current I2a routed 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.

[0228] The third antenna part ANT2c 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 all three 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.

[0229] Returning to [Fig.17A] for example, when the CD2 card is off-center with respect to the NFC reader, the dominant loop B1 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.

[0230] As explained with reference to [Fig. 18], the second antenna part ANT2b 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 eddy currents ZC covered with the coating 70.

[0231] The ANT2b 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 second part ANT2b (and possibly opposite or near at least one turn of the first part of the ANT2a antenna).

[0232] In operation, under the effect of the magnetic field FL1 to which the smart card CD2 is subjected, the RF chip 4 is thus able to use the second RF antenna ANT2 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 under specified operating conditions.

[0233] When a user presents the CD2 smart card in the vicinity of the NFC reader, contactless communication can thus be established between the NFC reader and the CD2 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 first part of the ANT2a antenna, or by the second part of the ANT2b antenna depending on whether the card is centered or offset with respect to the reader, within the limits of the operating conditions of the card.

[0234] As already indicated, various arrangements of the CD2 smart card can be envisaged, particularly with regard to the shape, dimensions, position, etc. configuration of the recess area 14 and the Fl and F2 slots.

[0235] Figure 21 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.

[0236] In this embodiment of the invention, the second antenna ANT2 comprises a fourth part ANT2d around the recessed area 14 and connecting the turns of the second part ANT2b to those of the third part ANT2c of the second antenna ANT2. The fourth antenna part ANT2d is in direct superposition with the conductor of the coating 70 of the metallic layer 8 and is also electrically insulated from this metallic layer like the first and second antenna parts ANT2a, ANT2b.

[0237] These four antenna parts are arranged so that the current flows in the same direction in these four parts.

[0238] 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.

[0239] Fig. 21 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 third and fourth antenna parts ANT2c and ANT2d are outside this region of maximum magnetic field.

[0240] 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 covered with the coating 70.

[0241] 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 second antenna ANT2b.

[0242] 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 adjacent turns of the ANT2b antenna from the edge of the metallic layer on which the slot F2 opens.

[0243] Furthermore, and as shown in the detail area of ​​[Fig. 21], the slot F2 also allows the incident magnetic field of the reader to pass through the metallic layer 8 while being in phase with the electric current induced in the turns of the second antenna ANT2b. As explained previously, the current in the second antenna ANT2b has the following components: (i) a first component corresponding to the image current captured by the second antenna ANT2b; and (ii) a second component created by magnetic induction through the opening of slot F2 in the portion of the antenna wires of the second antenna ANT2b that overlap slot F2.

[0244] Figure 22 schematically represents a method for manufacturing one of the CD2 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.

[0245] In the embodiment described here, the metallic layer 70 is entirely covered with coating 70.

[0246] 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 CD2 card, the first region RI entirely containing the recess area 14, its surface being smaller than that of the second region R2.

[0247] 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.

[0248] 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.

[0249] 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.

[0250] During a formation step S8, a second RF antenna ANT2 is formed (or assembled) on or in the card body 6 so 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 S8 training step is carried out so that the second RF antenna is intended to allow coupling with the first antenna, the second antenna having at least one turn located opposite the first slot Fl and at least one turn located opposite the second slot F2.

[0251] 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.

Claims

Demands

1. Smart card (CD1, CD2) comprising: - a card body (6) 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; - at least one RF antenna portion (ANT2, ANT2) electrically isolated from the metallic layer and the first RF antenna and configured to collect an image current (I2a) induced by first eddy currents (lia) circulating at least on the coating (70) of the metallic layer and to allow coupling with the first antenna, said smart card (CD1, CD2) being characterized in that: the metallic layer (8) is at least partially covered by a coating (70) more conductive than the metallic layer; and in that said recessed area (14) opens onto a peripheral edge (8a) of the metallic layer, said at least one antenna portion (ANT2) being a second RF antenna (ANT2) comprising: (i) a first antenna portion (AT2a) extending opposite a portion of the metallic layer covered by said coating (70) to collect said image current (I2a); and (ii) a second antenna part (AT2b), electrically connected to the first antenna part (AT2a), and extending opposite the recess area to permit said magnetic coupling.

2. Smart card (CD1, CD2) comprising: - a rectangular card body (6) 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; - at least one RF antenna portion (ANT2, ANT2) electrically isolated from the metallic layer and the first RF antenna and configured to collect an image current (I2a) induced by first eddy currents (lia) circulating at least on the coating (70) of the metallic layer and allow coupling with the first antenna, said smart card (CD1, CD2) being characterized in that: the metallic layer (8) is at least partially covered by a coating (70) more conductive than the metallic layer; and in that said metallic layer is constituted by a first region (RI) and a second region (R2) 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 (F1) 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 recess area, the second slot ending with a closed part in the second region;and - said at least one antenna part (ANT2) being a second RF antenna (ANT2) comprising at least one turn located opposite the first slot (F1) and at least one turn located opposite said second slot (F2).;

3. Smart card according to claim 1 or 2 characterized in that the metallic layer (8) is entirely covered by said coating (70).

4. Smart card according to any one of claims 1 to 3, characterized in that the thickness of the coating (70) is greater than the skin thickness of said coating (70).

5. Smart card according to any one of claims 1 to 4, characterized in that the conductivity of said coating (70) is greater than 3.5x07 S / m.

6. Smart card according to any one of claims 1 to 5, characterized in that said coating (70) is made of copper, silver or gold.

7. A method for manufacturing a smart card (CD1, CD2) from a card body (6) formed at least in part by a metallic layer (8) comprising a recessed area (14), the method comprising:

8. - formation on or in the card body of a first RF antenna (ANT1) in or opposite the recessed area of ​​the metallic layer; - assembly of an RF chip (4) with the board body such that the RF chip (4) is electrically connected to the first RF antenna; and - formation on or within the card body of at least one RF antenna portion (ANT2) electrically isolated from the metal layer and the first RF antenna and configured to collect an image current (I2a) induced by first eddy currents (lia) circulating at least on the coating of the metal layer and to allow coupling with the first antenna, said method being characterized in that it comprises a step for at least partially, preferably entirely, covering the metal layer (8) with a coating (70) more conductive than the metal layer (8) and in that said at least one antenna part (ANT2) is a second RF antenna comprising: (i) a first antenna portion (AT2a) extending opposite the metallic layer to collect an image current (I2a) induced by first eddy currents (lia) circulating at least on the coating of the metallic layer; and (ii) a second antenna part (AT2b), electrically connected to the first antenna part (AT2a), and extending opposite the recess area to allow magnetic coupling (FL1) between the first RF antenna and the second RF antenna. A method for manufacturing a smart card (CD1, CD2) from a card body (6) of generally rectangular shape formed at least in part by a metallic layer (8) comprising a recessed area (14), the method comprising: - cover at least partially, preferably entirely, the metallic layer (8) with a coating (70) that is more conductive than the metallic layer (8); - formation on or in the card body of a first RF antenna (ANT1) in or opposite the recessed area of ​​the metallic layer; - assembly of an RF chip (4) with the board body such that the RF chip (4) is electrically connected to the first RF antenna; and - formation on or within the card body of at least one RF antenna portion (ANT2) electrically isolated from the metal layer and the first RF antenna and configured to collect an image current (I2a) induced by first eddy currents (lia) circulating at least on the coating of the metal layer and to allow coupling with the first antenna, said method being characterized in that it comprises a step for at least partially, preferably entirely, covering the metal layer (8) with a coating (70) more conductive than the metal layer (8) and in that said metallic layer (8) consists of a first region (RI) and a second region (R2) entirely delimited by a straight line (LIM) parallel to a short side of the card (CD2), the first region (RI) entirely containing the recess area (14) and its surface being smaller than that of the second region (R2), a first slot (F1) of the metallic layer connecting the recess 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 recess area (14), the second slot (F2) ending with a closed part in the second region (R2), - said at least one antenna part being a second antenna comprising at least one turn located opposite the first slot and at least one turn located opposite the second slot.

Images