Substrate for an RFID transponder with metal inlay

Abstract

The present invention refers to a substrate for an RFID transponder comprising a carrier layer made of an insulating material; one or more metal inlays associated with the carrier layer; a main RFID antenna formed on the carrier layer and configured to communicate with an external electro-magnetic reader; a compensation antenna formed on the carrier layer and configured to offset the detuning effect of the one or more metal inlays and to boost communication of the main RFID antenna with the external electro-magnetic reader. According to the present invention, the main RFID antenna and the compensation antenna may be formed on a same surface of the carrier layer, or they may be not physically connected to each other, and / or they may be self-resonance antennas.

Description

[0001] SUBSTRATE FOR AN RFID TRANSPONDER WITH METAL INLAY

[0002] Technical field

[0003] The present invention refers to the field of substrate for RFID transponders, in particular substrates for RFID transponders comprising a metal frame, a metal plate and an RFID antenna.

[0004] State of the art

[0005] RFID transponders, such as smart cards, comprising a metal or metallized layer are known at the state of the art. The metal or metallized layer is typically added to the smart card so that the smart card looks precious, as though the entire smart card were made of metal.

[0006] However, since the metal or metallized layer has an effect of detuning an RFID antenna formed in the smart card, various modifications and / or additions are generally made to the structure of the smart card to offset the detuning effect during electromagnetic coupling, with the goal of improving coupling between the smart card and an external electromagnetic reader.

[0007] The patent application EP2807700 discloses for instance a dual-interface smart card comprising a booster antenna with a coupler coil in its card body, and a metallized face plate having a window opening for an antenna module having a module antenna. The attenuation caused by the metallized face plate is reduced in the dual-interface smart card of EP280770 in several ways, such as by disposing a ferrite element in the antenna module between the module antenna and the contact pads, or by arranging the booster antenna as a quasi-dipole.

[0008] There is a constant need in the field of smart card and RFID transponders to develop new solutions that may offset the effect of detuning on antennas by metal or metalized layers during electromagnetic coupling and that may adapt to different configurations of the RFID transponders, such as configurations complying with specific standards and requirements.

[0009] It is therefore an object of the present invention to provide an RFID transponder wherein the overall performance of the antennas is improved and the shielding effect of the metal layer is reduced.

[0010] Summary

[0011] The present invention is based on the idea of providing a substrate for an RFID transponder with a compensation antenna in order to reduce the detuning effect and boost the performance of the main Radio Frequency Identification (RFID) antenna. According to first aspect of the present invention, a substrate for an RFID transponder is provided, which comprises:

[0012] A carrier layer made of an insulating material;

[0013] One or more metal inlays associated with a carrier layer;

[0014] A main RFID antenna formed on the carrier layer and configured to communicate with an external electro-magnetic reader;

[0015] A compensation antenna formed on the carrier layer and configured to boost communication of the main RFID antenna with the external electro-magnetic reader,

[0016] Wherein the main RFID antenna and the compensation antenna are formed on a same surface of a carrier layer.

[0017] In the present disclosure, it is to be understood that the term “metal inlay” indicates any metal components that is partially or entirely inserted into the carrier layer as a reinforcement, or formed on one or more surfaces of the carrier layer, such as a metal plate or a metal frame.

[0018] In the present disclosure, it is to be understood that the term “metal frame” indicates an open case or structure made for admitting, enclosing, or supporting the carrier layer. Preferably, the metal frame may enclose the carrier layer and one or more additional plastic layers so that the overall thickness of the metal frame corresponds to the overall thickness of the carrier layer and the additional layers.

[0019] In the present disclosure, it is to be understood that the term "compensation antenna" indicates any antenna that might be used to enhance the transmission / reception performance of the main RFID antenna with an external electromagnetic reader and / or with a module of an RFID transponder, by compensating the effects of the eddy currents induced in the one or more metal inlays after exposure to the magnetic field of the external electromagnetic reader. For instance, the compensation antenna may be used to maximize the magnetic flux associated with the main RFID antenna by inducing a current having the same flow direction as the induced current of the main RFID antenna. The compensation antenna may be an antenna inductively coupled with the main RFID antenna.

[0020] Preferably, the carrier layer is a card shaped structure having a first surface and a second surface opposite to the first one. Alternatively, the carrier layer may have any shape suitable for accommodating the electronic components of the RFID transponder and may have a first surface and a second surface opposite to the first one. According to the present invention, the main RFID antenna and the compensation antenna are formed on the same surface of the carrier layer, for instance on the first surface or on the second surface.

[0021] The advantage of this configuration is that the manufacturing process of the main RFID antenna and the compensation antenna is simplified, because they are formed on the same surface and in a single manufacturing step. For instance, if the main RFID antenna and the compensation antenna are formed by means of wire-embedding technique, the wire-embedding process is simplified if the two antennas are formed on the same side, because a single wiring step needs to be performed.

[0022] Preferably, the compensation antenna is formed in proximity of the main antenna and of the metal inlays, so as to minimize the detuning effect of the metal inlays with respect to the performance of the main antenna.

[0023] The carrier layer may be a single carrier layer, or a multi-layered carrier. Preferably, the insulating material may be any type of appropriate plastic, such as polymer materials of various types, such as polycarbonate, PVC materials, and the like.

[0024] According to a second aspect of the present invention, a substrate for an RFID transponder is provided, which comprises:

[0025] A carrier layer made of an insulating material;

[0026] One or more metal inlays associated with a carrier layer;

[0027] A main RFID antenna formed on the carrier layer and configured to communicate with an external electro-magnetic reader;

[0028] A compensation antenna formed on the carrier layer and configured to boost communication of the main RFID antenna with the external electro-magnetic reader, wherein the main RFID antenna and the compensation antenna are not physically connected to each other.

[0029] The advantage of this configuration is that the main RFID antenna and the compensation antenna are separate and distinct antenna. On the other hand, if the compensation antenna were physically connected to the main RFID antenna, for instance by means of a connection wire, the resulting antenna would be longer and would have an increased resistance with respect to the main RFID antenna. According to a third aspect of the present invention, a substrate for an RFID transponder is provided, which comprises:

[0030] A carrier layer made of an insulating material;

[0031] One or more metal inlays associated with a carrier layer;

[0032] A main RFID antenna formed on the carrier layer and configured to communicate with an external electro-magnetic reader;

[0033] A compensation antenna formed on the carrier layer and configured to boost communication of the main RFID antenna with the external electro-magnetic reader,

[0034] Wherein the main RFID antenna and / or the compensation antenna are self-resonance antennas.

[0035] In the present disclosure, it is to be understood that the term “self-resonance antenna” indicates a coil antenna comprising an inductance part and a capacitance part.

[0036] The advantage of this configuration is that the capacitance part of each self-resonance antenna can be used to fine-tune the resonance frequency of the antenna. For instance, the capacitance part of the main RFID antenna can be used to fine-tune the resonance frequency of the main RFID antenna. For instance, the capacitance part of the compensation antenna can be used to fine tune the resonance frequency of the compensation antenna. In this way, also the final resonance frequency of the system comprising the compensation antenna inductively coupled with the main RFID antenna may be fine-tuned. For instance, the final resonance frequency of the coupling system may be fine-tuned to match a predefined resonance frequency, such as the resonance frequency for transactions operations, and may enable predefined operations, such as payments.

[0037] In the present disclosure, it is to be understood that the substrate for the RFID transponder may comprise one or more of the aspects of the present invention. For instance, the substrate of the present invention may comprise a main RFID antenna and a compensation antenna, which are formed on the same surface, or same side, of the carrier layer. Alternatively or in addition to the previous example, the substrate of the present invention may comprise a main RFID antenna and / or a compensation antenna configured as self-resonance antennas. Alternatively or in addition to the previous examples, the substrate of the present invention may comprise a main RFID antenna and a compensation antenna which are not physically connected to each other, for instance they are not connected by means of a wire, and which are inductively coupled to each other. According to an embodiment of the first aspect or the third aspect of the present invention, a substrate is provided, wherein the compensation antenna is not physically connected to the main RFID antenna.

[0038] Preferably, the main RFID antenna and the compensation antenna are coil antennas comprising a plurality of windings. Preferably, the compensation antenna surrounds the main RFID antenna and is configured to be inductively coupled with the main RFID antenna. The windings of the main RFID antenna are preferably not physically connected to the windings of the compensation antenna. In this way, the connection between the main RFID antenna and the compensation antenna is entirely based on inductive coupling and not on a galvanic electrical connection. The advantage of this configuration is that the cooperation performance between the two antennas is improved with respect to the case of the presence of a physical direct connection.

[0039] According to another embodiment of the first aspect or the second aspect of the present invention, a substrate is provided, wherein the main RFID antenna and / or the compensation antenna are self-resonance antennas.

[0040] The advantage of this configuration is that the capacitance part of each self-resonance antenna can be used to fine-tune the resonance frequency of the antenna. For instance, the capacitance part of the main RFID antenna can be used to fine-tune the resonance frequency of the main RFID antenna. For instance, the capacitance part of the compensation antenna can be used to fine tune the resonance frequency of the compensation antenna. In this way, also the final resonance frequency of the system comprising the compensation antenna inductively coupled with the main RFID antenna may be fine-tuned. For instance, the final resonance frequency of the coupling system may be fine-tuned to match a predefined resonance frequency, such as the resonance frequency for transactions operations.

[0041] According to an alternative embodiment of the first or third aspect of the present invention, a substrate is provided, wherein each of the main RFID antenna and the compensation antenna comprises an inductive loop or coil that represent an inductance contribution for the RFID transponder, and each antenna is connected to one or more corresponding capacitors that represent a capacitance contribution for the RFID transponder.

[0042] According to a preferred embodiment of the present invention, a substrate is provided, wherein the main RFID antenna and / or the compensation antenna comprise a first coiled portion having a first winding direction and a second coiled portion having a second winding direction opposite to that of the first coiled portion, wherein the first coiled portion form an inductance coil and the second coiled portion form a capacitance coil of the main RFID antenna and / or a compensation antenna. The advantage of this configuration is that each coupling antenna is provided with a second coiled portion that acts as a capacitance connected in series to the first coiled portion acting as an inductance. In this way, there is no need to connect an additional capacitor to the antenna for fine-tuning its resonance frequency. Accordingly, production costs are reduced and the manufacturing process is simplified.

[0043] According to another embodiment of one or more aspects of the present invention, a substrate is provided, wherein the main RFID antenna and the compensation antenna are concentric with each other and the compensation antenna is formed around the main RFID antenna.

[0044] The advantage of this configuration is that it optimizes the space occupied by the antennas on the card type substrate and maximizes the boosting effect of the compensation antenna on the main RFID antenna.

[0045] According to another embodiment of the present invention, a substrate is provided, wherein the metal inlay comprises a metal plate formed within the carrier layer.

[0046] For instance, the metal plate may be formed on or inside the carrier layer to increase the weight of the card type substrate and to give it more precious configuration.

[0047] According to a preferred embodiment of the present invention, a substrate is provided, wherein the main RFID antenna and the compensation antenna are formed outside a perimeter of the metal plate.

[0048] The advantage of this configuration is that the electromagnetic interference between the coupling antennas and the metal plate is reduced.

[0049] According to another embodiment of the present invention, a substrate is provided, wherein the metal inlay comprises a metal frame formed along a perimeter of the carrier layer.

[0050] For instance, the metal frame may be formed along the edges of the carrier layer having a card type structure. Preferably, the metal frame may be shaped so as to leave uncovered a portion of the carrier layer on both the first surface of the carrier layer and the second surface of the carrier layer, opposite to the first one.

[0051] According to a preferred embodiment of the present invention, a substrate is provided, wherein the main RFID antenna and the compensation antenna are formed within a perimeter of the metal frame. The advantage of this configuration is that the electromagnetic interference between the coupling antennas and the metal frame is reduced.

[0052] According to another aspect of the present invention, an RFID transponder is provided, which comprises:

[0053] - a substrate as the ones described above;

[0054] - an electronic module coupled with the main RFID antenna;

[0055] - one or more layers of insulating material attached to the substrate.

[0056] The advantage of this configuration is that the communication between the RFID transponder and the external electromagnetic reader is improved due to the presence of the compensation antenna, which boosts the signal of the main RFID antenna. For instance, the read-range of the RFID transponder may be increased.

[0057] In the present disclosure, it is to be understood that the expression “electronic module coupled with the main RFID antenna” may indicate both a configuration where the electronic module is inductively coupled with the main RFID antenna, and a configuration where the electronic module is directly, electronically connected with the main RFID antenna. For instance, the electronic module may be a contact module for operating the RFID transponder in contact mode, or a dualinterface module for operating the RFID transponder in contact and contactless mode.

[0058] Preferably, the substrate further comprises an auxiliary coupling antenna which is inductively coupled with the electronic module and which is positioned on the carrier layer in correspondence with the position occupied by the electronic module in the final RFID transponder. Preferably, the auxiliary coupling antenna is inductively coupled both with the electronic module and with the main RFID antenna for enabling communication between the electronic module and the external electromagnetic reader. Alternatively, the auxiliary coupling antenna may be inductively coupled with the electronic module and may be electrically connected to the main RFID antenna for enabling communication between the electronic module and external electromagnetic reader. Accordingly, the inductive coupling between the main RFID antenna and the electronic module may be a direct inductive coupling or and indirect inductive coupling (i.e. via the auxiliary coupling antenna).

[0059] According to another aspect of the present invention, a method for operating a substrate as the ones described above is provided, the method comprising the following steps:

[0060] Exposing the substrate to an electro-magnetic field generated by an external reader; Generating a main induced current having a first direction within the main RFID antenna by means of inductive coupling with the electro-magnetic field;

[0061] Generating an eddy current having a second direction opposite to the first direction within the metal inlay by means of inductive coupling with the electro-magnetic field;

[0062] Generating an additional induced current within the compensation antenna by means of inductive coupling with the electro-magnetic field, wherein the additional induced current has a direction equal to a first direction and is configured to boost a communication response of the main RFID antenna with the external reader.

[0063] The advantage of this method is that it enables operating a substrate according to the present invention.

[0064] Figures

[0065] Further illustrative embodiments and other aspects of the present invention will be described in more detail in the following specification, while also referring to the accompanying drawings, in which

[0066] Fig. 1A schematically illustrates a top view of a substrate according to an embodiment of the present invention;

[0067] Fig. 1 B schematically illustrates an equivalent circuit for the electronic system comprising the main antenna and the auxiliary antenna for the electronic module, according to an embodiment of the present invention;

[0068] Fig. 2A schematically illustrates a top view of a substrate according to another embodiment of the present invention;

[0069] Fig. 2B schematically illustrates an equivalent circuit for the electronic system comprising the main antenna and the electronic module, according to an embodiment of the present invention;

[0070] Fig. 3 schematically illustrates a top view of a substrate according to the prior art;

[0071] Fig. 4 schematically illustrates the directions of the induced currents in a substrate according to an embodiment of the present invention;

[0072] Fig. 5 schematically illustrates a diagram of the reflectance of the coupling antennas formed in a substrate according to an embodiment of the present invention; Fig. 6 schematically illustrates a top view of a substrate according to an alternative embodiment of the present invention.

[0073] Detailed description

[0074] In the following, the present invention is described with reference to particular embodiments, as is illustrated in the enclosed figures. However, the present invention is not limited to the particular embodiments described in the following detailed description and shown in figures. Instead, the described embodiments simply exemplify the different features of the present invention, the scope of which is defined in the claims. Further modifications and variations of the present invention will be clear to the skilled person.

[0075] In the following detailed description, the terms “right”, “left”, “top”, “bottom”, and variations thereon are employed with reference to the orientation shown in the figures.

[0076] The substrate 100 of Fig. 1A includes a carrier layer 102, which may typically comprise any type of appropriate plastic, such as polymer materials of various types, such as polycarbonate, PVC materials, and the like.

[0077] The substrate 100 of Fig. 1A includes two metal inlays that give additional weight to the substrate 100 and make it look more precious, as if the entire substrate were made of metal.

[0078] The metal inlays of the substrate of Fig. 1A include a frame 120 and a metal plate 110. The frame 120 is physically connected to the carrier layer 102 and is formed around its edges. Preferably, the frame 120 is a continuous frame entirely formed around the edges of the carrier layer 102. Preferably, the frame 120 is designed so as to leave uncovered a significant portion of the top surface and of the bottom surface of the carrier layer 102. Preferably, a thickness of the frame 120 is higher than a thickness of the carrier layer 102, so that the frame 120 can accommodate other layers attached to the carrier layer 102, such as additional plastic layers.

[0079] The metal plate 110 is a metal component formed on a portion of the area the carrier layer 102. Preferably, the shape and the dimensions of the metal plate 110 are designed so as to occupy the area of the carrier layer not occupied by the electronic components, such as the main RFID antenna 140, the auxiliary coupling antenna for the electronic module 130, and the compensation antenna 150. Preferably, the metal plate 110 may have a thickness higher than a thickness of the carrier layer 102 and may protrude from the carrier layer 102. Preferably, one or more additional plastic layers may be attached to the carrier layer 102 in the portions not occupied by the metal plate 110 so as to form a surface flush with the surface of the protruding portion of the metal plate 102. Preferably, the substrate 100 of the present invention does not comprise any additional layer, such as a ferrite layer, to shield the effect of the metal plate 110 on the main RFID antenna 140.

[0080] According to some embodiments, the substrate 100 of the present invention may correspond to the card-type information substrates 100, and / or 200A / 200B comprising the frames 110 and 210, respectively, which are disclosed in detail in the international application WO 2021 / 074680 of the same applicant, with reference to Figs. 1A, 1 B, 2A, and 2B, whose content is herein entirely incorporated by reference.

[0081] According to some embodiments, the substrate 100 of the present invention may correspond to the pre-form 690 including a frame 610 and a metal containing plate 680, which is disclosed in detail in the international application WO 2021 / 074680 of the same applicant, with reference to Figs. 6A-6J, whose content is herein entirely incorporated by reference.

[0082] The substrate 100 of Fig. 1A comprises a main RFID antenna 140 for enabling communication between an external electromagnetic reader and the electronic module of the RFID transponder (not shown).

[0083] With continued reference to Fig. 1 A, the substrate 100 further comprises an auxiliary antenna 130 which is inductively coupled with the electronic module of the RFID transponder (not shown).

[0084] As shown in Fig. 1A and in greater detail in Fig. 6, the main RFID antenna 140 is electrically connected with the auxiliary coupling antenna for the electronic module 130 by means of the wire portion 144. In this way, once the electronic module comprising a chip is added to the RFID transponder in correspondence with the auxiliary coupling antenna 130, the main RFID antenna 140 may communicate with the electronic module.

[0085] Fig. 1 B schematically illustrates the simplified equivalent circuit (neglecting coil resistance) for the electronic system comprising the main RFID antenna 140 and the auxiliary coupling antenna for the electronic module 130, as shown in Fig. 1A.

[0086] As schematically shown in Fig. 1 B, the main RFID antenna 140 may be approximated with a first inductance L1 and the auxiliary coupling antenna for the electronic module 130 may be approximated with a second inductance L2. Since the main RFID antenna 140 and the auxiliary coupling antenna for the electronic module 130 are connected by means of the wire portion 144, the main RFID antenna 140 further comprises a portion having a reversed winding direction: this portion has a reversed current flow and can be approximated with a capacitor C1 added to the main RFID antenna 140. As shown in the schematic circuit of Fig. 1 B, the oppositely-charged plates A and B of the capacitor C1 may be obtained by means of the coiled portions of the main RFID antenna 140 having opposite winding directions, as explained with reference to Fig. 6.

[0087] Accordingly, the equivalent circuit for the electronic system comprising the main RFID antenna 140 and the auxiliary coupling antenna for the electronic module 130 comprises a first and a second inductance in series with a capacitor C1.

[0088] The substrate 100 of Fig. 1A further comprises a compensation antenna 150 for boosting the communication performance of the main RFID antenna 140, as will described in detail below.

[0089] The main RFID antenna 140 and the compensation antenna 150 are advantageously formed on the same surface of the carrier layer 102, in order to improve their inductive coupling. With reference to the substrate 100 of Fig. 1A, the main RFID antenna 140 and the compensation antenna 150 are formed on the top surface of the carrier layer 102.

[0090] Preferably, the main RFID antenna 140 and the compensation antenna 150 of Fig. 1A may be self-resonance antennas.

[0091] As shown in Fig. 1A, the compensation antenna 150 may comprise a capacitive element C to fine-tune its resonance frequency and enable communication with the main RFID antenna 140 and the external electro-magnetic reader. The capacitive element C may be a capacitor, such as a Surface Mount Capacitor, or a capacitive coil 152, as discussed with reference to Fig. 6.

[0092] With continued reference to Fig. 1A, the main RFID antenna 140 and the compensation antenna 150 are formed within the outline of the metal frame 120.

[0093] With continued reference to Fig. 1A, the main RFID antenna 140 and the compensation antenna 150 are formed outside the outline of the metal plate 110.

[0094] As visible in Fig. 1A, the main RFID antenna 140, the auxiliary coupling antenna for the electronic module 130, and / or the compensation antenna 150 does not comprise any portion overlapping with the metal frame 120 or the metal plate 110 when viewed from the principal direction. In this way, the electromagnetic interference between the coupling antennas 140 and 150 and the metal frame 120 and the metal plate 110 is minimized.

[0095] The main RFID antenna 140, the auxiliary coupling antenna for the electronic module 130, and the compensation antenna 150 may be formed by embedding wire on the carrier layer 102. According to alternative embodiments, the main RFID antenna 140, the auxiliary coupling antenna for the electronic module 130, and the compensation antenna 150 may be formed by means of other manufacturing techniques, such as printing, etching, laser etching, coil winding techniques, or by conductive material deposition. Fig. 2A schematically illustrates a top view of a substrate according to another embodiment of the present invention.

[0096] The substrate 100 of Fig. 2A corresponds to the substrate of Fig. 1A and it differs from that in the configuration of the connection between the main RFID antenna 140 and the electronic module 160, comprising the electronic chip. In fact, in the substrate 100 of Fig. 2A the electronic module 160 is directly connected to the main RFID antenna 140 and it is not indirectly connected to it by means of inductive coupling, as in the configuration of Fig. 1 A. As shown in Fig. 2A, the winding direction of the main RFID antenna 140 is the same as the direction of the electrical connection between the main RFID antenna 140 and the electronic module 160.

[0097] Fig. 2B schematically illustrates an equivalent circuit for the electronic system comprising the main antenna 140 and the electronic module 160, according to the embodiment shown in Fig. 2A.

[0098] As schematically shown in Fig. 2B, the main RFID antenna 140 may be approximated with a first inductance L1 and the electronic module 160 may be approximated with a capacitor C2.

[0099] Accordingly, the equivalent circuit for the electronic system comprising the main RFID antenna 140 and the electronic module 160 comprises a first inductance L1 in series with a capacitor C2.

[0100] As shown in the schematic circuit of Fig. 2B, the capacitor C2 may be obtained by means of the chip capacitance of the electronic module.

[0101] Fig. 3 schematically illustrates, for comparison purposes, a top view of a substrate 100’ according to the prior art.

[0102] The substrate 100’ according to the prior art corresponds to the substrate 100 of the present invention, in that it comprises a carrier layer 102’ made of an insulating material, a metal frame 120’ and a metal plate 110’ associated with said the carrier layer 102’, and a main RFID antenna 140’ formed on the carrier layer 102’ and configured to communicate with an external electromagnetic reader.

[0103] However, the substrate 100’ according to the prior art does not comprise a compensation antenna configured to boost communication of the main RFID antenna 140’ with the external electromagnetic reader. Therefore, the communication between the main RFID antenna 140’ of the prior art and the external electro-magnetic reader is weak, for instance has a short communication range.

[0104] During operation of the substrate 100 of the present invention, the main RFID antenna 140 generates a magnetic flux, which is used for the power supply of the electronic module of the RFID transponder (not shown) and for sending messages between the external reader and the electronic module. Therefore, one requirement for the main RFID antenna 140 is that its induced current after communication with the external reader is maximized, so that also the corresponding magnetic flux is maximized.

[0105] However, the magnetic flux associated with the induced current of the main RFID antenna 140 is reduced because of the formation of eddy currents within the metal inlays, such as the metal frame 120 and the metal plate 110. In fact, the eddy currents formed within the metal inlays may have a flowing direction opposite to that of the induced current in correspondence with the main RFID antenna 140.

[0106] This concept is schematically shown in Fig. 4, where the induced current of the main RFID antenna 140 has a first direction D1 and the eddy currents in the metal frame 120 and in the metal plate 110 have an opposite direction D2.

[0107] In this respect, it should be understood that the term “eddy current” refers to undesired currents associates with any physical mechanism resulting in losses of electromagnetic radiation emitted or received by the main RFID antenna 140, due to the presence of the metal inlays, such as the metal frame and / or the metal plate.

[0108] The present invention is hence based on the idea of adding a compensation antenna 150 having a winding direction so that the induced current has a flowing direction equal to the first direction D1 . In this way, the magnetic flux associated with the main RFID antenna 140 is maximized and the communication with the external reader is improved. For instance, the reading range of the RFID transponder comprising the substrate 100 of the present invention may be increased.

[0109] According to preferred embodiments, the compensation antenna 150 may be inductively coupled with the main RFID antenna 140. The compensation antenna 150 is preferably not physically connected to the main RFID antenna 140.

[0110] According to other preferred embodiments, the main RFID antenna 140 and the compensation antenna 150 may be advantageously formed on the same surface of the carrier layer 102, in order to improve their inductive coupling and simplify the manufacturing process of the antennas.

[0111] According to other preferred embodiments, the main RFID antenna 140 and the compensation antenna 150 of Fig. 1A may be self-resonance antennas, in order to ensure fine-tuning of the resonance frequency of the system comprising the two coupling antennas 140 and 150.

[0112] Preferably, both the main RFID antenna 140 and the compensation antenna 150 are Radio Frequency (RF) antennas and can be used for operating Radio Frequency Identification (RFID) devices, such as RFID transponders, for instance RFID smart cards for payments. Accordingly, the improved communication performance of the main RFID antenna 140 may be an improved communication in the field of Radio Frequencies, or improved RF performance.

[0113] The communication performance of the main RFID antenna 140 when inductively coupled with the compensation antenna 150 can be described by different physical parameters. Illustrative physical parameters associated with the RF performance of the antenna are the reflection coefficient of the antenna, that quantifies the level of the incident waveform of the electromagnetic field that is reflected, or the intensity decrease due to coupling to a standardised coupling coil in accordance with standardised procedures for evaluating RF performance, also referred to and known as S-parameter.

[0114] Fig. 5 schematically illustrates the S-parameter of the main RFID antenna 140 and of the compensation antenna 150 according to an embodiment of the present invention, in the frequency range comprised between 8 MHz and 20 MHz. As shown in Fig. 5, the main RFID antenna 140 has a resonance frequency comprised between 13 MHz and 20 MHz, in particular between 14 MHz and 14.5 MHz. Preferably, the compensation antenna has a resonance frequency comprised between 14 MHz and 20MHz. Preferably, the target resonance frequency for RF communication with RFID transponders is comprised between 12 and 18 MHz.

[0115] With continued reference to Fig. 5, the main RFID antenna 140 when boosted by the compensation antenna 150 has a resonance frequency comprised between 14 and 21 MHz.

[0116] From Fig. 5, it is hence evident that the RF performance of the main RFID antenna 140 when coupled with the compensation antenna 150 is improved. In fact, the value of the S-parameter, which measures the energy loss, decreases, for instance from - 1 dB to -1.25 dB. In other words, the S-parameter value of the main RFID antenna including the compensation antenna is lower than S-parameter value of the main RFID antenna without the compensation antenna.

[0117] Fig. 6 schematically illustrates a top view of a substrate 100 according to an alternative embodiment of the present invention.

[0118] In the substrate 100 of Fig. 6, the main RFID antenna 140 and the compensation antenna 150 comprise capacitance elements 142 and 152, respectively.

[0119] As schematically shown in Fig. 6, the main RFID antenna 140 comprises a coiled wire 146 having a first winding direction starting from point A and ending in the auxiliary coupling antenna for the electronic module 130 (from left to right, with reference to the illustrative orientation of the substrate shown in Fig. 6). The winding direction is defined by the flow of the induced current in case of exposure to an electro-magnetic field perpendicular to the plane defined by the substrate 100 and entering into it.

[0120] In correspondence with the auxiliary coupling antenna for the electronic module 130, the crossing portion 144 of the wire of the main RFID antenna 140 crosses over the coiled wire 146 of the auxiliary coupling antenna for the electronic module 130 and of the main RFID antenna 140.

[0121] After the crossing portion 144, the winding of the wire of the main RFID antenna 140 is reversed with respect to the previous coiled wire 146. This reversed portion generates a capacitance in the main RFID antenna 140 because, at the opposite ends of the reversed portion, opposite charges are obtained.

[0122] In a similar way, as schematically shown in Fig. 6, the compensation antenna 150 comprises a coiled wire 156 having a first winding direction starting from point C (from right to left, with reference to the illustrative orientation of the substrate shown in Fig. 6). The winding direction is defined by the flow of the induced current in case of exposure to an electro-magnetic field perpendicular to the plane defined by the substrate 100 and entering into it.

[0123] In correspondence with the corner at the bottom-right of the substrate 100 of Fig. 6, the crossing portion 154 of the wire of the compensation antenna 150 crosses over the coiled wire 156 of the compensation antenna 150.

[0124] After the crossing portion 154, the winding of the wire of the compensation antenna 150 is reversed with respect to the previous coiled wire 156. This reversed portion generates a capacitance in the compensation antenna 150 because, at the opposite ends of the reversed portion, opposite charges are obtained.

[0125] Accordingly, the adjacent wires having the same winding direction (and the same current flow direction) represent the inductance part, or inductance coils 146 and 156, of the main RFID antenna 140 and of the compensation antenna 150, respectively.

[0126] On the other hand, the adjacent wires having opposite winding direction (and opposite current flow direction) with respect to the inductance coils 146 and 156 of the main RFID antenna 140 and of the compensation antenna 150 represent the capacitance part, or capacitance coils 142 and 152 of the main RFID antenna 140 and of the compensation antenna 150, respectively.

[0127] The capacitance coils 142 and 152 may be advantageously used in the main RFID antenna 140 and of the compensation antenna 150 to tune the resonance frequency of each coupling antenna (and hence of the combination of the two coupling antennas) to match a predefined frequency for operational purposes, for instance, a predefined frequency of an external reader for transactions operations.

[0128] Even if the present invention has been described with reference to the embodiments described above, it is clear to the skilled person that it is possible to apply different modifications, variations and improvements of the present invention in light of the teachings described above and the field, and within the scope of the enclosed claims, without departing from the scope and purpose of the present invention.

[0129] For example, it is to be understood that, even if in the attached figures the main RFID antenna 140 and the compensation antenna 150 are represented as being formed on the same surface of the carrier layer 102, according to alternative embodiments (not shown), the main RFID antenna 140 and the compensation antenna 150 may be formed on different sides of the carrier layer 102.

[0130] Finally, those fields considered known to the skilled person have not been described to avoid covering in a useless way the described invention.

[0131] REFERENCE NUMBERS

[0132] 100: substrate

[0133] 102: carrier layer

[0134] 110: metal plate

[0135] 120: metal frame

[0136] 130: auxiliary coupling antenna for electronic module

[0137] 140: main RFID antenna

[0138] 142: capacitance coil of main RFID antenna

[0139] 144: cross-wire of main RFID antenna

[0140] 146: inductance coil of main RFID antenna

[0141] 150: compensation antenna

[0142] 152: capacitance coil of compensation antenna

[0143] 154: cross-wire of compensation antenna 156: inductance coil of compensation antenna

[0144] 160: electronic module

[0145] 100’: substrate according to the prior art

[0146] 102’: carrier according to the prior art

[0147] 110’: metal plate according to the prior art

[0148] 120’: metal frame according to the prior art

[0149] 130’: auxiliary coupling antenna for electronic module according to the prior art

[0150] 140’: coupling antenna according to the prior art

[0151] D1 : first direction of induced current

[0152] D2: second direction of induced current

[0153] L1 , L2: inductance

[0154] C1 , C2: capacitor

Claims

CLAIMS1. A substrate (100) for an RFID transponder comprising:A carrier layer (102) made of an insulating material;One or more metal inlays (110, 120) associated with said carrier layer (102);A main RFID antenna (140) formed on said carrier layer (102) and configured to communicate with an external electro-magnetic reader;A compensation antenna (150) formed on said carrier layer (102) and configured to boost communication of said main RFID antenna (140) with said external electro-magnetic reader,Wherein said main RFID antenna (140) and said compensation antenna (150) are formed on a same surface of said carrier layer (102).

2. A substrate (100) for an RFID transponder comprising:A carrier layer (102) made of an insulating material;One or more metal inlays (110, 120) associated with said carrier layer (102);A main RFID antenna (140) formed on said carrier layer (102) and configured to communicate with an external electro-magnetic reader;A compensation antenna (150) formed on said carrier layer (102) and configured to boost communication of said main RFID antenna (140) with said external electro-magnetic reader,Wherein said main RFID antenna (140) and said compensation antenna (150) are not physically connected to each other.

3. A substrate (100) for an RFID transponder comprising:A carrier layer (102) made of an insulating material;One or more metal inlays (110, 120) associated with said carrier layer (102);A main RFID antenna (140) formed on said carrier layer (102) and configured to communicate with an external electro-magnetic reader;A compensation antenna (150) formed on said carrier layer (102) and configured to boost communication of said main RFID antenna (140) with said external electro-magnetic reader,Wherein said main RFID antenna (140) and / or said compensation antenna (150) are selfresonance antennas.

4. The substrate (100) of claim 1 or 3, wherein said compensation antenna (150) is not physically connected to said main RFID antenna (140)5. The substrate (100) of claim 1 , 2, or 4, wherein said main RFID antenna (140) and / or said compensation antenna (150) are self-resonance antennas.

6. The substrate (100) of any of previous claims, wherein said main RFID antenna (140) and / or said compensation antenna (150) comprise a first coiled portion (146, 156) having a first winding direction and a second coiled portion (142, 152) having a second winding direction opposite to that of said first coiled portion, wherein said first coiled portion (146, 156) form an inductance coil and said second coiled portion form a capacitance coil of said main RFID antenna (140) and / or of said compensation antenna (150).

7. The substrate (100) of any of previous claims, wherein said main RFID antenna (140) and said compensation antenna (150) are concentric with each other and said compensation antenna (150) is formed around said main RFID antenna (140).

8. The substrate (100) of any of previous claims, wherein said metal inlay comprises a metal plate (110) formed on or inside said carrier layer (102).

9. The substrate (100) of any of previous claims, wherein said metal inlay comprises a metal frame (120) formed along a perimeter of said carrier layer (102).

10. The substrate (100) of claim 8, wherein said main RFID antenna (140) and said compensation antenna (150) are formed outside a perimeter of said metal plate (110).11 . The substrate (100) of claim 9, wherein said main RFID antenna (140) and said compensation antenna (150) are formed within a perimeter of said metal frame (120).

12. An RFID transponder, for example a smart card, comprising:- a substrate (100) of any of claims 1 to 11 ;- an electronic module coupled with said main RFID antenna (140);- one or more layers of insulating material attached to said substrate (100).

13. A method for operating a substrate (100) of any of previous claims 1 to 11 comprising the following steps:Exposing said substrate (100) to an electro-magnetic field generated by an external reader;Generating a main induced current having a first direction (D1 ) within said main RFID antenna (140) by means of inductive coupling with said electro-magnetic field;Generating an eddy current having a second direction (D2) opposite to said first direction (D1 ) within said metal inlay (110, 120) by means of inductive coupling with said electromagnetic field;Generating an additional induced current within said compensation antenna (150) by means of inductive coupling with said electro-magnetic field, wherein said additional induced current has a direction equal to said first direction (D1 ) and is configured to minimize the detuning effect of said one or more metal inlays (110, 120) and to boost a communication response of said main RFID antenna (140) with said external reader.

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