Patent Publication Number: US-9836689-B2

Title: Shield element for mounting on an object

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a shield element for attachment to an object, which is NFC-capable in particular, to prevent wireless data transmission. An object can be understood in this context as any arbitrary object, in which an RFID/NFC transponder can theoretically be installed, in particular chip cards and passports, 
     for example. However, the invention is in no way restricted to this type of objects, but rather functions with all different types of objects having an RFID/NFC transponder. 
     In the course of the propagation of RFID and/or NFC technology and the applications thereof in the mass market, contactless smart cards are also becoming more and more widespread, for example, check cards or credit cards, on which sensitive personal data are stored, for example, health insurance card, passport, driver license, etc., and/or which enable cashless payment at corresponding NFC terminals in retail trade, for example, “Paypass” in Austria. By means of corresponding read devices or read terminals, data can be read out from these cards in a contactless manner at distances of up to approximately 5 cm. Using correspondingly stronger read devices, which do not conform to the standards, but are certainly easily implementable, however, it is also possible to achieve substantially greater read ranges if there is an intention to defraud. 
     For this reason, more concerns are increasingly being expressed by data protection organizations with respect to the endangerment of data protection and/or possible financial damage due to unauthorized and/or unintentional readout of such cards. To prevent unauthorized and/or unintentional data accesses to such smart cards, different shields are known from the prior art, in particular in the form of protective envelopes. 
     Such protective envelopes typically contain at least one metal layer, which is located flatly in direct proximity to the card when the card is inserted into the envelope. Eddy currents are thus induced in the metal layer by external magnetic fields generated by read devices, which typically have a frequency of 13.56 MHz, these eddy currents attenuating the read field according to the law of induction sufficiently that a data access to the card is suppressed. All such products presently on the market share the feature that the RFID/NFC card has to be inserted into an envelope to achieve the desired shielding effect, which is accompanied by disadvantages for some applications in practice. 
     If the wireless functionality of the chip card is actually to be made available, it is necessary in the case of some known shields to remove the card from the shield for contactless transaction. Other non-wireless transactions using the chip card, such as using the magnetic strip or merely presenting the card, also require the removal of the card from the shield and/or from the envelope. 
     In addition, the overall size and/or overall thickness of the chip card is substantially enlarged by the envelope in the case of some shields known from the prior art. It is no longer possible to use the chip card in accordance with its actual function, for example, as an ATM card, since the chip card with the shield does not fit into the intake of the read device and in addition the contact points or the magnetic strip are not accessible to the read device. In addition, chip cards become thicker by a factor of 3-10 due to the envelope and no longer have space in many typical wallets. 
     BRIEF SUMMARY OF THE INVENTION 
     The object of the invention is to provide a shield element which is simple to produce and which enables effective shielding. Preferred embodiments of the invention which solve some of the above-mentioned individual problems are described in the dependent claims. 
     The invention achieves this object in a shield element of the type mentioned at the outset using the features as claimed. The invention relates to a shield element for attachment to an object, in particular a flat object, preferably provided as a chip card, which has a main body, an RFID or NFC transponder comprising a transponder chip, and a coiled transmission antenna connected to the RFID or NFC transponder chip. According to the invention, it is provided that the shield element comprises a carrier made of electrically nonconductive material, wherein the carrier has a closed or closable conductor track, which, upon application of the shield element to the object, shields the electromagnetic fields, which are generated by an external read device and are oriented onto the transmission antenna of the RFID or NFC transponder chip. 
     One advantageous arrangement of the antenna having improved shielding effect provides that the carrier is designed as a film, wherein the conductor track is in particular applied, printed, or vapor deposited onto the film or is integrated into the film, and
         wherein the film is preferably designed as an adhesive film, which can be glued onto the main body of the object, and/or   wherein the total thickness of the film is preferably less than 0.5 mm.       

     A lesser thickness of an overall arrangement comprising an object and a shield element provides that the carrier is designed as a film, wherein the conductor track is in particular applied, printed, or vapor deposited onto the film or is integrated into the film, and
         wherein the film is preferably designed as an adhesive film, which can be glued onto the main body of the object, and/or   wherein the total thickness of the film is preferably less than 0.5 mm.       

     A preferred adaptation to the object to be shielded provides that the conductor track is arranged, in particular exclusively, in the outer circumferential region of the carrier, and/or that the carrier has the form of the object. 
     The shielding effect is further improved if the conductor track is designed as a continuous conductor loop, which in particular has an ohmic resistance of at most 5 ohms. 
     One embodiment of a conductor track, which manages with less metal area, provides that the conductor track has the form of an antenna having one or more turns, which is in particular at a distance of at most 5 mm from the transmission antenna of the object upon application of the shield element to the object. 
     One arrangement which further improves shielding provides that the conductor track has the form of an antenna, which extends along the transmission antenna of the object upon application of the shield element to the object. 
     An additional improvement of the shielding effect is achieved if the antenna is designed in the form of a coil having at least one turn, which extends along the outer region of the carrier. 
     A simple option for rapidly activating the wireless communication provides that the conductor track forming the coiled antenna is closed per se in a starting state and is interruptible via an interrupter switch. 
     For this purpose, it can advantageously be provided that the opener is designed in particular as a push switch or as a temperature-dependent resistor having positive temperature coefficient. 
     Alternative effective shielding can be achieved in that the coiled antenna is part of a resonant oscillating circuit, comprising the coiled antenna and at least one capacitor. 
     In applications in the RFID/NFC field, it can advantageously be provided that the resonant frequency of the oscillating circuit is less than 50 MHz, in particular less than 10 MHz. 
     Simple detuning of the oscillating circuit can be achieved in that the oscillating circuit has at least one switch, which is arranged such that upon actuation of the switch, an element of the oscillating circuit is short-circuited or deactivated, or a further element of the oscillating circuit, in particular a further capacitor, resistor, or a further coil is switched into the oscillating circuit, so that the resonant frequency changes by at least 10%. 
     A simple activation can be achieved by means of electronic activation, in that the switch or switches is/are formed by an electronic switch, in particular a field effect transistor. 
     An activation by touch can be achieved in that a touch sensor, in particular a capacitive touch sensor, is provided, which closes or opens the electronic switch upon detection of a touch. 
     An advantageous refinement of the shield element, which enables simple handling and mechanical protection of the object, provides that the main body has a container for the object, or the shield element is connected to a container, in particular glued thereto or is integrated into the container. 
     In addition, to achieve improved shielding, it can be provided that the conductor track is arranged on the container such that, for the case in which the object is located in the container, wireless communication between the RFID or NFC transponder of the object is effectively suppressed by the conductor track of the shield element. 
     It is preferably provided that the container is designed in the form of an envelope or a case. 
     A combination is particularly advantageous, wherein the shield element is applied to the object and in particular is glued thereon or is integrated into the object. 
     An advantageous deactivation of the shielding and/or an activation of the object provides that the oscillating circuit is tuned such that upon application of the shield element to the carrier object, a shared resonant frequency of the oscillating circuit and the RFID or NFC transponder including transmission antenna results, which differs by at least 1%, in particular 3%, from the system frequency of the RFID transponder, wherein the system frequency of the RFID transponder, and the transmission frequency of the external read device, is in particular at 13.56 MHz. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Multiple exemplary embodiments of the invention will be described in greater detail on the basis of the following figures of the drawing. 
         FIG. 1  shows a first object to be shielded. 
         FIG. 2  shows a first exemplary embodiment of a shield element. 
         FIG. 3  shows the magnetic field B T , which originates from an external RFID and/or NFC read device and is oriented onto the object, without shielding effect. 
         FIG. 4  shows the counter field B W  generated by the shield element. 
         FIG. 5  shows the field resulting from the fields shown in  FIGS. 3 and 4 . 
         FIG. 6  shows an alternative shield element attached to the object shown in  FIG. 1 . 
         FIG. 7  schematically shows the switching behavior of the embodiment of the invention shown in  FIG. 6 . 
         FIG. 8  schematically shows an alternative embodiment of a shield element having two capacitors. 
         FIG. 9  shows a shield element which has a container for the object. 
         FIG. 10  and  FIG. 11  schematically show an embodiment of the shield element in which the shielding can be canceled by means of touch. 
         FIG. 12  shows an equivalent circuit diagram of the shield element shown in  FIG. 10  and a chip card, which shows a transponder having an antenna and a transponder chip. 
         FIG. 13  shows the resonance capability of the system shown in  FIG. 12  as a function of the frequency. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a chip card  1 , which has a main body  10 . An RFID or NFC transponder chip  11  and a coiled transmission antenna  12 , which is connected thereto, are arranged in the main body  10 , the chip and the antenna jointly forming a transponder. In addition, the chip card  1  has further functions and has a magnetic strip (not shown) and an electrical contact field for use for contact-related data transmission, for example, in the case of an ATM card. The chip card  1  does not have a voltage supply located thereon and acquires the energy required for its operation from the electromagnetic field produced by a read device. The data transmission from the chip card  1  to the read device preferably takes place via load modulation, so that the chip card  1  can be implemented as a solely passive component having low buffer capacity. 
       FIG. 2  shows a first exemplary embodiment of a shield element  2 , which comprises a carrier  21  made of electrically nonconductive material. In the present exemplary embodiment, the carrier is designed as a film  21   a , onto which a conductor track  22  is printed. The conductor track  22  consists of electrically conductive material, wherein the ohmic total resistance along the conductor track  22  is 5Ω in the present exemplary embodiment. Of course, it is also possible to form conductor tracks  22  which have a lower resistance. Alternatively to printing conductor tracks  22  onto the film  21   a , of course, it is also possible to vapor deposit the conductor tracks  22  on the film  21   a , to implement them from a metal coating of the film  21   a  by means of etching technology, or to integrate them in the film  21   a . To achieve good adhesion of the film  21  on the object  1 , the film  21   a  is designed as an adhesive film. The adhesive film can be applied to the chip card  1  such that the circumferential edge of the adhesive film  21   a  is congruent with the circumferential edge of the chip card  1 . In some cases, it is also possible to arrange the conductor track  22  on the carrier  21  so that the area enclosed by the conductor track  22  is significantly less, in particular only half as large, as the area enclosed by the transmission antenna  12 . In such cases, the shielding effect is less strong, however, smaller shield elements  2  can be produced. 
     The total thickness of the film  21   a  is a thickness of 0.48 mm in the present exemplary embodiment. Of course, films are also to be produced in a lesser thickness, which does not make any difference for the shielding effect of shield element  2 . 
     In the present exemplary embodiment, a closed conductor track  22  is arranged on the carrier  21 ,  21   a , which, upon application of the shield element  2  to the object  1 , shields electromagnetic fields which are oriented from an external read device (not shown) onto the transmission antenna of the RFID or NFC transponder  11  of the chip card  1 . In the present exemplary embodiment, a part of the conductor track  22  extends exactly in parallel to the turns of the coiled transmission antenna  12 . In addition, the conductor track  22  also has additional short-circuit parts, which, like the circumferentially extending conductor track  22 , are led to an interrupter switch  23 . The additional short-circuit parts shown in  FIG. 2  are not necessary for most practical embodiments of the object  1 , and the desired shielding effect is caused solely by the outer circumferential part of the conductor track  22 . However, for special embodiments of objects  1 , the additional short-circuit parts shown in  FIG. 2  can improve the shielding effect. Alternatively, the conductor track  22  can also be embodied as a coiled antenna  22   a  ( FIG. 6 ). The interrupter switch  23  is closed in the normal state, i.e., the ends of the coiled antenna  22   a  or conductor track  22  which are connected to the interrupter switch  23  are short-circuited in the starting state. Upon actuation of the interrupter switch  23 , however, the conductor loop  22  can be interrupted, whereby the shielding effect of the shield element  2  is canceled. 
     Alternatively, it can also be provided in the embodiment shown in  FIG. 2  that the interrupter switch  23  is designed as a push switch or as a temperature-dependent resistor having positive temperature coefficient. 
     The shielding effect of the shield element  2  is shown in greater detail in  FIGS. 3 to 5 .  FIG. 3  shows the magnetic field B T , which is generated by an external RFID or NFC read device (not shown) and is directed onto the object or the chip card  1 , without the occurring shielding effect. This state can be produced if the conductor track  22  of the shield element  2  is interrupted by the interrupter switch  23 . In this state, the magnetic field B T  can permeate the transmission antenna unobstructed, whereby a data communication is enabled between the transponder, comprising the transponder chip  11  and the transmission antenna  12 , and an external RFID or NFC read device. 
       FIG. 4  shows the counter field B W , which results when the conductor track  22  or antenna  22   a  is closed. The smaller the distance between the conductor track  22  and the transmission antenna  12 , the greater the shielding effect of the shield element  2  as well. Fundamentally, upon application of the shield element  2  to the object  1 , the conductor track  22  is to be at a distance of at most 5 mm from the transmission antenna  12 . 
       FIG. 5  shows the resulting field, which results as a total of the externally excited field shown in  FIG. 3  and the counter field B W  shown in  FIG. 4 , which is generated by the shield element  2 . Since complete shielding can never be achieved, this field B res  is never equal to 0. However, a very small residual field remains, using which data communication is not possible. 
     If the interrupter switch  23  shown in  FIG. 2  is actuated, the counter field shown in  FIG. 4  is thus not provided and a data communication can be enabled via the externally excited field B res =B T . 
     An alternative embodiment, which is shown in  FIG. 6 , has a coil antenna  22   a  as a conductor track. It is known from physics that two oscillating circuits, which have the resonant frequencies w 1  and w 2 , respectively, upon separate observation, have a shared resonant frequency w 0  upon close magnetic coupling, which is less than f 1  and is also less than f 2 , i.e., f 0 &lt;f 1  and f 0 &lt;f 2 . 
     The coil antenna  22 ,  22   a  of the shield element  2  shown in  FIG. 6  is, as shown in  FIG. 7 , connected in parallel to a push switch  242  and to a capacitor  241  designed as a plate capacitor. In the present case, an oscillating circuit  24  is formed by this specific arrangement, the resonant frequency of which is selected such that upon application of the shield element  2  on the object  1 , with open switch  241 , the resulting resonant frequency of the combination consisting of the shield element  2  and the object  1  deviates enough from the system frequency of the RFID or NFC transponder, typically of 13.56 MHz, that no data communication is possible with an external RFID or NFC read device. As shown in  FIG. 6 , the shield element  2  has a carrier  21  in the form of a film  21   a . This film  21   a  is glued onto the chip card  1 . 
     If the switch  242  is open, the resonant frequency, which is predefined by the capacitor  241  and the coil antenna  22   a , of the oscillating circuit  24  formed on the shield element  2  is in a range less than 50 MHz, in particular less than 10 MHz, whereby the resulting resonant frequency of the combination consisting of the shield element  2  and the object  1  is also sufficiently far below the system frequency of the RFID or NFC transponder that no data communication is possible between the transponder and an external RFID or NFC read device. If the switch  242  is closed, the resonant frequency of the oscillating circuit  24  thus changes and is in a range which is not suitable for moving the resulting resonant frequency of the combination consisting of the shield element  2  and the object  1  sufficiently far away from the system frequency of the RFID or NFC transponder, whereby a data communication becomes possible between the RFID or NFC transponder in the chip card  1  and an external read device. 
     An alternative embodiment of an oscillating circuit is only schematically shown in  FIG. 8 . The oscillating circuit  24  shown in  FIG. 8  has the antenna  22   a , shown in the form of a coil  22   a , and two capacitors  241   a ,  241   b . The first capacitor  241   a  is connected in parallel to the coil  22   a . The second capacitor  241   b  is connected in series to the switch  242 . The series circuit comprising the second capacitor  241   b  and the switch  242  is connected in parallel to the coil  22   a . Both capacitors  241   a ,  241   b  are formed on the film  21  in the form of two conductor layers opposite to one another. 
     It is fundamentally sufficient for the oscillating circuit  24  to have a switch  242 , which is arranged such that upon the actuation of the switch  242 , i.e., upon opening or closing of the switch  242 , an element of the oscillating circuit  24  is short-circuited or deactivated, or a further element, such as a capacitor, a resistor, or a further coil, is switched into the oscillating circuit  24 , and the resonant frequency thus changes. In some cases, a change of the resonant frequency by approximately 10% is sufficient to cause the shielding effect of the shield element  2  to disappear and to enable a data communication with an external read device. 
       FIG. 9  shows a further embodiment of the invention in greater detail, in which the carrier  21  has the shape of a container for the object  1 . Alternatively, the shield element  2  or the carrier  21  thereof can also be connected to the container, in particular glued thereto or integrated therein. As also in the shield elements shown in  FIGS. 2 and 6 , a conductor track  22 , which is designed in the form of a coil antenna  22   a , is located in the outer circumferential region. As a result of the special design of the carrier body as a container, a chip card  1  can be inserted into the carrier  21  of the shield element  2 . The shielding effect is designed identically in this case to the shielding shown in  FIG. 6  or in  FIG. 2 . The magnetic fields resulting due to the shielding also correspond to the magnetic fields shown in  FIGS. 3 to 5 . The conductor track  22  is arranged in this case on the container such that, for the case in which the object  1  is located in the container, a wireless communication between the RFID or NFC transponder of the object  1  and an external RFID or NFC read device (not shown) is effectively suppressed as a result of the arrangement of the shield element  2 , in particular the conductor track  22  thereof. Shield elements  2  which have a container for the object  1  are typically manufactured in the form of envelopes or cases. In particular chip cards  1  may be transported comfortably therein in wallets. 
     A further preferred embodiment of the invention is shown in  FIG. 10 .  FIG. 10  shows a shield element  2 , in which the shielding can be canceled by means of touching a touch sensor  245 , which is situated on the shield element  2 , comprising two electrodes  246   a ,  246   b  and a detection unit  247 . In this advantageous embodiment, which corresponds otherwise to the embodiment shown in  FIG. 6 , the switch  242  is implemented by an electronic switch, in the present case by a field effect transistor. Furthermore, the two electrodes  246   a ,  246   b  of the touch sensor  245  are arranged adjacent to one another in the interior of the film  21   a . For example, if a human finger touches the electrodes  246   a ,  246   b  or this finger enters the region of the electrodes  246   a ,  246   b , this can be detected by the detection unit  247 . The detection unit acquires the energy required for its operation from the coil antenna  22   a  and/or the field linked to the coil antenna  22   a . Upon detection of a touch, the detection unit  242  activates the electronic switch  242 , which short-circuits the capacitor  241   a ; C T  and therefore changes the resonant frequency of the oscillating circuit formed from the coil antenna  22   a  and the capacitor C T . 
     Furthermore, in all embodiments of the shield element  2 , the option exists of changing the resonant frequency of the oscillating circuit formed from the coil antenna  22   a  and the capacitor C T  in that a further element, such as a capacitor  241   b , a resistor, or a further coil is switched into the oscillating circuit by an electronic switch, which is implemented in the form of a field effect transistor, for example. One example of such an embodiment is shown in  FIG. 11 . The activation of the field effect transistor can be performed in particular in this case via a touch sensor  245 , which closes or opens the electronic switch  242  upon detection of a touch. Such a touch switch  245  can be implemented as a capacitive touch sensor  245  as a result of the specific conditions, in particular on a film, wherein electrode areas  246   a ,  246   b , which are arranged adjacent to one another in a plane in or on the carrier film, form a capacitor, the capacitance of which changes upon touching of the electrode areas and/or upon approach to the electrode areas. 
     If the shield element  2  and the object  1  are joined together, as a result of the shielding effect of the shield element  2 , a data communication of the RFID or NFC transponder or the transmission antenna thereof with an external read device becomes impossible. In addition, a suppression of the shielding effect can be generated by a special activation, so that a data communication of the external RFID or NFC transponder and the transmission antenna  22  thereof with an external read device is again enabled. As shown in  FIG. 2 , it is particularly advantageous to glue the shield element  2  to the object, so that the shield element  2  is applied permanently. Alternatively, as shown in  FIG. 9 , the shield element  2  can be designed as a container, wherein the object to be shielded, in particular in the form of a chip card  1 , is introduced into the container of the shield element  2 . 
       FIG. 12  shows an equivalent circuit diagram of the shield element  2  and a chip card  1  as a coupled overall system. The chip card  1  has a transponder having a transmission antenna  12  and a transponder chip  11 . It is clear from this illustration that the transmission antenna  12  of the object  1  and the coiled antenna  22   a  of the shield element  2  are inductively coupled to one another. It is presumed that the influences of the touch sensor  245  and the switch on the overall system are small and only affect the capacitance of the illustrated capacitor  241 . 
     In all of these embodiments, it is possible to prepare the shield element  2  for its application to a specific object  1 . Due to the mutual coupling of the individual parts of the RFID or NFC transponder and the transmission antenna  12  and the elements of the oscillating circuit  24 , an expanded oscillating circuit is formed, in which a shared resonant frequency results. The oscillating circuit  24  is tuned to the RFID transponder and the transmission antenna  12  such that upon application of the shield element  2  to the carrier object  1 , a shared resonant frequency of the oscillating circuit  24  and the RFID or NFC transponder including transmission antenna  12  results, which differs by at least 1%, in particular at least 3%, from the system frequency of the RFID transponder or the external read device. The system frequency of the RFID transponder and the transmission frequency of the external read device are normally at 13.56 MHz in standard applications. 
     By switching in or out further capacitors, inductors, or resistors by means of the above-mentioned switch  242  into or from the oscillating circuit thus produced, said circuit can be detuned so that a shielding effect disappears and a data communication of the RFID or NFC transponder via its transmission antenna  12  with an external read device becomes possible. 
       FIG. 13  shows the resonance capability of the system shown in  FIG. 12  as a function of the frequency. The resonance curve R 1  of the transponder, consisting of transponder chip  11  and transmission antenna  12 , of the object  1  has the resonant frequency w 1 . It is apparent that the resonant frequency of the transponder is in the range B of the permissible transmission frequencies. In the starting state, i.e., switch  242  open, the shield element  2  has a resonance curve R 2  having a resonant frequency w 2 , which has approximately the same order of magnitude as the resonant frequency w 1  of the transponder. The resonance curve R 2  of the shield element  2  having open switch is identified with w 2  in  FIG. 13 . If one assumes ideal coupling between the shield element  2  and the chip card  1  or the transponder  11 , the resonant frequency w 0  of the resonance curve R 0  of the resulting system thus results according to 
     
       
         
           
             
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               0 
             
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                     w 
                     1 
                     2 
                   
                   · 
                   
                     w 
                     2 
                     2 
                   
                 
                 
                   
                     w 
                     1 
                     2 
                   
                   + 
                   
                     w 
                     2 
                     2 
                   
                 
               
             
           
         
       
     
     The resonant frequency w 0  of the resulting system is less than the two resonant frequencies w 1 , w 2 . Due to this shift of the resonant frequency, a communication of the chip card  1  with a read device, the transmission frequency range of which is within the range B of the permissible transmission frequencies, is not possible. 
     The resonance curve R 2 ′ shows the resonance of the shield element  2  with closed switch  242 . If the switch  242  is closed, the resonant frequency w 2 ′ of the oscillating circuit  242  is substantially higher than with open switch  242 , since the capacitance in the oscillating circuit  24  is substantially reduced as a result of the short-circuit of the switch  242 . Since the intrinsic resonant frequency w 1  of the object  1  or of the transponder is identical to the case of the open switch  242 , a value which essentially corresponds to the resonant frequency w 1  results as the resonant frequency w 0 ′ of the overall system with closed switch. Since the resonant frequency w 0 ′ of the overall system is hardly shifted in relation to the resonant frequency w 1  of the transponder, a data communication is possible in the range B of the permissible transmission frequencies. 
     The shield element  2  normally does not have a separate power supply and functions as a solely passive component. However, it is also conceivable to provide a separate power supply in the form of a battery on the carrier  21  of the shield element.