The patent's inventors are Charrat, Bruno (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "Embodiments of the present invention relate to
"Known NFC cards intended to be inserted within handheld devices are, for example, NFC Subscriber Identity Modules, also called SIM-NFC, or NFC Secure Digital (SD) cards. International Publication WO 98/58509 discloses a SIM-NFC card including contact pads, a microprocessor, an NFC module, and an antenna coil. The antenna coil has one or more coplanar coaxial windings parallel to the plane of the card, and therefore presents a magnetic axis perpendicular to the plane of the card. It can perform contact communications with the mobile telephone through the contact pads and an NFC communication with an external NFC device through the antenna coil.
"When the card and the external NFC device are placed sufficiently close to each other, the antenna coil of the card is inductively coupled to an antenna coil of the external NFC device, and data can be exchanged using conventional NFC techniques such as those defined by standards ISO 14443, ISO 15693, and
"In most applications, the external device emits a magnetic field while the NFC card is passive and sends data by load modulation. To that end, the antenna coil of the card is associated with passive components (e.g. capacitors) to form an antenna circuit tuned to a working frequency of the external device, for example 13.56 MHz.
"Handheld devices often contain metal parts or metal components such as a printed circuit board. When an NFC card is inserted in a handheld device, such metal parts or components reduce the inductance of the antenna coil, thereby altering the tuning frequency of the antenna circuit and reducing the maximum communication distance between the NFC card and the external device.
"It is difficult for NFC card manufacturers to know in advance in what conditions an NFC card will be used, that is, what will be the metallic environment of the card and how the NFC card will be arranged with respect to the printed circuit board, that is to say with its longitudinal axis parallel or perpendicular to one edge of the printed circuit board. The location for the card may vary widely from handheld device to handheld device. The location may be more or less electromagnetically shielded, and the handheld device may include a variable number of metal parts that are close to the card. Consequently, the maximum communication distance of the card depends heavily on the environment around the card and may vary greatly depending on the handheld device within which the card is inserted.
"In addition, the magnetic field emitted by external device induces eddy currents in the metal parts, which create a counter magnetic field that tends to neutralize the magnetic field, thereby reducing even more the maximum communication distance between the NFC card and the external device.
"It may therefore be desired to provide an NFC card that offers a maximum communication distance less dependent on the environment surrounding the card, when the card is inserted in a handheld device."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Embodiments of the invention relate to a NFC card including an antenna circuit including at least one antenna coil having one magnetic axis, and at least one integrated circuit linked to the antenna circuit, in which the magnetic axis of the antenna coil is substantially parallel to the plane of the card, and the magnetic axis of the antenna coil is at an angle of 45.degree..+-.10.degree. with respect to a longitudinal axis of the card 1.
"In one embodiment, the card further includes at least one electrically conductive screen extending near the antenna coil, which does not cross the magnetic axis, and does not include any magnetically permeable material between the the at least one conductive screen and the antenna coil.
"In one embodiment, the antenna circuit has a tuning frequency which has been set in the presence of the at least one electrically conductive screen, and does not detune when a metallic element is placed near the electrically conductive screen.
"In one embodiment, the conductive screen extends on or near the upper or the lower face of the card.
"In one embodiment, the NFC card includes a first conductive screen extending on one side of the antenna coil without crossing its magnetic axis, and a second conductive screen extending on another side of the antenna coil without crossing its magnetic axis.
"In one embodiment, the antenna coil is wound around a magnetically permeable core.
"In one embodiment, the antenna coil is wound around the magnetically permeable core with a 45.degree..+-.10.degree. angle with respect to a longitudinal axis of the magnetically conductive core.
"In one embodiment, the integrated circuit is configured to implement an active load modulation method including emitting bursts of magnetic field by means of the antenna coil when data are to be sent, in order to compensate the negative effect of the screen on the maximum communication distance offered by the card as far as the sending of data by load modulation is concerned.
"In one embodiment, the conductive screen includes at least one slot to reduce the effect of eddy currents circulating in the conductive screen in the presence of an external magnetic field.
"In one embodiment, the conductive screen is split into at least two sub-screens to reduce the effect of eddy currents circulating in the conductive screen in the presence of an external magnetic field.
"Embodiments of the invention also relate to a method for tuning an antenna coil of an NFC card, including the steps of providing a card according to the invention, and setting a tuning frequency of the antenna circuit in the presence of the at least one electrically conductive screen.
"Embodiments of the invention also relate to a method for performing a contactless communication between an NFC card and an NFC external device, including the steps of providing an NFC card according to the invention, setting a tuning frequency of the antenna circuit of the card in the presence of the at least one electrically conductive screen, emitting a first oscillating magnetic field with the external device, placing the card near the edges of a printed circuit board, and sensing, with the antenna coil of the NFC card, a counter magnetic field generated by eddy currents in the printed circuit board, to increase the maximum communication distance between the card and the external device.
"In one embodiment, the method further includes using the conductive screen to protect the tuning frequency of the antenna circuit against the detuning effect of the printed circuit board, to increase the maximum communication distance between the card and the external device.
"In one embodiment, the method further includes emitting bursts of a second oscillating magnetic field with the antenna coil of the NFC card, while the external device emits the first oscillating magnetic field, to transfer data from the card to the external device."
For the URL and additional information on this patent, see: Charrat, Bruno;
Keywords for this news article include: Electronics, Circuit Board,
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