NFC card sensitive to eddy currents

1. An NFC card comprising:

an antenna circuit comprising at least one antenna coil having one magnetic axis, and

at least one integrated circuit linked to the antenna circuit,

wherein 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 between 20° and 70° with respect to a longitudinal axis of the card.

2. The NFC card according to claim 1 , wherein the card further comprises at least one electrically conductive screen extending near the antenna coil, which does not cross the magnetic axis, and the card does not include any magnetically permeable material between the at least one conductive screen and the antenna coil.

3. The NFC card according to claim 2 , wherein 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.

4. The NFC card according to claim 2 , wherein the at least one conductive screen extends on or near the upper or the lower face of the card.

5. The NFC card according to claim 2 , wherein the at least one conductive screen comprises 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.

6. The NFC card according to claim 1 , wherein the antenna coil is wound around a magnetically permeable core.

7. The NFC card according to claim 6 , wherein the antenna coil is wound around the magnetically permeable core with a 45°±10° angle with respect to a longitudinal axis of the magnetically conductive core.

8. The NFC card according to claim 2 , wherein the integrated circuit is configured to implement an active load modulation method comprising emitting bursts of magnetic field by way of the antenna coil when data are to be sent, in order to compensate the negative effect of the at least one screen on the maximum communication distance offered by the card during sending of data by load modulation.

9. The NFC card according to claim 2 , wherein the at least one conductive screen comprises at least one slot to reduce the effect of eddy currents circulating in the conductive screen in the presence of an external magnetic field.

10. The NFC card according to claim 2 , wherein the at least one 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.

11. A method for tuning an antenna coil of an NFC card, the method comprising:

providing a card according to claim 2 , and

setting a tuning frequency of the antenna circuit in the presence of the at least one electrically conductive screen.

12. A method for performing a contactless communication between an NFC card and an NFC external device, the method comprising:

providing an NFC card comprising:

an antenna circuit including at least one antenna coil having one magnetic axis, and

at least one integrated circuit linked to the antenna circuit,

wherein 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 between 20° and 70° of with respect to a longitudinal axis of the card, and

wherein the card further comprises at least one electrically conductive screen extending near the antenna coil, which does not cross the magnetic axis, and the card does not include any magnetically permeable material between the at least one conductive screen and the antenna coil,

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.

13. The method according to claim 12 , further comprising using the at least one 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.

14. The method according to claim 12 , further comprising 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.