NFC antenna

A near-field communication antenna includes a conductive plane; and four slots in the conductive plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application No. 19171840.2, filed on Apr. 30, 2019, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally concerns electronic devices and, more specifically, devices integrating a near-field communication (NFC) antenna. The present disclosure more particularly tackles NFC antennas used for point of sale (POS) and mobile point of sale (mPOS) applications.

BACKGROUND

Near-field radio frequency communication systems are becoming increasingly common, particularly since the development of near-field communication technologies according to ISO 14443 standard or the NFC Forum. Such systems use a radio frequency electromagnetic field, emitted by an antenna of a device (terminal or reader), to communicate with another device (card or tag).

NFC antennas are usually required to cope with challenging environments. Several constraints, such as a reduced available space, a limited supply voltage for the NFC system, and a disturbing ambient electric noise, frequently reduce the performance of such antennas.

SUMMARY

There is a need to improve the performance of existing near-field communication antennas.

One embodiment addresses all or some of the drawbacks of known near-field communication antennas.

One embodiment provides a near-field communication antenna comprising:

a conductive plane; and

four slots in said conductive plane.

According to an embodiment, the above-described antenna is capable of meeting the EMVCo standard.

According to an embodiment, said four slots have a length comprised between approximately 20 mm and approximately 50 mm, preferably between 20 mm and 50 mm.

According to an embodiment, said four slots have a length preferably around 40 mm, preferably equal to 40 mm.

According to an embodiment, said four slots have a width comprised between approximately 1 mm and approximately 3 mm, preferably between 1 mm and 3 mm.

According to an embodiment, said four slots have a width preferably around 1 mm, preferably equal to 1 mm.

According to an embodiment, said four slots form a square whose sides are non-contiguous.

According to an embodiment, said four slots of said antenna are equidistant from the middle of said square by a length of approximately 25 mm.

According to an embodiment, said four slots are joined together by two additional internal slots in said conductive plane, said internal slots being perpendicular to each other and forming the arms of a cross centered on the middle of said square.

According to an embodiment, the above-described antenna further comprises a hole centered on the middle of said square.

According to an embodiment, said four slots are joined to said hole by four additional internal slots.

According to an embodiment, one of said internal slots extends to an edge of said conductive plane.

One embodiment provides an electronic device comprising an antenna such as the above-described antenna.

One embodiment provides a point of sale terminal comprising such a device.

One embodiment provides a mobile phone comprising such a device.

According to an embodiment, said hole is facing a wireless charging module of said mobile phone.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the communication protocols (electromagnetic field modulation techniques), be they secure or non-secure, between the device and the outside have not been detailed, the described embodiments being compatible with usual techniques of generation and of modulation of radio frequency signals for near-field communication.

Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements linked or coupled together, this signifies that these two elements can be connected or they can be linked or coupled via one or more other elements.

FIG. 1schematically shows, in the form of blocks, an example of a near-field communication system of the type to which the described embodiments apply.

Near-field communication (NFC) circuits can especially be found in communicating electronic devices of the type of cell phone1. Typically, a cell phone or smartphone, equipped with NFC functionalities, is capable of communicating not only over the wireless telephone network (for example, GSM) or according to medium-range radio frequency protocols (for example, Wi-Fi, Bluetooth), but also in near-field (also called contactless mode), in quasi-contact at 4 to 5 centimeters, according to standards, for example ISO 14443 or NFC Forum. Reference will be made hereafter to an NFC device to designate a device integrating near-field contactless communication functionalities.

The NFC device (telephone1inFIG. 1) is capable of communication by near-field electromagnetic coupling with another NFC device3. This other device3, for example, a terminal (TERM), radiates a magnetic field intended to be captured by the NFC circuits of the phone. Although the case of a telephone1and of a terminal3(for example, a contactless payment terminal) is considered, all that will be described more generally applies to any system where an electromagnetic transponder or NFC device detects an electromagnetic field radiated by a reader or terminal. In other words, the embodiments apply to any system where two NFC devices1and3are capable of communication by near-field electromagnetic coupling.

According to applications, for a communication, one of the devices operates in so-called reader mode while the other operates in so-called card mode, or the two devices communicate in peer-to-peer mode (P2P). Each device1,3comprises various electronic circuits, among which a circuit forming a near-field communication interface, or NFC interface, between the NFC device and the outside. Such an interface is used, among others, in reader mode, to generate a radio frequency signal transmitted by an antenna and, in card mode, to decode a detected radio frequency signal. The radio frequency field generated by one of the devices is detected by the other device, which is located within its range and which also comprises an antenna.

In the example of a smartphone-type mobile terminal1, the latter comprises at least one display12as well as elements14(buttons, keys, print sensor, touch-screen, cameras, etc.) forming user interface elements.

FIG. 2schematically shows, in the form of blocks, an example of a near-field contactless payment terminal3.

In the example ofFIG. 2, the near-field contactless payment terminal3is capable of communication by near-field electromagnetic coupling with another NFC device (for example, the telephone1inFIG. 1, a contactless payment card, a NFC tag etc.). The terminal3typically comprises (represented in dotted lines):

a matching circuit33or network, capable of filtering electromagnetic interference (EMI);

an antenna5, capable of receiving or transmitting signals; and

other circuits or components depending on the desired application, represented inFIG. 2by block37.

The near-field operation of terminal3is generally based on the use of the NFC controller31associated with a contactless front end (CLF). The controller31communicates, on the one hand, with the transmit/receive antenna5and, on the other hand, with a host circuit or host processor, represented by block37in the example ofFIG. 2. The host circuit37is, for example, capable of relaying information between the controller/router31and different applications hosted by terminal3.

Among such applications, some are so-called secure applications (as opposed to non-secure applications) which use specific validation or control circuits. Such secure applications are then totally or partly hosted by specific circuits commonly called secure elements (not shown inFIG. 2) which are provided with processing and/or key/code/signature/etc. storage circuits enabling to validate/process/authenticate/etc. a secure operation or transaction. For example, a secure transaction is a payment operation (a contactless payment operation), an access control operation, an application or peripheral unlocking operation, etc.

The controller31particularly contains a routing table defining the parameters and communication channels between the radio frequency contactless front end and the elements of terminal3according to the executed application. Such a routing table enables the host circuit37to correctly route communications towards the different elements and enables the controller31to correctly transmit the communications received from circuit37. In certain cases, secure elements are capable of directly communicating with the controller31without passing through the host circuit37.

Usually, the antenna of terminal3is a loop antenna consisting of a loop or coil of conductive wire (not shown). The conductive wire of a loop antenna is generally made of copper or aluminum. Such type of antenna is notably sensitive to ambient electromagnetic noise emitted by the surrounding environment.

Mobile devices, such as telephone1(FIG. 1), also usually comprise loop antennas. In mobile devices1, it is critical to embed the smallest antenna as possible. Moreover, most of the mobile devices1have a metallic casing and also encompass several metallic parts. This also reduces the performance of a loop antenna because of eddy currents circulating inside this metallic casing and/or inside these metallic parts. A high output power is thus generally required in order to compensate for the losses by eddy currents. These eddy currents circulating in metallic surrounding parts and/or casing often lead to a low radiofrequency (RF) performance of the loop antenna, which reduces the chances to successfully pass the EMVCo certification tests.

According to the disclosed embodiments, the loop antenna is replaced by a slot antenna5configured for operating in NFC frequency range.

FIG. 3illustrates an embodiment of a NFC slot antenna5.

According to this embodiment, the NFC slot antenna5comprises a conductive plane51, which is preferably made of copper. In this plane51, slots are formed according to a specific pattern. In the embodiment ofFIG. 3:

four external slots531,532,533, and534are arranged in such a way as to form a square shape, whose sides are disjoint or non-contiguous; and

two internal slots551and552are arranged in such a way as to form a cross shape, centered with respect to the above-described square, whose arms are orthogonal to the four external slots531,532,533, and534.

In other words, the two internal slots551and552form the arms of a “cross potent” or “crutch cross” with one of the external slots531,532,533, and534at each of its four ends.

All four external slots531,532,533, and534do not intersect nor touch each other. The two internal slots551and552, however, intersect perpendicularly in the middle555of the square formed by the four external slots531,532,533, and534. The internal slot551hence meets the two parallel external slots531and533in their middle. Furthermore, the internal slot552meets the two parallel external slots532and534in their middle.

According to the embodiment ofFIG. 3, the conductive plane51of the NFC slot antenna5has a rectangular shape with rounded corners. The cross potent shape, formed by the external slots531,532,533, and534and the internal slots551and552, is closer to one of the two narrow sides of plane51(inFIG. 3, the top/upper side511) than to the other narrow side of plane51(inFIG. 3, the bottom/lower side513). The external slots531and533are preferably parallel to both narrow sides511,513of plane51. The middle555of the square formed by the four external slots531,532,533, and534is preferably equidistant to both long sides512,514of plane51.

One of the internal slots, for example slot551, extends to an edge of plane51, in this case, the narrow side511of plane51. In other words, the slot551separates or cuts, partially and longitudinally, the plane51of antenna5in two halves. The slot551thus only opens onto the top narrow side511of plane51, whereas it does not open onto the narrow side513of plane51. Two contact pick-up pads515, one on each side of slot551, are located close to where slot551opens onto the narrow side511of plane51.

The internal slot551hence opens:

at one end, onto the narrow side511of plane51; and

at the other end, onto the external slot533.

Meanwhile, the internal slot552opens:

at one end, onto the external slot532; and

at the other end, onto the external slot534.

According to a particular example of the embodiment ofFIG. 3, the conductive plane51of the NFC antenna5has:

a length of around 80 mm, preferably equal to 80 mm; and

a width of around 58 mm, preferably equal to 58 mm.

The external slots531,532,533, and534preferably have a large length to width ratio. In the embodiment ofFIG. 3, the four external slots531,532,533, and534have:

a length comprised between approximately 20 mm and approximately 50 mm, preferably between 20 mm and 50 mm, preferably around 40 mm, preferably equal to 40 mm; and

a width comprised between approximately 1 mm and approximately 3 mm, preferably between 1 mm and 3 mm, preferably around 1 mm, preferably equal to 1 mm.

In the embodiment ofFIG. 3, the external slots531,532,533, and534are equidistant to the middle555of the square they form by a distance of approximately 25 mm, preferably equal to 25 mm.

The slot antenna5can operate at frequencies suitable for NFC applications, for example at a frequency of around 13.56 MHz.

A NFC slot antenna, such as antenna5depicted inFIG. 3, is mechanically stronger than a loop antenna. The design of NFC slot antenna5also leads to fewer losses. The NFC slot antenna5can therefore operate at a lower output power than the power required to operate a loop antenna.

Thanks to its particular geometry, which provides an extended conductive area compared to loop antennas, the antenna5also produces a favorable loading effect on the antenna usually used for the measurement test bench of the standard EMVCo, called EMVCo PICC antenna. This advantage greatly improves the fulfillment of the standard conditions by the antenna5and facilitates the respect of the EMVCo certification tests.

Moreover, the antenna5is characterized by a lower quality factor than loop antennas, hence allowing one to avoid the use of damping resistors in order to reduce the quality factor. The antenna5also provides a way to easily focus a magnetic field according to required testing positions, by simply placing the external slots531,532,533, and534at specific locations.

FIG. 4illustrates another embodiment of a NFC slot antenna.

According to this preferred embodiment, the NFC slot antenna5also comprises the conductive plane51, which is preferably made of copper. In this plane51, several slots and a hole are formed according to a specific pattern. In the embodiment ofFIG. 4:

four external slots531,532,533, and534are arranged in such a way as to form a square shape, whose sides are disjoint or non-contiguous as in the embodiment ofFIG. 3;

a round/circular hole517is centered on the middle555of the above-described square shape; and

four internal slots561,562,563, and564are arranged in such a way as to respectively join each of the four external slots531,532,533, and534with the hole517.

All four external slots531,532,533, and534do not intersect nor touch each other. The four internal slots561,562,563, and564are arranged in such a way that:

the internal slot561meets the external slot531perpendicularly in its middle and one end of the internal slot561opens onto the hole517;

one end of the internal slot562meets the external slot532perpendicularly in its middle and the other end of the internal slot562opens onto the hole517;

one end of the internal slot563meets the external slot533perpendicularly in its middle and the other end of the internal slot563opens onto the hole517; and

one end of the internal slot564meets the external slot534perpendicularly in its middle and the other end of the internal slot564opens onto the hole517.

The antenna5ofFIG. 4is similar to the antenna5ofFIG. 3, except that the antenna5ofFIG. 4features a hole517in its conductive plane51. A NFC slot antenna5like the one depicted inFIG. 4can therefore be easily obtained/produced from the slot antenna5ofFIG. 3by making, through the plane51, a hole517centered inside the square formed by the four external slots531,532,533, and534. The fabrication/manufacturing of the NFC slot antenna5ofFIG. 4can consequently be facilitated in this way.

According to the embodiment ofFIG. 4, the conductive plane51of the NFC slot antenna5has a rectangular shape with rounded corners. The squared shape formed by the external slots531,532,533, and534, with the hole517centered on its middle555, is closer to one of the two narrow sides of plane51(inFIG. 4, the top/upper side511) than to the other narrow side of plane51(inFIG. 4, the bottom/lower side513). The external slots531and533are preferably parallel to both narrow sides511,513of plane51. The middle555of the square formed by the four external slots531,532,533, and534is preferably equidistant to both long sides512,514of plane51. It is worth noting that the middle555of the above-mentioned square, formed by the four external slots531,532,533, and534, is coincident with the center of the circular hole517of plane51.

One of the internal slots, for example slot561, extends to an edge of plane51, in this case, the narrow side511of plane51. In other words, the slot561separates or cuts, partially and longitudinally, the plane51of antenna5in two halves. The slot561thus not only opens onto the top narrow side511of plane51, but also onto the round hole517. Two contact pick-up pads515, one on each side of slot561, are located close to where slot561opens onto the narrow side511of plane51.

The internal slot562opens:

at one end, onto the round hole517; and

at the other end, onto the external slot532.

The internal slot563opens:

at one end, onto the round hole517; and

at the other end, onto the external slot533.

The internal slot564opens:

at one end, onto the round hole517; and

at the other end, onto the external slot534.

According to a particular example of the embodiment ofFIG. 4, the conductive plane51of the NFC antenna5has:

a length of around 80 mm, preferably equal to 80 mm; and

a width of around 58 mm, preferably equal to 58 mm.

The external slots531,532,533, and534preferably have a large length to width ratio. In the embodiment ofFIG. 4, the four external slots531,532,533, and534have:

a length comprised between approximately 20 mm and approximately 50 mm, preferably between 20 mm and 50 mm, preferably around 40 mm, preferably equal to 40 mm; and

a width comprised between approximately 1 mm and approximately 3 mm, preferably between 1 mm and 3 mm, preferably around 1 mm, preferably equal to 1 mm.

In the embodiment ofFIG. 4, the external slots531,532,533, and534are equidistant to the center of the hole517by a distance of approximately 25 mm, preferably equal to 25 mm.

The slot antenna5depicted inFIG. 4can operate at frequencies suitable for NFC applications, for example at a frequency of around 13.56 MHz.

A NFC slot antenna, such as antenna5depicted inFIG. 4, is mechanically stronger than a loop antenna. The design of NFC slot antenna5also leads to fewer losses. The NFC slot antenna5can therefore operate at a lower output power than the power required to operate a loop antenna.

Thanks to its particular geometry, which provides an extended conductive area compared to loop antennas, the antenna5also produces a favorable loading effect on the antenna usually used for the measurement test bench of the standard EMVCo, called EMVCo PICC antenna. This advantage greatly improves the fulfillment of the standard conditions by the antenna5and facilitates the respect of the EMVCo certification tests.

Moreover, the antenna5is characterized by a lower quality factor than loop antennas, hence allowing one to avoid the use of damping resistors in order to reduce the quality factor. The antenna5also provides a way to easily focus a magnetic field according to required testing positions, by simply placing the external slots531,532,533, and534at specific locations.

a parallel inductance of around 140 nH;

a parallel resistance of around 0.4Ω; and

a parasitic capacitance of around 5.8 pF.

FIG. 5schematically shows, in the form of blocks, an example of a mobile phone comprising a NFC slot antenna of the type to which the described embodiments apply.

InFIG. 5, a smartphone, for example, the mobile phone1depicted inFIG. 1, is equipped with a NFC slot antenna such as the antenna5ofFIG. 4. The antenna5is, in this example, mounted on a motherboard16(represented by a dotted rectangle inFIG. 5) of smartphone1. This motherboard also features a wireless/inductive charging module18(represented by a hatched circle inFIG. 5).

InFIG. 5, the antenna5is arranged such that the hole517, inside the plane51of antenna5, is facing the wireless charging module18. The hole517is preferably facing an antenna of the wireless charging module18. This allows both the wireless charging module18and the NFC slot antenna5to exchange signals with the outside of smartphone1without interfering with each other. Furthermore, using a NFC slot antenna5can allow one to save valuable space inside smartphone1.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. In particular, the geometry of the NFC antenna5can be tuned in order to meet other requirements. For example, one can adjust to his needs the dimensions and locations of the slots531,532,533,534,551,552,561,562,563, and564, the radius and the position of the center555of the hole517, the overall dimensions of plane51, etc. In broad terms, the design of the slot antenna5can be adapted to fit another application.

Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.