EP1145377A1

EP1145377A1 - Antenna arrangement in a metallic environment

Info

Publication number: EP1145377A1
Application number: EP99959506A
Authority: EP
Inventors: Philippe Porte
Original assignee: Gemplus Card International SA; Gemplus SA
Current assignee: Gemplus SA
Priority date: 1998-12-22
Filing date: 1999-12-21
Publication date: 2001-10-17
Also published as: AU1665500A; FR2787640B1; CN1336022A; WO2000038275A1; FR2787640A1; US6452563B1; CN1230941C

Abstract

The invention concerns an arrangement for an antenna (A) having the general shape of a loop, directly in the proximity of at least a metallic element (10). The invention is characterised in that each metallic element (10) comprises an orifice (18) arranged substantially opposite the surface defined by the antenna (A), and a slot (16) forming a gap width, arranged through the thickness of the metallic element (10), between the internal edge (21) delimiting the orifice (18) and the external edge (20) of said metallic element (10). The invention is applicable to scanners and radio frequency communication devices.

Description

ARRANGEMENT OF AN ANTENNA IN A METALLIC ENVIRONMENT

The present invention relates to an arrangement of an antenna in a metallic environment.

The invention relates more particularly to the arrangement of an antenna in the general form of a loop, of the type comprising at least one turn; said antenna extending directly near and substantially parallel to at least one metallic element. It is known from the state of the art that the presence of metal, in the immediate vicinity of a loop-shaped antenna, generates disturbances in the emission and / or reception of electromagnetic waves. Indeed, such an antenna generally has the function of transmitting or picking up a predominantly magnetic field. If it is positioned in the immediate vicinity of a metal element, it will naturally tend to behave like a short-circuited turn. The antenna performance will therefore be degraded, or even completely wiped out.

The use of loop-shaped antennas is becoming widespread and has many applications since they are found, for example, in the body of contactless type microprocessor cards, in the support element of so-called "smart" electronic labels, but especially in many readers and other radio frequency communication devices.

For many applications, such as access control or vending machines, it is important that the antennas and the associated electronics can be protected against vandalism and therefore be integrated into a metallic environment.

In order to avoid the problems mentioned above, that is to say those resulting from the influence of the metallic environment on the functioning of the antenna, it has already been proposed to interpose a layer of "absorbent" material between the antenna and the metallic support element. However, it is generally an expensive material such as ferrite, which appreciably limits the advantage of this solution.

More generally, the antenna is voluntarily distant from the metallic environment, the relative position between these two elements being determined to obtain satisfactory operation of the antenna. However, this type of arrangement has the drawback of considerably increasing the total size of the assembly.

Also, the technical problem to be solved by the object of the present invention is to propose an arrangement of an antenna in the general form of a loop, directly near at least one metallic element, an arrangement which would make it possible to avoid the problems of the state of the art by offering a minimum size, while remaining a limited production cost.

The solution to the technical problem posed consists, according to the present invention, in that each metallic element comprises, on the one hand, a light formed substantially opposite the surface delimited by the antenna, and on the other hand, a slot forming air gap, formed through the thickness of the metallic element, between the internal edge delimiting the light and the external edge of said metallic element. The combination of the light and the air gap provided on each metallic element makes it possible to avoid any phenomenon of shielding of the antenna by said metallic element. The invention as thus defined has the advantage of guaranteeing perfect functioning of the antenna in a metallic environment, even in the absence of absorbent material interposed or of significant separation between said antenna and the metallic element considered. Thus, the antenna offers identical or equivalent performance to that which it would have in a non-metallic environment, while benefiting from the advantages specific to the use of metal, in particular in terms of security and more particularly resistance to vandalism.

In a particularly advantageous manner, the antenna extends in a manner substantially parallel to the metallic element of which it is directly in the vicinity, in order to limit as much as possible the overall size. The antenna and the adjoining metal element are thus positioned side by side with a reduced intermediate space, which may even be zero.

According to a feature of the invention, the surface delimited by the internal edge of the light is substantially equal to the surface of the antenna. The formal and dimensional characteristics of the light have a direct impact on the performance of the antenna, since the passage of electromagnetic waves are carried out precisely through said light, independently of the essential presence of the air gap.

According to another feature of the invention, the internal edge of the light is shaped so as to be substantially parallel to the contour of the antenna. In other words, the shape of the light corresponds substantially to the projection of the outline of the antenna on the metallic element. Optimized operation is in fact obtained when the respective surfaces of the light and the antenna are equivalent.

In a particularly advantageous manner, the internal edge of the light coincides with the mean axis of the loop constituting the antenna. The shape of the light here corresponds to the projection of the mean axis of the antenna on the metal element. It should be noted that the mean axis designates the median line passing longitudinally through the loop, and this regardless of the number of turns constituting the antenna. This conformation constitutes an optimal solution in the sense that on either side of the mean axis, that is to say in the case where the shape of the light is larger or smaller than this limit, the performances of the antenna are significantly reduced.

According to a variant of the invention, the antenna extends between two metallic elements, with respect to each of which said antenna is positioned directly in the vicinity. Of course, each metal element is in accordance with the invention, that is to say that it has a lumen and an air gap as defined above.

This configuration, in which two metal elements are positioned on either side of the antenna, corresponds for example to the integration of an antenna inside any metal part, such as a watch case for example .

According to another variant of the invention, the antenna extends outside of an assembly comprising two metal elements between which is formed a space capable of receiving a removable device also provided with a loop-shaped antenna; the external antenna being positioned directly near the external face of one of the metallic elements. This configuration can relate, for example, to an insertion reader, a contactless card reader or an electronic label reader. According to another characteristic of the invention, the different metallic elements being integral, the respective slots and slots are associated so as to constitute a single air gap. The important thing is that the air gap specific to each metallic element is not short-circuited by any portion of the adjacent metallic element. This leads to positioning the slots substantially opposite, and this regardless of their respective dimensions. Thus, it can be considered that the integral metal elements have only one air gap.

Advantageously, the metal elements intended to be positioned near the antenna can be symmetrical. This means that their identical shapes can be positioned easily opposite, symmetrically with respect to the antenna, so that a single air gap can be very easily available. The lights of the various metal elements, just like the slots, moreover, are positioned precisely opposite one another.

According to another feature of the invention, the different metallic elements belong to the same part. This configuration is of course equivalent to that for which the different parts, coming to be positioned near the antenna, are integral.

Other characteristics and advantages of the invention will appear on reading the description which follows with reference to the accompanying drawings, given by way of non-limiting examples. This detailed description will make it clear what the invention consists of and how it can be implemented.

Figure 1 is a schematic exploded perspective view, which illustrates a first example of arrangement of a loop antenna according to the teachings of the invention. Figure 2 is an end view, according to arrow F2 of Figure 1, which illustrates the loop antenna in position on its metal support piece.

Figure 3 is a schematic sectional view along line 3-3 of Figure 2.

Figures 4 and 5 are views similar to those of Figures 2 and 3 which illustrate a second example of arrangement according to the invention, in which the antenna is integrated between two adjacent metal elements.

Figure 6 is a side elevational view illustrating another application of an arrangement according to the teachings of the invention.

It represents a card provided with an antenna, in the approach position with a view to its introduction into a reading device with a metallic environment also comprising a loop antenna. FIG. 7 is a side view at the end of the reading device, according to arrow F7 in FIG. 6.

Figure 8 is a bottom view, along arrow F8 of Figure 6, of the assembly illustrated in Figure 6. For reasons of clarity, the same elements have been designated by identical references. Likewise, only the elements essential for understanding the invention have been shown, and this without respecting the scale and in a schematic manner.

The particular embodiment, illustrated in FIGS. 1 to 3, relates to the integration of a loop antenna A behind a metal plate 10. Although basic, this configuration is very important due to the fact that it is likely to be applied very widely. We are thinking here in particular of the arrangements of an antenna behind a metal front face, for example of a vending machine type distributor or of an access control device of the metro tripod type.

In this exemplary embodiment, the metal element therefore consists of a metal plate 10 delimited by two opposite flat faces 12 and 14. In accordance with the teachings of the invention, the metal plate 10 comprises a slot 18 and a slot 16 forming an air gap .

More specifically, the slot 16 is formed through the thickness of the metal plate 10, between the internal edge 21 delimiting the lumen 18 and the external edge 20 of said metal plate 10. In other words, it is a slot through which extends on the one hand axially along the axis XX of the antenna A, the axis being substantially perpendicular to the mean plane of the loop of said antenna A. The slot 16 thus opens at each of the opposite faces 12, 14 of the metal plate 10. On the other hand, the slot 16 also extends transversely with respect to this same axis XX, from an external lateral edge 20 of the plate 10, here vertically downwards when considering the figures 1 and 3, in order to open radially inwards, at the level of the internal edge 21 of the slot 18.

From an electromagnetic point of view, the slot 16 constitutes an air gap which makes it possible to "open" the metal environment near which the loop antenna A is positioned; the portion of the plate 10 disposed facing the surface of said antenna A is obviously free of any metal. In this first example chosen to illustrate the invention, the loop antenna A is rectangular. Regardless of its shape which can be variable, it should be noted that the loop antenna A can be of any design, that is to say in particular constituted by a loop winding of one or more turns.

The metal plate 10 here serves directly as a support for the loop antenna A. The latter is fixed, for example by gluing, on the face 12 while the opposite face 14 remains free. In this extreme configuration, the antenna A is truly positioned directly near the metal element, since it extends perfectly parallel to the internal face 12 of the plate 10. The portion of this face 12, along from which extends the loop antenna A, is here perfectly flat.

As can be seen in FIGS. 1 to 3, the internal edge 21 delimiting the light 18 has a rectangular contour which corresponds substantially to the rectangular contour of the antenna A. As a result, the surface delimited by the internal edge 21 light 18 is substantially equal to the surface of antenna A.

More precisely, the dimensions as well as the relative positioning of the antenna A and of the light 18 are such that the internal edge 21 of the light 18 is parallel to the rectangular profile of the loop antenna A. In other words , each linear portion 22, 24, 26, 28 of the internal edge 21 is individually parallel to each linear portion 32, 34, 36, 38 materializing the outline of the antenna A.

In order to optimize the performance of the loop antenna A, the internal edge is dimensioned so as to coincide with the mean axis of the antenna A, that is to say with the mean axis of its coil when it comprises only one, or with the mean axis of the group of turns constituting the loop antenna A in the opposite case.

It is during the fixing of the antenna A on the metal plate 10 forming a support, for example by gluing its face 30 on the corresponding parts of the face 12 of the plate 10, that precise and optimal positioning is ensured. of the loop A antenna with respect to the light 18.

The arrangement which has just been described, with reference to FIGS. 1 to 3, thus allows the integration of a loop antenna A in a metallic environment whatever the conformation of the support 10, the latter being not necessarily a plate but which can be any part, especially of greater thickness. This integration is of course independent of the external shape of said metal part.

The metal part is not necessarily a single part with a continuous structure. It can also be constituted by an assembly of different metallic elements. Similarly, the invention is also not limited to the case where the antenna loop is of rectangular outline.

Integration according to the invention is advantageously obtained without adding any material or component, and therefore in a very economical manner. It also allows the plating of the antenna A against the part 10, that is to say that it does not impose unnecessarily increasing the size of the assembly.

As can be seen in Figures 4 and 5, the second embodiment chosen to illustrate the invention relates to the integration of a loop antenna within a metallic environment.

For obvious reasons of simplicity and therefore of clarity, the antenna here is of the same type as that previously described. Likewise, the metallic environment is simply composed of two adjacent metallic plates 10 and 10 ′, moreover substantially similar to the plate 10 described with reference to FIGS. 1 to 3. The design of the arrangement illustrated in FIGS. 4 and 5 presents furthermore a symmetry with respect to a plane P which corresponds to the mean plane of the loop antenna A (FIG. 5). Thus, each metal element 10, 10 ′ has a through slot 16, 16 ′ forming an air gap, which extends axially in a direction substantially perpendicular to the mean plane P of the loop of the antenna A, throughout the entire thickness of said element 10, 10 '. This slot 16, 16 'also extends transversely from an external lateral edge 20, 20' of the metal element 10, 10 ', to the internal edge 21, 21' of a central lumen 18, 18 'formed axially through said metallic element 10, 10 ′, substantially facing the internal area of the antenna which is delimited by the loop.

As indicated previously, each metal plate 10, 10 ′ is therefore shaped in a manner substantially analogous to its counterpart in the first embodiment example. It basically differs from it only by the presence of a housing 40, 40 ′ of shape complementary to the part of the loop antenna A with which it is intended to come into contact, or at least nearby. The assembly is shaped so that the antenna A is perfectly integrated between the metal plates 10, 10 'when the respective internal faces 12, 12' of said plates are in contact with one another. This means that the antenna A is advantageously interposed here without any play, whatever the direction considered. This characteristic also makes it possible to precisely position the antenna A in its metallic environment, since said antenna A is trapped between the two metal plates 10 and 10 ', in the housing 40-40'.

The design symmetry is such that the slots 16 and 16 'are aligned one opposite the other so as to constitute a single air gap forming "opening or interruption" of the metallic environment. The third example, chosen to illustrate the invention, relates to a particular embodiment using two antennas in the general form of a loop. The first antenna is equivalent to those previously described, in that it is integral with the metallic environment. It is in fact positioned directly near the external face of a metallic element. The second antenna is on the other hand linked to an independent and removable device, capable of taking place inside the metallic environment, in a similar manner to the second embodiment, with the difference that this arrangement is not fixed. In this, this third embodiment can be considered as a combination of the first two.

An example of this type of configuration is illustrated in FIGS. 6 to 8, in the form of an insertion reader for contactless cards. Thus, there is shown a reading device 44 comprising a slot 42 through which can be inserted and / or removed a card C incorporating a loop antenna A '. Obviously, the reading device 44 is provided with a receiving and / or transmitting antenna A intended for exchanging data with the antenna A 'of the card C.

The main body of the reading device 44 is constituted by two adjacent metal plates 10 and 10 'each comprising a slot 16, 16' forming an air gap and a central lumen 18, 18 '. Everything is consistent and arranged substantially similar to their counterparts in Figures 4 and 5.

It is not the same with regard to the associated antenna A, since the positioning of the latter relative to the metallic environment corresponds rather to the arrangement illustrated in FIGS. 1 to 3. In this specific case, the 'Antenna A indeed extends near the external face 14 of the plate 10 and is therefore not directly in contact with the other plate 10'. In the end, this corresponds to the arrangement of a loop antenna in a metallic environment constituted here by the superposition of two identical and symmetrical metallic plates 10, 10 ′.

The space provided between the metal plates 10, 10 ′, which in the second embodiment was intended to receive the loop antenna permanently, is here shaped so as to be able to occasionally accommodate the card C, after its insertion through the slot 42 formed in the front panel 41. Thus, when the card C is in the data exchange position in the reading device 44, its precise positioning with respect to the openings 18 and 18 'is such that the arrangement of the 'antenna A' relative to the plates 10, 10 'is then similar to that illustrated in Figures 4 and 5, that is to say that we find the case of an antenna A' arranged inside itself of a metallic environment.

Here again, to optimize both the performance of the antenna A and that of the antenna A ', it is desirable that the outline of the aligned lights 18 and 18' coincide with the mean axis of the antennas A and A '. In the event that the geometry and / or the dimensions of the two antennas A and A 'are slightly different, a compromise is determined between the best possible coupling of the two antennas and the respective individual performance of the latter in relation to the metallic environment.

Claims

1. Arrangement of an antenna A in the general form of a loop, directly near at least one metallic element 10, 10 ', characterized in that each metallic element 10, 10' comprises, on the one hand, a light 18 , 18 'formed substantially opposite the surface delimited by the antenna A, and on the other hand, a slot 16, 16' forming an air gap, formed through the thickness of the metallic element 10, 10 ', between the internal edge 21, 21 'delimiting the lumen 18, 18' and the external edge 20, 20 'of said metal element 10, 10'.

2. Arrangement according to claim 1, characterized in that the antenna A extends substantially parallel to the metal element 10, 10 'of which it is directly close.

3. Arrangement according to any one of claims 1 or 2, characterized in that the surface delimited by the internal edge 21, 21 'of the light 18, 18' is substantially equal to the surface of the antenna A.

4. Arrangement according to one of claims 1 to 3, characterized in that the internal edge 21, 21 'of the light 18, 18' is substantially parallel to the contour of the antenna A.

5. Arrangement according to any one of claims 1 to 4, characterized in that the internal edge 21, 21 'of the light 18, 18' coincides with the mean axis P of the loop constituting the antenna A.

6. Arrangement according to any one of claims 1 to 5, characterized in that the antenna A extends between two metal elements 10, 10 ', with respect to each of which said antenna A is positioned directly in the vicinity.

7. Arrangement according to any one of claims 1 to 5, characterized in that the antenna A extends outside an assembly comprising two metal elements 10, 10 'between which is provided a space suitable for receiving a removable device C provided with a loop-shaped antenna A ′, the external antenna A being positioned directly near the external face 14, 14 ′ of one of the metal elements 10, 10 ′.

8. Arrangement according to any one of claims 1 to 7, characterized in that the different metal elements 10, 10 'being integral, the slots 18, 18' and slots 16, 16 'respectively are associated so as to constitute a single air gap.

9. Arrangement according to any one of claims 1 to 8, characterized in that the openings 18, 18 'of the different metallic elements 10, 10' are opposite one another.

10. Arrangement according to any one of claims 1 to 9, characterized in that the slots 16, 16 'of the different metal elements

10, 10 'are opposite each other.

11. Arrangement according to any one of claims 1 to 10, characterized in that the different metallic elements 10, 10 'are of substantially identical shapes.

12. Arrangement according to any one of claims 1 to 11, characterized in that the different metal elements 10, 10 'belong to the same part.

13. Arrangement according to any one of claims 1 to 12, characterized in that the portion of the metal element 10, 10 ', near which extends the antenna A, is planar.

14. Arrangement according to any one of claims 1 to 13, characterized in that at least one of the metal elements 10, 10 'is a metal plate.