WO2008135641A1

WO2008135641A1 - System for reading rfid tags and showcase for this system

Info

Publication number: WO2008135641A1
Application number: PCT/FR2007/000769
Authority: WO
Inventors: Fabien Blanc Paques
Original assignee: Supertec
Priority date: 2007-05-04
Filing date: 2007-05-04
Publication date: 2008-11-13
Also published as: EP2153373A1

Abstract

This system for reading RFID (Radio Frequency Identification) tags comprises fastening/unfastening mechanisms (18, 30) positioned with respect to a wall of a showcase in such a way as to only allow the fixing of each passive antenna (32) at a location where the angle of incidence (α ) of all the field lines produced by one of the induction antennas (42) which cross the interior surface delimited by the passive loop of this removable passive antenna is less than 45°.

Description

RFID LABEL READING SYSTEM AND DISPLAY FOR THIS

SYSTEM

The present invention relates to an RFID tag reading system and a display stand for this system.

The applicant knows RFID (Radio Frequency Identification) tag reading systems comprising: a) an RFID tag reader, b) a display of objects equipped with RFID tags, this display comprising:

a wall extending in a vertical direction,

a set of one or more induction antennas fixed to the wall, each antenna of this set being adapted to be fed simultaneously by the same reader so as to produce a common reading lobe comprising all the points of the space where the electromagnetic radiation is powerful enough to allow the reading of an RFID tag,

at least one removable passive antenna comprising a conductor forming a passive loop, this passive loop delimiting an inner surface, and mechanical coupling / uncoupling mechanisms enabling a user to fix each removable passive antenna to the wall in a position such that this removable passive antenna is fed via an electromagnetic coupling with at least one of the induction antennas and thus contributes to the formation of a portion of the common reading lobe without being electrically connected to the reader.

In this description, an antenna is defined as being the part composed of one or more radiating electrical conductors connected, optionally, to an impedance matching circuit of the antenna. An RFID tag reader is also defined as being an electronic circuit capable of supplying the antenna so that it radiates an electromagnetic field and receives the information transmitted by the RFID tags present in the reading lobe of the antenna. For this purpose, typically, the The reader is able to modulate the electrical signals transmitted to the antenna and to demodulate the electrical signals received by the antenna. The reader is also able to retrieve the identifier of the RFID tag read from the received demodulated signals, for transmission to a processing unit. In known systems, the coupling / uncoupling mechanisms make it possible to place the removable passive antenna almost at any position relative to the set of induction antennas. Under these conditions, so that the removable passive antenna can operate regardless of its position vis-à-vis the wall, the power supply of the reader is chosen equal to the maximum allowed, namely, for example, 4 watts. However, the higher the power of a reader, the higher its cost and consumption.

The invention aims to provide an RFID tag reading system in which the removable passive antenna has the same performance as in known systems but using a lower power reader.

It therefore relates to an RFID tag reading system in which the coupling / uncoupling mechanisms are positioned relative to the wall so as to allow only the attachment of each removable passive antenna to a place where the angle of the incidence of all the field lines produced by at least one of the induction antennas which feeds it and which cross the interior surface delimited by the passive loop of this removable passive antenna is less than 45 °.

In the above system, since the passive antenna can only be positioned at a location where the field lines have an angle of incidence of 45 ° or less, the magnetic flux passing through the passive loop is maximized. This results in electromagnetic coupling between the passive loop and the more efficient induction antennas. The magnetic losses due to this electromagnetic coupling are therefore limited, irrespective of the position at which the removable passive antenna has been fixed. Thanks to this, at equal performance, the above system requires a lower power reader than that used in existing systems. The performance of the removable passive antenna can, for example, be represented by the maximum height of the reading lobe measured in a direction perpendicular to the plane of the antenna.

The invention also relates to a display capable of being implemented in the reading system above. Embodiments of this display can include one or more of the following features:

• the angle of incidence is less than or equal to 20 °;

Each induction antenna comprises a radiating electrical conductor forming an induction loop extending in a vertical plane, each radiating electrical conductor defining a band, in the vertical plane, located on either side of the radiating electrical conductor, the inner and outer limits of this strip extending parallel to the radiating electrical conductor and these inner and outer limits being spaced from the electrical conductor radiating a constant distance equal to one-third of the greatest height or width of the induction loop,

each removable passive antenna comprises several strands placed end to end to form the passive loop, and the coupling / disengagement mechanisms are positioned relative to the wall so that, systematically, the orthogonal projection on the vertical plane of the strand the removable passive antenna closest to the wall is entirely within the band or bands defined by the radiating electrical conductor (s);

The set of induction antennas comprises:

an active induction antenna fixed to the wall and extending parallel to a reading plane, this active induction antenna being able to be directly electrically connected to the RFID tag reader, and to produce its own reading lobe when it is powered by the RFID reader in the absence of any other passive antenna electromagnetically coupled with this active induction antenna, and - at least one passive induction antenna powered by electromagnetic coupling with the active induction antenna, this passive induction antenna comprising a passive induction loop fixed to the wall and extending parallel to the reading plane, this loop delimiting a surface interior of which at least a part is placed outside the reading lobe specific to the active induction antenna;

at least one removable support capable of supporting one of the objects equipped with an RFID tag and in which the passive loop of the removable passive antenna is mounted without any degree of freedom on this support;

the passive loop of the passive passive antenna extends in a plane forming an angle of between 45 ° and 135 ° with a plane in which the induction antenna extends, the field lines of which pass through at an angle of incidence less than 45 °, the inner surface delimited by this passive loop;

- The coupling / uncoupling mechanisms allow a user to fix each removable passive antenna to the wall without the aid of tools.

These embodiments of the display stand also have the following advantages:

guaranteeing that the orthogonal projection of a strand of the removable passive antenna is in a band located on either side of the loop of the induction antenna ensures optimum electromagnetic coupling between these two antennas, a set of induction antennas formed of an active induction antenna and at least one passive induction antenna arranged parallel to the same plane makes it possible to produce a common reading lobe which spreads more uniformly along at least one direction of this plane,

rigidly fixing the passive antenna on the support makes it possible to maintain a spatial relation between the support and the removable passive antenna even in case of displacement of this support, and

the fact that the planes in which the passive loop and the induction antenna extend respectively are non-collinear allows a reading of an RFID tag placed in any plane that is not perpendicular to both the plane of the passive antenna and the induction antenna.

The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and with reference to the drawings in which: FIG. 1 is a schematic perspective illustration of an RFID tag reading system comprising a display stand,

FIG. 2 is a perspective view of a shelf for the display unit of FIG. 1; FIG. 3 is a perspective view of the arrangement of the various antennas of the display unit of FIG.

FIG. 4 is a schematic illustration of different reading lobes and electromagnetic coupling produced by the antennas of the display unit of FIG. 1; FIG. 5 is a sectional view of a portion of the antenna assembly showing FIG. angle of incidence of the field lines,

FIG. 6 is a schematic illustration showing the orthogonal projection of a strand of a removable passive antenna on the plane of an induction antenna; FIG. 7 is a schematic and perspective illustration of another possible configuration; for the display of Figure 1,

FIG. 8 is a schematic illustration of the arrangement of the antennas in the configuration of FIG. 7, and

FIG. 9 is a schematic and perspective illustration of another embodiment of a tablet for the display of FIG.

In these figures, the same references are used to designate the same elements.

In the remainder of this description, the features and functions well known to those skilled in the art are not described in detail. Figure 1 shows a system 2 for reading passive RFID tags. RFID tags are here associated with objects to present to a prospective buyer. To simplify FIG. 1, only one object 4 equipped with an RFID tag 6 has been represented. The tag 6 includes an antenna extending over most of its surface and an electronic circuit capable of storing information. The antenna is used to power the electronic circuit when it is placed in a magnetic field whose power is sufficient. The electronic circuit notably memorizes a unique identifier of the object 4. The electronic circuit is also able to transmit this identifier via the antenna of the RFID tag.

Typically, the frequency of the carrier implemented in the system 2 to read the RFID tags is 13.56 MHz. The system 2 comprises a display 10 formed of a vertical wall 12 supported by a foot 14. The display 10 comprises a screen 16 fixed to the wall 12 so as to be able to present different messages, such as advertising messages, to potential buyers.

The display also includes removable media suitable for presenting objects equipped with RFID tags. These supports are alternately mechanically coupled and uncoupled from the wall 10 according to the products to be presented. For this purpose, the display unit 10 comprises mechanisms for coupling / uncoupling the supports. Typically, these mechanisms are formed of two parts that cooperate to fix without any degree of freedom the support to the wall 10. One of these parts is secured to the support while the other part is secured to the wall 10. Here, the part integral with the wall 10 is, for example, formed of a rail 18. Advantageously, these mechanisms do not require the use of a particular tool, such as a screwdriver, to mechanically couple and uncouple the support and the wall. At first, the supports are described as being horizontal tablets. In Figure 1, two horizontal shelves 20 and 22 have been shown. These tablets are, for example, identical. The tablet 20 will be described in more detail with reference to FIG.

The display unit 10 also comprises an assembly 24 of induction antennas suitable for creating a common lobe for reading RFID tags. The common reading lobe is defined as the set of points of the three-dimensional space in which the energy of the electromagnetic radiation produced by the assembly 24 is sufficient to read the RFID tag of the objects to be presented. This assembly 24 is typically integrated in the thickness of the wall 10 or located behind the wall 10 and is not visible from the front face of the wall 10. The system 2 also comprises a reader 28 of RFID tags electrically connected to the assembly 24. For example, the reader 28 is fixed without any degree of freedom to the display 10. Here, it is integrated in the foot 14.

To simplify FIG. 1, the electrical connection between the reader 28 and the assembly 24 has not been shown.

FIG. 2 represents in more detail the tablet 20. The tablet 20 is a parallelepiped made of a material whose relative permeability is less than or equal to 5000 and preferably less than or equal to 200. For example, the tablet 20 is made of wood . This shelf 20 is here equipped with hooks 30 adapted to cooperate with the rail 18 to mechanically couple the shelf 20 to the wall 12 so that it can support the objects to be presented.

A passive antenna 32 is fixed without any degree of freedom to the tablet 20. For example, the antenna 32 is incorporated in the thickness of the tablet 20. This antenna 32 is formed of an electrical conductor 34 defining a passive loop which extends in a plane parallel to the upper face of the tablet 20. This loop also defines an inner surface 36. Here, the passive loop has the shape of a parallelogram whose corners are rounded. More specifically, the conductor 34 is here formed of four strands A, B, C and D placed end to end. Strands A and B are parallel to the plane of wall 12. Strands C and D extend perpendicularly to the plane of wall 12.

The antenna 32 also comprises an impedance matching circuit 38 connected to each of the ends of the conductor 34. This circuit 38 is designed to adapt the impedance of the antenna 32 to that of the reader 28. The antenna 32 is electrically isolated from the reader 28. On the other hand, it can be powered by means of electromagnetic coupling. In the latter case, the antenna 32 produces its own reading lobe. Here, the antenna 32 is arranged relative to the upper surface of the tablet 20 so that at least 85% of the surface of the upper face of the tablet 20 is included in this reading lobe of the antenna 32 when it is powered by electromagnetic coupling.

FIG. 3 shows in more detail the assembly 24 as well as the different possible positions of the antenna 32 with respect to this assembly 24. In Figure 3, to simplify the figure, the wall 12 and the shelves have not been shown.

The assembly 24 comprises a single active induction antenna 40 and two passive induction antennas 42 and 44. Only the antenna 40 is directly electrically connected to the reader 28. Here, by directly connected means that the antenna 40 n is not powered by the reader 28 via an electromagnetic coupling.

More specifically, the antenna 40 comprises an electrical conductor 46 defining a loop in a vertical plane. The width of this loop 46 is greater than or equal to the width of the passive loop of the antenna 32. The antenna 40 also comprises an impedance matching circuit 48 connected to both ends of the conductor 46 and also electrically connected to the reader 28.

The structure of the antennas 42 and 44 is, for example, identical to that of the antenna 40 and will therefore not be described here in more detail. The loops of the antennas 42 and 44 extend in a plane parallel to that in which extends the conductor 46 of the antenna 40.

Figure 3 also shows three possible positions of the antenna

32 relative to the assembly 24 when it is fixed to the wall 12. It is recalled that when the antenna 32 is fixed to the wall 12, the latter extends in a horizontal plane perpendicular to the plane in which s 'extend the antennas 40,

42 and 44.

FIG. 4 shows, in side view and in section, the reading lobes produced by the assembly 24. When the antenna 40 is powered by the reader 28 and in the absence of the antennas 42 and 44, this antenna produces its own reading lobe 50 and a lobe 52 of electromagnetic coupling. The electromagnetic coupling lobe proper to the antenna 40 is defined as being the set of points of the space where the following relation is verified: 10Log - ^ -> α _o (1)

"max where: P is the power of the electromagnetic radiation at a point in space when the antenna 40 is powered by the reader 28,

- Pm _a x is the maximum power of the electromagnetic radiation produced by the antenna 40 when it is fed by the reader 28, and - α _c is a predetermined constant.

To obtain an effective electromagnetic coupling, the constant α ₀ is chosen greater than or equal to -1OdB and preferably greater than or equal to -5 dB.

The antennas 42 and 44 are arranged in the same plane parallel to that of the antenna 40 and one above the other. In addition, in this plane, the position of the antennas 42 and 44 is chosen so that it is entirely comprised in the lobe 52 produced in the absence of the antennas 42 and 44. Preferably, the position of the antennas 42 and 44 is chosen so that at least a part of these antennas is outside the reading lobe 50. For example, the position of the antennas 42 and 44 is chosen so that at least one third of the internal surface of the antennas 42 and 44 is located outside the reading lobe 50 produced in the absence of antennas 42 and 44.

The distance separating the plane containing the antenna 40 from the plane containing the antennas 42 to 44 is less than 10 cm, and preferably less than 5 cm. Since the antennas 42 and 44 are located in the lobe 52, they are electromagnetically coupled with the antenna 40, when the antenna 40 is itself powered by the reader 28.

When the antennas 42 and 44 are powered, these in turn each produce its own reading lobe, respectively, 54 and 56. The fact that part of the electromagnetic energy radiated by the antenna 40 is absorbed by the antennas 42 and 44 results in a reduction in the size of the lobes 50 and 52 relative to the case where the antennas 42 and 44 would be omitted. Figure 4 shows the lobes 50 and 52 produced by the antenna 40 only in the case where the antennas 42 and 44 are present. The meeting of reading lobes 50, 54 and 56 forms a reading common lobe 58 of which only the front part of the outer envelope has been represented in FIG. 4. As can be seen in FIG. 4, the antennas 42 and 44 make it possible to spread the common lobe 58 in directions parallel to the plane of the antennas 42 and 44. Thus, the common lobe 58 is here much more extensive in the vertical direction that if the reading lobe was only produced by the antenna 40 without the presence of the antennas 42 and 44.

The antennas 42 and 44 each also produce their own electromagnetic coupling lobe. The meeting of the electromagnetic coupling lobes produced by the antennas 40, 42 and 44 form a common lobe 60 of electromagnetic coupling. In Figure 4, only the front portion of the outer casing of the common lobe 60 has been shown. In a manner similar to what has been explained with respect to the reading lobes, the use of the antennas 42 and 44 makes it possible to spread here, in the vertical direction, the common lobe 60.

For the antenna 32 to be powered by electromagnetic coupling, the latter must be entirely placed inside the common lobe 60.

In addition, to limit the energy losses due to the electromagnetic coupling, the antenna 32 is here positioned relative to the assembly 24 at a location where the field lines created by the antenna 42 or 44 are perpendicular to the surface 36 of the antenna 32. In the case of the assembly 24, there are three possible positions, namely a low position, a middle position and a high position.

Figure 5 shows in more detail the positioning of the antenna 32 in the high position. In Figure 5, the circular lines 64 and 66 show an example of field lines produced by the antenna 42. The antenna 32 is placed in a horizontal plane. The strand B extends parallel to the upper horizontal strand of the antenna 42 so that the orthogonal projection of the strand B on the vertical plane containing the antenna 42 coincides with the upper horizontal strand of the antenna 42. In these conditions the field line 64 intersects with an angle α of almost zero incidence, the surface 36. It is the same for all the field lines which cross the surface 36 and which are produced by the antenna 42. In the figure 5, the angle of incidence α was amplified to be visible. It has been established that, in order to limit energy losses due to magnetic coupling, the angle of incidence α must be less than 45 °. However, preferably, the position of the antenna 32 is chosen so that the angle α is less than 20 °, or more preferably less than 5 °. Thus, there is a margin of tolerance on the positioning of the antenna 32 relative to the antenna 42.

In FIG. 6, this margin of tolerance is represented by a band 70 situated on either side of the conductor forming the loop of the antenna 42.

This band 70 is delimited by an outer limit 72 and by an inner limit 74. The limits 72 and 74 extend parallel to the conductor forming the loop of the antenna 42. The horizontal portions of the limits 72 and 74 are spaced apart from the conductor 42. by a distance hβ. The distance hβ is less than or equal to one third of the height of the antenna 42 in the vertical direction. The vertical portions of the boundaries 72 and 74 are, in turn, spaced from the conductor of the antenna 42 by a distance LB- The distance LB is less than or equal to one third of the width of the antenna 42 measured in a horizontal direction. However, preferably, so as to minimize the energy losses due to electromagnetic coupling, the distances hβ and Lb are chosen to be less than a fifth, respectively, of the greatest height and the greatest width of the antenna 42. In FIG. 6, three horizontal bold lines 76, 78 and 80 represent possible projections of the B-strand of the antenna 32 on the plane of the antenna 42, respectively, when the antenna 32 is in the high position, in the middle position and in the low position.

In order to allow the positioning of the antenna 32 only in the positions described with reference to FIGS. 3 to 6, the mechanisms of coupling / uncoupling of the shelf 20 to the wall 12 are provided only in places which guarantee a positioning of the antenna 32. For this purpose, for example, the position of the rails, such as the rail 18, merges with the projections 76, 78 and 80. No other rail is provided in the wall 12 to fix the tablet 20 at a location other than those marked by projections 76, 78 and 80. Under these conditions, it is understood that the tablet 20 can only be positioned at a location which minimizes the energy losses due to the electromagnetic coupling between the antenna 32 and the assembly 24.

Preferably, the display rack 10 is a multi-rack display, that is to say that different types of media can be attached.

FIG. 7 represents a configuration of the display rack 10 in which the support fixed to the wall 12 is formed of a horizontal rod 90 arranged parallel to the wall 12 and supported by two vertical uprights 92 and 94.

Typically, the rod 90 is intended to receive hangers 96. These hangers are, for example, equipped with an electronic tag 98 located in a vertical plane perpendicular to the wall 12.

The amounts 92 and 94 are removable. For this purpose, mechanical coupling / uncoupling mechanisms for fixing these amounts 92 and 94 to the wall 12 are provided. To simplify Figure 7, these mechanisms have not been represented.

In this configuration, the display unit 10 comprises two removable passive antennas 100 and 102. The antennas 100 and 102 are rigidly fixed, respectively, to the uprights 92 and 94. For example, the antennas 100 and 102 are incorporated in the thickness of the uprights 92 and 94. Figure 8 shows in more detail the antennas 100 and 102 and their position vis-à-vis the assembly 24. The antennas 100 and 102 are, for example, identical. The structure of the antenna 100 is, for example, identical to that of the antenna 32 and will not be described here in more detail.

The antennas 100 and 102 are entirely located inside the electromagnetic coupling common lobe 60 produced by the assembly 24. In addition, the antennas 100 and 102 are positioned vis-à-vis the assembly 24 at a location where the angle of incidence of the field lines created by the assembly 24 is perpendicular to the surface 36 of each of these antennas 100 and 102. For this purpose, the antennas 100 and 102 are arranged in a vertical plane perpendicular to the wall 12. In addition, the position of the antennas is chosen so that the orthogonal projection of the strand B in the plane of the antennas

42 and 44 is confused with the vertical strands of antennas 42 and 44. Thus, this projection is included in the bands 70 delimited around the antennas

42 and 44.

It is thus understood that in a manner similar to that explained with respect to the antenna 32, this position minimizes the energy losses due to the electromagnetic coupling of the antennas 100 and 102 with the assembly 24. Here, the mechanisms of coupling and uncoupling of the uprights 92 and 94 are positioned relative to the wall 12 so as to allow only the positioning of the antennas 100 and 102 in the positions described with reference to Figure 8. Many other embodiments are possible. For example, Figure 9 shows a tablet 110 equipped with two vertical uprights 112 and 114 respectively at the right and left ends of the tablet.

A removable passive antenna 116 is housed inside this tablet 110.

This antenna 116 comprises an electrical conductor forming a loop. This loop extends both in the horizontal plane of the tablet 10, but also rises on both sides in the uprights 112 and 114.

When the tablet 110 is fixed on the wall 12 of the display, a horizontal portion AC of the rear end of the antenna 116 extends parallel to the lower horizontal strand of the antenna 42. The two ends AG and AD of this rear strand are vertical and extend parallel to the left and right vertical strands of the antenna 42. Thus, the orthogonal projection of the rear strand of the antenna 116 in the plane of the antenna 42 is included in the band 70.

Such a tablet can be advantageously used to present objects such as books. The antennas have been described here in the particular case where they form loops delimiting a substantially rectangular surface. Alternatively, the loops may delimit surfaces having other shapes such as, for example, the shape of an ellipse.

The removable passive antenna is not necessarily attached to the support. For example, the support may be a rod extending perpendicularly to the plane of the wall 12 and the antennas may be incorporated in vertical uprights, such as the uprights 92 and 94 of FIG. 8. Finally, the set of induction antennas can be used independently of passive passive antennas and mechanisms of coupling / uncoupling thereof to obtain a wider reading common lobe.

Claims

A RFID (Radio Frequency Identification) tag reading system comprising: a) a reader (28) of RFID tags, b) a display (10) of objects (4) equipped with RFID tags (6), this display comprising:

A wall (12) extending in a vertical direction,

an assembly (24) of one or more induction antennas fixed to the wall, each antenna of this set being adapted to be fed simultaneously by the same reader so as to produce a common reading lobe (52) comprising set of points in the space where the electromagnetic radiation is sufficiently powerful to allow the reading of an RFID tag, at least one removable passive antenna (32) comprising a conductor (34) forming a passive loop, this passive loop defining an inner surface (36), and

mechanical coupling / uncoupling mechanisms (18, 30) enabling a user to fix each removable passive antenna to the wall in a position such that this removable passive antenna is powered via electromagnetic coupling with at least one of the induction antennas and thus contributes to the formation of a portion of the common reading lobe without being electrically connected to the reader, characterized in that the mechanisms (18, 30) for coupling / uncoupling are positioned by relative to the wall (12) so as to allow only the fixing of each removable passive antenna at a location where the angle of incidence (α) of all the field lines produced by at least one of the induction antennas which feeds and which pass through the inner surface (36) delimited by the passive loop of this removable passive antenna is less than 45 °.

2. Display stand adapted to be implemented in a system according to claim 1, this display comprising:

a wall (12) extending in a vertical direction, an assembly (24) of one or more induction antennas fixed to the wall, each antenna of this set being adapted to be fed simultaneously by the same reader so as to produce a common reading lobe (52) comprising set of points in the space where the electromagnetic radiation is powerful enough to allow the reading of an RFID tag,

at least one removable passive antenna (32) comprising a conductor (34) forming a passive loop, this passive loop defining an inner surface (36), and mechanisms (18, 30) for mechanical coupling / uncoupling allowing a user to fix each removable passive antenna to the wall in a position such that this removable passive antenna is powered via an electromagnetic coupling with at least one of the induction antennas and thus contributes to the formation of a part of the common reading lobe without being electrically connected to the reader, characterized in that the coupling / uncoupling mechanisms (18, 30) are positioned with respect to the wall (12) so as to allow only the attachment of each passive antenna removable at a location where the angle of incidence (α) of all the field lines produced by at least one of the induction antennas which feeds it and which pass through the surface this interior (36) delimited by the passive loop of this removable passive antenna is less than 45 °.

3. Display unit according to claim 2, wherein said angle of incidence (α) is less than or equal to 20 °.

4. Display stand according to any one of claims 2 to 3, wherein:

each induction antenna (40, 42, 44) comprises a radiating electrical conductor forming an induction loop extending in a vertical plane, each radiating electrical conductor defining a strip, in the vertical plane, located on the side and other of the radiating electrical conductor, the inner and outer limits of this strip extending parallel to the radiating electrical conductor and these inner and outer limits being spaced from the radiating electrical conductor by a distance constant equal to one third of the greatest height or width of the induction loop,

each removable passive antenna (32) comprises several strands placed end to end to form the passive loop, and the mechanisms (18, 30) for coupling / uncoupling are positioned relative to the wall so that, systematically, the orthogonal projection on the vertical plane of the strand of the removable passive antenna closest to the wall is entirely within the band or bands defined by the radiating electrical conductor (s).

5. Display unit according to any one of claims 2 to 4, wherein the assembly (24) of induction antennas comprises:

an active induction antenna (40) fixed to the wall and extending parallel to a reading plane, this active induction antenna (40) being able to be directly electrically connected to the reader (28) of RFID tags and producing its own read lobe (50) when powered by the RFID reader in the absence of any other passive antenna electromagnetically coupled with that active induction antenna, and

at least one passive induction antenna (42, 44) supplied electromagnetically with the active induction antenna, said passive induction antenna comprising a passive induction loop fixed to the wall and extending parallel to the reading plane, this loop defining an inner surface of which at least a portion is placed outside the lobe (50) for reading specific to the active induction antenna.

6. Display according to any one of claims 2 to 5, wherein the display comprises at least one removable support (20) adapted to support one of the objects equipped with an RFlD tag and in which the passive loop of the removable passive antenna (32) is mounted without any degree of freedom on this support.

7. Display unit according to any one of claims 2 to 6, wherein the passive loop of the removable passive antenna (32) extends in a plane making an angle (γ) between 45 ° and 135 ° with a plane in which extends the induction antenna whose field lines cross, with an angle of incidence less than 45 °, the inner surface (36) delimited by this passive loop.

8. Display unit according to any one of the preceding claims, characterized in that the coupling / uncoupling mechanisms allow a user to fix each removable passive antenna to the wall without the aid of tools.