WO2004015808A2

WO2004015808A2 - Array of modular transmission antennas for an rf identification system

Info

Publication number: WO2004015808A2
Application number: PCT/CH2003/000539
Authority: WO
Inventors: Jean-Claude Berney
Original assignee: Burrus, Xavier
Priority date: 2002-08-08
Filing date: 2003-08-08
Publication date: 2004-02-19
Also published as: WO2004015808A3

Abstract

The invention relates to arrays of modular transmission antennas for an RF identification system, which can be configured in many different ways as required. The antennas of the array are all serially connected. Each antenna comprises a main winding that is coiled onto a ferrite core and is pretuned to the operating frequency by means of internal capacities. Simple cabling means make it possible to quickly and easily obtain the most sophisticated combinations.

Description

Patent application

Assembly of modular transmission antennas for RF identification system

The most common radio frequency (RF) identification systems working for example at 125 kHz use transmission antennas supplied by an electronic control unit and collaborating with labels or smart cards comprising a take-up reel. These transmission antennas must on the one hand generate a magnetic flux sufficient at the base frequency to supply said labels or smart cards via their take-up coil, and on the other hand recover the signals generated in return by them. this. The power of these transmission antennas strongly depends on the distance at which one wants to be able to supply and read the labels, and ranges from a few tens of milliwatts to several tens of watts.

In most known cases, these transmission antennas include air coils (without magnetic core) with turns of relatively large surface area adapted to the distance at which it is desired to be able to supply and read said labels or smart cards. According to current estimates, the detection distance is more or less equal to the dimensions of the turns of the coil of the transmission antenna. For a 40 cm square coil, there will be a detection distance of around 40 cm. For a 60 cm side antenna, there will be a detection distance of the order of 60 cm, etc. However, this is a fairly simplistic interpretation insofar as it is necessary to increase the energy in the transmission antennas as a function of the power 4 of the distance to simply supply 'normally said labels or smart cards so that they can respond and send an energy return signal always constant. This means that the ratio between this return signal and the energy required. at the level of the transmission antennas is a function inverse to the power 4 of the reading distance. The coil of these transmission antennas forms a choke which is most often associated with a capacitance so as to form a series resonant circuit tuned to the working frequency so as to multiply the NI by the quality factor. These tuning capacities are generally integrated into the electronic control means of these antennas. Transmission antennas of this type operate preferentially when said labels or smart cards are in the axis of the turns.

'It is possible, but in a very limited way, to make combinations of two antennas, distributed for example on either side of a passage, provided that these two transmission antennas are substantially on the same axis.

The patent WO98 / 52141 mentions transmission antennas comprising coils of relatively small diameter in comparison with the turns of the conventional transmission antennas mentioned above. Unlike the conventional antennas, coils of these transmitting antennas are mounted on magnetic cores elongated and operate preferentially when said smart tags or cards are in parallel with the windings of the coil and said magnetic cores ^•.

The present invention presents a form of execution of this type of antenna by providing the advantage of modularity, great flexibility of use and a wide variety of combinations. It concerns an assembly modular transmission antennas for an RF identification system each comprising a choke formed by a main winding wound on a magnetic core characterized in that said assembly comprises several modular transmission antennas connected in series with each other and supplied with power by electronic control means connected to at least one of them, said modular transmission antennas having similar electrical characteristics and being pre-tuned individually in resonance at the working frequency by means of own capacitors connected in series with the chokes formed by the main windings of the modular antennas of said assembly.

The fig. 1 shows by way of example the electrical diagram of a modular transmission antenna according to the invention.

The fig. 2 shows by way of example the electrical diagram of an assembly of 3 modular transmission antennas according to the invention.

The fig. 3 shows two exemplary embodiments of modular transmission antennas according to FIG. 1.

The fig. 4 shows a first example of assembly of modular transmission antennas according to the invention.

The fig. 5 shows a second example of antenna assembly ^of: transmitting modular according to the invention. The fig. 6 shows a third example of assembly of modular transmission antennas according to the invention.

The fig. 7 shows by way of example a modular transmission antenna according to the invention to which an interesting branch connection has been added to the electronic control means and measuring coils.

The fig. 8 schematically shows by way of example the electronic means of the control unit associated with the modular transmission antennas according to the invention.

The fig. 9 shows by way of example a particular embodiment of said electronic means according to FIG. 8.

The fig. 10 represents the form of the signals at different points of said electronic means of FIGS. 8 and 9.

The fig. 1 shows by way of example the electrical diagram of a modular transmission antenna according to the invention. It comprises a magnetic core (1) on which is wound a number of turns forming a self (2) of value L = n ² / R. As the coil is of small diameter and relatively large length, the reductance R would be too high with an air coil to obtain sufficient self. The magnetic core (1) therefore makes it possible to reduce the reductance of the anemia and to obtain a suitable self in the desired volume. The antenna choke (2) is pre-tuned to the working frequency, for example 125 kHz, by means of series capacitors (3, 4) so that the frequency resonance at all (fo) is equal to the desired value, according to the well-known formula fo = 1/2 π (LC) ^1/2 .

In the example of FIG. 1, the resonance capacitor C is formed of two capacitors of value 2C in series placed at each end of the inductor. The same result can be obtained with a single capacitance of value C, but this allows good symmetry in the construction of the transmission antenna, as we will see in detail in Figure 3. By applying a voltage U ( 5) at the resonance frequency at the terminals thereof, we will obtain a current inversely proportional to the impedance of the self multiplied by the quality factor of the resonant self / capacitor assembly. This current directly determines the flux generated by the antenna, according to the well-known formula φ = NI / R. Thus the higher the quality factor of the antenna, the more it is able to supply labels or smart cards to a great distance, and therefore receive their information in return. This parameter is therefore particularly important. However, in order for the antenna to benefit from this high quality factor, it is imperative that it works at its own resonant frequency, which preferably requires certain specific arrangements described in FIGS. 9 and 10.

Let us briefly recall and very schematically the mode of operation of tags and smart cards for RF identification systems. They include a take-up coil (6) which feeds an integrated circuit (7). The first condition for the label to work is that the voltage generated at the terminals of the coil (6) by the flux delivered by the modular transmission antenna (1,2) is sufficient to make the integrated circuit work (7) . If this is the case, the latter will establish communication with the antenna by modulating the load across the coil. receiver (6) at a frequency and according to a known procedure by switching for example a resistor (8) by means of an electronic switch (9). The receiving coil (6) and the modular transmission antenna (1,2) are coupled in the manner of a transformer, so that the load variations at the level of the coil (6) induce current variations in the 'antenna (1,2). The analysis of these current variations makes it possible to reproduce and interpret the signals transmitted by the label. It is clear that the further it is from the antenna, the weaker the coupling and the more delicate the signal restitution. The position of the take-up reel (6) in the flow is also of great importance and presents blind spots where transmission becomes impossible. Certain forms of execution of these labels or smart cards like those described in patents WO 98/52141 or WO 00/69016 allow these blind spots to be reduced without however completely eliminating them.

The fig. 2 shows by way of example the electrical diagram of an assembly of 3 modular transmission antennas according to the invention. In this figure, three transmission antennas with identical characteristics are connected in series. We then have three chokes (10, 11, 12) each with their two capacities of value 2C in series (13, 14, 15, 16, 17, 18). The 3 inductors and the 6 capacitors are in series such that the resonant frequency of the assembly is fo = 1/2 π (3Lx2C / 6) ^1/2 = 1/2 π (LC) ^1/2 . We therefore see that the resonance frequency remains the same. On the other hand, if the number of modular antennas is multiplied, it is in principle to increase the operational coverage of the system, and it is desirable not to reduce the number of NIs per antenna. For this, it is necessary to maintain the voltage U at the terminals of each antenna at its set value, and thereby to multiply the working voltage Ut across the set by the number of modular antennas. In the case shown, this voltage is therefore equal to Ut = 3U.

The fig. 3 shows two embodiments of modular transmission antennas according to the fig. 1. In fact, these are two identical antennas (20, 20 ') placed 180 degrees relative to each other. Each antenna has a certain number of turns (21, 21 ') wound on magnetic cores in the form of fenite sticks (22, 22') so as to produce inductors capable of generating the magnetic flux necessary to supply the labels "and RF chip cards as mentioned above. These antennas are mounted in ad hoc boxes (23, 23 ') comprising at each of their ends connection elements, connectors, cables or the like, all the means known to those skilled in the art being conceivable. In the case shown, these are simple terminals for banana plugs (24, 24 ', 25, 25', 26, 26 'and 27, 27'). In this example, although many other combinations are possible, these terminals are subdivided into input terminals (I) and output terminals (O) so as to facilitate the interconnections between the modular antennas as described in FIGS. 4, 5 and 6. These input and output terminals can be differentiated for example by color, red input terminals (I) and blue output terminals (O). Each end of each antenna housing

, transmission (23, 23 ') has an input terminal (24, 24', and 25, 25 ') on the left, and an output terminal on the right (26, 26', and 27, 27 '). Input terminals

(24, 24 ') are electrically connected by a capacitor (28, 28') to the antenna winding input (21, 21 '), while the output terminals (27, 27') are electrically connected by a capacitor (29, 29 ') at the output of the coil of said antenna. These capacitors (28, 28 'and 29, 29') correspond to the capacities (3, 4) of Figure 1 which allow to pre-tune the antenna modular to the working frequency according to the relationship given in paragraph 4 on page 4, fo = l / 2 π (LC) ^1/2 . It is clear that, according to other embodiments, the pre-tuning capacities could be placed outside the boxes of the transmission antennas, for example in the electronic control box thereof or even incorporated in the wiring, without this changing their characteristics at the transmission level. However, the configuration described here has certain advantages. Due to the quality factor of the series resonant circuits formed by the coils (21, 21 ') with the capacitors (28, 28' and 29, 29 '), the overvoltage at the terminals of the coils (21, 21') can reach several hundreds of volts. This could be dangerous and would require special precautions if this voltage

“Appeared directly on the comiexion terminals. By incorporating the pre-tuning capacitors of the transmission anemie in the box, the voltage on the connection terminals is limited to U, a voltage necessary to excite the series resonance of the assembly, while simplifying the interconnections between modules. antenna. It can be seen in the drawing in FIG. 3 that the terminals 25 and 26, respectively 25 '^' and 26 'are directly connected electrically to each other by connections 30 and 30' parallel to the antenna coils (21 , 21 '). These are simply connections that simplify the wiring that ensures the passage of current flowing through the transmission antennas to the electronic control unit. These connections could also be made outside the antenna boxes, but we have just

, in the following figures that the configuration described here has interesting advantages. Finally, why did you represent two similar antennas (20, 20 ') 180 degrees from each other. Take the example of antenna 20. If the current enters the antenna through input 24, exits through output 27 and returns through input 25 to exit through output 26, the current will pass through the turns of the coil 21 in a clockwise direction, which generates a flux which we will call phase A. If on the contrary the current enters through the input 25,

'' comes out through outlet 26, comes back through inlet 24 and comes out through outlet 27, current will also pass through the coils of coil 21 clockwise, which always generates a phase flux A. The direction of this flow is determined by a graphic symbol (31) at the end of the housing (23). The phase of the flux with respect to the current therefore remains the same provided that one enters the antenna through one of the input terminals (24, 25) and that one leaves it through one of the output terminals (27 , 26). For the antenna 20 'which is arranged 180 degrees from the antenna 20, we have exactly the opposite. Whether the current enters through input 24 'or through input 25', current will flow through coil 21 'counterclockwise, which will generate a phase flow A + 180 degrees, i.e. a reverse flow to that generated by

^; the antenna 20. The graphic symbol 31 'indicating the phase of the flux in the antenna 20' is therefore 180 degrees with respect to the corresponding graphic symbol 30 of the antenna 20. These graphic symbols allow the installer to report immediately if the fluxes delivered by antennas which are close to each other are in phase or against phase. The interest of these different features will emerge in more detail from the descriptions in FIGS. 4 to 6.

The fig. 4 shows a first example of assembly of modular transmission antennas according to the invention. These transmission antennas are 4 in number, placed in series in pairs (40a, 40b, and 40c, 40d) of each. side of the space in which we want to be able to supply labels and smart cards and communicate with them, for example a door passage. We can see that the 4 antennas are oriented in the same direction as the antenna 20 of FIG. 3. Thus the graphic symbols (41a, 41b, 41c and 41d) which indicate the phase of the flux generated by each antenna are all directed upwards. For the direction of flow to be correct and consistent with the graphic symbol, the outputs (0) must be connected to inputs (I). Thus the current delivered by the electronic control circuit enters by a first electrical connection in the antenna 40a by the input 42a, passes through the coil and exits by the output 43 a. It then enters the antenna 40b through the inlet 42b passes through the coil and exits through the outlet 43b. In the configuration shown, the second pair of antennas (40c and 40d) is fed from above. Also the current enters it in the anemia 40c by the entry 44c, connected to the exit 43b of the antenna 40b. In order for the direction of the flow generated by the antenna 40c to be connected, it is on the return that the current must pass through the coil. The current therefore flows straight from the input 44c to the output 45c directly electrically connected to each other (see connections 30 and 30 'in FIG. 3). From the output 45c, the current arrives in the antenna 40d by the input 44d and passes directly on the output 45d, as in the case of the antenna 40c. At this point, the 4 antennas are electrically connected, but only the coils of the antennas 40a and 40b are connected. Furthermore, if you want the current to flow, you must complete the wiring so as to complete the circuit and return to the electronic control circuit, while passing through the coils of the antennas 40c and 40d. Thus the output 45d of the antenna 40d is connected to the input 42d of the latter. The current flows through the coil of this antenna and exits through the output 43d connected to the input 42c of the antenna 40c. The current then crosses the coil of this antenna and exits through the output 43c. This is connected to the input 44b of the antenna 40b, which is itself directly connected to the output 45b. Finally, this output is connected to the input 44a of the antenna 40a which is directly connected to the output 45a. So the current goes passes directly from the input 44b of the coil 40b to the output 45a of the coil 40a. This output is connected by a second electrical link to the electronic control circuit. Thus the loop is closed and the current flows through the coils of the 4 antennas. We can see the following points: 1 / The current always crosses the coils passing from terminals 42 to terminals 43 so that the flow is always in the right phase. 2 / The current always passes by direct connection from terminals 44 to terminals 45. These direct connections could pass outside without crossing the antennas, but the proposed solution has the advantage of the systematic and pennet to avoid eneurs of connection .

Each output is connected to an input by the shortest path and the wiring between antennas is thus very simplified. As the fluxes 46 generated by the 4 antennas are in phase, there is a relatively unidirectional orientation of these in the space covered by the antennas. This is not necessarily the best solution since labels and smart cards have blind spots depending on their position relative to the flow. It may therefore be preferable to vary the orientation of these flows to overcome this defect. This is the subject of the variants of FIGS. 5 and 6.

The fig. 5 shows a second example of assembly of modular transmission antennas according to the invention. In this combination, there are 4 transmission antennas as in the previous figure placed in series in pairs (50a, 50b and 50c 50d ) on each side of the space to be covered. The difference is that the modular antennas 50b and 50c are rotated 180 degrees relative to the antennas 40b and 40c in the previous figure. Thus the graphic symbols 51a and 5 ld are they up, and the graphic symbols 51b and 51c down. This means that the fluxes generated by the antenna modules 50b and 50c are in 180 degree opposition to the fluxes generated by the antenna modules 50a and 50d. We come further to what this means in terms of flow distribution. But first let's quickly examine the current flow in the antenna modules, taking into account the fact that the connection between the two modular antenna pairs is made from the bottom, and no longer from the top as in the figure 4. The current generated by the electronic control means anive at the input 52a of the antenna 50a, crosses the coil and leaves through the output 53a. It then passes through the input 54b of the antenna 50b and exits directly on the terminal 55b to enter via the terminal 52b, cross the coil and exit via the terminal 53b, return to the coil 50a and pass directly through the terminals 54a and 55a. In this case the current always passes through the antennas passing from terminals 52 and 53 (42 and 43 in FIG. 4), but in an opposite direction taking into account the fact that the antenna modules 50a and 50b are arranged at 180 degrees l of each other. The fluxes generated by these two antennas are therefore opposite 180 degrees. The current then passes through the input 52d of the antie 50d, crosses the coil and exits through the output 53 d. It then goes to the input 54c of the antenna 50c and comes out directly on the terminal 55c to enter through the terminal 52c, cross the coil and exit through the terminal 53c, return to the coil 50d and cross it directly through the terminals 54d and 55d to return to the electronic control circuit. In this case the current also passes through the antennas passing from terminals 52 and 53 (42 and 43 in FIG. 4), but in an opposite direction taking into account the fact that the antenna modules 50d and 50c are arranged at 180 degrees l of each other. The fluxes generated by these two antennas are therefore opposite 180 degrees. As can be seen in the figure, the fluxes generated by this arrangement of antennas modules are no longer unidirectional but stand in opposition and separate in 4 different orientations (56) which can make it relatively independent of the position of labels and smart cards passing through the space covered by this assembly of modular antennas . Note that, in this example, the two pairs of antennas could have been connected from the top rather than from the bottom in the example of the previous figure, and vice versa. This demonstrates the diversity of possible combinations in terms of connecting the modular antennas to each other. For example, it is not essential for the antennas to be parallel, as shown in the example in FIG. 6.

The fig. 6 shows a third example of assembly of modular transmission antennas according to the invention. This combination is formed by 3 modular antennas 60a, 60b and 60c arranged at 120 degrees from each other. These three antennas are rotated, in the direction of the center, as shown by the position of the graphic symbols 61a, 61b and 61c indicating the phase of the flux delivered by each antenna. The current delivered by the electronic control means arrives via the terminal 62, crosses the coil of the antenna 60a in the direction of the center, passes inside the antenna 60b and returns by crossing the coil of the latter in the direction of the Center. It then passes inside the coil 60c and returns by crossing the coil of the latter always in the direction of the center, and finally passes over the terminal 63 of the electronic control means passing inside the coil 60a. Thus the current crosses the coils of the three modular antennas in the direction of the center. The flows generated by them add up in a circular distribution (64). not only in the plane of the drawing, but also in space along the axis of each antenna. If a label or smart card crosses this space, it will encounter very diverse orientation flows and the risk that it will not be detected due to a bad position of its take-up reel is almost zero. Many other combinations are of course possible to adapt to each particular case. The number of modular transmission antennas connected in series according to the invention is limited not in theory, but by practical possibilities, surface to be covered, power of the electronic control means, etc. 8 to 10 seem to be a maximum.

The fig. 7 shows by way of example a modular transmission antenna according to the invention, to which an interesting branch connection has been added to the electronic control means and measuring coils. This transmission antenna (70) which we will call the mother antenna is very similar to that of FIG. 3 and has a main winding (71) wound on a magnetic core (72) co-exists with the other modular antennas. This mother antenna is mounted in a housing (73) which is only shown here very partially. At each end of this housing there are input terminals I (74, 75) and output terminals O (76, 77). The main winding (71) is connected on one side to the capacitor 78 and on the other to the capacitor 79. Until then, everything is identical to the antenna of FIG. 3.

The first difference consists in the fact that the connection between the input 74 and the capacitor 78 is unbroken to interpose a cable with two conductors (80) which is connected to the electronic control means so that the current delivered by them arrives by one of the conductors and leave by the other. Note that the cable 80 can be inserted anywhere in the supply circuit of the main coil of the mother antenna (71) without this changes anything functionally. If we short-circuit the terminals

74 with 76 and 75 with 77, the current arrives through the first conductor of the cable

'80 on the capacitor 78, crosses the main coil 71 and the capacitor

79, passes through terminal 77 towards terminal 75 and returns via terminals 76 and 74 to the second conductor of cable 80. The loop is thus closed and the current flows conectly in antenna 70. The aim is however to work with several modular antennas in series. For this, it is sufficient to connect them to terminals 74, 76 or 75, 77, for example according to different combinations of FIGS. 4, 5 and 6. Thus, the antenna / electronic control wiring is completely separated from the wiring of the modular antennas between they. The mother antenna is the only one to be connected to the electronic control means, for example by a shielded cable if these are at a certain distance, while the wiring between the modular transmission antennas which are located nearby another is simplified. Note that the mother antenna can replace any of the modular transmission antennas, regardless of their number and combination.

The second difference consists in the fact that the mother antenna 70 has an additional two-wire winding (81) wound on the magnetic core (72). By this winding, two identical measuring coils are obtained, the voltage at the terminals of which is proportional to the flux passing through said magnetic core, according to the well-known relation e = - n dΦ / dt = - Ldi / dt. The inputs and outputs of these two measuring coils are connected to the 4 conductors, a cable (82) which is connected like cable 80 to the electronic control means. It is for convenience of description that the two cables 80 and 82 have been separated. We could easily use only one cable to 6 conductors, just as one could have only one measurement coil, or even have measurement coils, in a second modular transmission antenna. These possibilities are technically possible variants but without real interest. It is preferable that all the particular functions are grouped together within a single antenna, that which we have called the mother antenna, and that only the latter is connected to the electronic control means.

The fig. 8 schematically shows by way of example the electronic means of the control unit associated with the modular transmission antennas according to the invention. In a well known configuration, these coimnande means comprise an oscillator (90), for example at 250 kHz which attacks the clock input of a flip-flop (91). This flip-flop presents on its outputs Q and Q / square signals at the frequency of 125 kHz, 180 degrees out of phase put them with respect to the others, intended to co-control the power amplifier which

'feeds the modular transmission antennas according to the invention. Thus, the output Q of the flip-flop (91) goes to a preamp (92) which controls in all or nothing a first pair of MOSFET N and P (93, 94) whose sources are connected to the terminals V-, respectively V + from the power supply (95) and the drains to a first output from the power amplifier (96). For this purpose, the MOSFET N gate (93) is connected to the output of the preamp 92 by the capacitor 97 and to V- by the resistor 98. Likewise the MOSFET P gate (94) is connected to the output of the amplifier 92 by capacity 99 and at V + by resistor 100. Symmetrically, the output Q / of the flip-flop (91) goes to a preamp (101) which controls in all or nothing a second pair of MOSFET N and P ( 102,

103)) whose sources are connected to terminals V-, respectively V + of

<the power supply (95) and the second output drains of the amplifier of power (104). The MOSFET N switch (102) is connected to the output of the amplifier 101 by the capacitor 105 and to V- by the resistor 106. Likewise the MOSFET P switch (103) is connected to the output of the amplifier 101 by the capacitor 107 and at V + by the resistor 108. The two pairs of MOSFETs N and P work in all or nothing and in counterphase so that, when V + appears on the first output (96), V- appears on the second output (104), and vice versa. The jumps of the N and P MOSFETs are decoupled by capacitors (97, 99, 105 and 107) so that the gate-source control signals which they receive from amplifiers 92 and 101 remain independent of the relative value of the voltages V +, V- compared to the supply voltage of these amplifiers. Indeed, in the configuration described, the power supply (95) actually consists of 3 modules in series (95a, 95b and 95c) whose outputs are connected to a 3-position selector A (109) allowing to choose three values of V + with respect to V-, for example 12 volts (position A = 1 = U), 24 volts (position A = 2 = 2U), or 36 volts (position A = 3 = 3U). Thus the voltages delivered by the power supply (95) depend on the position A of the selector (109) according to the relation AU. As we will see later, this allows to quickly adapt to the number of modular transmission antennas of the assembly according to the invention. In our case, this assembly (110) comprises a combination of 3 modular antennas completely identical to that described in FIG. 2. One of the sides of this assembly is connected to the output (96) of the first pair of MOS FETs of power via an adjustment capacitor (111) formed for example of one or more fixed value capacitors. Although the modular antennas are pre-tuned, there may be, depending on their arrangement in relation to each other, interactions which can cause slight variations in the resonant frequency. It is therefore preferable to provide these adjustment means to make a final adjustment. precise when everything is definitely in place. Here the modular antennas are pre-tuned to a frequency slightly higher than the working frequency so that they can be brought back to the exact value by means of the adjustment capacity 111. The second side of the assembly 110 is connected to a selector with two positions B (112) allowing to connect either to V- (position B = 1) or to the output (104) of the second pair of power MOS FETs (position B = 2). If the selector 112 is in position B = 1, the assembly of modular transmission antennas according to the invention (110) is connected between V + and V-, either at a voltage AU, for a first half-period, and between V- and Y-, ie 0, during the second half-period. The peak-peak voltage across the terminals of assembly 110 is therefore AU = or BA-U. On the other hand, if the selector 112 is in position B = 2, the antenna assembly 110 is connected between V + and V-, either at a voltage AU, during the first half-period, and between V- and V +, either at a voltage -AU during the second half-period. The peak-peak voltage across the terminals of assembly 110 is therefore 2 AU, or always B-AU. The peak-peak voltage at the terminals of the transmission antenna assembly 110 can therefore be selected using the selectors A and B in 6 combinations ranging from U (A = l, B≈l) to 6 U (A = 3 , B = 2). However, we saw in Figure 2 that to maintain the NI in modular transmission antennas, it was necessary to multiply the voltage across the assembly by the number of antennas. Thus, in the example represented here which comprises 3 modular antennas in series, A is in position 3 and B is in position 1. There is thus at the terminals of assembly 110 a peak-peak voltage of 3U corresponding to the number d antennas. Note that if the voltage is increased as a function of the number of antennas, the current remains constant, and neither the power MOS FETs are overloaded since they are adapted to the maximum voltages. neither the modules supply (95). By increasing the number of these to 4 and adapting the number of positions A of the selector 109, we. could feed up to 8 antennas, and so on. This way of making pennet of making electronic means of coimnande can be adapted very easily to all the possible combinations of assembly of modular transmission antennas according to the invention. However, the creation of control means specific to a specific application is of course still possible.

In fact, as we have seen in FIG. 7, only one of the modular transmission antennas of assembly 110, called the mother antenna and positioned anywhere in the combination, is connected to the electronic control means. This mother antenna comprises two identical measuring coils but phase shifted by 180 degrees (120, 121) having at their terminals a voltage directly related to the flux generated by the current flowing in the antennas. The main component of this flow is of course in relation to the current supplied at the working frequency by the electronic control means to supply the labels and smart cards. When these respond, this flux is modulated according to a known procedure at a much lower frequency, for example 2 kHz for 125 kHz (see FIG. 1), which generates corresponding variations in current. To recover this return signal, you must filter and integrate these. flow / current modulations. The methods currently used generally analyze the voltage or the current directly at the terminals of the main coil to which are added components which are not directly related to the flux in the coil, but which depend on the number of modular antennas, losses brass, stray capacitances, etc. By introducing one or more at the level of the mother antenna , measurement coils completely independent of the main coil, a voltage truly representative of the flux is obtained in the coils of the modular transmission antennas. This voltage is independent of the number of antennas, and any variation in the flux produced by the presence of a label or smart card near any one of the modular antennas of the assembly results in a corresponding variation of this- this. To detect these flux variations and restore the signals back from labels and smart cards, the voltage across the measuring coils (120, 121) is rectified by means of two diodes (122, 123) working alternately. This is a two-wave rectifier at the output of which there is a frequency twice the working frequency (250 kHz), which allows

. better separate signals back at 2 kHz from the base frequency. This separation is generally made by means of a low pass filter which eliminates the base frequency (124), this filter being connected to a demodulation circuit (125) which is restored via a trigger type amplifier. de Schmidt (126) signals conforming to the return signals from labels or smart cards which are in the field of operation of one or other of the modular transmission antennas according to the invention. The possibilities of configurations of these different circuits are extremely numerous, and we will not go into more detail in their description insofar as this is not directly part of the object of the invention. Figures 9 and 10, however, provide some additional information of interest for understanding it.

The fig. 9 shows by way of example a particular embodiment of said electronic means according to FIG. 8. One of the measurement coils of FIG. 8, for example the coil 120, is connected to the input - of an operational amplifier (130 ) through a voltage divider formed by resistors 131 and 132. The output of this amplifier

130 is connected to the input + by a voltage divider formed by the diode 133 and ι resistors 134 and 135 in order to obtain a slight negative hysteresis, but of course only when said output is at least. The amplifier 130 therefore operates as an asymmetrical Schmidt trigger, and delivers an all or nothing signal at its output as soon as the voltage of the negative half-period at the terminals of the coil 120 reaches a minimum value fixed by said hysteresis. As the amplifier 130 has a high gain, the introduction of this pennet avoid irrational behavior due to the presence of background noise of low amplitude. The output of amplifier 130 is connected by a capacitor

(136) to a resistor (137) connected to the + of the power supply and to the input of an inverter (138), so as to generate on the output of the latter a short positive pulse corresponding to the negative flank of the voltage at the output of

. amplifier 130. This negative edge occurs as soon as said minimum voltage has been reached at the moment when the voltage across the terminals of the coil 120 passes through 0 to become positive as shown in FIG. 10.

In addition we find an oscillator (140), but this time at the frequency of 500 kHz. This oscillator is connected to the clock input of a divider by 4 formed by two D flip flops (141, 142) so as to obtain on the inputs of amplifiers 143 and 144 corresponding to amplifiers 92 and 101 of figure 8 square at 125 kHz, 180 degrees out of phase with each other, intended to co-control the power amplifier which feeds the modular transmission antennas. The pulses at the output of amplifier 138 are directed _t to the reset inputs of oscillator 140 and flip-flops 141 and 142. An electronic switch 145 nevertheless allows these pulses to be sent as an option on the input flip-flop set 142. At startup, this. circuit behaves like that of Figure 8 and the modular antennas are powered by the power amplifier at the frequency generated by the oscillator 140 and the flip-flops 141 and 142. However we said above that due to the high quality factor of the antenna, it ^was: desirable to work at the exact resonance frequency of the assembly according to the invention. Also, as soon as the voltage across the measuring coil 120 reaches the minimum required voltage, the short pulses generated at the output of amplifier 138 reset the oscillator 140 and flip flops 141 and 142 to 0. Thus the signals Canes generated by these circuits at the outputs of amplifiers 143 and 144 be synchronized with the proper resonant frequency of the antennas. Note that this frequency adaptation only concerns a few per thousand, 1 or 2 percent at most, but this is enough to improve the performance of the antennas. However, for this synchronization to work correctly, the phases between the square signals at the outputs of amplifiers 143 and 144 must be perfectly defined with respect to the reset pulses generated at the output of amplifier 138. Furthermore, by switching from the reset input of the flip flop 142 to the set input by means of the switch 145, the phases of the outputs of the amplifiers 143 and 144 are reversed, which makes it possible to carry out an additional advantageous function. let's show in figure 10 below

The fig. 10 represents the form of the signals at different points of said electronic means of FIGS. 8 and 9. Firstly there is the sinusoidal voltage across the terminals of the measuring coil 120. This voltage (150) e = - n dΦ / dt = - Ldi / dt is 90 degrees out of phase, i.e. a quarter of a period from the current in the coil (151). When the amplitude of the voltage 150 reaches the minimum required, short pulses (152) are generated at the output of the amplifier 138 when the voltage 150 reverses from least to most. In the first case (switch 145 on reset), the Q outputs of fliptlops 141 (153) and 142 (154) are reset to 0. As the flip flop 142 switches to the positive blank of its clock input, its output passes at 1 after 1/4 of period and the outputs of amplifiers 143 and 144 which control the power amplifier which supplies the modular transmission antennas are in line with the current in these antennas (151). This represents a perfectly synchronized oscillator and the current will increase very quickly to the maximum amplitude possible with said power amplifier. There are thus three stages in the dismantling, supply at the natural frequency of the generator, synchronization of said generator at the resonant frequency of the assembly of the modular transmission antennas according to the invention as soon as the amplitude is sufficient, and stabilization at the maximum amplitude This is very important because, to write in RF type tags and smart cards, it is necessary to modulate all or nothing the signal transmitted by the antennas at relatively high frequency. This implies that we must be able to activate and reduce this signal as quickly as possible. The use of a generator which synchronizes in order to reach without blow the maximum amplitude pennet to solve this problem on switching on. To quickly reduce this signal, the problem is more difficult insofar as, due to the quality factor of the transmission antenna, this reduction normally takes place exponentially according to a non-negligible time constant. It is therefore necessary to dampen the antenna to reduce this constant. This is where switch 145 comes in. This switch allows you to invert the signals at the outputs of amplifiers 143 and 144 (155) so that the power amplifier works in counter-phase with the current in the antennas. From this mother, we thus produce a sort of synchronized anti-oscillator which You can reduce the current very quickly to bring it back below the minimum value. As soon as the switch 145 is returned to the reset position, the signals at the outputs of amplifiers 143 and 144 will be restored to their connected phase and said current will be restored as soon as possible. The switch 145 therefore allows to simply modulate the signals of the modular transmission antennas according to the invention with all the desired speed.

There are of course very many variants of modular antenna assemblies according to the invention, but their description would not add any additional elements to its understanding.

Claims

claims

/ Assembly of modular transmission antennas for RF identification system each comprising a choke formed from a main winding (21, 71) wound on a magnetic core (22,

72), characterized in that said assembly comprises several modular transmission antennas connected in series with each other (10,11,12 / 40a, b, c, d / 50a, b, c, d / 60a, b , c) and supplied by electronic control means (90-109) connected to at least one of them, said modular transmission antennas having similar electrical characteristics and being pre-tuned individually in resonance at the working frequency by means of own capacities (13, 14, 15, 16, 17, 18) connected in series with the inductors formed by the main windings of the modular antennas of said assembly.

/ Assembly of modular transmission antennas according to claim 1, characterized in that the capacities specific to each antenna (28, 29) are connected inside the same housing thereof.

/ Assembly of modular transmission antennas according to claims 1 and 2, characterized in that each antenna comprises at least one input terminal (24) and one output terminal (27), said own capacitors (28, 29) and the main winding of said antenna (21) being connected in series between these two terminals. / Assembly of modular transmission antennas according to claims 1 to 3, characterized in that said input (24) and output (27) terminals are each placed at one end of the housing of said antenna.

5 / assembly of modular transmission antennas according to claims 1 to 4, characterized in that each antenna has a second pair of input (25) and output (26) terminals directly connected to each other electrically and placed so that there is an input terminal and an output terminal at each end of the housing of said antenna.

6 / assembly of modular transmission antennas according to claim 1, characterized in that the wiring means comprising two conductors (80) are interposed (74, 78) in the supply circuit of the main winding (71) of one of the antennas called mother antenna (70), these wiring means being arranged so as to supply all of the antennas when they are connected to the power amplifier (90-109) of the electronic control means.

Il Assembly of modular transmission antennas according to claim 1, characterized in that one of the antennas has an additional winding (81) wound on its magnetic core

(72), and wiring means (82) permitting to connect said winding to the filtering and demodulation circuits (122-126) of the electronic coimnande means, this winding forming at least one measuring coil (120, 121) having at its terminals a voltage directly representative of the current flowing in all of the antennas.

/ Assembly of modular transmission antennas according to claims 1, 6 and 7, characterized in that the additional winding (81) is incoφor in the mother antenna (70) of mother only that it is directly connected to the means electronic components (80, 82).

/ Assembly of modular transmission antennas according to claims 1 and 7, characterized in that said additional winding (81, 120) is also connected to an adjustment circuit (130-138) of the signals delivered by the electronic means of coimnande to the power amplifier (140-144), this circuit being arranged so as to synchronize these signals at the natural resonant frequency of all the antennas.

0 / assembly of modular transmission antennas according to claim 1, characterized in that the electronic control means comprise a power supply (95) having several output voltages and a coin-switch (109) permitting to select the supply voltage of the power amplifier as a function of the number of modular transmission antennas of the assembly.