FR2832530A1 - Manufacture of labels with LC resonant circuits has wound spirals or inductance coil and pairs of electrodes forming condensers - Google Patents

Abstract

Manufacturing procedure for a label with an LC resonant circuit (1) includes a stage in which an electronic circuit is engraved on thin conducting layers e.g. of aluminum, the circuit comprising a series of wound spirals (3) or an inductance coil and a number of electrodes in pairs forming condensers (2, 2'). Manufacturing procedure for a label with an LC resonant circuit (1) includes a stage in which an electronic circuit is engraved on thin conducting layers e.g. of aluminum, the circuit comprising a series of wound spirals (3) or an inductance coil and a number of electrodes in pairs forming condensers (2, 2'). In a subsequent stage a layer of a dielectric material is injected between the conducting layers and the condenser electrodes so that the electrodes face one another precisely.

Description

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METHOD FOR MANUFACTURING A LABEL WITH CIRCUITS
RESONANCE
The present invention relates to a method of manufacturing a label with resonance circuits. It applies in particular, but not exclusively, to labels with LC resonant circuits, serving as anti-theft devices for products offered on display but also for the identification of goods or packages.

 At present, there are labels on the market with LC resonant circuits, particularly resonant labels which are used to protect against shoplifting in retail stores, for example in clothing stores. or everyday consumer products. Thus, these labels consist of a coiled spiral, defining an inductance L, and a capacitor, defining a capacitance C, placed on either side of a dielectric made of polyethylene, polystyrene or polypropylene; these three elements, said spiral, said capacitor and said dielectric forming an anti-resonant circuit called a plug circuit. This plug circuit has the particularity of having maximum absorption at its resonant frequency. This resonant frequency is a function of the various aforementioned elements chosen to form the LC resonant electrical circuit.

 Thus, the current method of manufacturing labels with LC resonant circuits consists first of all in constituting the resonant circuit as indicated above by etching respectively on two thin plates, generally made of aluminum, the LC electric circuit and then having between the two plates the dielectric used. It is then necessary to perform a solder between the two plates of the aluminum capacitor to close the circuit of these labels.

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 This method of manufacturing labels with LC resonant circuits has a number of drawbacks. Indeed, the last step consisting of welding is a delicate operation and likely to be poorly performed; this resulting in major subsequent malfunctions of the label with LC resonant circuits. In addition, this operation represents a significant cost requiring skilled labor and requires a relatively long time to be performed.

 The object of the invention is more particularly to remedy the drawbacks of the prior art by proposing a manufacturing method allowing the elimination of the conventional welding step and thus making it possible to simplify the manufacture of labels with LC resonant circuits.

 To this end, the invention proposes a method for manufacturing a label with LC resonant circuits, in particular for the protection against theft of retail items, comprising only a step of engraving an electronic circuit respectively on two thin conductive plates , for example made of aluminum, characterized in that the electronic circuit comprises a plurality of coiled spirals, or inductance coil, as well as a plurality of electrodes each forming one of the two electrodes of a plurality of pairs of electrodes each constituting a capacitor.

 Advantageously, the method for manufacturing labels with LC resonant circuits comprises a subsequent step consisting in the injection between aforesaid plates of a dielectric layer so that the two plates are fixed to each other by the intermediate of said dielectric. Each of the electrodes forming one of the electrode pairs of a

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 capacitor is therefore precisely opposite the other electrode of said capacitor.

 According to a possibility offered by the invention, the direction of winding of the wound spirals, or inductance coils, may be the same.

Thus, the two spirals will wind in the positive trigonometric direction, or opposite, for example one of the two spirals winding in the in the positive trigonometric direction and the other spiral winding in the direction of rotation of the hands a watch; these two directions of rotation being opposite, or opposite.

 Advantageously, the dielectric used to be injected between the two thin conductive plates, and between the two electrodes of the capacitors, will be a plastic, for example polyethylene, polystyrene or polypropylene.

 Thanks to the method according to the invention, a label with LC resonant circuits is obtained comprising a dielectric disposed between two thin conductive plates, and between the two electrodes of the capacitors, characterized in that said plates each comprise at least one wound spiral, or coil inductance, as well as a plurality of electrodes each forming one of the two electrodes of a pair of electrodes constituting a capacitor; each of the electrodes forming one of the electrode pairs of a capacitor located precisely opposite the other electrode of said capacitor, separated by the above dielectric.

 Advantageously, the two plates will be made of aluminum.

 Thanks to these features, the invention makes it possible to obtain a label with a resonance circuit in

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 a single manufacturing step: the etching of the conductive plates. The method according to the invention makes it possible to obtain the manufacture of a label with LC resonant circuits having a lower cost price than the manufacturing method of the prior art in which the step of welding said plates remains. Furthermore, this manufacturing process makes it possible to achieve high reliability in terms of production due to the absence of possible bad welds causing malfunctions, or even non-functioning of the label, of the labels produced.

verticale des deux spirales enroulées représentées sur la figure 5 ; An embodiment of the invention will be described below, by way of nonlimiting example, with reference to the appended drawings in which:
FIG. 1 schematically illustrates a label with LC resonant circuits according to the prior art;
FIG. 2 is a diagram illustrating a double LC circuit in parallel according to the method of the invention;
FIG. 3 illustrates the faces, upper a and lower b, of the aluminum plates engraved according to the method of the invention;
Figure 4 illustrates the two faces shown in Figure 3 fixed to each other by means of a dielectric;
FIG. 5 illustrates an embodiment of the method for manufacturing an LC circuit label;
Figure 6 shows a section

vertical of the two coiled spirals shown in Figure 5;

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FIG. 7 illustrates another embodiment of the method for manufacturing an LC circuit label;
Figure 8 shows a vertical section of the two coiled spirals, or inductors, shown in Figure 7;
FIG. 9 represents the two visible faces, upper and lower, of an LC circuit label according to the invention.

 The different figures make it possible to appreciate the steps of the method according to the invention making it possible to obtain a label with LC circuits 1, serving in particular for the protection against theft of items of details. We have chosen to illustrate the invention by making said label 1 with a double LC circuit in parallel, but it will of course be possible to use more capacitors 2 and coiled coils 3, or inductors, provided that the electrical circuit of the label has an axial symmetry, that is to say that said circuit can be divided into two equivalent electrical circuits whose union forms the electrical circuit of the label 1 according to the invention.

 LC 4 circuit labels of the prior art have the same elements as those of the invention, that is to say a wound spiral 3, or inductor, a capacitor 2 and a dielectric 5 s 'extending between the two electrodes of said capacitor 2; the elements of this electrical circuit being interconnected by a conducting wire 6.

However, unlike the labels 4 of the prior art, the label 1 according to the invention comprises at least one wound spiral, in this case two spirals 3 and 3 ′, as well as a plurality of capacitors 2 and 2 .

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 Furthermore, in the prior art, the manufacturing of the LC circuit label 4 comprises a step of welding the two upper aluminum plates, not shown in the example of FIG. 1. This welding 10 is carried out conventionally at near the capacitor.

 In FIGS. 2 to 8 representing an LC circuit according to the invention, there is at least one plane of symmetry X'X. Thus, on the right or left side of this plane X'X, there is a wound spiral 3 and 3 ', or inductance coil, as well as two electrodes 12,13 and 12', 13 'each of which forms one of the two electrodes of the pair of electrodes constituting a capacitor 2 or 2 '.

 The method according to the invention therefore consists in using a double LC circuit. On one side of a first plate 7, usually made of aluminum, is engraved one of the electrodes 12 or 12 ′ of a capacitor 2, a spiral wound 3 or 3 ′, or inductance coil, as well as one of the electrodes 13 or 13 '' from a capacitor 2 ', while on the face of a second plate 8, also made of aluminum, is engraved the second electrode 12 or 12' of the capacitor 2, a spiral wound 3 or 3 ', or coil d 'inductance, as well as the second electrode 13 or 13' of the capacitor 2 '. A dielectric 9 is disposed between the plates 7 and 8 along the plane X'X, that is to say that this dielectric 9 is placed between the two electrodes 12, 12 ′ and 13, 13 ′ of the two capacitors 2 and 2 .

 Thus, the method for manufacturing an LC circuit label 1 comprises a step consisting in injecting, between the two plates 7 and 8, a layer of dielectric 9 so that the two plates 7 and 8 are fixed l 'to each other via said dielectric 9. Each of the electrodes 12, 12' and

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 13, 13 ′ forming one of the pairs of electrodes of a capacitor 2 or 2 ′ is located precisely opposite the other electrode of said capacitor 2 or 2 ′, in particular after the dielectric 9 has been injected between the electrodes 12, 12 'or 13, 13'.

 Furthermore, the dielectric 9 used to be injected between the two thin aluminum plates 7 and 8 will ideally be a plastic, for example polyethylene, polystyrene or polypropylene.

 Of course, the calculation of the values necessary for the operation of the electrical circuit LC 1 according to the invention is not conventional due to the superposition of the windings of the inductors of the two wound spirals 3 and 3 ′, or inductance coils, causing a self-induction phenomenon. Of course, it will then be necessary to watch the phases of the windings of the wound spirals determined by the direction of winding of the latter.

 Thus, the method according to the invention can be envisaged according to two different configurations.

 As can be seen in FIGS. 5 and 6, the winding direction of the two spirals 3 and 3 ′, or inductance coils, is not the same, noted INT / INT or EXT / EXT for one and the other of the two spirals 3 and 3 ', or inductance coils. One of the two spirals 3 or 3 ′ is, for example, wound in the positive trigonometric direction and the other spiral 3 or 3 is wound in the direction of rotation of the needles of a watch.

 In the same way, as can be seen in FIGS. 7 and 8, the direction of winding of the two spirals 3 and 3 ′, or inductance coils, is the same, according to another embodiment of the invention , noted INT / EXT for the two spirals 3 and 3 ', or coils

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 inductance. These spirals 3 and 3 ′, or inductance coils, are for example both wound in the positive trigonometric direction.

 In practice, if we consider as the basis of the resonant frequency, the most standard value used for protection against shoplifting of retail products, namely 8.2 MHz, the various calculations to determine the values to be chosen for the impedance of the wound spirals 3 and 3 ′, or inductance coils, as well as for the values of the capacitances, in Henry, of the capacitors 2 and 2 ′ are detailed below.

F = 1/ (2n -J LC)
Où F est exprimé en Hertz, L en Henry et C en Farad. According to the case of an electric circuit LC, the values of the inductance L of the wound spirals 3 and 3 'and of the capacitance C, in Henry, of the capacitors 2 and 2' are determined using the following known formula:

F = 1 / (2n -J LC)
Where F is expressed in Hertz, L in Henry and C in Farad.

 However, in practice and considering the manufacture of labels comprising discrete components (capacitors and inductors, or coils wound, conventional found in trade), the classic formula is not suitable in the case of geometric overlap inductors, due to self-induction between the two wound spirals 3 and 3 ', or inductance coils. The values in this case will be found by experimenting with different Farad values of the capacitor. Thus, for the sought frequency of 8.2 MHz, 11.4 0.5 RH must be considered for the inductance of said spirals 3 and 3 ', and 20 + 0.5 pF for the Farad value of one of the capacitors 2 or 2 while the second capacitor 2 or 2 has a value of 17 0.5 pF.

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 The invention is described in the foregoing by way of example. It is understood that a person skilled in the art is able to carry out different variants of the invention without going beyond the scope of the patent.

Claims (9)

1. Method for manufacturing a label with LC resonant circuits, in particular for the protection against theft of retail items, comprising only a step of engraving an electronic circuit respectively on two thin conductive plates, for example made of aluminum, characterized in that the electronic circuit comprises a plurality of wound spirals, or inductance coil, as well as a plurality of electrodes each forming one of the two electrodes of a plurality of pairs of electrodes each constituting a capacitor.  2. Method for manufacturing labels with LC resonant circuits (1) according to claim 1, characterized in that it comprises a subsequent step consisting of injection between the above-mentioned plates (7 and 8) and between the two electrodes ( 12, 12 'and 13, 13') of the capacitors (2 and 2 ') of a dielectric layer (9) so that the two plates (7 and 8) are fixed to each other by l 'intermediate said dielectric (9); each of the electrodes (12, 12 ′ and 13, 13 '), forming one of the pairs of electrodes of a capacitor (2 or 2 ′), located precisely opposite the other electrode of said capacitor (2 or 2 ').  3. Method for manufacturing labels with LC resonant circuits (1) according to claim 1, characterized in that the wound spirals (3 and 3 '), or inductors, are wound in the same direction, for example all both in a positive trigonometric direction.  4. Method for manufacturing labels with LC resonant circuits (1) according to claim 1, characterized in that the two wound spirals (3 and 3 '), or inductors, are wound in the same <Desc / Clms Page number 11>  opposite or opposite direction, for example one of the spirals being wound in the positive trigonometric direction and the other spiral being wound in the direction of rotation of the needles of a watch.  5. Method for manufacturing labels with LC resonant circuits according to claim 2, characterized in that the dielectric (9) used to be injected between the two thin plates (7 and 8), and the electrodes (12, 12 ′ and 13,13 ') of the capacitors (2, 2'), is a plastic, for example polyethylene, polystyrene or polypropylene.  6. LC resonant circuit label (1) comprising a dielectric (9) arranged between two thin conductive plates (7 and 8) characterized in that said plates (7 and 8), and between the two electrodes (12, 12 ′ and 13,13 ') of the capacitors (2 and 2'), each include a plurality of wound spirals (3 or 3 '), or inductors, as well as a plurality of electrodes (12,12' and 13, 13 ') each forming one of the two electrodes of a pair of electrodes (12, 12' and 13, 13 ') constituting a capacitor (2 or 2'); each of the electrodes forming one of the pairs of electrodes of a capacitor located precisely opposite the other electrode of said capacitor (2 or 2 ′), separated by the above dielectric (9).  7. LC resonant circuit label (1) according to claim 6, characterized in that the two above-mentioned plates (7 and 8) are made of aluminum.  8. Label with LC resonant circuits (1) according to claim 6, characterized in that the inductance of said spirals (3 and 3 ') is 11.4 0.5 H (calculation with conventional wound spirals commercially available ). <Desc / Clms Page number 12>  9. Label with LC resonant circuits (1) according to claim 6, characterized in that the value of the capacitance, in Farad, of one of the capacitors (2 or 2 ') is 20 0.5 pF, while the capacitance of the second capacitor (2 or 2 ') has a value of 17 0.5 pF (calculation with conventional capacitors available on the market).