EP0919049B1 - Resonant circuit for electronic anti-theft element - Google Patents

Abstract

A resonant circuit for an anti-theft element consists of two spiral printed circuits and one dielectric layer. The spiral printed circuits are wound in opposing directions and arranged on opposite sides of the dielectric layer so that they at least partly overlap. At least one selected area is provided in which a conductive path arises between the two spiral printed circuits whenever a sufficiently high energy is applied by means of an external alternating field.

Description

The invention relates to a resonant circuit for the electronic article surveillance.

Resonance resonant circuits, which at a predetermined resonance frequency, which is usually 8.2 MHz, to resonance vibrations are excited for the purpose of General anti-theft protection in department stores. They are often an integral part of adhesive labels or Cardboard hang tags attached to the items to be secured are attached. Typically, the department store is with one electronic surveillance system in the exit area equipped that recognizes the resonant circuits and one Alarm triggers when a secured item is in an unauthorized manner Way a secured surveillance zone happens. Once a Customer has paid for the goods, the resonant circuit deactivated. The measure prevents a Alarm is triggered as soon as an item is lawfully purchased has been passed and subsequently the surveillance zone.

The deactivation systems that are often placed in the checkout area are generating a resonance signal with a larger one Amplitude as it is generated in the surveillance systems. A resonance label is usually accompanied by a signal whose field strength is greater than 1.5 A / m, deactivated.

Different deactivation mechanisms for Resonant circuits have become known. Either will the isolation between opposite one another Printed conductors destroyed, which creates a short circuit, or a piece of a conductor track is overloaded and melts, which creates an interruption. As a result of Deactivating the resonant properties of the Resonant circuit, i.e. the resonance frequency and / or the "Q" factor modified so much that the Resonance label no longer by the surveillance system is detected.

Regarding the deactivation of resonance labels different methods have been described. In the US PS 4,876,555 or in the corresponding EP 0285 559 B1 suggested using a needle to make a hole in the Insulation layer between two opposite To generate capacitor areas. This will be a Deactivation mechanism made that is error free and is permanent. US Pat. No. 5,187,466 also describes a method for Generation of a deactivatable resonant circuit by means of a short circuit.

With regard to the first-mentioned US Pat. No. 4,876,555 and EP 0 285 559 B1 it should be noted that the one disclosed there Resonant circuit has capacitor plates on are arranged on both sides of the dielectric. The between dielectric layer lying between the two capacitor plates has a through hole.

A process is described in the previously mentioned US Pat. No. 5,187,466 described that with a resonant circuit Capacitor plates on both sides of the dielectric is applied, the capacitor plates first be short-circuited and the short-circuit later Electric power is melted.

EP 0 181 327 B1 describes a deactivable device Resonance label described, which results from a dielectric carrier layer, capacitor plates to both Sides of the dielectric layer and a spiral Turn on either side of the dielectric Layer. To ensure that a the resonance label has been reliably deactivated a selected area prepared for deactivation. In particular, the dielectric layer is thinner here than in the other areas.

The invention has for its object a resonant circuit propose that be reliably disabled can.

The object is achieved in that the resonant circuit from two spiral conductor tracks and one dielectric layer, the two conductor tracks are wound in opposite directions and to both Sides of the dielectric layer are arranged such that they overlap at least partially, with at least one selected area is provided in which a conductive Path between the two conductor tracks is created as soon as one sufficiently high energy through an external alternating field is fed. The invention therefore has no separate ones Capacitor plates on; rather, these are directly through the two at least partially overlapping Conductor tracks formed.

According to an advantageous development of the invention Resonant circuit has the dielectric Layer essentially a uniform thickness and none additional manufacturing defects (e.g. air pockets).

This configuration is particularly advantageous in connection with the training that the selected area to the outer end regions of the conductor tracks, where the Induction voltage of the conductor tracks is maximum. Here it is completely redundant, any place of the To prepare the resonant circuit in particular. Under The deactivation area lies in the use of physical laws automatically in a predeterminable range the outer ends of the spiral traces.

An alternative embodiment of the invention Resonant circuit suggests that the selected one Area at any point of the overlapping Conductor tracks lie and are prepared in such a way that when they are created of the deactivation signal the conductive path on the prepared site.

In particular, it is provided in this connection that the dielectric layer is thinner in the selected area than in the other areas or that it is prepared location around a hole in the dielectric layer acts. Another embodiment of the invention Resonant circuit provides that the dielectric Another physical layer in the selected area or chemical in nature.

An advantageous development of the invention Resonant circuit provides that the dielectric Layer consists of at least two components. By means of a such a configuration can be very homogeneous, containing negligible air pockets Manufacture dielectric layers. Here it turned out to be proven favorable when the melting point of one component above the manufacturing temperature for the Resonant circuits, i.e. this layer is during of the manufacturing process does not melt. The components are furthermore according to a further training of the Obtain the resonant circuit so that it can either by Coating or lamination can be put together.

In the previous place was already on the advantageous Embodiment of the resonant circuit according to the invention referenced, the deactivation area due to physical conditions in the overlapping outer End areas of the spiral conductor tracks occurs. Around intensifying this effect sees an advantageous Development of the resonant circuit according to the invention before that the areas of overlap between the two Conductors and thus the capacity between the spiral Traces at the inner ends of the traces focus.

Another improvement in terms of a safe Deactivation can also be achieved in that the outer ends of the two traces in a small one Area overlap and that is at the outer ends of the Conductors a relatively long area without overlap connects.

Fig. 1: eine Draufsicht auf eine Ausführungsform des erfindungsgemäßen Resonanzschwingkreises,

Fig. 2: einen Querschnitt gemäß der Kennzeichnung II-II in Fig. 1,

Fig. 3: eine schematische Darstellung der Spannungen bei zwei sich teilweise überlappenden spiralförmigen Leiterbahnen,

Fig. 4: eine Draufsicht auf den äußeren Endbereich der spiralförmigen Leiterbahnen,

Fig. 5: einen vergrößerten Querschnitt durch die obere Spule und die obere Komponente der dielektrischen Schicht und

Fig. 6: einen detaillierten Querschnitt durch den erfindungsgemäßen Resonanzschwingkreis.

The invention is explained in more detail with reference to the following figures. It shows:

1: a plan view of an embodiment of the resonant circuit according to the invention,

2: a cross section according to the marking II-II in Fig. 1,

3: a schematic representation of the voltages with two partially overlapping spiral conductor tracks,

4: a plan view of the outer end region of the spiral conductor tracks,

5 shows an enlarged cross section through the upper coil and the upper component of the dielectric layer and

6: a detailed cross section through the resonant circuit according to the invention.

Fig. 1 shows an embodiment of the invention Resonant circuit 6 in plan view. 2 is the in Fig. 1 shown resonant circuit 6 in cross section see.

The resonant circuit 6 is deactivated by a short circuit between the two spiral Conductor tracks 2, 3, which are preferably made of aluminum are generated through the dielectric layer 4 becomes. An applied alternating magnetic field, e.g. is emitted by the monitoring system AC voltages in the two spiral conductor tracks 2, 3 of the resonant circuit 6. The two spiral Conductor tracks 2, 3, which at least partially overlap, are wrapped in opposite directions. Therefore points the outer end of the lower coil 2 has a positive potential relative to the inner end of the lower coil 2 if that inner end of the upper coil 3 has a positive potential with respect to the outer end of the upper coil 3. It stays So it should be noted that the points / areas in which the induced alternating voltages between the two coils 2, 3 are maximum, located in the end regions of the coils 2, 3.

Since in the example shown in FIG. 1 the upper coil 3 has fewer turns than the lower coil 2, the highest voltages between the ends of the upper coil 3 and the positions directly below the lower coil 2 generated. Fig. 3 illustrates the voltage relationships in different areas of the two themselves at least partially overlapping coils 2, 3 one Resonant circuit 6, according to an advantageous Further development of the resonant circuit 6 according to the invention can be used.

Fig. 3 shows the different voltages in different Areas of the two overlapping coils 2, 3 over their length during the electromagnetic Induction occur.

With the resonant circuit 6 described above with uniform thickness of the dielectric layer 4 between the Coils 2, 3 are deactivated in the end areas of upper coil 3 and lower coil 2, since here the induced Potential is maximum. Because the electric field strength occurs concentrated on a small radius surface, there is a deactivation exactly at the ends of the Conductor tracks 2, 3 - as shown in Fig. 4.

However, if the dielectric layer 4 is not uniform is thick or contains air bubbles 7, which is due to Manufacturing errors is quite possible Deactivation in different areas of coils 2, 3 occur. Such manufacturing defects can be local Cause vulnerabilities and even holes through Air pockets in the dielectric layer 4 cause. As a result, the dielectric layer 4 breaks thereon local vulnerabilities together, though that Voltage potential here is lower than at the ends of upper coil 2 and lower coil 3. Because the voltage potential is lower at the local weak points than at the ends of the conductor tracks 2, 3, is used to generate the Deactivation short circuit available electrical energy less than the electrical energy that to create a deactivation short at the ends the upper coil 3 would be necessary.

Fig. 5 shows a cross section of a one layer existing dielectric 4 with manufacturing defects, here Air bubbles 7 and irregularities in the area Surface.

Therefore, it is a further aim of the present one to form a dielectric layer which is essentially a has uniform thickness and is largely free of local vulnerabilities that arise as a result of manufacturing. Such a uniform dielectric layer 4 provides one Deactivation in places where maximum Voltage and energy can be found, i.e., related to that Example shown at the ends of the upper conductor track 2. Short circuits caused by such deactivation are very robust and not very susceptible to unintentional reactivation.

According to an advantageous development of the invention The resonant circuit 6 consists of the dielectric layer 4 from at least two components 4a, 4b, an upper one Component 4a and a lower component 4b. The lower one Component 4b is stamped onto the lower coil 3 applied. The upper component 4a is on the upper coil 2 applied. The upper component has 4a a relatively low melting point that allows her to Serve hot melt adhesive and the two coils 2, 3 during hot stamping the upper coil 2 towards the lower coil 3 glue. The upper component 4a of the dielectric layer 4 melts during hot stamping of the upper coil 2. Die lower component 4b of the dielectric layer 4 has one higher melting point and does not melt during the Hot stamping on the top spool 2. The uniformity of the lower component 4b of the dielectric layer 4, which is not melts, improves the uniformity in the thickness of the dielectric layer 4 overall.

6 shows a cross section of a resonant circuit 6 with a dielectric layer 4 consisting of two components 4a, 4b. The lower component 4b can either be coated the lower coil 3 or by laminating the lower one Component 4b of the dielectric layer 4 on the coil 3 getting produced. The coil material is usually located (A1) in the form of wide roll material, so that the Uniformity of the surface of the dielectric layer 4 can be maintained and other flaws that for example caused by air pockets 7, be minimized.

Reference list

1

Backing material

2nd

upper coil

3rd

lower coil

4th

dielectric layer

4a

upper component

4b

lower component

5

Adhesive layer

6

Resonant circuit

7

Trapped air

Claims (11)

1. A resonant circuit (6) for electronic article surveillance, comprising two coiled conductive tracks (coils 2, 3) and one dielectric layer (4), wherein said two coiled conductive tracks (2, 3) are wound in opposite directions and are disposed on either side of the dielectric layer (4) such as to overlap at least in part, and wherein at least one selected area is provided in which a conductive path is produced between the two coiled conductive tracks (2, 3) as soon as energy in sufficiently high amount is applied by an external alternating field.
2. The resonant circuit as claimed in claim 1,
   wherein the dielectric layer (4) is of substantially uniform thickness and has no additional manufacturing defects (air inclusions 7, for example).
3. The resonant circuit as claimed in claim 1 and 2,
   wherein the selected area is at the outer end areas of the coils (2, 3) where the induced voltage of the coils (2, 3), i.e., conductive tracks, is at its highest level.
4. The resonant circuit as claimed in claim 1,
   wherein the selected area (8) is at any desired point on the overlapping coils (2, 3) and is treated such that the conductive path is built up in the selected area (9) when the deactivation signal is applied.
5. The resonant circuit as claimed in claim 4,
   wherein the dielectric layer (4) is thinner in the selected area than it is in the remaining areas, or the selected area (8) is a hole in the dielectric layer (4).
6. The resonant circuit as claimed in claim 4,
   wherein the dielectric layer (4) has a different physical or chemical property in the selected area.
7. The resonant circuit as claimed in claim 1 or 2,
   wherein the dielectric layer (4) is comprised of at least two components (4a, 4b).
8. The resonant circuit as claimed in claim 1 or 7,
   wherein the melting point of the one component (4a; 4b) lies above the production temperature for the resonant circuits (6).
9. The resonant circuit as claimed in claim 7 or 8,
   wherein the components (4a, 4b) are of a nature enabling them to be joined together by either a coating or a laminating process.
10. The security element as claimed in claim 2,
    wherein the areas of overlap between the two coiled conductive tracks (2, 3), and hence the capacitance between the coiled conductive tracks (2, 3), are concentrated at the inner ends of the coiled conductive tracks (2, 3).
11. The resonant circuit as claimed in claim 10,
    wherein the outer ends of the two coiled conductive tracks (2, 3) overlap in a small area and a relatively long length of track with no overlap is adjacent to the outer ends of the conductive tracks (2, 3).

Images