EP0919050A1

EP0919050A1 - Electronic anti-theft element

Info

Publication number: EP0919050A1
Application number: EP97940042A
Authority: EP
Inventors: Richard Altwasser; Peter Lendering
Original assignee: Meto International GmbH
Current assignee: Meto International GmbH
Priority date: 1996-08-06
Filing date: 1997-07-29
Publication date: 1999-06-02
Anticipated expiration: 2017-07-29
Also published as: CA2262573C; NO313066B1; CA2262573A1; JP2001504604A; ATE191095T1; US6262663B1; JP3634382B2; NO990517D0; EP0919050B1; PT919050E; NO990517L; WO1998006075A1; AU4203397A; ES2147456T3

Abstract

An electronic anti-theft element consists of at least one spiral printed circuit, a capacitor and a dielectric layer arranged therebetween, or of two spiral printed circuits which are arranged on respective sides of a dielectric layer in an at least partially overlapping manner (forming resonant circuit). The object of the invention is to provide a resonant circuit which is less liable to be reactivated. For that purpose, in at least one selected area (a rated break point) of the dielectric layer a short-circuit is created between the opposite capacitor plates or spiral printed circuits when a sufficiently high energy is supplied by a magnetic alternating field. The selected area is locally reinforced, preventing the suppression of the short-circuit by mechanical stress and the reactivation of the anti-theft element.

Description

Securing element for electronic article surveillance

The invention relates to a fuse element for the electronic type kels sherung, consisting of at least one spiral conductor track and a capacitor with an intermediate dielectric layer or consisting of two spiral conductor tracks, which are arranged at least partially overlapping on both sides of a dielectric layer {-> Resonant circuit).

Resonant circuits, which are excited to resonate at a predetermined resonance frequency, which is usually 8.2 MHz, are generally used to secure goods against theft in department stores. They are often an integral part of adhesive labels or hanging labels made of cardboard that are attached to the items to be secured. Typically, the department store is equipped with an electronic monitoring system in the exit area, which detects the resonant resonant circuits and triggers an alarm if a secured article passes through a secured monitoring zone in an unauthorized manner. Once a If the customer has paid for the goods, the resonant circuit is deactivated. The measure prevents an alarm from being triggered as soon as an item has been legally purchased and subsequently passes through the surveillance zone.

The deactivation systems, which are often placed in the checkout areas, generate a resonance signal with a greater amplitude than is generated in the monitoring systems. A resonance label is usually deactivated in a field strength greater than 1.5 A / m. Different deactivation mechanisms for resonant resonant circuits have become known. Either the insulation between mutually opposite conductor tracks is destroyed, which leads to a short circuit, or a piece of conductor track is overloaded and melts, causing an interruption. As a result of the deactivation, the resonant properties of the resonant circuit, i.e. the resonance frequency and / or the "Q" factor are modified so strongly that the resonance label is no longer detected by the monitoring system.

The deactivated resonant circuit can be unintentionally reactivated by mechanical manipulation, for example by kinking, packing and transporting the goods or by bending the label and thus the resonant circuit. Unintentional reactivation of a resonant circuit attached to a legally purchased item can then trigger an alarm, which is quite a nuisance for both the buyer and the department store.

To date, no prior art has become known that addresses the problem of reducing the risk of inadvertent reactivation of resonance tags that have already been deactivated. Different methods have been described with regard to the deactivation of resonance labels. In US Pat. No. 4,876,555 or in the corresponding EP 0285 559 B1 it is proposed to use a needle to create a hole in the insulation layer between two opposite capacitor surfaces. This creates a deactivation mechanism that is error-free and permanent.

US Pat. No. 5,187,466 also describes a method for generating a deactivatable resonant circuit by means of a short circuit, which cannot be destroyed under normal circumstances.

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

In the already mentioned US Pat. No. 5,187,466, a method is described which is applied to a resonant circuit with capacitor plates on both sides of the dielectric, the capacitor plates only being short-circuited and the short-circuit being later melted by exposure to electrical energy.

Other important techniques in the field of deactivating resonance labels have become known, but they are also not concerned with reducing the risk of inadvertent reactivation. A patent family that goes in this direction includes, inter alia, EP 0 181 327 B1, US Pat. No. 4,567,473 and US Pat. No. 4,498,076. The resonance label according to the invention described in these patents is composed as follows: a carrier material which serves as a dielectric, capacitor plates on both sides of the planar, dielectric Carrier materials, a deactivation zone and an oscillating circuit which is arranged on the dielectric. The prior art has so far not mentioned any measures which prevent an unwanted reactivation after successful deactivation.

The object of the invention is to propose a resonant circuit with a reduced probability of reactivation.

The object is achieved in that at least one selected area (a desired breakdown point) is provided in the dielectric layer, in which a short circuit between the opposite capacitor plates or the spiral conductor tracks is created with a correspondingly high energy supply by an alternating magnetic field, and wherein the selected area is locally reinforced so that destruction of the short circuit Path) is prevented by mechanical stress and thus reactivation of the securing element.

According to an advantageous development of the fuse element according to the invention, it is provided that the dielectric layer has essentially a uniform thickness and no additional manufacturing defects (e.g. air closures).

It is further proposed that in the case of two at least partially overlapping conductor tracks, these are wound in opposite directions, the selected region being at the outer ends of the conductor tracks. This is where the highest induction voltage occurs.

An advantageous embodiment of the fuse element according to the invention proposes that the dielectric layer in train the selected area thinner than in the remaining areas.

According to an alternative, the selected area is distinguished by the fact that the dielectric layer here has a different chemical or physical nature than in the remaining areas.

According to an advantageous development of the fuse element according to the invention, the dielectric layer consists of at least two components. In this context, it is particularly advantageous if the melting point of one component of the dielectric layer is above the manufacturing temperature for fuse elements. Furthermore, an embodiment provides that the components of the dielectric layer are designed in such a way that they are produced either by coating or by lamination.

According to an advantageous embodiment of the security element according to the invention, the selected area in which the deactivation takes place is reinforced by the application of additional pressure. Printing together improves the adhesion between the capacitor plates or the at least partially overlapping conductor tracks. It has proven to be advantageous if the reinforcement is achieved in a three-dimensional form by pressure molding the capacitor plates or the at least partially overlapping conductor tracks. It is particularly advantageous here if the improved adhesion and the shaping of the capacitor plates or the conductor tracks are achieved in one operation.

If the resonant circuit is bent or bent in the area of the reinforced zone, in which the deactivation also takes place, there is still the risk of warping, shearing, displacement or detachment of the resonant circuit at the deactivation Job. As a result, the resonant circuit was undesirably reactivated. In order to prevent this danger, according to a development of the invention, weakened zones are provided on both sides of the reinforced zone. If a bending moment attacks from the outside, the probability that the resonant circuit in the area of the weakened zones will bend or even break is much greater than a bending or breaking within the reinforced zone. The weakened zone can therefore also be referred to as the preferred bending or breaking zone.

The weakened zones can be formed by narrowing the width of the conductor track. Another possibility is that the adhesive layer in these weakened zones is treated in such a way that the bond between the spiral conductor tracks is considerably reduced. It is also possible to perforate the conductor tracks in the weakened zones.

According to an advantageous development of the invention, the resonant circuit is designed such that the capacitance between the upper and lower conductor tracks is concentrated at the inner ends of the coils. In particular, a large overlap area of the conductor tracks is provided at the inner ends of the coils, which results in a correspondingly large capacitance, while the overlap at the outer coil ends is very small.

An advantageous development of the device according to the invention proposes that the overlap regions between the two conductor tracks and thus the capacitance between the conductor tracks concentrate at the inner ends of the conductor tracks. In particular, it is provided that the outer ends of the two conductor tracks overlap in a small area and that the outer ends of the conductor tracks are followed by a relatively long area without overlap. An advantage of this topology is that the deactivation takes place in the overlap area between the outer ends of the upper and lower conductor tracks, since this is the point with the highest voltage potential between the conductor tracks.

The deactivation point is therefore located with a high degree of certainty in the selected area.

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: an equivalent circuit diagram of the voltages occurring 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

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

7: a plan view of a reinforced area,

8a: a cross section through a suitable tool,

8b: a top view of the tool shown in FIG. 8a, 9: a plan view of a conductor track with a weakened zone,

10: a plan view of a further conductor track with a weakened zone,

11a: a plan view of an embodiment of the lower coil,

11b: a plan view of an embodiment of the upper coil,

11c: the resonant circuit composed of the coils shown in FIGS. 11a and 11b, and

FIG. 12: an equivalent circuit diagram for the voltage conditions of the embodiment of the resonant circuit according to the invention shown in FIG. 11c.

Fig. 1 shows an embodiment of the resonant circuit 6 according to the invention in plan view. In FIG. 2 the resonant circuit 6 shown in FIG. 1 can be seen in cross section. The resonant circuit 6 is deactivated by creating a short circuit between the two spiral conductor tracks 2, 3, which are preferably made of aluminum, through the dielectric layer 4. An applied alternating magnetic field, such as that emitted by the monitoring system, induces alternating voltages in the two spiral conductor tracks 2, 3 of the resonant circuit 6. The spiral conductor tracks 2, 3 overlap at least partially and are wound in n opposite directions. Therefore, the outer end of the lower coil 2 has a positive potential relative to the inner end of the lower coil 2 when the inner end of the upper coil 3 has a positive potential with respect to the outer end of the upper coil 3. It must therefore be noted that the points / areas in which the induced alternating voltages between the two coils 2, 3 are maximum are in the end areas of the coils 2, 3.

Since the upper coil 3 has fewer turns than the lower coil 2 in the example shown in FIG. 1, the highest voltages are generated between the ends of the upper coil 3 and the locations of the lower coil 2 directly below.

3 illustrates the voltage relationships in different areas of the two at least partially overlapping coils 2, 3 of a resonant circuit 6, which can be used according to an advantageous development of the resonant circuit 6 according to the invention.

In the resonant circuit 6 described above with a uniform thickness of the dielectric layer 4 between the coils 2, 3, the deactivation takes place in the end regions of the upper coil 2 and lower coil 2, since the induced potential is maximum here. Since the electric field strength occurs concentrated on a surface with a small radius, deactivation occurs precisely at the ends of the conductor tracks 2, 3 - as shown in FIG. 4.

However, if the dielectric layer 4 is not uniformly thick or contains air bubbles 7, which is quite possible due to manufacturing errors, deactivation can occur in different areas of the coils 2, 3. Such manufacturing defects can cause local weak spots and even holes through air closures 7 in the dielectric layer 4 cause. As a result, the dielectric layer 4 breaks down at these local weak points, although the voltage potential here is lower than at the ends of the upper coil 2 and lower coil 3. Since the voltage potential at the local weak points is lower than at the ends of the conductor tracks 2, 3, the electrical energy available for generating the deactivation short circuit is smaller than the electrical energy that would be necessary for generating a deactivation short circuit at the ends of the upper coil 3.

FIG. 5 shows a cross section through a dielectric layer with manufacturing defects, here air bubbles 7 and irregularities in the area of the surface. In order to avoid such manufacturing errors, the dielectric layer 4 is designed according to a further development so that it has a substantially uniform thickness and is largely free of local weak points 7. Such a uniform dielectric layer 4 represents a deactivation in the end regions of the spiral Conductors 2, 3 are safe, since the induced voltage and energy are maximum here. A short circuit caused by such a deactivation is very robust and less susceptible to inadvertent reactivation.

According to an advantageous development of the resonant circuit 6 according to the invention, the dielectric layer 4 consists of at least two components 4a, 4b, an upper component 4a and a lower component 4b. The lower component 4b is applied to the lower coil 3 before punching and hot stamping. The upper component 4a is applied to the upper coil 2. The upper component 4a has a relatively low melting point, which enables it to serve as a hot melt adhesive and to glue the two coils 2, 3 to the lower coil 3 during the hot stamping of the upper coil 2. The upper component 4a of the dielectric Layer 4 melts during hot stamping of the upper coil 2. The lower component 4b of the dielectric layer 4 has a higher melting point and does not melt during hot stamping onto the upper coil 2. The uniformity of the lower component 4b of the dielectric layer 4, which does not melt, improves the uniformity in the thickness of the dielectric layer 4 as a whole.

6 shows a cross section through a resonant circuit 6 with a dielectric layer 4, which consists of two components 4a, 4b. The lower component 4b can be produced either by coating the lower coil 3 or by laminating the lower component 4b of the dielectric layer 4 onto the coil 3. The coil material (AI) is usually in the form of a wide roll material, so that the uniformity of the surface of the dielectric layer 4 can be maintained and other defects, which are caused, for example, by air pockets 7, are minimized.

It can happen that the short circuit is broken by kinking or other mechanical manipulations, even if the dielectric layer 4 is so uniform that defects 7 are largely reduced and the deactivation short circuit only occurs at the end of the upper conductor path, where the induced energy is at a maximum is. (Of course, this is only the case if no otherwise prepared breakthrough point is provided.) Shear or sliding movements of the two metal layers relative to one another or delamination of the two layers can lead to inadvertent reactivation.

According to the resonant circuit 6 is local in the

Reinforced area of the ends of the upper coil 2 or in the area of the prepared area. The reinforced zone 10 is less susceptible to shear and slide movements or a Delaminate. Local reinforcement can reduce the stress on the resonant circuit 6 by kinking or bending, since the two spiral conductor tracks 2, 3 only shear, slide, kink or delaminate in the vicinity, but not within the locally reinforced zone 10.

According to an advantageous development of the resonant circuit 6 according to the invention, the regions around the ends of one of the two conductor tracks 2, 3, here the upper conductor track 2, are reinforced by the fact that an additional pressure is applied to a local zone 10, the metal, preferably aluminum, is shaped so that it takes on a non-planar shape. The local application of pressure results in better adhesion between the two conductor tracks 2, 3 and between the lower conductor track 3 and the dielectric layer 4. If this pressure is applied to a pressure with a predetermined profile (stamp 12) by means of a shaping tool 11 the conductor tracks 2, 3 are shaped such that the resistance of the resonant circuit 6 against reactivation is considerably improved. Incidentally, the tool 11 can also be designed flat and have predetermined dimensions.

With regard to the structural properties of metals, it is well known that a metal sheet with grooves, bulges or other incorporated structures is not as easy to bend as a flat sheet. The same principle is used here to create a locally reinforced zone 10. Any large-scale folding or bending of the resonant circuit 6 leads to the resonant circuit 6 being bent, folded, sheared or delaminated in the vicinity but not within the reinforced zone 10. This reduces the risk of unintentional reactivation. The actual shape of the reinforced zone 10 is not critical, the actual profile of the molded one Conductor 2, 3 in the reinforced zone 10 is also not critical.

7 shows a top view of an embodiment of a reinforced zone 10 at one end of the upper conductor track 2.

FIG. 8 a shows a cross section and FIG. 8 b shows a top view of a tool 11 that can be used to produce the reinforced zone 10.

If there is a bending or bending of the resonant circuit 6 in the area of the reinforced zone 10, i.e. the zone in which the deactivation is known to take place and which has been intentionally reinforced, there is still a risk of warping, shearing, shifting or detaching the resonant circuit 6. This would lead to an undesired reactivation of the resonant circuit 6. In order to prevent this danger, an additional development of the invention provides for weakened zones 13 on both sides of the reinforced zone 10. If a bending moment acts from the outside, it is likely that the resonant circuit 6 will bend or even break in the area of the weakened zones 13. The weakened zone 13 can therefore also be referred to as the preferred bending or breaking zone. The weakened zone 13 can be formed either by narrowing the width of the conductor track 2, 3, as shown in FIGS. 9 and 10, or by appropriate treatment of the adhesive layer in this weakened zone 13, specifically in the way that the bond between the conductor tracks 2, 3 is considerably weaker here. Another way to obtain weakened zones 13 is to perforate the conductor tracks 2, 3.

According to an additional development of the invention, the conductor tracks 2, 3 and the resonant circuit 6 are like this formed that the capacitance between the upper and lower conductor tracks 2, 3 is concentrated at the inner ends of the spiral conductor tracks 2, 3. FIGS. 11a, 11b and 11c show a corresponding resonant circuit 6. From the figures it can be seen that there is a large overlap area of the conductor tracks 2, 3 at the inner ends of the coils 2, 3, which results in a results in proportionally large capacitance, while the overlap at the outer ends of the coils 2, 3 is very small.

The equivalent circuit diagram of this arrangement is shown in FIG. The voltage difference generated between the two coils 2, 3 is considerably greater at the outer coil ends than at any other point between the coils 2, 3. When looking at FIGS. 11c and 12 together, it can also be seen that the outer The lower conductor track 3 is largely not covered by the upper conductor track 2 at all. Thus, no deactivation can take place along this overlap-free section 9. If you follow the outer turn of the lower conductor track 3 back from the end point, where there is a small overlap area with the upper conductor track 2, it is found that the next point at which there is an overlap of the conductor tracks 2, 3 and thus the possibility of Deactivation exists, a piece back on the outer turn of the lower conductor track 3. This point has a considerably lower voltage potential between the upper and lower conductor tracks 2, 3.

Even if the dielectric layer 4 between the two conductor tracks is not of absolutely uniform thickness or is not absolutely free of other weak points 7, the deactivation takes place at this outer overlap point, since there is a considerably higher potential difference between the conductor tracks 2, 3 at this point . Another advantage is that, due to the uneven distribution of the potential difference along the conductor tracks 2, 3, the energy available for a deactivation short circuit between the conductor tracks 2, 3 must be higher than with a uniform distribution of voltage and capacitance. However, higher energy in turn means a more reliable short circuit and thus automatically less risk of unwanted reactivation.

Reference list

Carrier material upper coil lower coil dielectric layer a upper component b lower component adhesive layer resonant circuit or fuse element air inclusion (prepared) selected area overlap-free area 0 reinforced zone 1 tool 2 punch 3 weakened zone

Claims

claims

1.Fuse element for electronic article surveillance, consisting of at least one spiral conductor track and a capacitor with a dielectric layer in between or consisting of two spiral conductor tracks which are at least partially overlapping on both sides of a dielectric layer (-> resonant circuit), in the dielectric layer (4) is provided with at least one selected area (8) (a desired breakdown point), in which a short circuit between the opposite capacitor plates or the spiral conductor tracks (2, 3) is created with a correspondingly high energy supply due to an alternating magnetic field , and wherein the selected area (8) is locally reinforced in such a way that destruction of the short circuit by mechanical stress and thus reactivation of the securing element (6) is prevented.

2. Fuse element according to claim 1, wherein the dielectric layer (4) has a substantially uniform thickness and no additional manufacturing defects (e.g. air pockets (7)).

3. Fuse element according to claim 1 or 2, wherein in the case of two at least partially overlapping conductor tracks (2, 3) these are wound in opposite directions, the selected region (8) in a region at the outer ends of the conductor tracks (2, 3 ) because the highest induction voltage occurs here.

4. Fuse element according to claim 1, wherein the. Selected area (8) is characterized in that the dielectric layer (4) is thinner than in the remaining areas or that it has a hole.

5. Fuse element according to claim 1, wherein the selected area (8) is characterized in that the dielectric layer (4) has a different chemical or physical nature than in the remaining areas.

6. Fuse element according to claim 1 or 2, wherein the dielectric layer (4) consists of at least two components (4a, 4b).

7. Fuse element according to claim 6, wherein the melting point of one component (4a; 4b) of the dielectric layer (4) lies above the manufacturing temperature for fuse elements (6).

8. Fuse element according to claim 3, wherein the components of the dielectric layer (4) are such that they are produced either by coating or by lamination.

9. Fuse element according to claim 1, 3, 4 or 5, wherein the reinforcement in the reinforced zone (10) is achieved by the application of additional pressure to the adhesion between the capacitor plates or the at least partially overlapping conductor tracks (2, 3rd ) to improve .

10. Fuse element according to claim 9, wherein the reinforced zone (10) is achieved in a three-dimensional shape by pressure molding the capacitor plates or the at least partially overlapping conductor tracks (2, 3).

11. Fuse element according to claim 9 or 10, wherein the improved adhesion and the shaping of the capacitor plates or the conductor tracks (2, 3) is achieved in one operation.

12. Security element according to claim 1, 3, 4 or 5, wherein weakly formed zones (13) are provided on both sides or overleaf to the selected area (8).

13. Fuse element according to claim 12, wherein the weakly formed zones (13) are formed by narrowing the width of the conductor track (2; 3).

14. Fuse element according to claim 12 or 13, wherein the dielectric layer (4) in the weakly formed zones (13) is less strongly connected to the capacitor plates or the conductor tracks (2, 3) than in the remaining areas.

15. Fuse element according to claim 12 or 13, that the weakly formed zones (13) are characterized in that here the capacitor plates or the conductor tracks (2, 3) are perforated.

16. Fuse element according to claim 2, wherein the overlap regions between the two conductor tracks (2, 3) and thus the capacitance between the conductor tracks (2, 3) concentrate at the inner ends of the conductor tracks (2, 3).

17. Fuse element according to claim 16, wherein the outer ends of the two conductor tracks (2, 3) overlap in a small area and wherein a relatively long overlap-free area (9) adjoins the outer ends of the conductor tracks (2, 3).