DE4416982A1 - Electronic goods security oscillating circuit - Google Patents

Abstract

The antitheft circuit includes a first capacitor (3) whose dielectric has a reduced breaking strength at least at one point. At least one further capacitor (4) is connected in series with the first (3). Preferably, the dielectric of the further capacitor(s) is prepared to form at least a region of reduced breakdown strength.The circuit coil (2) may be formed as a flat spiral with each end connected to a capacitor (3,4). At least one further capacitor may be connected in the spiral. The circuit is preferably formed in a goods security tag.

Description

The invention relates to a resonant circuit for electronic article surveillance, the dielectric of the capacitor belonging to the resonant circuit we at least at one point has a reduced dielectric strength.

Such resonant circuits are known per se and are becoming electronic Goods security used. The resonant circuit is a capacitor and a coil is formed, wherein the dielectric of the capacitor, which has a reduced dielectric strength at least at one point, when the energy in the resonant circuit is increased, a conductive bridge is formed between the capacitor surfaces. This usually happens after Breakdown voltage exceeded due to thermal influences or Field emission, which is the metal structure of the capacitor surfaces dissolved atoms as a conductive bridge between the capacitor surfaces beat.

During the intact resonant circuit with working capacitor from appropriate security systems can be registered, this applies after deactivation in the manner described above for the resonant circuit no more to.

A disadvantage of the known oscillating circuit for securing goods is that that due to aging, use, deformation during transport or the like the connection of the capacitor areas can be broken again, so that the label can be registered again by the security system, d. H. again is activated.  

This is primarily due to the fact that the cross section of the short circuit bridge is extremely small. Oscillating circuits of the known type are usually designed for a frequency range of approximately 7 to 11 MHz and comprise a capacitor with a capacitance of approximately 10 to 60 pico farads (pF). The breakdown voltage is effectively around 25 volts. The resulting energy for the described deactivation process, generally called burn-through process, is in a range from 10 ^-8 to 10 ^-7 watt seconds. From this energy, neglecting losses due to electromagnetic radiation and heat dissipation in the dielectric, the capacitor covers and the carrier material, conclusions can be drawn as to the maximum of the metal mass evaporated from the conductive areas of the breakdown area in the capacitor or dissolved by field emission. The short-circuit bridge created by never blow can only have a cross section in the order of a few atoms. Since the path of a short-circuit bridge through the dielectric is not always the shortest path that can be predetermined, the cross section of the short-circuit bridge can practically not be predetermined.

An alternative deactivation method provides that on the surface of the Resonant circuit is applied to a conductive surface. The resonance frequency the resonant circuit is changed so far that a registration is prevented by the electronic article surveillance system. This The procedure requires that the resonant circuit be accessible. About that it is also labor-intensive and time-consuming because the conductive surface is practical table only applied to the resonant circuit by hand, for example glued can be.

Proceeding from this, the invention is based on the object To improve the resonant circuit of the generic type so that the mentioned disadvantages are avoided and a reactivation of Resonant circuit is largely excluded, the quality of the Short-circuit bridge should be at least roughly determinable.

The generic solution to this task is the generic one Vibration circuit developed by the invention in that at least one  another capacitor in series with the first capacitor in Resonant circuit is arranged.

The inventive design of the resonant circuit is the Probability that the short formed on both capacitors Open the bridges again and the label is reactivated Lich reduced. By arranging two capacitors, the deak Activation take place in that both capacitors with through simultaneously Impact voltage can be applied, or the capacitors can be designed so that they are in a row and with different frequencies be charged. There is a possibility during the deactivation a test current of the second capacitor through the already short-circuited to let a first capacitor flow. So the short circuit bridge can be and further reduce the likelihood of reactivation gladly. Each additional capacitor advantageously also has a pre parried dielectric.

It is advantageously proposed that the two capacitors and the coil be arranged in the form of a spiral in the same plane, am Start and end point of the spiral coil with one of the two Capacitor plates is connected while the other two capacitor plates are contacted by a connection bridging the spiral. This measure is of particular advantage because that of conventional, only through contact having a capacitor having resonant circuits no longer needed. Here it was necessary that the coil with both condensates gate plates on both sides of the dielectric was contacted. this will realized through the so-called crimp via, which is not always is stable. In the embodiment according to the invention, this process can omitted.

Advantageously, there is at least one further capacitor in the spiral interposed.

It is advantageously proposed that the resonant circuit be on a goods security ration label is arranged. This can advantageously be stuck on.  

The configuration according to the invention makes it possible to oscillate circle on a stick-on carrier in the form of an anti-theft tag train, its deactivation with a very high probability is retained even if the goods bearing the label are transported or is used. Deactivation due to aging is almost over closed.

The resonant circuit according to the invention for security is simple and producible and enables a rough determination of the quality of the Short circuit bridge. Due to the possibility of testing at least the short jumper on the first capacitor during the phase in which the breakdown voltage is applied to the second capacitor, one There is a high probability that the label will not be reactivated the. The last short-circuit bridge created has the quality as in is known from the prior art resonant circuits.

Further advantages and features of the invention result from the following Description based on the figures. Show:

Fig. 1 is a schematic equivalent circuit diagram of an oscillating circuit according to the invention;

Fig. 2 is a schematic equivalent circuit diagram of a known from the prior art oscillation circuit; and

Fig. 3 is a schematic representation of an embodiment of the inventive resonant circuit.

As shown in the figures, a resonant circuit 1 for security comprises a coil 2 and a capacitor 3 . Compared to the conventional resonant circuits 1 according to FIG. 2, the resonant circuit shown in FIGS. 1 and 3 has further capacitors connected in series. In the resonant circuit shown in Fig. 1, the capacitors 3 , 4 and 5 are connected in series. It goes without saying that this series connection can be continued. The formation of short-circuit bridges on a large number of capacitors ensures that reactivation by breaking the short-circuit bridge is practically excluded. If one assumes a reactivability of 1% in the case of resonant circuits known from the prior art, this proportion is reduced to only 0.01% when equipped with two capacitors connected in series.

In the schematic embodiment shown in FIG. 3, the capacitors 3 and 4 are each connected to one end of the coil 2 arranged spirally in the same plane. The capacitors are connected in series through connection 6 , which is insulated from the coil.

The embodiment shown in Fig. 3 is extremely enlarged. The actual design is greatly miniaturized and is produced in the form of self-adhesive security labels for application to goods to be secured.

For deactivation, conventional ones known from the prior art can be used Deactivators are used. There is also the possibility modify a deactivator such that the two or more condensates in order to form a short-circuit bridge, whereby the previously formed short-circuit bridge is checked simultaneously that can.

Reference list

1 resonant circuit
2 coil
3 capacitor
4 capacitor
5 capacitor
6 connection

Claims (6)

1. resonant circuit for goods security, the dielectric of the capacitor of the resonant circuit has at least at one point a reduced dielectric strength, characterized in that at least one second capacitor ( 4 ) connected in series to the first capacitor ( 3 ) in the resonant circuit ( 1 ) is. 2. resonant circuit according to claim 1, characterized in that the dielectric of the additional capacitors ( 4 , 5 ) is prepared in order to form at least a region of reduced dielectric strength. 3. Oscillating circuit according to one of the preceding claims, characterized in that the coil ( 2 ) is formed spirally in one plane and is connected to one end in each case with a capacitor ( 3 , 4 ) arranged in the same plane. 4. resonant circuit according to claim 3, characterized in that in the spiral-shaped coil ( 2 ) at least one additional capacitor is interposed. 5. resonant circuit according to one of the preceding claims, characterized ge indicates that it is designed as a security tag. 6. resonant circuit according to claim 5, characterized in that the Wa security label is provided with an adhesive.