Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-02-08
2001-07-17
Lee, Benjamin C. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572700
Reexamination Certificate
active
06262663
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a security element for electronic article surveillance, comprising at least one coiled conductive track and a capacitor having a dielectric layer arranged therebetween, or comprising two coiled. conductive tracks that are disposed on either side of a dielectric layer so as to overlap at least in part to form a resonant circuit.
BACKGROUND OF THE INVENTION
Resonant circuits which are excited to resonate at a predetermined resonant frequency which is conventionally at 8.2 MHz are widely accepted to protect articles against pilferage in department stores. Frequently the circuits are an integral part of adhesive labels or cardboard tags which are affixed to the articles to be maintained under surveillance. Typically, the department store has an electronic surveillance system installed in the exit area, which detects the resonant circuits and produces an alarm when a protected article passes through a surveillance zone in an unauthorized manner. The resonant circuit is deactivated when a customer has paid the merchandise. This prevents an alarm being produced once an article has been rightly acquired by purchase, passing through the surveillance zone subsequently.
The deactivation systems which are frequently installed in the checkout areas generate a resonant signal of a higher amplitude than it is produced in the surveillance systems. A resonant label is normally deactivated with a field strength greater than 1.5 Ampere-turns per meter, A/m.
A variety of deactivating mechanisms for resonant circuits are known in the art. They involve either destroying the insulation between two opposing conductive tracks, producing a short circuit, or subjecting a length of conductive track to overload and causing it to melt, thereby interrupting the circuit path. As a consequence of deactivation, the resonant properties of the resonant circuit, that is, the resonant frequency and/or the “Q” factor are modified so severely that the resonant label stops being detected by the surveillance system.
There is a risk that the deactivated resonant circuit may be reactivated inadvertently by mechanical manipulation including, for example, folding, packaging and transporting the merchandise, or bending the label and hence the resonant circuit. Any accidental reactivation of a resonant circuit which is affixed to an article rightly acquired by purchase may then produce an alarm leading to embarrassment both for the customer and for the department store.
So far no state of the art has become known which concerns itself with the problem of diminishing the risk of an accidental reactivation of resonant labels that are already deactivated. With regard to the deactivation of resonant labels, different methods have been described in the art. In U.S. Pat. No. 4,876,555 and its corresponding European Patent, EP 0 285 559 B
1
a it is proposed to use a needle to produce a hole in the insulating layer between two opposite capacitor surfaces. This results in a fault-free and permanent deactivation mechanism.
U.S. Pat. No. 5,187,466 describes likewise a method for generating a deactivatable resonant circuit by means of a short circuit that cannot be destroyed under normal circumstances.
As regards the first mentioned U.S. Pat. No. 4,876,555 and its corresponding European Patent, EP 0 285 559 B
1
, it should be noted that the resonant circuit therein disclosed includes capacitor plates which are disposed on either side of a dielectric material. The dielectric layer arranged between the two capacitor plates has a through hole.
In U.S. Pat. No. 5,187,466 referred to in the foregoing, a method is described which is applied to a resonant circuit having capacitor plates on either side of a dielectric, and in which the capacitor plates are first short-circuited and the short circuit is melted later by the application of electrical energy.
Still further important techniques in the field of the de-activation of resonant labels are known which however do not concern themselves with the reduction of the risk of an accidental reactivation. A patent family extending in this direction comprises, among others, European Patent, EP 0 181 327 B
1
, U.S. Pat. No. 4,567,473 and U.S. Pat. No. 4,498,076. The resonant label of the present invention which is described in these patents is composed of the following components: a substrate material serving as a dielectric, capacitor plates on either side of the planar dielectric substrate material, a deactivation zone and a resonant circuit which is disposed on the dielectric material. Heretofore the state of the art has not indicated any provisions that would prevent an undesirable reactivation after deactivation has taken place successfully.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a resonant circuit in which the probability of reactivation is reduced.
This object is accomplished in that provision is made in the dielectric layer for at least one selected area (a zone of preferred breaking) in which a short circuit is produced between the opposed capacitor plates or the coiled conductive tracks by the supply of energy in a sufficiently high amount by an alternating magnetic field, and in which the selected area is strengthened locally such that a destruction of the short circuit (conductive path) by mechanical loads, and hence a reactivation of the security element, are prevented.
According to an advantageous further aspect of the security element of the present invention, provision is made for the dielectric layer to be of substantially uniform thickness and to have no additional manufacturing defects (air inclusions, for example).
According to a yet further proposal, in the event that two, at least partly overlapping tracks, are used they are wound in opposite directions, with the selected area being located at the outer ends of the tracks. This is the point where the induced voltage is at its highest level.
In an advantageous aspect of the security element of the present invention, it is proposed to make the dielectric layer in the selected area thinner than in the remaining areas.
According to an alternative solution, the selected area is characterized in that the dielectric layer has in this area a different physical or chemical property than in the remaining areas.
According to an advantageous further aspect of the security element of the present invention, the dielectric layer is comprised of at least two components. In this connection it is particularly advantageous for the melting point of the one component of the dielectric layer to lie above the production temperature for security elements. According to a still further aspect, the components of the dielectric layer are of a nature enabling them to be fabricated by either a coating or a laminating process.
According to an advantageous feature of the security element of the present invention, the selected area in which the deactivation takes place is strengthened by the application of additional pressure. Compression enhances the bond between the capacitor plates or the at least partly overlapping tracks. It has proven to be advantageous to use pressure forming techniques for strengthening which involves forming the capacitor plates or the at least partly overlapping tracks into a three-dimensional shape. In this regard it is particularly advantageous if the enhanced bonding and the forming of the capacitor plates or tracks are accomplished in a single operation.
When the resonant circuit is bent or folded in the area of the strong zone, that is the zone where deactivation takes place, there is still a risk that the resonant circuit may buckle, shear, slide or delaminate at the point of deactivation. This would cause undesirable reactivation of the resonant circuit. In order to forestall this risk, a further aspect of the present invention involves providing weak zones on either side of the strong zone. When an external bending moment is applied, the resonant circuit is much more likely to fold or even break in the area of the weak zones than t
Altwasser Richard
Lendering Peter
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