Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1995-07-31
1998-03-31
Hofsass, Jeffery
Communications: electrical
Condition responsive indicating system
Specific condition
340551, 340568, 340505, 34082554, G08B 1314
Patent
active
057343276
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a detection tag for a resonance detection system, comprising a support consisting of electrically insulating material and a resonant circuit supported thereby, which has an inductive element formed by a conductor track disposed on the support in a predefined patter, and a capacitive element formed by at least two capacitor electrodes which are kept apart by the support and are constructed as electroconductive electrode regions, the ends of the track being connected to the one and to the other capacitor electrode, respectively.
A detection tag of this type is disclosed by the laid-open European Patent Application 0 463 233 A2.
The support of this known tag is provided on one side with a conductor track according to a spiral and rectangular pattern and on both sides is provided with electroconductive regions which form capacitor electrodes or plates of 4 capacitors. The capacitive element of the support is formed by a connection in parallel of 2 branches, in which two capacitors connected in series are incorporated. Said capacitive element is connected to the ends of the spiral track, as a result of which a resonant circuit is obtained having a resonant frequency which differs from a detection frequency which is used in an anti-theft system. The detection tag is activated by a capacitor being short-circuited in order to tune the resonant circuit to the detection frequency. If the activated detection tag has to be deactivated, a following capacitor is short-circuited, so that the resonant frequency of the tag once more differs from the detection frequency of the anti-theft system.
The capacitors to be short-circuited are provided with an indentation, as a result of which the corresponding plates are situated at a reduced mutual distance locally. The first capacitor is short-circuited by electromagnetic energy being supplied with a frequency which corresponds to the current resonant frequency of the tag and at a level which is sufficiently high to produce a discharge transversely to the support at the indentation of the capacitor in question. Short-circuiting of the second capacitor is effected in corresponding manner.
The known tag has the drawback that as a result of using indentations in the capacitors the resonant frequencies are not precisely defined, so that high energy levels or an additional tuning action are necessary.
SUMMARY OF THE INVENTION
The object of the invention is to provide a detection tag of the type mentioned in the preamble, which overcomes the abovementioned drawback.
This object is achieved according to the invention by at least one electroconductive island region being disposed on the support so as to be adjacent to, and in the same plane as, one of the capacitor electrodes, those edges of the island region and the capacitor electrode, which face one another, being situated at a discharge gap distance.
This arrangement has the advantage that, for the purpose of predefining a discharge path by means of the discharge gap, neither the quality factor nor the resonant frequency of the resonant circuit of the detection tag are adversely affected. Both variables remain precisely defined, even after the discharge, and indeed are not subject to scatter.
It should be noted that the European Patent Application 0 458 923 does disclose a discharge along the surface of the support, but this is used for short-circuiting a capacitor and not for increasing the capacitance of said capacitor. Moreover, an additional connection through the support is required.
Preferred embodiments are specified in the subordinate claims.
DESCRIPTION OF THE DRAWINGS
The invention will be described below in more detail with reference to the drawings, in which:
FIG. 1 shows an embodiment of the invention with two possible resonant frequencies;
FIG. 2 illustrates another embodiment of the invention with two possible resonant frequencies; and
FIG. 3 depicts a further embodiment of the invention with four possible resonant frequencies;
FIG. 4 shows yet another embodi
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patent: 4970495 (1990-11-01), Matsumoto
patent: 5103210 (1992-04-01), Kode
Angel Willem
Batterink Henri
Dutch A & A Trading B.V.
Hofsass Jeffery
Wong Albert K.
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