Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-12-07
2001-11-06
Lee, Benjamin C. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572300, C340S572700, C029S602100, C029S025420, C029S832000, C361S765000, C361S777000
Reexamination Certificate
active
06313747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to resonant tags used in the prevention of shoplifting, and the like. More particularly, the present invention relates to resonant tags capable of being attached to small-sized products because of their small size.
2. Description of the Background Art
A monitoring system composed of a combination of a tag, which resonates with a wave of a radio frequency, with transmitting and receiving antennas has heretofore been used in retail stores, libraries, etc. for the purpose of preventing shoplifting. The resonant tag has a structure that a coil and a plate are formed with an electroconductive metal foil on one side of an insulating film, another plate is formed on the other side thereof, and an LC circuit is constituted as a whole, and resonates with a wave of a specific radio frequency. If a product attached with this tag passes through a monitoring region without effecting checking, it resonates with the radio-frequency wave transmitted from the transmitting antenna, and the receiving antenna detects this resonance to give an alarm. As the resonant frequency, a frequency of 5 to 15 MHz is generally adopted for reasons of easy distinction from various noise frequencies.
The conventional resonant tags are in the form of a rectangle of 32 mm×35 mm in demensions even in the smallest and are considerably large, and so such a tag has been hard to be attached to small-sized cosmetics such as lipsticks, jewelry, and the like. The reason for it is that a circuit, which resonates with a wave of 5 to 15 MHz and has a sufficient gain and dimensions desired for the market, has been unable to be formed.
On the other hand, EPO 142380A2 discloses a resonant tag in which a circuit has been formed on each side. This tag has substantially the same patterns on both sides of a dielectric film, said patterns having been formed in a coil turned reversely to each other when viewed from the same direction and almost superimposed on each other. When the circuits are formed on both sides in such a manner, not only the number of the spiral coils is doubled, but also a capacitor is formed between the coiled portions on the front and back sides of the film, said coiled portions being superimposed on each other. Therefore, there is no need to form a separate capacitor portion. However, even in this tag, the dimensions thereof cannot be reduced smaller than a certain size. More specifically, the mere formation of the circuits on both sides cannot provide a smaller-sized resonant tag having sufficient resonance property.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a small-sized resonant tag used in a detection system serving for the prevention of shoplifting, and the like making good use of a wave of a radio frequency, particularly, a resonant tag in the form of a rectangle (including a square) the dimensions of which are at most 25 mm×28 mm, preferably at most 23 mm×26 mm.
The present inventors have carried out an extensive investigation as to the miniaturization of resonant tags. As a result, it has been found that when a coiled circuit is formed on each side of an insulating film, the thickness of the insulating film and the proportion of an opening part located in the center of each coiled circuit greatly influence the resonant property of the resulting resonant tag, thus leading in the completion of the present invention.
According to the present invention, there is thus provided a resonant tag comprising an insulating thin film having a thickness of 10 to 30 &mgr;m, and coiled circuits made of a metal foil respectively formed on both sides of the insulating thin film, wherein the coiled circuits are formed in an electrically connected relation to each other with a space at the center of the insulating thin film, said both coils are formed taking turns in reverse directions to each other when viewed from the same direction and almost superimposed on each other except portions that cannot be superimposed on each other because the turning directions of the coils are reversed with the exception of the outermost peripheries when viewed from a direction perpendicular to the thin film, thereby forming a capacitor to constitute an LC circuit, the widths of portions of said both circuits, which correspond to each other, are almost equal except the outermost peripheries, the area of a portion of each side of the thin film, said portion being surrounded by the innermost peripheries of both coils and having no metal foil on both sides, is at least 16% based on the whole area of said one side of the tag, a thin-wall part where the thickness of its corresponding insulating film portion is thinner than that of its remaining portion is formed in part of the portions where said both circuits are superimposed on each other, the resonant tag resonates with a wave of the predetermined radio frequency and undergoes dielectric breakdown at the thin-wall part when applying the prescribed voltage or higher voltage to the tag, whereby the resonant tag can be prevented from resonating with the wave of said radio frequency, and the resonant tag has an area of at most 700 mm
2
.
According to the present invention, there is also provided an apparatus for detecting products, which comprises a pair of antennas respectively transmitting and receiving a wave of a radio frequency, and the resonant tag described above.
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Imaichi Hideaki
Matsumoto Takeshi
Mazoki Gary Thomas
Piccoli Anthony Frank
Checkpoint Manufacturing Japan Co., Ltd.
Knobbe Martens Olson & Bear LLP
Lee Benjamin C.
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