Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-11-24
2001-09-04
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572500, C340S572600
Reexamination Certificate
active
06285284
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tag for notifying that an article the theft of the which is monitored is taken out without permission and to a method of mounting the tag.
2. Description of the Related Art
Conventionally, there is disclosed, as this type of antitheft tags, an antitheft tag arranged such that the resonant circuit section of a tag mounted on an article whose theft is monitored is in resonance with the radio wave having a particular frequency and transmitted from a radio wave transmitter, a separation sensing means senses whether or not the tag is separated from the article whose theft is monitored and a separation notifying unit controls a notifying sound output means based on the sensed output from the separation sensing means (Japanese Unexamined Patent Publication No. 8-185584). In the antitheft tag, the resonant circuit section is composed of conductive metal foils having a predetermined shape which are formed on both the sides of an insulting dielectric thin film by etching or the like. For example, a dielectric circuit portion and a capacitor circuit portion are formed on the front surface of the thin film as a front surface flat pattern. The dielectric circuit portion is composed of a conductive metal foil and formed to a swirl shape, and the capacitor circuit portion is formed so as to continue to the center of the swirl of dielectric circuit portion. The separation sensing means is a removal sensing switch having an actuating lever which projects to the surface of the tag on which the tag is mounted. A power supply and a buzzer are electrically connected to the sensing switch. The separation notifying unit is a circuit composed of the removal sensing switch, the power supply and the buzzer which acts as the notifying sound output means. When the tag is mounted on the article, the actuating lever is pressed by the article, whereby the removal sensing switch is turned off. Whereas, when the tag is removed from the article, the actuating lever projects, whereby the removal sensing switch is turned on.
Further, a transmitting antenna and a receiving antenna stand at a predetermined interval at the entrance and the exit of a shop where the article whose theft is monitored is sold. These antennas are electrically connected to a controller. The controller causes the transmitting antenna to transmit a radio wave having a frequency with which the resonant circuit section resonates as well as checks the signal level of the signal received by the receiving antenna at all times. Further, a speaker for issuing a warning is connected to the control output of the controller.
In the antitheft tag arranged as described above, when the article whose theft is monitored is going to pass between the transmitting antenna and the receiving antenna regardless of that the price for it is not paid, the receiving antenna receives a signal whose receiving level is modulated because the radio wave transmitted from the transmitting antenna is resonated by the resonant circuit section of the tag mounted on the article whose theft is monitored. As a result, the controller issues a warning from the speaker so that the taking-out of the article whose price is not paid can be checked. In contrast, when the tag is removed from the article, the sensing switch is turned on by the projection of the actuating lever and the buzzer is sounded. Thus, the theft of the article can be reliably monitored.
However, in the conventional antitheft tag, when the tag is mounted on an article whose surface is formed of a conductive material such as aluminum and the like or a ferromagnetic material such as a steel sheet and the like, the resonance frequency of the resonant circuit section is changed and the tag is not resonated sometimes as compared with a case that the tag is mounted on an article whose surface is formed of an insulating material and a non-magnetic material because the self-inductance of the resonant circuit section changes.
An object of the present invention is to provide an antitheft tag having a resonant circuit section whose resonance frequency does not change depending upon the material of the surface of an article whose theft is monitored and a method of mounting the antitheft tag.
Another object of the present invention is to provide an antitheft tag whose thickness can be reduced and which can be made at a low cost and a method of mounting the antitheft tag.
SUMMARY OF THE INVENTION
An invention according to a first aspect of the invention relates to the improvement of an antitheft tag which is mounted on an article, the theft of which is monitored and which includes a resonant circuit section resonating with the radio wave having a particular frequency and transmitted from a transmitting antenna.
The characteristic arrangement of the invention resides in that an electromagnetic shield layer is interposed between the mounting surface of the article and the resonant circuit section.
In the antitheft tag, when the resonant circuit section is mounted on the article whose surface is formed of a conductive material such as aluminum or the like or a ferromagnetic material such as steel sheet or the like through the electromagnetic shield layer, the resonant circuit section is electromagnetically shielded from the article by the electromagnetic shield layer. Accordingly, the self-inductance of the resonant circuit section does not almost change from the self-inductance thereof when it is mounted on an article whose surface is formed of an insulating material or a non-magnetic material.
In the antitheft tag, a high conductivity layer may be interposed between the mounting surface of the article and the electromagnetic shield layer.
In the antitheft tag, the resonant circuit section is electromagnetically shielded from the article by the electromagnetic shield layer as well as the Q value of the resonant circuit section is increased by the high conductivity layer. As a result, the self-inductance of the resonant circuit section does not almost change and a resonant width is made sharp. In addition, the thickness of the electromagnetic shield layer can be greatly reduced by interposing the thin high conductivity layer and further the tag can be made at a low cost. Note that the Q value is a value defined by &ohgr;L/r when an angular frequency is represented by &ohgr; and the resistance component of the resonant circuit section is represented by r. It is known that a loss caused by an eddy current and the like is reduced and the resonant width is made sharp by a higher Q value. Further, a reason why the Q value is increased by interposing the high conductivity layer as described above is that the self-inductance L of the resonant circuit section is not almost changed by the material of the article located just below the high conductivity layer. This is because the electromagnetic wave transmitted from the transmitting antenna is shielded by the high conductivity layer and does not reach the article located just below the high conductivity layer.
In the antitheft tag, the electromagnetic shield layer may be formed of an insulating material.
In the antitheft tag, when the resonant circuit section is mounted on the article whose surface is formed of a conductive material such as aluminum or the like or a ferromagnetic material such as the steel sheet or the like through the electromagnetic shield layer, the resonant circuit section is electromagnetically shielded from the article by the electromagnetic shield layer while being space apart therefrom by a predetermined interval which corresponds to the thickness of the electromagnetic shield layer. As a result, the self-inductance of the resonant circuit section does not almost change from that when the resonant circuit section is mounted on the article whose surface is formed of an insulating material or a non-magnetic material.
In the antitheft tag, the electromagnetic shield layer may be composed of a composite material of ferrite powder and plastic or rubber.
Ferrite is an oxide represen
Ishiyama Kouichi
Miyake Masami
Nakazato Minoru
Soe Takeshi
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pham Toan
Wu Daniel J.
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