Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1998-09-14
2001-05-08
Lefkowitz, Edward (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572100
Reexamination Certificate
active
06229444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a theft monitoring tag for informing that an article is being stolen.
2. Description of the Related Art
A theftproof tag is conventionally disclosed in which a resonance circuit of the tag attached to an article resonates with an electric wave at a specified frequency output from a wave transmitter, a separation detecting means detects whether or not the theft monitoring tag is separated from the article, and a separation informing unit controls a sound output on the basis of the detection output of the separation detecting means (Japanese Unexamined Patent Publication No. 8-185584). In this theftproof tag, the resonance circuit comprises an insulating dielectric thin film and a conductive metallic foil formed in a predetermined shape on either side of the thin film by etching or the like. For example, a coil unit is formed in a spiral form on the surface of the thin film by using a conductive metallic foil, and a surface-side plane pattern of a capacitor connected to the coil unit is formed at the center of the spiral shape of the coil unit.
A transmitting antenna and a receiving antenna are provided in a standing condition at the entrance of a store which sells the theft monitored article at a predetermined distance therebetween, with these antennas being electrically connected to a control unit. The control unit controls the transmitting antenna to transmit an electric wave at a frequency at which the resonance circuit resonates, and checks the signal level of the received signal of the receiving antenna. A speaker is connected to the control output from the control unit for generating an alarm.
In the theftproof tag constructed as described above, when a theft monitored article passes between the transmitting and receiving antennas without payment of money, the resonance circuit of the tag attached to the theft monitored article resonates with an electric wave transmitted from the transmitting antenna, and the receiving antenna receives a received signal modulated to the receiving level. As a result, the control unit controls the speaker to generate an alarm, thereby preventing the article from being stolen without payment of money. When money is paid for the article, a store clerk applies a strong electromagnetic wave to the tag to break the capacitor so that the tag does not operate, or temporarily stops the alarm speaker so as not to generate an alarm.
However, in the conventional theftproof tag, the center line of the spiral coil unit extends perpendicularly to the attaching surface of the article, and thus the electric wave transmitted from the resonance circuit passes through the article. Therefore, if the tag is attached to an article with the surface made of a conductive material such as aluminum, or a ferromagnetic material such as a steel sheet, the magnetic flux generated in the resonance circuit passes through the article to change the self-inductance of the coil unit. Thus, the resonance frequency of the resonance circuit is changed to decrease the Q value, thereby causing the possibility that the tag will not operate, as compared with a tag attached to an article with the surface made of an insulating material or a nonmagnetic material. Assuming that the angular frequency is L, and the resistance component of the resonance circuit is r, the Q value is defined as L/r. It is known that as the Q value increases, the loss due to an eddy current or the like decreases, and the resonance width decreases.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a theftproof tag which causes neither a change in the resonance frequency of a resonance circuit nor a decrease in the Q value of a coil unit regardless of the material of the surface of an article.
It is another object of the present invention to provide a theftproof tag in which a display plate bonded to the surface of a magnetic core member can be smoothed, thereby improving the appearance of the display plate and decreasing the total thickness.
In accordance with an embodiment of the present invention, there is provided a theftproof tag comprising a resonance circuit attached to a theft monitoring article, resonating with an electric wave at a specified frequency transmitted from a transmitting antenna, and comprising a coil unit and a capacitor electrically connected to both ends of the coil unit.
This construction is characterized in that the coil unit comprises a magnetic core member made of a composite material composed of a powder or flakes of a soft magnetic metal and a plastic, and a winding wound around the periphery of the magnetic core member and connected to the capacitor, and in that a portion of the periphery of the magnetic core member faces the attaching surface of the article.
The magnetic core member may be made of a sintered ferrite sheet, a composite material composed of ferrite powder and a plastic, or a composite material composed of soft magnetic metal powder or flakes, a ferrite powder and a plastic.
In this theftproof tag, since the resonance circuit, which is attached to an article with a surface made of a conductive material such as an aluminum sheet, or a ferromagnetic material such as a steel sheet, resonates to transmit an electric wave in the magnetic core direction of the magnetic core member, i.e., substantially parallel with the attaching surface of the article, the electric wave does not pass through the article and is thus not affected by the material of the article. As a result, the coil unit causes less change in the self-inductance regardless of the material of the surface of the article, and thus the resonance frequency of the resonance circuit changes less, and the Q value of the coil unit is decreased less, thereby decreasing the resonance width of the resonance frequency and improving the resonance properties of the tag.
In accordance with the present invention, the soft magnetic metal is carbonyl iron powder.
In the present invention, the soft magnetic metal may be a reduced iron powder.
In the present invention, the soft magnetic metal may be formed in flakes by further flattening a soft magnetic metal powder pulverized by atomization.
In the present invention, the soft magnetic metal may be a flake-shaped amorphous alloy.
In the theftproof tag of the present invention, the resonance properties of the tag can be improved by forming the soft magnetic metal in an appropriate shape using any one of the above materials.
The theftproof tag of the present invention is further characterized in that the article is made of a ferromagnetic material, and a nonmagnetic electromagnetic shielding sheet or electromagnetic shielding foil having conductivity is bonded to the coil unit facing the attaching surface of the article.
In this theftproof tag, since the electromagnetic shielding sheet or electromagnetic shielding foil is bonded to the coil unit which faces the attaching surface of the article made of a ferromagnetic material, the portion of the magnetic flux emitted from the magnetic core member, which passes through the portion of the article to which the tag is attached, passes above the electromagnetic shielding sheet having high conductivity and does not pass through the article. Since the electromagnetic shielding sheet is non-magnetic and electrically conductive, it causes less hysteresis loss and substantially no eddy current. As a result, the article made of a ferromagnetic material does not influence the resonance circuit, and the coil unit is electromagnetically cut off from the article, thereby completely preventing a change in self-inductance of the coil unit and a decrease in the Q value thereof.
In the theftproof tag of the present invention, the capacitor is bonded to the coil unit facing the attaching surface of the article so that one of the electrodes of the capacitor also serves as the non-magnetic electromagnetic shielding sheet or foil having conductivity.
In the theftproof tag, since the article is made of a ferromagnetic material
Endo Takanori
Miyake Masami
Mori Tomohiro
Tsuchida Takashi
Yahata Seiro
Lefkowitz Edward
Mitsubishi Materials Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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