JPH10198873A - Tag for preventing theft - Google Patents

Abstract

PROBLEM TO BE SOLVED: Not to change the resonance frequency of a resonance circuit part, out of whatever material the surface of an article for theft monitoring is formed, to reduce the loss resistance of the resonance circuit part, i.e., to make a Q value high even though a resonance frequency is high, and to enable a sharp resonance of the resonance circuit part. SOLUTION: A tag 12 that is attached to an article 11 for theft monitoring has a resonance circuit part 14, and the part 14 resonates radio waves of a specific frequency that is sent from a transmitting antenna. A flat plate curled shielded coil 16 whose both ends are shirt-circuited is inserted between the attaching plane of the article 11 and the part 14. Also, the coil 16 is larger than a resonant coil 18 of the part 14, and each strand 16a of the coil 16 is arranged to be between strands 18a of the coil 18 when a layered body of the part 14 and the coil 16 is projected from its top or bottom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tag for notifying unauthorized removal of an article to be monitored for theft.

[0002]

2. Description of the Related Art Conventionally, as this kind of anti-theft tag,
The resonance circuit part of the tag attached to the theft monitoring article resonates with the radio wave of a specific frequency from the radio wave transmitting device, and the separation detecting means detects whether the tag has been separated from the theft monitoring article and separates the tag. An anti-theft tag is disclosed in which a separation notification unit controls a notification sound output unit based on a detection output of a detection unit (Japanese Patent Application Laid-Open No. 8-185584).
In this anti-theft tag, the resonance circuit portion is formed by forming a conductive metal foil of a predetermined shape on both surfaces of an insulating dielectric thin film by etching or the like. For example, an induction circuit portion formed in a spiral shape by a conductive metal foil on the surface of a thin film, and a surface-side planar pattern of a capacitor circuit portion continuous with the induction circuit portion is formed at the spiral center of the induction circuit portion. Is done. The separation detection means is a removal detection switch having an operation bar protruding from a surface of the tag attached to the article, and a power supply and a buzzer are electrically connected to the detection switch.
A circuit constituted by the detachment detection switch, the power supply and the buzzer is a separation notification unit, and the buzzer is a notification sound output unit. When the tag is attached to the article, the operation bar is pushed by the article and the removal detection switch is turned off, and when the tag is removed from the article, the operation bar is projected and the removal detection switch is turned on.

At the entrance of a store selling the theft monitoring article, a transmitting antenna and a receiving antenna are erected at a predetermined interval from each other, and these antennas are electrically connected to a control unit. The control unit causes the transmission antenna to transmit a radio wave having a frequency that resonates in the resonance circuit unit,
The signal level of the received signal from the receiving antenna is always checked. Further, a speaker for issuing an alarm is connected to the control output of the control unit. In the anti-theft tag configured as described above, when an article monitored for theft attempts to pass between the transmitting antenna and the receiving antenna without being cleared, the radio wave transmitted from the transmitting antenna is transmitted to the anti-theft article. Since the signal is resonated by the resonance circuit of the attached tag, a reception signal whose reception level is modulated is received by the reception antenna. As a result, the control unit issues an alarm from the speaker and can check the removal of uncleared goods. When the tag is removed from the article, the operation bar protrudes and the removal detection switch is turned on, so that the buzzer sounds and the theft can be monitored reliably.

[0004]

However, in the above-mentioned conventional anti-theft tag, when the tag is attached to an article whose surface is formed of a conductive material such as aluminum or a ferromagnetic material such as a steel plate, the resonance circuit portion is not provided. Because the self-inductance of the coil changes, the resonance frequency of the resonance circuit changes compared to when the tag is attached to an article whose surface is made of an insulating or non-magnetic material. Was inappropriate. It is an object of the present invention to provide an anti-theft tag in which the resonance frequency of the resonance circuit portion does not change regardless of the material of the surface of the theft monitoring article. Another object of the present invention is that even if the resonance frequency is high, the loss resistance of the resonance circuit can be reduced, that is, the Q value can be increased, and the width of the resonance frequency band of the resonance circuit can be narrowed to enable sharp resonance. To provide an anti-theft tag.

[0005]

The invention according to claim 1 is
As shown in FIGS. 1 and 6, this is an improvement of the anti-theft tag 12 having a resonance circuit portion 14 attached to the theft monitoring article 11 and resonating with a radio wave of a specific frequency transmitted from the transmission antenna 13. The characteristic structure is that a flat-plate spiral coil 16 short-circuited at both ends is interposed between the mounting surface of the article 11 and the resonance circuit section 14. In the anti-theft tag according to the first aspect, the resonance circuit section 14 is connected to the article 11 whose surface is formed of a conductive material such as aluminum or a ferromagnetic material such as a steel plate via the shielding coil 16.
Is attached, when the resonance circuit section 14 resonates, a reverse induced current flows through the shield coil 16. For this reason, among the magnetic fields generated by the resonance circuit unit 14 resonating, the magnetic field on the surface of the article 11 is canceled by the magnetic field generated by the induction current flowing through the shielding coil 16. As a result, since no eddy current is generated on the surface of the article 11, the self-inductance of the resonance circuit portion 14 is almost the same as when the article is attached to an article whose surface is formed of an insulating material or a non-magnetic material.

The invention according to claim 2 is the invention according to claim 1, wherein the shielding coil 16 has the same size as the resonance coil 18 of the resonance circuit section 14 or as shown in FIGS. It is characterized in that it is formed larger than the resonance coil 18. In the anti-theft tag according to the second aspect, since the resonance coil 18 is completely shielded by the shielding coil 16, even if the resonance coil 18 resonates, no eddy current is generated in the article 11. The self-inductance hardly changes without being affected by the article 11 at all.

The invention according to claim 3 is the invention according to claim 1 or 2, and furthermore, as shown in FIGS. 1 and 2, a laminated body of the resonance circuit section 14 and the shielding coil 16 is formed on the upper or lower surface thereof. Each wire 16 of the shielding coil 16 when projected from
a is disposed between the element wires 18a of the resonance coil 18. In the anti-theft tag according to the third aspect, the distribution capacitance between the resonance coil 18 and the shielding coil 16 is reduced, so that the eddy current generated on the surface of the article 11 can be reduced. As a result, the loss resistance of the resonance circuit section 14 can be reduced, that is, the Q value can be increased, so that the width of the resonance frequency band of the resonance circuit section 14 can be narrowed, and the resonance circuit section 14 has sharp resonance. Become. Further, even when the resonance frequency is high, the loss resistance such as the hysteresis loss of the resonance circuit section 14 can be reduced, that is, the Q value can be increased similarly to the above.

The invention according to claim 4 is the invention according to claims 1 to 3
The invention according to any of the above, further as shown in FIG.
5 mm thickness between the shielding coil 16 and the resonance coil 18
The following non-conductive and non-magnetic coil insulating layer 20 is interposed. In the anti-theft tag according to the fourth aspect, the distributed capacitance between the resonance coil 18 and the shielding coil 16 can be reduced by the coil insulating layer 20. As a result, the eddy current generated on the surface of the article 11 can be further reduced as compared with the third aspect of the present invention, so that the Q value can be further increased, and the resonance circuit section 14 has a sharper resonance.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIGS. 1 to 6, the tag 12 attached to the theft monitoring article 11 has a resonance circuit section 14 that resonates with a radio wave of a specific frequency transmitted from the transmission antenna 13 and a resonance circuit section 14 that resonates with the mounting surface of the article 11. A flat-plate spiral shielding coil 16 interposed between the circuit unit 14 and the circuit unit 14. In this embodiment, the article 11 is drinking water, edible oil, candy, or the like stored in a container 11a made of a steel plate, which is a ferromagnetic material. The resonance circuit section 14 includes a dielectric layer 17 formed of an insulating material such as paper or a plastic thin plate, a resonance coil 18 provided on the lower surface of the dielectric layer 17 and formed in a substantially square flat plate spiral shape, and a dielectric layer 17. First electrode layer 19a provided on the lower surface and electrically connected to resonance coil 18
And a second electrode layer 19b provided on the upper surface of the dielectric layer 17 so as to face the first electrode layer 19a (FIGS. 1 to 3).
The first electrode layer 19a, the dielectric layer 17, and the second electrode layer 19b form a capacitor 19. Further, a through hole 17a (FIG. 3) is formed in the dielectric layer 17 so as to face the inner end of the resonance coil 18, and a conductive line 19c having a front end facing the through hole 17a is connected to the second electrode layer 19b (FIG. 1 and FIG. 3). The resonance coil 18, the first electrode layer 19a, the second electrode layer 19b, and the conduction line 19c are formed of a conductive material such as aluminum or copper. When the resonance coil 18 and the first electrode layer 19a are laminated on the second electrode layer 19b and the conduction line 19c via the dielectric layer 17, the inner end of the resonance coil 18 is electrically connected to the tip of the conduction line 19c via the through hole 17a. (See FIG. 1).

The shielding coil 16 is formed in a substantially square flat plate spiral shape from a conductive material such as aluminum or copper (FIGS. 1 to 3). Preferably, the shielding coil 16 is formed larger than the resonance coil 18. The resonance circuit section 14
And the shielding coil 16 are laminated via a coil insulating layer 20 which will be described later, and when this laminated body is projected from the upper surface or the lower surface, each wire 16a of the shielding coil 16
8 are preferably disposed between the individual wires 18a (FIG. 2). That is, each wire 16a of the shielding coil 16
Is formed to be the same as the pitch of each wire 18 a of the resonance coil 18, and the outermost wire 16
It is preferable that a is formed slightly larger than the outermost strand 18 a of the resonance coil 18. The reason why the shielding coil 16 is formed larger than the resonance coil 18 is to complete the electromagnetic shielding between the resonance coil 18 and the article 11 by the shielding coil 16, and each wire 16 a of the shielding coil 16 is formed as described above. The difference from each element wire 18a of the resonance coil 18 is as follows.
This is for reducing the distributed capacitance between the shielding coil 16 and the resonance coil 18 and increasing the Q value.

A short-circuit insulating layer 21 is provided on the lower surface of the shielding coil 16.
A short-circuit line 22 is provided via the wire (FIGS. 1 and 3). The short-circuit insulating layer 21 is formed of an insulating material such as paper or a plastic thin plate, and the short-circuit line 22 is formed of a conductive material such as aluminum or copper. First and second through-holes 21a and 21b (FIG. 3) are formed in the short-circuit insulating layer 21 at positions facing the outer end and the inner end of the shielding coil 16, respectively. It is formed by bending so as to face the two through holes 21a and 21b, respectively. Shielding coil 16
The outer end and the inner end of the shielding coil 16 are electrically connected to each other by the short-circuit line 22, that is, short-circuited (see FIG. 1). .

The above-described coil insulating layer 20 is interposed between the shield coil 16 and the resonance coil 18 (FIGS. 1 to 3). The coil insulating layer 20 is formed of a non-magnetic and non-conductive paper or plastic thin plate, and the thickness thereof is preferably 5 mm or less because there is a distributed capacitance between the resonance coil 18 and the shielding coil 16. , 0.1mm
More preferably, it is within the range of １1 mm. The reason why the coil insulating layer 20 is configured as described above is to reduce the loss resistance of the resonance circuit section 14, that is, to increase the Q value.
Also, this is to suppress a decrease in the self-inductance of the resonance circuit unit 14 due to the shielding coil 16. In addition, the reason why the thickness of the coil insulating layer 20 is limited to the above-mentioned thickness is that the effect on the Q value and the self-inductance increases as the thickness increases, but when the thickness is too large, the tag 12 projects from the article 11,
This is because the handling is inconvenient and the appearance is impaired. Further, on the upper surface of the second electrode layer 19b and the conductive line 19c, a display plate 2 such as a price tag in which a price (not shown) is displayed by a numerical value or a bar code.
7 are laminated, and a base insulating layer 28
The adhesive layer 29 is laminated via (FIG. 1). Display board 2
7 and the base insulating layer 28 are formed of an insulating material such as paper or a plastic thin plate.

At the entrance (not shown) of the store selling the article 11, the transmitting antenna 13 and the receiving antenna 23 are provided.
Are erected at a predetermined interval from each other (FIG. 6). The receiving antenna 23 is connected to a control input of the control unit 24, and the transmitting antenna 13 is connected to a control output of the control unit 24.
The control output of the control unit 24 includes a speaker 2 for issuing an alarm.
6 is connected. The control unit 24 is configured to cause the transmission antenna 13 to transmit a radio wave having a frequency that resonates in the resonance circuit unit 14 and to always check the signal level of the reception signal from the reception antenna 23. That is, the signal level when the radio wave transmitted from the transmission antenna 13 is directly received by the reception antenna 23 is set as a reference value, and the transmission antenna 1
When the radio wave transmitted from the antenna 3 resonates in the resonance circuit unit 14 of the tag 12 and is received by the receiving antenna 23, the signal level becomes higher than the reference value by a predetermined value. At this time, the control unit 24 sounds the speaker 26. It is configured to be.

In this embodiment, drinking water, edible oil and candy contained in a container made of a steel plate which is a ferromagnetic material are described as the articles. However, it is contained in an aluminum container which is a conductive material. It may be drinking water or the like, or an article formed of an insulating material, a non-magnetic material, or any other material. If the article is a book, the tag of the present invention can be attached to the sales card with an adhesive, and the book purchased properly can be removed at the checkout place of the store, so that the transmitting antenna and the receiving antenna can be used. The loudspeaker does not give an alarm when passing through. Further, in this embodiment, the resonance coil and the shielding coil are formed in a substantially square flat plate spiral shape, but may be formed in a rectangular, circular or other shape as long as the flat spiral shape is used. When a tag is interposed between a display plate such as a price tag and an article, a square slightly smaller than the display plate, a rectangle close to a square having a small difference between long and short sides, or the like is appropriate.
Further, in this embodiment, the shielding coil is formed larger than the resonance coil. However, even if the resonance coil resonates, no eddy current is generated in the article and the self-inductance of the resonance circuit does not change, the shielding coil is formed. It may be formed to have the same size as the resonance coil.

An example of a method for manufacturing the anti-theft tag configured as described above will be described. A pair of conductive foils 3 formed of aluminum foil, copper foil, or the like on both surfaces of the coil insulating layer 20
1 and 32 (FIG. 4A), and the conductive foil 31 on the upper surface of the coil insulating layer 20 is connected to the resonance coil 18 and the first electrode layer 1.
Coated with a resist film 33 having a shape corresponding to 9a,
The conductive foil 32 on the lower surface of the coil insulating layer 20 is
6 was coated with a resist film 34 having a shape corresponding to FIG. 6 (FIG. 4B). In this state, an aqueous solution of caustic soda is used in the case of an aluminum foil, and an aqueous solution of ferric chloride is used as an etching solution in the case of a copper foil.
After removing the portions of 2 which are not covered with the resist films 33 and 34, the resist films 33 and 34 are peeled off (FIG. 4C). The resonance coil 18 and the first electrode layer 1 are formed on both sides of the coil insulating layer 20 by such an etching method.
9a and the shielding coil 16 were formed.

On the other hand, the second electrode layer 19b and the conductive line 19c
Were laminated on the lower surface of the display panel 27 by an etching method, and the short-circuit line 22 was laminated on the upper surface of the insulating base layer 28 by an etching method. In addition, through holes 17a are formed at predetermined positions of the dielectric layer 17.
(FIG. 3) is formed, and the first
After forming the second through holes 21a and 21b (FIG. 3), an adhesive (not shown) was applied to both surfaces of the dielectric layer 17 and the short-circuit insulating layer 21. A cover 27 having a second electrode layer 19b and a conductive line 19c, a dielectric layer 17, a coil insulating layer 20 having a resonance coil 18, a first electrode layer 19a and a shielding coil 16, a short-circuit insulating layer 21, and a short-circuit line from above. The base insulating layer 28 having an adhesive layer 22 and the adhesive layer 29 were superposed in this order and laminated and adhered to each other at a predetermined pressure (FIG. 1). Tag 1
If the tag 2 is manufactured, the efficiency is good and the relative positional relationship between the resonance coil 18 and the shielding coil 16 can be set very accurately, so that the resonance characteristics of the tag 12 are stabilized. The resonance coil and the shielding coil may be formed in a flat plate spiral shape by winding a conductive wire having an insulated surface, or may be formed in a flat plate spiral shape by punching a conductive material such as aluminum foil or copper foil. It may be formed.

The operation of the anti-theft tag configured as described above will be described. When the article 11 to which the tag 12 is attached passes from the transmitting antenna 13 and the receiving antenna 23 in order to take it out of the store without permission, the resonance circuit section 14 of the tag 12 picks up the radio wave transmitted from the transmitting antenna 13 and resonates. And the alternating current flows through the resonance coil 18. Due to this current, a resonance magnetic field is generated around the resonance coil 18 as shown by the solid line arrow in FIG. 5, and this magnetic field causes an induced current to flow through the shield coil 16 in a direction opposite to that of the resonance coil 18, and around the shield coil 16. A shielding magnetic field is generated as indicated by a broken arrow. Since the directions of the resonance magnetic field and the shielding magnetic field on the surface of the article 11 are opposite to each other, they are canceled each other, no eddy current is generated on the surface of the article 11, and the self-inductance of the resonance circuit section 14 has an insulating property. It is almost the same as when it is attached to an article made of a material or a non-magnetic material. As a result, a radio wave having a frequency determined in advance by the self-inductance of the resonance coil 18 and the capacitance of the capacitor 19 is re-emitted from the resonance circuit unit 14. When the receiving antenna 23 receives the re-radiated radio wave, the control unit 24 detects that the unpaid article 11 is taken out without permission based on the received signal. Emits.

Even if the frequency of the radio wave transmitted from the transmitting antenna 13 is high, that is, even if the resonance frequency of the resonance circuit section 14 is high, each of the wires of the shielding coil 16 is projected when projected from the upper or lower surface of the tag 12. The non-conductive and non-magnetic coil insulating layer 20 having a predetermined thickness is interposed between the shield coil 16 and the resonance coil 18. Therefore, the distributed capacitance between the resonance coil 18 and the shielding coil 16 decreases. As a result, the eddy current generated on the surface of the article 11 can be further reduced, and the Q value can be increased.
Can be narrowed, and the resonance circuit section 14 has sharp resonance. Therefore, the resonance circuit section 14 of the tag 12 resonates only by the radio wave of the specific frequency transmitted from the transmission antenna 13, and the resonance circuit section 14 resonates by the radio wave of a frequency slightly different from the above frequency transmitted from other than the transmission antenna 13. And the speaker 26 does not malfunction.

On the other hand, when the fee is paid regularly, a strong radio wave is radiated or heat is applied to the tag 12 at an accounting place (not shown) to destroy the capacitor 19 and the like of the resonance circuit section 14. Short circuit. As a result, even when the article 11 passes between the transmission antenna 13 and the reception antenna 23, the resonance circuit unit 14 does not resonate, so that the control unit 24 does not sound the speaker 26. The use of a shielding coil reduces the self-inductance of the resonance coil, but the resonance coil operates at the same resonance frequency as that when no shielding coil is used by increasing the number of turns of the resonance coil or increasing the capacity of the capacitor. You can do it.

[0020]

Next, examples of the present invention will be described in detail together with comparative examples. <Embodiment 1> As shown in FIGS. 1 to 3, the coil insulating layer 20 of the tag 12 is made of non-conductive and non-magnetic paper in the form of a plate having a length, width and thickness of 40 mm, 40 mm and 0.1 mm, respectively. And the upper surface of the coil insulating layer 20 has a diameter of 0.1 mm.
A resonance coil 18 formed by winding a 2 mm surface of a conducting wire having a surface insulated nine times in a substantially square flat plate spiral shape was attached.
The length of the outermost side of the resonance coil 18 was 30 mm, and the length of the innermost side was 10 mm. However,
The capacitor 19 shown in FIGS. 1 to 4 was not connected to both ends of the resonance coil 18. This is because the resonance frequency of the resonance circuit section 14 changes depending on the material of the article 11 because the self-inductance of the resonance coil 18 changes, and the capacitance of the capacitor 19 does not change even when the material of the article 11 changes. is there. Further, the shielding coil 16 formed by winding the same substantially square flat plate spirally nine times on the lower surface of the coil insulating layer 20 was attached, and both ends thereof were short-circuited by the short-circuit wire 22. A short-circuit insulating layer 21 was interposed between the shield coil 16 and the short-circuit line 22. Further, the display panel 27, the base insulating layer 28 and the adhesive layer 29 shown in FIG. 1 were not laminated. The tag 12 configured as described above was used as Example 1.

<Embodiment 2> As shown in FIGS. 1 to 3, the tag 1 was manufactured under the same conditions as those of the above-mentioned embodiment 1 except that an acrylic plate having a thickness of 0.95 mm was used as the coil insulating layer 20.
2 was produced. <Comparative Example 1> A tag was produced in the same manner as in Example 1 except that a shielding coil was not used, although not shown.

<Comparative Test and Evaluation> Examples 1 and 2
Each of the tags of Comparative Example 1 and an acrylic plate (1 m thick)
m), aluminum plate (thickness 1 mm) and steel plate (thickness 1 mm)
The resonance coils of these tags were connected to an RF impedance analyzer HP 4191A (manufactured by Yokogawa Hewlett-Packard Company), and the self-inductances L and Q values of the resonance coils were measured while changing the frequency. Here, the Q value means that the angular frequency is ω and the resistance of the resonance circuit is r.
Is a numerical value defined by ωL / r, and it is known that the higher the Q value, the smaller the loss due to eddy current and the like, and the sharper the resonance width. The Q value is directly displayed on the RF impedance analyzer. Table 1 shows the results.

[0023]

[Table 1]

As is apparent from Table 1, when the tag of Comparative Example 1 was placed on an acrylic plate, an aluminum plate, or a steel plate, the self-inductance of the resonance circuit portion, that is, the resonance coil showed different values. On the other hand, the self-inductance of the resonance coil hardly changed when the tags of Example 1 and Example 2 were placed on any of an acrylic plate, an aluminum plate, and a steel plate. When the tags of Examples 1 and 2 were placed on an acrylic plate, the Q value was lower than when the tag of Comparative Example 1 was placed on an acrylic plate, but the tags of Examples 1 and 2 were replaced with an aluminum plate. When the tag of Comparative Example 1 was placed on an aluminum plate and a steel plate,
The value was significantly higher, and the Q value was higher in Example 2 than in Example 1. This is presumably because the tags of Examples 1 and 2 have less loss resistance due to eddy currents and the like and the resonance width is sharper than the tags of Comparative Example 1.

[0025]

As described above, according to the present invention, the anti-theft tag attached to the theft monitoring article has the resonance circuit portion which resonates with the radio wave of the specific frequency transmitted from the transmitting antenna. Since a flat-plate spiral shielding coil short-circuited at both ends is interposed between the mounting surface of the article and the resonance circuit section, the surface of the article is made of a conductive material such as aluminum or a ferromagnetic material such as a steel plate. Even if the resonance circuit section resonates in the state formed by the above, an induced current in the opposite direction flows through the shielding coil, and the magnetic field on the surface of the article among the magnetic fields generated by the resonance circuit section resonating causes the induced current to flow through the shielding coil. Are canceled by the magnetic field generated by the flow of As a result, since no eddy current is generated on the surface of the article, the self-inductance of the resonance circuit portion is almost the same as when the surface is attached to an article formed of an insulating material or a non-magnetic material. If the shield coil is formed to have the same size as or larger than the resonance coil of the resonance circuit, the resonance coil is completely shielded from the article by the shield coil. Does not occur, and the self-inductance of the resonance circuit portion hardly changes without being affected by the article.

Further, when the laminated body of the resonance circuit portion and the shield coil is projected from the upper surface or the lower surface thereof, if the respective wires of the shield coil are disposed between the respective wires of the resonance coil, the resonance coil and the shield coil can be formed. Since the distribution capacity between the shielding coils is reduced, the eddy current generated on the article surface can be reduced. As a result, the loss resistance of the resonance circuit can be reduced, that is, the Q value can be increased, so that the width of the resonance frequency band of the resonance circuit can be narrowed, and the resonance circuit has sharp resonance. Further, even when the resonance frequency is high, the loss resistance such as the hysteresis loss of the resonance circuit portion can be reduced, that is, the Q value can be increased, similarly to the above. Further, if a non-conductive and non-magnetic coil insulation layer having a thickness of 5 mm or less is interposed between the shield coil and the resonance coil, the distributed capacitance between the resonance coil and the shield coil can be further increased by the coil insulation layer. Can be reduced. As a result, the eddy current generated on the surface of the article can be further reduced, so that the Q value is further increased, and the resonance circuit section has a sharper resonance.

[Brief description of the drawings]

FIG. 1 shows an anti-theft tag according to an embodiment of the present invention.
Sectional view on the AA line of FIG.

FIG. 2 is a sectional view taken along line BB of FIG. 1;

FIG. 3 is an exploded perspective view of a resonance circuit portion and a shielding coil of the anti-theft tag.

FIG. 4 is a process chart showing a method of manufacturing the resonance circuit portion and the shielding coil.

FIG. 5 is a diagram showing the direction of a magnetic field generated when a current flows through a resonance coil by a radio wave of a specific frequency from a transmission antenna and an induced current flows through a shielding coil due to the current.

FIG. 6 is a diagram showing a state in which an article to which the tag is attached is passed between a transmitting antenna and a receiving antenna.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Article 12 Tag 13 Transmission antenna 14 Resonant circuit part 16 Shielding coil 16a Shielding coil element wire 18 Resonance coil 18a Resonance coil element wire 20 Coil insulating layer

Claims (4)

[Claims] An anti-theft tag (12) having a resonance circuit (14) attached to a theft monitoring article (11) and resonating with a radio wave of a specific frequency transmitted from a transmission antenna (13), An anti-theft tag comprising a flat spiral coil (16), both ends of which are short-circuited, between a mounting surface of an article (11) and the resonance circuit section (14). 2. The anti-theft tag according to claim 1, wherein the shielding coil (16) is formed to have the same size as or larger than the resonance coil (18) of the resonance circuit section (14). 3. When the laminated body of the resonance circuit section (14) and the shielding coil (16) is projected from the upper surface or the lower surface thereof, each element wire (16a) of the shielding coil (16) is connected to the resonance coil (18). Each strand
(18a) The anti-theft tag according to claim 1 or 2, which is disposed so as to be located between them. 4. A non-conductive and non-magnetic coil insulating layer (20) having a thickness of 5 mm or less is interposed between a shielding coil (16) and a resonance coil (18). Or anti-theft tag described.