FI98866C - Product protection sensor - Google Patents

Abstract

An article surveillance tag comprising a thin, planar, elastic substrate (5); the oscillatory circuit comprising a first and a second capacitor (C2, C3) whose electrodes are formed by conducting regions on opposite sides of the substrate, and a first pair of conductor branches (10, 11), whose branches are arranged on the opposite sides of the substrate (5), their first ends being connected to the electrodes of the first capacitor (C2), and at least one of the conductor branches (10, 11) being shaped as a coil. In order that the tag might be easily detected, it comprises a second pair of conductor branches (12, 13), whose branches are arranged on the opposite sides of the substrate (5) and the first ends of said branches are connected to the electrodes of the second capacitor (C3); at least one of the conductor branches (12, 13) being shaped as a coil, the second ends of the first and the second pairs of conductor branches (10, 12; 11, 13) located on the same side of the substrate (5) being connected to one another, and the second ends of the conductor branches located on the opposite sides of the substrate being electrically connected to one another to provide an oscillary circuit.

Description

98866

The present invention relates to a product protection sensor comprising a thin, plate-like, elastic substrate on both sides of which components made of a flexible material are arranged, which together form at least one oscillation circuit, the oscillation circuit comprising first and second capacitors having the electrodes consist of conductive regions 10 on opposite sides of the substrate so that the electrodes on opposite sides of the substrate are substantially in the same positions and the same size, and a first pair of conductor branches arranged on opposite sides of the substrate and having first ends connected to electrodes of the first 15 capacitors, wherein at least one of the conductor branches is formed as a winding.

The invention relates to a sensor for preventing theft in shops and shops, which can be affixed or integrated in packaging, labels, tags or the like, and which has an oscillation circuit formed by a capacitor and a coil. When an object having a product protection sensor is exposed to the electromagnetic field of the EAS Electronic Dectection System generated by the system's transmitter and associated antenna 25, the product protection sensor causes a change in the field. Based on this change, the receiver of the monitoring system detects the presence of the sensor. The transmitter and receiver of the monitoring system are located in a location or locations where it is desired to indicate that the sensor has a product in connection with an unauthorized outlet, such as a store exit.

Product protection sensors are usually made of a thin plastic film coated on both sides with a metal film. Color-35 material is transferred onto the metal films using gravure printing technique. Next, the metal 98866 · 2 is etched away. Etching does not occur where there is i dye. Finally, the toner is removed.

The components of product protection sensors are generally dimensioned so that the resonant frequency of the sensors, i.e. the detector frequency, is about 8.2 MHz. The resonant frequency of the sensors must be independent of temperature, metal objects and contact. In addition, the sensor should be as cheap and small in size as possible so that it can be easily attached to a wide variety of applications. This requires that the sensor be made of as thin a material as possible and that the surface area of the sensor be as small as possible. However, the quality factor and surface area of the resonator determine how easily the sensor can be detected. That is, if the surface area of the sensor is small, its 15 goodness numbers must be as large as possible.

Product protection sensors are already known, in which a resonant circuit is formed on a thin film without bushings from two capacitors and conductor branches, at least one of which is formed as a winding. In known sensors 20, the coil on one side of the membrane may contain several turns, but it is generally not possible to accommodate a few more turns on the other side. The number of turns cannot be increased without the stray capacitance between the lower and upper windings tuning the reso-25 voltage circuit.

The product protection sensor must also be able to be deactivated, ie destroyed as easily as possible, so that the person who actually bought the item to which the product protection sensor is attached does not cause unnecessary alarms when out-30 while supporting the store.

Known product protection sensors are disclosed, for example, in U.S. Pat. No. 5,241,299 and in FI-A-920 695. In these publications, the deactivation of a product protection sensor takes place by exposing the sensor to a electromagnetic

II

3 98866 to an ethical field, where the formation of an induced voltage between the plates of the capacitor causes a breakthrough through the insulation at the plates, so that the capacitor is short-circuited. To facilitate breakthrough, in the above-mentioned reference publications, a pit or weakening is formed in the insulating material between the plates of the capacitor.

The most significant weakness of the above-mentioned known solutions is that ensuring that the capacitor is short-circuited places great demands on the properties of the insulating material, in addition to which the insulating material must be weakened or the insulating material layer must be dimensioned very precisely between the plates. These requirements increase the raw material and / or manufacturing costs of the product protection sensor.

In addition, a product protection sensor is already known, the deactivation of which is based on the disconnection of a conductor branch belonging to a resonant circuit. In this known solution, a special attenuation is made in the conductor branch, from which the conductor branch is broken when the product protection sensor is exposed at a resonant frequency to an electromagnetic field having a certain minimum power level. One such product sensor is known from WO 93/01571. However, maximizing the QA of the product protection sensor, ie the Q value, requires that the conductor width is minimized (100 - 200 μπι). In this case, in practice it is very difficult and expensive to make an even narrower attenuation in the conductor in order to concentrate the power at one point when the sensor is deactivated. 30 The addition of a separate resistive point would also increase the price of the product.

The object of the present invention is to solve the above-mentioned problems and to provide a product protection sensor which is relatively inexpensive and simple to manufacture, which can be easily and reliably detected by the EAS equipment, which is small in size and can be deactivated easily. These objects are achieved by a sensor according to the invention, characterized in that the product protection sensor comprises a second pair of conductor branches, the conductor branches of which are arranged on opposite sides of the substrate, the first ends of which are connected to the electrodes of the second capacitor. and the other end of the conductor branches on the same side of the base of the second pair of conductor branches are connected together, and the other ends of the conductor branches on opposite sides of the base are electrically connected together to form an oscillation circuit. The term electrically interconnected in this context means that the other ends of the conductor branches are connected together, for example galvanically or capacitively, so that an electrical interaction necessary for the operation of the resonant circuit is formed between them.

The invention is based on the idea that when the resonator circuit of the sensor is formed of several parallel windings, the surface area of the sensor as a whole can be efficiently utilized. The windings are placed in parallel so that the area between the parallel-connected windings forms a gradiometer so that no current from a homogeneous field is induced in it. In this case, the quality number of the product bog 25 sensor is kept high.

When, in a preferred embodiment, the parallel conductor branches are connected at least at one point to form one common conductor branch portion, a large common conductor portion portion 30 is obtained from the total current of the resonator circuit, whereby the conductor branch portion is easily broken and the sensor is deactivated. Since the deactivation of the product protection sensor according to the invention does not require the short-circuiting of the capacitor electrodes, as in the known solutions, one work step is omitted during the manufacture of the sensor, i.e. the thinning of the membrane point between the electrodes. This naturally lowers the manufacturing cost by 5,988,666. In addition, a cheaper film material can be used in the product protection sensor according to the invention.

The current 5 prevailing in the common branch part of the conductor branches consists of the sum of the currents of the separate conductor branches. The number of parallel windings, the number of capacitors and the number of turns in the winding can, of course, vary depending on the application. However, when using parallel windings, it is important that approximately the same current flows in the existing windings. This is achieved according to the invention by connecting the other end of the windings on the same side of the film.

The number of windings for one sensor is preferably between 2-8. The number of turns in the windings is preferably between 2-4.

The most significant advantages of the product protection sensor according to the invention are thus that the goodness of the resonant circuit can be maximized due to very thin conductor branches which do not need separate attenuation to deactivate the sensor, that the sensor surface can be very efficiently filled with windings, but the resonator inductance can be kept low. in parallel, and that due to the low inductance, the ka-25 passivity becomes high, so that the voltage level remains low and the sensor is not sensitive to contact. The current is also high, making it possible to destroy the sensor with current.

When the surface area is large enough and the plastic-30 film of the sensor is thin enough, both surfaces of the sensor can be effectively utilized by using two-layer coils with turns on different sides of the film. Because the inductance is small, the voltage between the coils on different sides of the film is small, and the extra capacitance that reduces the Q-value of the sensor, the capacitance due to the overlap can be eliminated.

IITA.

Preferred embodiments of the product protection sensor according to the invention appear from the appended dependent claims 2-9.

The invention will now be described in more detail by means of a few preferred embodiments of a product protection sensor according to the invention with reference to the accompanying figures, in which Figure 1 illustrates a first preferred embodiment of a product protection sensor, Figure 2 shows a circuit diagram of a second preferred embodiment of a sensor according to the invention; the structure of the product protection sensor, Fig. 4 illustrates a third preferred embodiment of the product protection sensor according to the invention, and Fig. 5 illustrates a fourth preferred embodiment of the product protection sensor according to the invention.

Figure 1 illustrates a first preferred embodiment of a product protection sensor according to the invention. The area of the sensor shown in Fig. 1 is preferably about 5 to 10 cm 2. The sensor is manufactured in a manner known per se by laminating a thin metal film on both sides of a thin plastic film 5, after which the excess metal is etched away.

The sensor shown in Figure 1 comprises three capacitors C1, C2 and C3. The electrodes of these capacitors consist of conductive regions made on opposite sides of the membrane and located at substantially the same points and of substantially the same size, which are insulated from each other by the membrane 5. The electrodes of the capacitors C1, C2, C3 preferably consist of a plurality of superimposed strips, whereby eddy currents can be reduced and thereby the quality factor of the sensor can be improved.

The condensate-35 relay electrodes on the Selm side of the membrane 5 are connected to each other by conductor branches. Ku

II

In the case of Fig. 1 98866, a conductor branch 1 formed as a winding connects the electrodes above the membrane 5 of the capacitors C1 and C2, and a conductor branch 2 illustrated by a broken line in Fig. 1 connects the electrodes below the membrane 5 of the capacitors C1 and C2. The conductor branch 4, which is also shown as a broken line, connects the electrodes of the capacitors C1 and C3 below the membrane 5, respectively. The width of the conductor branches is about 100 - 200 μπι.

It can be seen from Figure 1 that one end of the conductor branch 3 formed as a coil is connected to the electrode above the film 5 of the capacitor C3, and that the other end of the conductor branch 3 is connected to the conductor branch 1 so that the conductor branches 1 and 3 travel from one common conductor X The product protection sensor shown in Figure 1 thus comprises two windings 1 and 3 connected in parallel. Utilization of several coils connected in parallel allows efficient utilization of the sensor surface without increasing the inductance of the resonator. When the inductance is small, the capacitance becomes correspondingly higher (the resonant frequency of the resonator circuit depends on the result of the inductance and capacitance). A large capacitance results in a low voltage level, and thus the sensor is not sensitive to contact.

When the product protection sensor of Figure 1 is exposed to an electromagnetic field with a resonant frequency of 8.2 MHz, currents 1 and 3 are generated in the windings. Since the windings 1 and 3 are connected at the conductor branch section X, the sum of the currents prevailing in the windings 1 and 3 is formed in the common section X. In the common point 30, the selective power can be calculated from the formula: P = I2 * R, where I is the sum of the currents of the individual conductor branches and R is the resistance. The power per unit length of the common conductor branch section X is thus proportional to the second power of the number of windings, i.e. the number of conductor branches. According to the invention, these 35 features are utilized for the deactivation of the SPC.

If the series resistance of the winding is R, then in the resonance an effective current I = 2ΠίΑΒ / R is induced in the winding, where B is the rms value of the magnetic flux density, A is the area of the sensor 5 and f is the frequency. When "destroyed" by current in the sensor, the surface area should be as large as possible and the series resistance R of the winding as small as possible. This favors solutions where there are a lot of parallel conductors and only a few rounds in series. Optimizing the sensor quality factor Q 10 means the same as minimizing R.

The product protection sensor of Figure 1 is deactivated at its resonant frequency by exposing it to an electromagnetic field whose intensity exceeds a certain minimum limit. In this case, the power generated in the conductor X is so large that it is interrupted. To facilitate deactivation, the common conductor branch section X can be made of a different material than the other parts of the resonant circuit. A material whose resistance increases sharply with increasing temperature is suitable for this purpose. Suitable materials for this purpose are, for example, carbon-containing mixtures or, for example, zinc dioxide. Thanks to such a material, the breaking of the conductor X is made to take place at a lower power.

Figure 2 shows a circuit diagram of another preferred embodiment of a sensor 25 according to the invention. The sensor shown in Figure 2 is very similar to the sensor of Figure 1, but comprises four capacitors C1 to C4, as well as six coil-shaped conductor branches 10-15. The dashed line ha-30 passing between the electrodes of the capacitors detects the plastic film 5, which insulates the components above and below each other.

It can be seen from Figure 2 that one end of the conductor branches 11, 13 and 15 below the membrane 5 is connected to the electrode 16 of the capacitor C1. In contrast, the other end of the conductor branches 10, 12 and 14 li 98866 above the membrane 5 are connected via a common conductor branch portion X to the capacitor. C1 to the electrode 17 above the membrane 17. The conductor branch portion X is thus relatively easily broken when the resonator is deactivated, as described above.

The lower conductor branches of Fig. 2 are arranged crosswise to illustrate that the outermost 10 of the parallel windings above is guided below to the innermost 11, etc. (cf. Fig. 3).

Figure 3 illustrates the structure of a product protection sensor according to the diagram of Figure 2. In Fig. 3, the conductor branches 10, 12 and 14 arranged above the film 5 are drawn in solid lines, and the conductor branches 11, 13 and 15 arranged below the film are drawn in broken lines. That is, for example, the electrodes above the membrane of the capacitors C1 and C2 are connected by a conductor branch 10 formed as a winding. Respectively, the electrodes below the membrane of the capacitors C1 and C2 are connected by a conductor branch 11. The electrodes below the membrane 5 are in the same places and of the same size as the electrodes above the membrane.

In the sensor of Fig. 3, its coils connected in parallel are arranged so that the loop between the two parallel coils does not cause a "short-circuit current" in the homogeneous field and thus degrade the sensor quality Q. The coils of Fig. 3 are arranged in parallel so that the coils area forms a gradiometer so that no current from a homogeneous field is induced in it. In this case, the quality factor of the product protection sensor is made high. This structure requires the use of several separate capacitors. The conductor branches of Fig. 3 are arranged so that above the parallel windings, the outermost edge 10 is guided below to the innermost 11, etc. In other words, the mutual length of the conductor branches is the same. This structure allows full utilization of both sides of the film without leading to an increase in stray capacitance, and with it a decrease in Q-value.

If desired, the sensor branches and capacitors required for activating the product protection sensor can be added to the sensor shown in Figure 3. In this case, the activation is preferably performed in a manner known per se at a higher frequency than the detection frequency of the sensor. Activation can be performed, for example, by burning one of the conductor branches across the sensor so that the resonant frequency of the resonant circuit changes to the detection frequency.

Figure 4 illustrates a third preferred embodiment of a product protection sensor according to the invention. The product protection sensor of Fig. 4 is very similar to the sensor of Fig. 3, i.e. it consists of a membrane 5, on opposite sides of which are arranged parallel, wound-shaped conductor branches 10, 11, 12, 13, 14 and 15. The conductor branches below the membrane 5 are in Fig. 4, similar to Fig. 3, drawn in broken lines.

The sensor of Figure 4 comprises 4 capacitors C1, C2, C3 and C4 like the sensor of Figure 3. However, in Figure 4, all of the sensor capacitors are placed inside the winding to maximize the area of the capacitors. The number of parallel conductor branches in this embodiment can increase up to ten, preferably 5-10. The sensor of Figure 4 does not comprise a separate cut-off point, although such a sensor may be made to that sensor, similar to that shown in the sensor of Figure 3.

Figure 5 illustrates a fourth preferred embodiment of a product protection sensor according to the invention. The product protection sensor shown in Figure 5 is very similar to the sensor of Figure 3. However, in the embodiment of Figure 5, one of the capacitors is replaced by a lead-through part 18. This lead-through part protrudes through the membrane 5 so as to connect the conductor branches 10, 12 and 14 above the membrane 5 in Fig. 5 with the conductor branches 35, 13 and 15 below the membrane 5. The shape or size of the lead-through part 18, 98866 u, or the size is, of course, irrelevant, as long as it ensures a sufficiently good galvanic connection between the other ends of the conductor branches on opposite sides of the film for the operation of the resonator circuit.

In the case of Figure 5, the lead-through part 18 is arranged some distance from the edges of the film 5. Therefore, the film 5 is perforated during manufacture to provide a penetration. However, the lead-through part 18 can also be fitted to the "outside" of the film, i.e. to its outer edge, so that the film does not have to be punctured. In this case, the conductor branches 10 to 15 extend to the outer edge of the membrane 5, where they join the lead-through part 18.

The cut-off point is provided in the product protection sensor shown in Fig. 5 when, in the case of Fig. 3, i.e. the conductor branches 10, 12 and 14 above the membrane are connected to the lead-through part 18 by a common conductor branch section X. If a cut-off point is not required. that the conductor branches 10, 12 and 14 above the membrane are connected to the lead-through part 18, respectively, when the conductor branches 11, 13 and 15 below the membrane 5, i.e. each separately.

It is to be understood that the foregoing description and the accompanying figures are intended only to illustrate the present invention. Various variations and modifications of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims.

Claims (9)

A product protector comprising a thin, disk-like, elastic substrate (5) with components of elastic material disposed on both slides, which together form at least one oscillation circuit, the oscillation circuit comprising a first and second capacitors (C2, C3), whose electrodes consist of conductive regions arranged on opposite sides of the substrate, such that the electrodes on opposite sides of the substrate are substantially equal in size and are substantially in corresponding places, and a first conductor pair (1, 2; 10, 11) with the conductors arranged on opposite sides of the substrate (5), the first ends of the conductors being coupled to the electrodes of the first capacitor (C2), at least one of the conductors (1; 10, 11) being formed as a coil, characterized in that the product protector comprises a second conductor pair 20 (3, 4; 12, 13) with the conductors arranged on opposite sides of the support (5), the first ends of the conductors being coupled to the other the electrodes of the capacitor (C3), at least one of the conductors (3; 12, 13) is formed as a coil, the conductor (1, 3; 2, 4; 10, 12; 11, 13) located on the same side of the first and second conductor pairs on the same side of the support (5) are interconnected, and that the other ends of the conductors located on opposite sides of the support are electrically connected to form an oscillation circuit. Product protection sensor according to claim 1, characterized in that the other ends of the conductors on the opposite sides of the substrate are electrically coupled by means of an insertion part (18). 35 98866 16 Product protection sensor according to claim 2, characterized in that the other ends of the conductors (11, 13) located on one side of the support (5) are connected to the feed member (18), and that the other ends of the conductors (10, 12) on the opposite side 8r of the substrate (5) connected to the conductor part (18) via a common conductor part (X). Product protection sensor according to claim 1, characterized in that the other ends of the ρά opposite sides of the substrate located conductors are electrically connected by means of a capacitor (C1), to the first electrode (16) of which the other end of the conductors (11, 13) of the first and second conductor pairs located on the same side of the support (5) to which the electrode (16) is coupled, and to the second electrode (17) the other end of the conductors (10, 12.). the first and second conductor pairs located on the same side of the support (5) to which the electrode (17) is coupled. The product protection sensor according to claim 4, characterized in that said second ends of the first electrode (16) of the capacitor (C1) connected to the capacitor (C1) are connected to it (16) separately, and that said second ends of the conductors (10, 12) connected to the second electrode (17) of the capacitor (C1) are connected to it (17) via a common conductor part (X). Product protector according to any of claims 1-5, characterized in that both conductors (10, 11; 12, 13; 14, 15) in the first and / or second conductor pairs are designed as coils. Product protection sensor according to any one of claims 30 to 6, characterized in that both conductors in the first and second conductor pairs (10, 11; 12, 13) are formed as coils, the conductors (10, 12) in the first and second the pair of conductors lying on the same side of the substrate (5) are arranged in parallel, so that if the first conductor pair (10) located on the substrate (5) lies on the surface, the first conductor pair is below the substrate (5). ) position conductors (11) at the bottom of the underside. Product protection sensor according to any of claims 1-7, characterized in that the width of the conductors (1 - 4; 10 5 - 15) is about 100 - 200 µm. Product protection sensor according to any of claims 1-8, characterized in that the sensor's surface is about 5-10 cm2 and the sensor's thickness is about 30 - 60 µm.