FI84668B - RESONANT ETIKETTKRETS OCH ELEKTRONISKT SAEKERHETSSYSTEM FOER DESS ANVAENDNING. - Google Patents

Description

1 84668

Resonant flag circuit and electronic security system using it

FIELD OF THE INVENTION This invention relates to a resonant flag circuit and an electronic security system for deactivating the resonant characteristics of a flag circuit.

Background of the invention

Such electronic security systems are known to detect the unauthorized removal of objects from a controlled area. Such systems have been used especially in retail stores to prevent theft of goods from stores and in libraries to prevent book theft. Such electronic security systems generally include an electromagnetic field located in a controlled area through which goods must pass when leaving protected areas. The resonant flag circuit is attached to the goods and its presence in the controlled area is detected by the receiving system to detect the unauthorized removal of the goods. Authorized personnel detach the flag circuit from the goods, which are lawfully removed from the store so that the goods can pass through the controlled area without triggering an alarm.

In addition, systems are known which electronically deactivate the resonant circuit so that the deactivation circuit can remain in the goods that are allowed to leave the store. One such system is disclosed in U.S. Patent No. 3,624,631, in which the fuse is in series with the inductor and is burned by an efficient high frequency transmitter 30. The resonant circuit is interrogated by the swept high frequency and the presence of this circuit in the monitored area causes energy to be absorbed at the resonant frequency indicated by the receiver for later activation of the alarm. When a scanned frequency is applied with an energy greater than the energy used for detection, the resonant circuit may return to deactivate the tuned circuit so that detection is not possible. Deactivation must be achieved by a scanned frequency transmitter operating at low enough radiation levels to meet the requirements of the traffic authorities, so that the fuse must be very small and of a substance that can melt with low power. The small fuse has a high resistance in series with the inductor of the resonant circuit. The series resistance reduces the Q value of the resonant circuit and thus reduces the sensitivity of the 10 circuits to be detected. The current level at which the fuse melts is determined by the geometry of the fuse and, in addition, by the thermal conductivity of the materials surrounding the fuse. Thus, the substances that cover and support the fuse greatly affect the melt flow.

Another electronic security system is disclosed in U.S. Patent No. 3,810,147, the inventor of which is the same as po. invention and using a resonant circuit having two separable frequencies, one for detection and one for deactivation. A small die is used in the deactivation circuit 20, which also has a second capacitor to provide a separable, deactivating resonant frequency.

The resonant circuit may have a resonant frequency that varies within a range due to manufacturing tolerances. 25 The deactivation frequency is at a fixed frequency and thus the resonant circuit cannot be precisely tuned to a fixed deactivation frequency. The series impedance of the inductor and capacitor must be as small as possible at the desired deactivation frequency so that the maximum possible current can pass through the fuse to cause it to burn out. Therefore, the capacitor must have the highest possible value and the inductor must have the lowest possible value. In the actual structure, the inductor is made in the form of one turn and the capacitor is made of as many as 35 large plates, taking into account the flag district financial 3 84668 and physical constraints. The size of the capacitor enlarges the entire resonant circuit and makes it more expensive.

Po. the invention provides a resonant flag circuit having at least one resonant frequency and operating in an electronic security system in which the flag circuit is electronically detected and deactivated to destroy or change the resonant characteristics of the flag circuit at the detection frequency. The resonant flag circuit according to the invention is characterized by what is stated in the patent applications below.

The resonant flag circuit is electronically deactivated by a break-through mechanism that operates within the resonant structure of the flag without the need for a fuse and without affecting the Q value of the resonant circuit and without degrading it. The Reso-15 nance flag circuit is flat in shape and has a flat helix on the surface of a thin, plastic base film and at least one capacitor formed by capacitor plates on opposite surfaces of the base film. Energy is applied to the flag circuit at or near the resonant frequency to provide electrical breakthrough through the base film between the capacitor plates. The resonant structure includes a means to ensure that the breakthrough almost always occurs in a predetermined area between the capacitor plates. In response to a sufficiently large, coupled energy, an electric arc is formed through the base film and causes the surrounding or nearby conductive region to evaporate, destroying the resonant properties of the circuit. Alternatively, electrical breakdown through the base film can cause plasma formation and metal evaporation between the capacitor plates 30 along the discharge path, creating a permanent short circuit between the capacitor plates, which destroys the resonant properties of the circuit.

The electronic security system according to the invention is characterized by what is stated in the claims below.

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Description of the drawings

The understanding of the invention will be facilitated by the following detailed description relating to the accompanying drawings, in which: Figure 1 shows a schematic diagram of a resonant flag circuit according to the invention; Fig. 2 shows a schematic diagram of a double-frequency resonant flag circuit according to the invention; Figures 3 and 4 show views of different sides of the resonant flag circuit of Figure 1; Figures 5 and 6 show views of different sides of the resonant flag circuit of Figure 2; Fig. 7 shows a block diagram of an electronic security system according to the invention; Fig. 8 shows a schematic diagram of an alternative embodiment of a single frequency resonant flag circuit; Fig. 9 shows a schematic diagram of an alternative embodiment of a dual-frequency resonant flag circuit; Figures 10, 11 and 12 are schematic views and views of the electric breakthrough mechanism used in the invention; Fig. 13 is a schematic diagram of an electronic device that determines the resonant frequency of a flag circuit to be deactivated; Figures 14 and 15 are waveforms used to illuminate the operation of the device of Figure 13; and Fig. 16 shows a block diagram of an electronic deactivator that provides deactivation energy for a controlled time interval.

30 Detailed Description of the Invention

Referring to Fig. 1, this shows in schematic form a resonant flag circuit including a capacitor C1 formed of capacitor plates 10 and 12 on opposite surfaces of the base plate 14, the base plate being dielectric, and an electrically insulating material, in its series, and an inductor L1 in series. to provide a single resonant frequency. One end of the inductor is connected to the capacitor plate 10 and its other end is connected to an electrical path 16 through a base plate 14 which is connected to the capacitor plate 12 via a path 18. The inductor and capacitor plate 10 are made entirely on one surface of the base plate. The inductor is typically made as a flat, rectangular coil on the surface of the base plate. The capacitor plate 12 and the associated connection path 10 are likewise made entirely on the opposite surface of the base plate. The flat flag structure is described below.

The portion 20 of the conductive path 18 facing the capacitor plate 10 is otherwise designed or shaped to be spaced apart from the capacitor plate 10 by a distance 15 less than the distance between the plates 10 and 12. When sufficient electrical energy is applied to the flag circuit at or near the resonant frequency of the circuit, the voltage across the capacitor plates 10 and 12 increases until an electrical breakthrough occurs at the overheating point formed by the notched portion 20 of the conductive path 20. Because the distance between the capacitor plates is the shortest here. The electric arc formed in the breakdown is maintained by energy which is continuously connected to the resonant circuit from an external power source. The electric arc 25 vaporizes the metal in the vicinity of the breakthrough region 20, which destroys the conductive path 18 and thus permanently destroys the resonant properties of the flag circuit.

An alternative embodiment of the resonant circuit is shown schematically in Figure 2, where the flag circuit 30 has two resonant frequencies. In addition to the capacitor C1 and the inductor L1 formed by the plates 10 and 12, the circuit of Fig. 2 includes a second capacitor C2 formed by the plates 22 and 24 and an inductor L2. The junction of the inductors L1 and L2 is connected to the capacitor plate 22. The other end of the inductor 35 is connected to the through-connection 26 in the base plate 646668 and is connected via a conductor path 28 to the capacitor plate 24. The conductor path 30 connects the capacitor plates 24 and 12 and includes a notched overheating portion 32 made with the resistive condensate plate 22.

One resonant frequency is used to detect the flag by means of a corresponding electronic security system and the other resonant frequency is used to deactivate the flag. Usually, a deactivation frequency 10 is selected which is authorized by the Ministry of Transport in the industrial, scientific and medical fields, so that the radiated energy for deactivating the flag can be relatively effective without special permission from the authorities. The detection frequency is usually selected from one of the frequency ranges intended for field disturbance sensors. The typical detection frequency is 8.2 MHz.

Capacitor C2 and inductor L2 are the primary parts that form the tuned resonant circuit at the deactivation frequency, while the inductor L1 and the capacitor C1 are the primary parts that form the tuned resonant circuit at the detection frequency. Due to the interconnection, all parts work together to obtain an accurate detection and deactivation frequency. When sufficient energy is applied to the circuit at the deactivation frequency 25, the voltage across the capacitor plates 22 and 24 increases until a breakdown occurs in the base film at the overheating point 32. The breakdown always occurs at the overheating point because this point or area 32 forms the shortest distance between the capacitor plates 22 and 24. . The electric arc formed in the breakthrough is maintained by the energy supplied to the resonant circuit from an external power source, and this arc causes the metal to evaporate in the vicinity of the breakthrough region, including the proximal portion of the conductive path 30. When the external energy is stopped, the 35 electric arc goes out. The resonant characteristics of the flag at the detection frequency of 7,84668 are permanently destroyed because there is no longer an electrical connection between the capacitor plate 24 and the capacitor plate 12.

In the resonant circuits of Figures 1 and 2, it is not necessary to use a small narrow fuse, so that no additional resistor is placed in series with the inductor and capacitor parts of the circuit. Therefore, the Q value of the resonant circuit does not deteriorate. Furthermore, since the electric arc occurs between the capacitor plates and not on the surface, the substances that cover or touch the surface of the capacitor plates do not significantly affect the ability of the electric arc to vaporize the metal in the vicinity of the arc. In order to maximize the voltage generated across the capacitor plates 22 and 24, the capacitance of the capacitor C2 should be as small as possible and the inductance of the inductor L2 15 should be as large as possible to obtain resonance at the desired deactivation frequency. Capacitor C2 can be made very small physically and does not significantly increase the size of the dual frequency flag circuit of Figure 2 or increase its cost.

The resonant flag circuit of Figure 1 is shown in a typical structure in Figures 3 and 4, which show opposite planar surfaces of the flag, respectively. According to Figure 3, the inductor L1 is made as a flat helix on the surface of a thin plastic base film 42. The plastic film acts as an insulator for its parallel plate capacitor and as a base plate supporting the circuit. The helical path extends between the outer conductive region 44 and the inner conductive region 46. The internal conductive region 46 acts as a capacitor plate 10. On the opposite surface of the flag, as shown in Figure 4, the conductive regions 48 and 50 are aligned with the respective conductive regions 44 and 46 and are interconnected by a conductive path 52. The conductive region 50 acts as a capacitor plate 12 and thus, the conductive regions 46 and 50 of the resistors form a capacitor C1. The conductive interconnect field 35 connects the conductive regions 44 and 48 together and thus closes the circuit 84668. The leading region 50 includes cavities 51 near the confluence region between the leading region 50 and the leading path 52. This region includes a notched portion 56 and forms a conductive region along a path 52 that abuts the conductive region 46 of the opposites and is spaced less than the distance between the conductive regions 46 and 50. The notch 56 forms an overshoot point where an electrical breakthrough occurs when energy is supplied from an external source at the resonant frequency of the flag circuit at a sufficiently high power to produce a through-10 stroke.

The dual frequency flag circuit of Figure 2 is shown in a typical structure in Figures 5 and 6, which show the corresponding planar surfaces of the flag. The inductor L1 is formed by a flat helix 60 on the surface of the plastic film 62, and this helix extends between the conductive regions 64 and 66. The conductor L2 is formed by a flat helix 68 on the surface of the film and extends between the conductive region 64 and the conductive region 70. As shown in Figure 6, the conductive regions 72,74 and 76 on the opposite surface of the base film are parallel to the respective conductive regions 64, 66 and 70 on the other surface of the base film. Conductive areas 72 and 74 are interconnected by conductive path 78 and conductive areas 72 and 76 are interconnected by conductive path 80. An overheating point is made in conductive path 78 by making a notch in path portion 25 82 with the conductive region 64 of the resistances. In Figure 2, the capacitor C1 is formed by the conductive regions 66 and 74, while the capacitor C2 is formed by the conductive regions 64 and 72. A conductive connection 84 between the conductive regions 70 and 76 is formed through the base film to close the circuit. The circuit operates as described and causes the resonant properties of the flag circuit to be destroyed at the detection frequency when the conductive path evaporates or a breakthrough occurs near the overheating point 82 in response to an electric arc.

The resonant flags described herein are similar to those described in U.S. Patent No. 3,810,147 to the same inventor.

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The structure of the flag circuits is preferably made by a method of manufacturing a planar circuit, which is the subject of U.S. Pat. No. 3,913,219 to the same inventor.

The device shown in Figure 7 is used to deactivate the resonant characteristics of the flag circuits described above. This apparatus includes an antenna 90 that detects the presence of a resonant flag circuit 92 and is coupled to a flag sensing system 94 that provides an output signal to a flag presence indicator 96 and a flag deactivation indicator 98. The flag sensing system 94 also provides a control signal to the flag deactivation system 100 having an antenna 102. The flag deactivation system may also be manually activated by manual control 104. When the presence of the flag circuit 92 is detected, the flag sensing system 94 and 15 triggers the deactivation system 100 and causes the antenna 102 to emit radiation at the flag circuit resonant frequency effectively enough to In the case of a doubled-20 hair flag, the deactivation system provides energy at the deactivation frequency of this flag. Indicators 96 and 98 may visibly or otherwise indicate the presence and deactivation of the flag.

If the flag circuit is a simple resonant circuit 25 according to Fig. 1, the sensing system 94 operates to determine the the resonant frequency of the detected flag 92 and provides a control signal to the deactivation system 100, which signal represents the measured resonant frequency of the flag. In response to the control signal, the deactivation system provides 30 radiation at this resonant frequency and efficient coupling to the flag circuit to destroy its resonant properties. The flag sensing system 94 may include a device shown in Fig. 13 that determines the approximate resonant frequency of the flag circuit. The voltage controlled oscillator 150 35 uses the flag sensing antenna 90 and the oscillator is controlled by the output of the microcomputer 152 by a D / A converter 154.

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The microcomputer stores digital values which, when converted to analog form by converter 154, use oscillator 150 to generate a stepwise frequency scan. The signal from the antenna goes to an A / D converter 156, where the digital output goes to a microcomputer 152, which stores such digital outputs.

The operation of the device of Figure 13 is described in conjunction with the waveforms of Figures 14 and 15. The output of the voltage controlled oscillator 150 is shown in Figure 14 and includes frequency stages, each of which occurs during a corresponding time slot or step number. Figure 15 shows the current through the antenna 90 with respect to time. In the absence of a resonant circuit, the current through the antenna decreases as the oscillator frequency increases, as shown by the linear portion of the waveform of Fig. 15. When the resonant circuit 92 is present near the antenna 90, the impedance of the resonant circuit is reflected to the antenna and causes a sudden decrease in the antenna current, as shown in Fig. 15. The converter 156 converts the current flowing through the antenna into digital values which are stored in the memory of the microcomputer 152. The step number corresponding to the minimum value of the stored current values corresponds to the approximate resonant frequency of the flag circuit. The stored digital value representing the resonant frequency is converted to an analog signal for controlling the oscillator 150 to provide an output at the resonant frequency for activating the deactivation system 100 (Fig. 7) and destroying the resonant characteristics of the flag circuit 92.

The deactivation energy is applied for a predetermined time 30 depending on the time for deactivating the ticket. After deactivation, the ticket sensing system 94 operates and detects the presence of the flag, and if the flag is deactivated, the pointer 98 receives voltage and indicates that deactivation has occurred. If the flag 92 continues to operate at the resonant frequency detected by the system 35 94, the deactivation system 100 will be triggered again for the second deactivation period. The deactivation cycle is repeated a specified number of times until deactivation occurs. If deactivation has not taken place after a predetermined number of cycles, the detector may receive a voltage and indicate to the user that 5. the flag is not deactivated. The user can then manually activate the deactivation system to deactivate the flag, or he can take other measures to deactivate or destroy the flag.

Once the resonant flag circuit 92 is detected by the flag sensing system 94, it may alternatively cause the deactivation system 100 to operate the antenna 102 with a relatively effective signal that is slowly swept frequency through the resonant frequency of the flag 92. The device can operate so that it alternately detects the presence and activates the deactivation field 15 cyclically until the flag is deactivated. Again, an appropriate expression can tell the user if a particular flag has not been deactivated.

If a dual frequency flag circuit is used, the flag sensing system 94 operates to detect the resonant detection frequency of the flag 20, and the deactivation system 100 provides power at the resonant deactivation frequency of the flag. U.S. Pat. No. 3,938,044 to the same inventor describes a device suitable for deactivating and detecting a dual frequency flag.

Figures 8 and 9 show resonant circuits having an alternative structure, and it is apparent that these are similar to the corresponding circuits in Figures 1 and 2. In the embodiments of Figures 8 and 9, a notch is made at one or more selected locations in one or both of the capacitor plates. to reduce the thickness of the film at this notch and thus to reduce the voltage required to provide an arc across the capacitor plates. In the embodiment of Figure 8, a notch is shown in the target receiver plate 12a. In the embodiment of Figure 9, the notch is shown in the capacitor plate 24a. When a sufficiently large energy is applied at the resonant frequency of the flag, an electrical breakdown occurs through the insulating film at the notch, and because the energy is coupled to the flag, an arc can remain and form a plasma between the capacitor plates. Due to the Q value of the resonant circuit, very little 5 energy is converted into heat in the resonant circuit itself and the energy is converted into heat in the arc formed between the plates. The energy of the arc rapidly heats the plasma and causes the metal forming the capacitor plates to evaporate. Evaporated metal conducts the arc and short-circuits the capacitor plates, temporarily destroying the resonant properties of the circuit and rapidly terminating the current flowing through the arc and the voltage across the arc. Therefore, the arc cools and causes the previously vaporized metal to form as a layer between the capacitor plates.

If a short circuit occurs, the flag is permanently destroyed. If a short circuit does not occur, a voltage is again generated across the capacitor plates in response to the connected energy, and the process is repeated. Since the plastic film has already been punctured and hei-20 hardened at the breakthrough point, the arc will normally form again at the same point and new metal will vaporize and deposit until a permanent short circuit occurs. Figures 10-12 show deactivation events. Figure 10 shows how the voltage breakdown begins through the plastic film 100 and between the plates 25 112 and 114. Figure 11 shows the formation of plasma after the discharge of the sheet and Figure 12 shows the final deposition of metal along the discharge path to cause a short circuit in the capacitor plates.

If the deactivation power is too high, it is possible to burn off part of the capacitor plate without forming a short circuit over the plates. This causes a small change in the resonant frequency each time an arc is formed and the voltage runs out until the arc can no longer form, even though the flag still has a resonant frequency. The deactivation power must be precisely controlled or the deactivation process must be monitored electronically to switch off the deactivator just after the first arc of the i3 84668 has been formed. The deactivator can again receive the voltage cyclically as described until a permanent short circuit has developed over the capacitor plates. Since the deactivator antenna is connected to the flag circuit, the impedance of the flag circuit is reflected back to the deactivation antenna. Once the arc is formed, the impedance of the resonant circuit changes abruptly and this change is reflected directly back to the deactivation antenna and can be detected by the deactivation system and can accurately control the deactivation system. Thus, when a sudden change in the deactivation antenna current caused by a change in impedance in the resonant flag circuit in response to arc breakdown is observed, the deactivation system can be disconnected and cyclically reconnected. en deactivation.

The deactivation system 100 can be controlled as shown in Fig. 20 16. The flag sensing system 94 provides a flag signal in response to a scanned high frequency signal passing through the resonant frequency of the flag circuit, and this signal is fed to a sharp cut-off high pass filter 160. The filter 160 filters out all of the modulation components and the flag signal spectrum. When an arc is formed over the capacitor plates, a relatively large and sudden change in current through the antenna 90 results, and this signal passes through a high pass filter 160 to a threshold detector 30 162 which triggers a timer 164 that determines the time interval for the operation of the flag deactivation system 100. The operation cycle can be repeated as needed to deactivate the resonant characteristics of the flag circuit.

The invention is not limited to what is shown and described in more detail, except as defined in the appended claims.

Claims (12)

14 84668 A resonant flag circuit comprising: a planar substrate (14; 42; 62) of dielectric material, a tuned circuit having a planar circuit structure disposed on the substrate, which resonates at the detection frequency of the flag circuit within a predetermined range; the tuned circuit having a pair of conductive regions 10 (10.12; 22.24; 46.50; 66.74; 10a, 12a; 22a, 28a) opposite each other on opposite sides of the substrate defining a capacitor (C1) of the tuned circuit; and means for deactivating the flag circuit in response to the deactivation frequency; 15. characterized in that the deactivation means comprise means (20; 32; 56; 82; 24a) in the conductive regions defining a path between the conductive regions and through the substrate, where the arc discharge is primarily in response to an electromagnetic field with a sufficiently deactivating frequency of energy content. to destroy or change the resonant properties at the detection frequency. Flag circuit according to claim 1, characterized in that said deactivation means (20; 32; 56; 25 82; 24a) comprise an embedded part in at least one conductive region (12; 24; 50; 72; 72; 28a) which provides the embedded part at a distance between the conductive regions (10,12; 22,24; 46,50; 10a, 12a; 22a, 28a) which is less than the distance between the conductive regions outside the embedded region. A flag circuit according to claim 1 or 2, characterized in that the arc discharge causes overheating to destroy or change the resonant characteristics of the circuit tuned to one conductive region (12; 24; 50; 75) in the path leading to said detection frequency 84668. A flag circuit according to claim 1 or 2, characterized in that the arc discharge causes a short circuit on the path 5 between the conductive regions (10a, 12a; 22a, 28a) to destroy or change the resonant characteristics of the circuit tuned at said detection frequency. A flag circuit according to any one of the preceding claims, characterized in that the deactivation frequency is equal to or approximately equal to the detection frequency, or is located within the same predetermined range, and is at a higher energy level than the detection frequency, and that said the tuned circuit comprises a single resonance detection / deactivation circuit (L1, 10,12; 40,46, 50; L1, 10a, 12a), and wherein the deactivation means (20; 56; 12a) 15 destroys or alters the single resonance detection / Resonant characteristics of the deactivation circuit in response to an electromagnetic field at the deactivation frequency. A flag circuit according to any one of claims 1 to 4, characterized in that the deactivation frequency is outside a predetermined range, and in that said tuned circuit comprises a detection circuit resonant at the detection frequency (L1, 10,12; 60,66,74; L1, 10b, 12b) on said substrate, and on said substrate of a deactivation frequency (L2,22,24; 68,64,72; L2,22a, 24a) having a planar circuit structure resonating at a deactivation frequency, deactivation means (32; 82; 24a) destroying or altering the resonant characteristics of the detection circuit in said predetermined range in response to an electromagnetic field at a deactivation frequency. An electronic security system for detecting a resonant flag circuit having capacitor plates on opposite sides of a substrate and electronically deactivating the resonant characteristics of the flag circuit, comprising: means for generating an electromagnetic field, the frequency of which is sweepable within a range; means (94) for detecting the resonance of the flag circuit in said frequency; and 5 means (100) for deactivating the flag circuit; characterized in that the deactivation means (100) operate in the presence of a resonant flag circuit to produce an electromagnetic field at the resonant frequency of the flag circuit having sufficient energy to cause an arc discharge between capacitor plates through the substrate to destroy or alter the resonant characteristics of the flag circuit. A system according to claim 7, characterized in that the deactivation means (100) 15 cause a short circuit between the capacitor plates in order to destroy or change the resonant characteristics of the flag circuit. A system according to claim 7, characterized in that the deactivation means (100) 20 causes gassing of the conductive region of the flag circuit to destroy or change the resonant characteristics of the flag circuit. A system according to any one of claims 7 to 9, characterized by: comprising: (96) means for indicating the presence of a resonant flag circuit to be detected; and means (98) for deactivating the resonant characteristics of the flag circuit. System according to any one of claims 7 to 10, characterized in that the deactivation means comprise: means (162) for detecting an arc discharge over the capacitor plates of the resonant flag circuit, and for generating a signal representative thereof; and 35 means (164) for determining the operating time of the deactivation means based on said signal. An electronic security system for detecting a resonant flag circuit according to any one of claims 1 to 8, and for electronically deactivating the resonant characteristics of the flag circuit, comprising: means for generating an electromagnetic field whose frequency is sweepable within a predetermined range; means (94) for operating the resonant frequency of the flag circuit in said range; and means (100) for deactivating the flag circuit; characterized in that the deactivation means (100) operate in the presence of a resonant flag circuit to produce a resonant frequency electromagnetic field having sufficient energy to cause an arc discharge between said conductive regions through the substrate to destroy or alter the resonant properties of the flag circuit. 18 84668