A frequency-division marker for an electronic article surveillance system

ES 2 297 545 T3

DESCRIPTION

Marker by frequency division for electronic article surveillance system.

Background

An Electronic Item Surveillance (EAS) system is designed to prevent unauthorized removal of an item from a controlled area. A typical EAS system may comprise a monitoring system and one or more security tags. The monitoring system can create an interrogation zone at an access point to the controlled area. A security tag can be attached to an article, such as a garment. If the tagged article enters the interrogation zone, an alarm may be triggered indicating an unauthorized removal of the tagged article from the controlled area.

EAS systems typically use the radio frequency (RF) spectrum to transmit signals between the monitoring system and the security tags. However, certain EAS systems may have only a limited amount of RF spectrum available to transmit such signals. As a consequence, there may be a need for improvements in EAS systems to take advantage of the availability of the RF spectrum.

US 2001/0040507 A1 shows a radio frequency detection and identification system. Especially shown is a marker for use in an EAS system having a first resonant circuit comprising a first coil and a second resonant circuit comprising a second coil. Both coils are flattened and are connected to first and second capacitors. The fields of the first and second resonant circuits are mutually coupled. Both circuits form an electrical circuit by the mutual connection of the wires.

US 5,517,179 shows a battery-free portable frequency division system, especially a transponder, which can be used in detection systems for article surveillance. The system also comprises two resonant circuits, which are connected by wire to form an electrical circuit. One of the resonant circuits includes a variable capacitor element.

Brief description of the drawings

The matter of the object that is considered as the embodiment is particularly pointed out and distinctly claimed in the concluding portion of the specification. However, the embodiments, both in terms of organization and operating procedure, together with objectives, characteristics and advantages thereof, can be better understood with reference to the detailed description that follows when read in conjunction with the accompanying drawings, in which:

Figure 1 illustrates an EAS system suitable for practicing one embodiment;

Figure 2 and illustrates a block diagram of a marker according to one embodiment;

Figure 3 is a block flow diagram of operations performed by a marker in accordance with one embodiment;

Figure 4 is a first circuit for the practical execution of a marker according to one embodiment; and Figure 5 is a second circuit for the practical execution of a marker according to one embodiment.

Detailed description

The embodiments may refer to an EAS system in general. More particularly, the embodiments may refer to a marker for an EAS security tag. The marker may comprise, for example, a frequency division marker configured to receive RF energy as input The frequency division marker can recondition the received RF energy and emit an output signal with a frequency that is less than that of the input RF energy In one embodiment, for example, the output signal may be half the frequency of the input RF energy. This type of frequency division marker may be suitable for use in low bandwidth conditions such as the Industrial, Scientific and Medical (ISM) Band of 13.56 Megahertz (MHz).

Conventional EAS systems are unable to effectively operate in the 13.56 MHz ISM band. Conventional EAS systems typically use a marker consisting of a single inductor-capacitor (LC) combination resonant circuit configured to resonate at a predetermined frequency. Due to the high operating frequency of the 13.56 MHz ISM band, such a marker may require an inductor with few turns, and a capacitor ranging from 10-100 picofarads (pF). However, detecting such a single resonance marker may require a relatively complicated detection system, such as "RF sweep" or "pulse" detection systems. An RF scanning detection system can generate signals and receive reflected signals in a relatively wide frequency range. An impulse detection system can create

ES 2 297 545 T3 a pulse of energy with a specific frequency to energize the marker, and then detect the marker signal waveform. In any case, the detection system requires generating power in a relatively wide spectrum that is not suitable for use with a 13.56 MHz system.

An EAS system that uses a frequency division dialer configured to operate in the 13.56 MHz ISM band can offer several advantages over conventional EAS systems. For example, the 13.56 MHz ISM band allows relatively high amounts of power to be transmitted, which can increase the detection range of an EAS system. In another example, an enhanced detector may be configured to perform continuous detection, and may use sophisticated signal processing techniques to improve the detection range. In yet another example, the relatively high operating frequency can allow the marker to have a relatively flat geometry as well as reduce degradation under constraints, thereby making it easier to apply the marker to a monitored item.

Numerous specific details may be set forth herein to provide a complete understanding of the embodiments of the invention. However, those skilled in the art will understand that embodiments of the invention can be practiced without these specific details. In other cases, well-known procedures, processes, components, and circuits have not been described in detail so as not to obscure embodiments of the invention. It can be appreciated that the specific structural and functional details shown in the present specification may be representative and do not necessarily limit the scope of the invention.

It is worth noting that any reference in the specification to "an embodiment" or "embodiment" means that a particular aspect, structure, or feature described in connection with the embodiment is included in at least one embodiment. The presence at various places in the specification of the term "in one embodiment" does not necessarily mean that they all refer to the same embodiment.

Referring now in detail to the drawings in which the same elements are designated by like reference numerals throughout, an EAS system suitable for practicing one embodiment is illustrated in Figure 1. Figure 1 is a block diagram of an EAS system 100. In one embodiment, for example, the EAS system 100 may comprise an EAS system configured to operate using a 13.56 MHz ISM band. However, the EAS system 100 can also be configured to operate using other portions of the RF spectrum, as desired for a given practical embodiment. The embodiments are not limited in this context.

As shown in Figure 1, the EAS system 100 may comprise a plurality of nodes. The term "node" as used herein can refer to a system, element, module, component, board, or device that can process a signal that represents information. The signal can be, for example, an electrical signal, an optical signal, an acoustic signal, a chemical signal, and others. The embodiments are not limited in this context.

As shown in FIG. 1, the EAS system 100 may comprise a transmitter 102, a security tag 106, a detector 112, and an alarm system 114. The security tag 106 may further comprise a marker 108. Although FIG. 1 shows a limited number of nodes, it can be appreciated that any number of nodes can be used in an EAS 100 system. The embodiments are not limited in this context.

In one embodiment, EAS system 100 may comprise a transmitter 102. Transmitter 102 may be configured to transmit one or more interrogation signals 104 in interrogation zone 116. Interrogation zone 116 may comprise an area between a set of pedestals of antennas arranged, for example, at the entry / exit point of a controlled area. The interrogation signals 104 may comprise electromagnetic radiation signals having a first predetermined frequency. In one embodiment, for example, the predetermined frequency can be 13.56 MHz. Interrogation signals 110 can trigger a response from a security tag, such as a security tag 106.

In one embodiment, the EAS system 100 may comprise a security tag 106. The security tag 106 may be designed to be attached to an item to be monitored. Examples of tagged items may include an article of clothing, a Digital Video Disc (DVD) or Compact Disc (CD), a jewelry box, a movie rental kit, packing material, and others. Security tag 106 was to comprise marker 108 encased within a security tag housing. The security tag housing can be hard or soft, depending on the item to which the security tag 106 is to be attached. The selection of housing can also vary depending on whether the security tag 106 is designed to be disposable or to be a reusable label. For example, a reusable security tag typically has a hard security tag housing to withstand the rigors of repeated attachment and detachment operations. A disposable security tag can have a hard or soft housing, depending on factors such as cost, size, type of tagged item, visual aesthetics, tagging situation (for example, tagged at source and tagged at the point of sale), and others. The embodiments are not limited in this context.

In one embodiment, the security tag 106 may comprise a marker 108. The marker 108 may comprise a frequency division device having an RF antenna for receiving interrogation signals, such as, for example, interrogation signals 104 for the transmitter 102. Dialer 108 may also comprise an RF sensor to output one or more dialer signals 110 in response to interrogation signals 104.

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The marker signals 110 may comprise electromagnetic radiation signals that have a second predetermined frequency that is different from the first predetermined frequency of the interrogation signals 104. In one embodiment, for example, the first predetermined frequency may be 13.56 MHz the second predetermined frequency may be one-half 13.56 MHz, or 6.78 MHz. Marker 108 can be explained in more detail with reference to Figures 2-5.

In one embodiment, EAS system 100 may comprise detector 112. Detector 112 may operate to detect the presence of security tag 106 within interrogation zone 116. For example, detector 112 may detect one or more Marker signals 110 from marker 108 from security tag 106. The presence of marker signals 110 indicates that an active security tag 106 is present in interrogation zone 116. In one embodiment, detector 112 may be configured to detect electromagnetic radiation having the second predetermined frequency of 6.78 MHz, which is half of the first predetermined frequency of 13.56 MHz generated by transmitter 102. Detector 112 It can generate a detection signal according to the detection of the security tag 106.

It is worth noting that since the marker signal is of a different frequency from the interrogation signal, a single frequency system can be used to detect the marker signal. Detector 112 can detect the marker signal as long as its front end circuitry is not saturated by the incoming 13.56 MHz fundamental signal. The use of the single frequency system can increase the processing time of the digital signal processor (DSP) to achieve better detection efficiency.

In one embodiment, the EAS system 100 may comprise an alarm system 114. The alarm system 114 may comprise any type of alarm system to provide an alarm in response to a detection signal. The detection signal can be received, for example, from the detector 112. The alarm system 114 was to comprise a user interface for programming conditions or rules to trigger an alarm. Examples of alarms may comprise an audible alarm, such as a siren or bells, a visual alarm such as flashing lights, or a silent alarm. A silent alarm may comprise, for example, an inaudible alarm such as a message to a monitoring system of a security company. The message can be sent by means of the computer network, a telephone network, an announcement system and others. The embodiments are not limited in this context.

In general operation, the EAS100 system can perform anti-theft operations in a controlled area. For example, transmitter 102 can send interrogation signals 104 to interrogation area 116. When security tag 106 is within the interrogation area, marker 108 can receive interrogation signals 104. Marker 108 may generate marker signals 110 in response to interrogation signals 104. Marker signals 110 may be approximately half the frequency of interrogation signals 104. Detector 112 can detect marker signals 110 and generate a detection signal. The alarm system 114 may receive the detection signal and generate an alarm signal to trigger an alarm in response to the detection signals.

Figure 2 may illustrate a marker in accordance with one embodiment. Figure 2 may illustrate marker 200. Marker 200 may be representative of, for example, marker 108. Marker 200 may comprise one or more modules. Although the embodiment has been described with the expressions of "modules" to facilitate the description, one or more circuits, components, registers, processors, subroutines of logic programs or any combination thereof can be substituted by one, several or all of the modules. . The embodiments are not limited in this context.

As shown in Figure 2, marker 200 may comprise a dual resonance device. More particularly, marker 200 may comprise a first resonant circuit 202 connected to a second resonant circuit 204. Although Figure 2 shows a limited number of modules, it can be appreciated that any number of modules can be used in marker 200.

In one embodiment, marker 200 may comprise a first resonant circuit 202. First resonant circuit 202 may be an LC resonant circuit configured to receive interrogation signals 104. First resonant circuit 302 may be resonant at a first frequency F to receive radiation electromagnetic at the first frequency F. For example, the first resonant circuit 202 may generate a first resonant signal having a first resonant frequency in response to interrogation signals 110. The first resonant frequency may be, for example, about 13.56 MHz.

In one embodiment, marker 200 may comprise a second resonant circuit 204. Second resonant circuit 204 may also be an LC resonant circuit configured to receive the first resonant signal from resonant circuit 202. Second resonant circuit 304 may be resonant to a second. frequency F / 2 which is half of the first frequency F to transmit electromagnetic radiation at the second frequency F / 2. For example, the second resonant circuit 204 may generate a second resonant signal that has a second resonant frequency in response to the first resonant signal. The second resonant frequency can be, for example, about 6.78 MHz.

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In one embodiment, the first resonant circuit 202 and the second resonant circuit 204 may be located relatively to each other such that both circuits are magnetically coupled. Magnetic coupling may allow the first resonant circuit 202 to transfer energy to the second resonant circuit 204 at the first frequency F in response to the reception by the first resonant circuit 202 of electromagnetic radiation at the first frequency F. The second resonant circuit 204 may be configured with a voltage-dependent variable capacitor in which the reactance varies with variations in energy transferred from the first resonant circuit 202. This variation may cause the second resonant circuit 204 to transmit electromagnetic radiation to the second. frequency F / 12 in response to the energy transferred from the first resonant circuit 202 at frequency F.

Figure 3 illustrates operations of a marker in accordance with one embodiment. Although Figure 3, as presented in the present specification, may include a particular set of operations, it can be appreciated that the operations only provide an example of how the general functionality described in the present specification can be performed in practice. Furthermore, the given operations do not necessarily have to be executed in the order presented, unless otherwise indicated. The embodiments are not limited in this context.

FIG. 3 illustrates a marker operation flow 300 that may be representative of operations performed by marker 200 in accordance with one embodiment. As shown in stream 300, an interrogation signal can be received in the first resonant circuit for a marker in block 302. A first resonant signal having a first resonant frequency can be generated in response to the interrogation signal in the block 304. The first resonant signal can be received in a second resonant circuit that overlaps the first resonant circuit in block 306. A second resonant signal having a second resonant frequency can be generated in response to the first resonant signal, the second being different. resonant frequency of the first resonant frequency in block 308. For example, the second resonant frequency may be approximately half of the first resonant frequency.

Fig. 4 is a first circuit for practically executing a marker in accordance with one embodiment. Figure 4 illustrates a circuit 400. Circuit 400 may comprise a dual resonance configuration for marker 200. In one embodiment, circuit 400 may comprise a first resonant circuit 402 and a second resonant circuit 404.

In one embodiment, circuit 400 may comprise one or more flattened coils. The term "flattened coil" as used herein can refer to a coil having a relatively flat geometry. For example, the flattened coil may be less than 1mm thick. In another example, the flattened coil can be approximately 0.2mm or 200 microns thick. The thickness of any given flattened coil can vary according to a given practical implementation, and the embodiments are not limited in that context.

In one embodiment, circuit 400 may comprise a first resonant circuit 402. First resonant circuit 402 may comprise a linear inductor-capacitor combination. For example, the first resonant circuit 402 may comprise a first flattened coil 406 having a pair of terminals and a capacitor C1 connected to the pair of terminals. The capacitor C1 can comprise a linear or a non-linear capacitor, depending on a given practical implementation. In one embodiment, for example, capacitor C1 may comprise a linear capacitor. The first resonant circuit 402 may be resonant at a first predetermined frequency when it receives electromagnetic radiation at the first predetermined frequency. The number of turns of the first flattened coil 406 may vary depending on the frequency of the interrogation signals 104. With an operating frequency of 13.56 MHz, the first flattened coil 406 may be approximately 10 turns, which may be sufficient for the resonance and transmitter coupling necessary to induce the appropriate operating voltage. When it receives electromagnetic energy from transmitter 102, the first resonant circuit stores and amplifies the field. The field can be passed to a second resonant circuit 404 through magnetic coupling which will be discussed later.

In one embodiment, circuit 400 may comprise a second resonant circuit 404. Second resonant circuit 404 may comprise a non-linear inductor-capacitor combination. For example, the second resonant circuit 404 may comprise a second flattened coil 408 having a pair of terminals and a non-linear capacitor D1 connected to the pair of terminals. The non-linear capacitor D1 can function as a voltage-dependent variable capacitor. The second resonant circuit 404 may receive the expanded field of the first resonant circuit 402, and generate a second resonant signal at a second resonant frequency that is half the frequency of the interrogation signal and the first resonant signal. In one embodiment, the second resonant circuit 404 can generate the second resonant signal at 6.78 MHz with a magnetic field threshold of approximately 10 mA / m rms.

An advantage of circuit 400 is that it can have a lower magnetic field threshold compared to conventional frequency division circuits. The frequency division process has a minimum threshold below which it will not work. Therefore, the transmission field at the marker must exceed a minimum magnetic field threshold. The lower the threshold, the more sensitive the marker will be. Conventional frequency division markers using an inductor-zener diode combination can have a turn-on threshold of approximately 100 mA / m rms. In one embodiment, circuit 400 may output a signal from

ES 2 297 545 T3 marker at 6.78 MHz with a magnetic field threshold of approximately 10 mA / m rms. As a result, marker 207 using circuit 400 can produce a more sensitive marker for improved EAS functionality.

As shown in Figure 4, a first flattened coil 406 and a second flattened coil 408 are positioned so that they overlap each other by a predetermined amount to form a double tuned circuit. The amount of overlap determines the degree of mutual coupling k between the magnetic fields of each resonant circuit. To perform frequency division, the coupling coefficient k between the first flattened coil 406 of the first resonant circuit 402 and the second flattened coil 408 of the second resonant circuit 404 should be in a range of 0.0 to 0.6. In one embodiment, for example, k can be 0.3 to produce sufficient coupling between the fields.

The second resonant circuit 404 can use a number of different non-linear capacitors such as D1. For example, the non-linear capacitor D1 can be implemented in practice using a zener diode, a varactor, a metal oxide semiconductor (MOS) capacitor, and others. The particular non-linear condenser element can be determined according to a number of different factors. For example, one factor can be the non-linearity of capacity (dC / dV). The loop at the magnetic field threshold can depend on the dC / dV value with a zero voltage bias condition. The higher the dC / dV value, the lower the threshold. In another example, a factor may be capacitive dissipation (Df). The dissipation factor determines the amount of energy an LC resonant circuit can store. The lower Df, the more efficiently the circuit can operate. Other factors such as the inductor-capacitance ratio and coil loss can also influence frequency division functionality.

An MOS capacitor can also be used as a non-linear element. An MOS capacitor can offer superior dC / dV characteristics. This can significantly improve the sensitivity of the device. Furthermore, proximate deactivation can be achieved by means of a breakdown mechanism of the MOS device. The MOS breakdown voltage can be controlled by adjusting the thickness of the oxide layers. To deactivate, a frequency F / 2 can be generated and resonated in the non-linear capacitor inductor resonator until the MOS breakdown voltage is reached.

Fig. 5 is a second circuit for practically executing a marker in accordance with one embodiment. Figure 5 illustrates a circuit 500. Circuit 500 may comprise a different dual resonant configuration for marker 200. In one embodiment, circuit 500 may comprise a first resonant circuit 502 and a second resonant circuit 504. The first resonant circuit 502 and the second resonant circuit 504 may be similar to the first resonant circuit 402 and the second resonant circuit 404, respectively. The first resonant circuit 502 may comprise a flattened first coil 506 and a linear capacitor C1. The second resonant circuit 504 may comprise a second flattened coil 508 and a non-linear capacitor D1.

In one embodiment, circuit 500 comprises a coil arrangement to achieve a 0.3 coupling. Circuit 500 may illustrate a dual resonance configuration that has one LC resonant circuit within another LC resonant circuit. As shown in circuit 500, second resonant circuit 504 may be nested within first flattened coil 506 of first resonant circuit 502. By placing the F resonant circuit outside of the F / 2 resonant circuit, this configuration can provide improved sensitivity by increasing the field capture area. Although the circuit 500 shows a second resonant circuit 504 that is nested within the first flattened coil 506, it will be appreciated that the reverse configuration can be implemented in practice and is still within the scope of the embodiments. The embodiments are not limited in this context.

Frequency division markers, such as circuits 400 and 500, can be manufactured in a number of different ways. For example, the inducing metal pattern can be deposited, etched, stamped, or otherwise positioned on a thin, flexible substrate. The non-linear capacitor can be attached to the terminals of the inductor. Conventional bonding techniques can produce a marker that has a slight protrusion due to the placement of the non-linear condenser element. To avoid this overhang, an organic semiconductor process can be used. The organic semiconductor process can manufacture conductor patterns and non-linear capacitor elements on a single flexible substrate on a serial production scale. The embodiments are not limited in this context.

Although the embodiments have been explained in terms of dual resonance configurations, it will be appreciated that a single LC resonant circuit can also be implemented in practice using the principles that have been explained herein. For example, a single LC resonant circuit comprising a non-linear capacitor and a flattened coil can be configured to operate in the 13.56 MHz band. Higher operating frequencies can produce reduced geometries and lower form factors for the single LC resonant circuit, while still emitting a detectable resonant signal at the appropriate frequency. The embodiments are not limited in this context.

One or more embodiments, or portions of embodiments, can be implemented in practice using an architecture that can vary according to any number of factors, such as computational speed, power levels, thermal tolerances, process cycle budgets, input data rates, output data rates, memory resources, data bus speeds, and other desired efficiency limitations. For example, a

ES 2 297 545 T3 portion of an embodiment can be implemented in practice using a logic program executed by a processor. The processor can be a dedicated or general purpose processor such as an Intel-built processor.^® Corporation, for example. The logic program may comprise segments of computer program code, programming logic, instructions, or data. The logic program can be stored on a medium accessible by a machine, computer, or other process system. Examples of acceptable media may include computer-readable media such as read-only memory (ROM), random access memory (RAM), programmable ROM (PROM), erasable PROM (EPROM), magnetic disk, optical disk, and others. In one embodiment, the medium can store programming instructions in a compressed and / or compiled format, as well as instructions that may have to be compiled or installed by an installer before being executed by the processor. In another example, a portion of an embodiment may be implemented in practice by dedicated hardware, such as an Application Specific Integrated Circuit (ASIC), a Programmable Logic Device (PLP) or DSP, and accompanying equipment structures. In yet another example, a portion of an embodiment may be implemented in practice by any combination of programmed general purpose components and custom hardware components. The embodiments are not limited in this context.