Electronic article surveillance systems implementing methods for determining security tag locations

Systems (100) and methods (600) for detecting a location of an EAS security tag (112). The methods involve: determining a first amplitude of a response signal generated by the EAS security tag and received at a first pedestal (102a), and a second amplitude of the response signal received at a second pedestal (102b); processing the first and second amplitudes to determine whether the EAS security tag resides within a specified distance range of the first or second pedestal, a detection zone of an EAS detection system, or a backfield of the EAS detection system; issuing an alarm when the EAS security tag is determined to reside within the specified distance range of the first/second pedestal or the detection zone of the EAS detection system; and preventing issuance of the alarm when the EAS security tag is determined to reside in the backfield of the EAS detection system.

BACKGROUND OF THE INVENTION

1. Statement of the Technical Field

The present invention relates generally to Electronic Article Surveillance (“EAS”) systems. More particularly, the present invention relates to EAS systems implementing methods for determining security tag locations relative to transceiver pedestals thereof.

2. Description of the Related Art

Electronic article surveillance (EAS) systems generally comprise an interrogation antenna for transmitting an electromagnetic signal into an interrogation zone, markers which respond in some known electromagnetic manner to the interrogation signal, an antenna for detecting the response of the marker, a signal analyzer for evaluating the signals produced by the detection antenna, and an alarm which indicates the presence of a marker in the interrogation zone. The alarm can then be the basis for initiating one or more appropriate responses depending upon the nature of the facility. Typically, the interrogation zone is in the vicinity of an exit from a facility such as a retail store, and the markers can be attached to articles such as items of merchandise or inventory.

One type of EAS system utilizes acoustomagnetic (AM) markers. The general operation of an AM EAS system is described in U.S. Pat. Nos. 4,510,489 and 4,510,490, the disclosure of which is herein incorporated by reference. The detection of markers in an AM EAS system by pedestals placed at an exit has always been specifically focused on detecting markers only within the spacing of the pedestals. However, the interrogation field generated by the pedestals may extend beyond the intended detection zone. For example, a first pedestal will generally include a main antenna field directed toward a detection zone located between the first pedestal and a second pedestal. When an exciter signal is applied at the first pedestal it will generate an electro-magnetic field of sufficient intensity so as to excite markers within the detection zone. Similarly, the second pedestal will generally include an antenna having a main antenna field directed toward the detection zone (and toward the first pedestal). An exciter signal applied at the second pedestal will also generate an electromagnetic field with sufficient intensity so as to excite markers within the detection zone. When a marker tag is excited in the detection zone, it will generate an electromagnetic signal which can usually be detected by receiving the signal at the antennas associated with the first and second pedestal.

It is generally desirable to direct all of the electromagnetic energy from each pedestal exclusively toward the detection zone between the two pedestals. As a practical matter, however, a certain portion of the electromagnetic energy will be radiated in other directions. For example, an antenna contained in an EAS pedestal will frequently include a backfield antenna lobe (“backfield”) which extends in a direction which is generally opposed from the direction of the main field. It is known that markers present in the backfield of antennas associated with the first or second pedestal may emit responsive signals, and create undesired alarms.

Several techniques have been implemented in the past to eliminate alarms causes by the backfield. One approach involves configuring the antenna in each pedestal in a manner which minimizes the actual extent of the backfield. Other solutions can involve changing from the traditional dual-transceiver pedestal to a TX pedestal/RX pedestal system, alternating TX/RX modes, and physical shielding of the antenna pedestals. A further approach involves correlating video analytics with marker signals. An ideal solution to the backfield problem is one which does not alter the detection performance of a system in a negative manner. For instance, although a system in which only one pedestal transmits and the other pedestal receives can reduce undesired alarms, pedestal separation in such a system must be reduced to accomplish the desired backfield reduction.

SUMMARY OF THE INVENTION

The present invention concerns implementing systems and methods for detecting a location of an EAS relative to an EAS detection system. The methods involve determining a first amplitude of a response signal generated by the EAS security tag and received at a first pedestal, and a second amplitude of the response signal received at a second pedestal spaced apart from the first pedestal. The first and second amplitudes are then processed to determine whether the EAS security tag resides within a specified distance range of the first or second pedestal, a detection zone of an EAS detection system, or a backfield of the EAS detection system. An alarm is issued when the EAS security tag is determined to reside within the specified distance range of the first or second pedestal or the detection zone of the EAS detection system. Issuance of the alarm is prevented when the EAS security tag is determined to reside in the backfield of the EAS detection system.

In some scenarios, the processing comprises: identifying which of the first and second amplitudes has the highest relative value; and determining whether the highest relative value exceeds a first threshold value. The alarm is issued when the highest relative value exceeds the first threshold value. The first threshold value is selected to facilitate an identification of an EAS security tag located within the specified distance range of a pedestal.

The processing may also comprise: computing a first ratio between the first and second amplitudes; and determining whether the first ratio exceeds a second threshold value. Issuance of the alarm is prevented when the first ratio is greater than a second threshold value. The second threshold value is selected to facilitate an identification of an EAS security tag located within the backfield of the EAS detection system.

The processing may further comprise: computing a second ratio between the first or second amplitude with the lowest value and an antenna mean noise amplitude for a corresponding one of the first and second pedestals; and determining if the second ratio is less than a third threshold value. The alarm is issued when the first ratio is less than the second threshold value and the second ratio is greater than a third threshold value. The third threshold value is selected to facilitate a detection of a false alarm condition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides a technique for identifying the approximate location of an EAS security tag with sufficient granularity to determine if the EAS security tag is located between a pair of EAS pedestals or behind one of the EAS pedestals in the “backfield.” The idea is to use detected amplitudes of signals respectively received at the pedestals and calculate a ratio of these detected amplitudes. The ratio indicates whether the EAS security tag is located between the pair of EAS pedestals or behind one of the EAS pedestals. For example, if the EAS security tag is at the center of an interrogation zone (i.e., the detection zone between the EAS pedestals), then the ratio will equal one. In contrast, if the EAS security tag moves towards one of the EAS pedestals, then the ratio will equal a value greater than one. A ratio range is then used to identify the interrogation zone between the EAS pedestals. In effect, the present invention provides a way to reduce undesired alarms of an EAS detection system having at least two transceiver pedestals between which an interrogation zone (or detection zone) is defined.

Notably, the solution of the present invention can be entirely implemented in software. As such, the present invention does not add new hardware or additional cost to existing EAS detection systems. Additionally, the present invention can also be readily ported to older EAS detection systems to enhance their performance accordingly. Furthermore, the present invention does not alter the detection performance of an EAS detection system in a negative manner.

Referring now toFIGS. 1 and 2, an exemplary architecture for an EAS detection system100is provided. Notably, the present invention is described herein in terms of an AM EAS system. However, the method of the invention can also be used in other types of EAS systems, including systems that use Radio Frequency (“RF”) type tags and Radio Frequency IDentification (“RFID”) EAS systems.

The EAS detection system100will be positioned at a location adjacent to an entry/exit104of a secured facility (e.g., a retail store). The EAS detection system100uses specially designed EAS marker tags (“security tags”) which are applied to store merchandise or other items which are stored within a secured facility. The security tags can be deactivated or removed by authorized personnel at the secure facility. For example, in a retail environment, the security tags could be removed by store employees. When an active security tag112is detected by the EAS detection system100in an idealized representation of an EAS detection zone108near the entry/exit, the EAS detection system will detect the presence of such security tag and will sound an alarm or generate some other suitable EAS response. Accordingly, the EAS detection system100is arranged for detecting and preventing the unauthorized removal of articles or products from controlled areas.

The EAS detection system100includes a pair of pedestals102a,102b, which are located a known distance apart (e.g., at opposing sides of entry/exit104). The pedestals102a,102bare typically stabilized and supported by a base106a,106b. The pedestals102a,102bwill each generally include one or more antennas that are suitable for aiding in the detection of the special EAS security tags, as described herein. For example, pedestal102acan include at least one antenna302suitable for transmitting or producing an electromagnetic exciter signal field and receiving response signals generated by security tags in the detection zone108. In some embodiments, the same antenna can be used for both receive and transmit functions. Similarly, pedestal102bcan include at least one antenna402suitable for transmitting or producing an electromagnetic exciter signal field and receiving response signals generated by security tags in the detection zone108. The antennas provided in pedestals102a,102bcan be conventional conductive wire coil or loop designs as are commonly used in AM type EAS pedestals. These antennas will sometimes be referred to herein as exciter coils. In some embodiments, a single antenna can be used in each pedestal. The single antenna is selectively coupled to the EAS receiver. The EAS transmitter is operated in a time multiplexed manner. However, it can be advantageous to include two antennas (or exciter coils) in each pedestal as shown inFIG. 1, with an upper antenna positioned above a lower antenna.

The antennas located in the pedestals102a,102bare electrically coupled to a system controller110. The system controller110controls the operation of the EAS detection system100to perform EAS functions as described herein. The system controller110can be located within a base106a,106bof one of the pedestals102a,102bor can be located within a separate chassis at a location nearby to the pedestals. For example, the system controller110can be located in a ceiling just above or adjacent to the pedestals102a,102b.

As noted above, the EAS detection systems comprises an AM type EAS detection system. As such, each antenna is used to generate an Electro-Magnetic (“EM”) field which serves as a security tag exciter signal. The security tag exciter signal causes a mechanical oscillation of a strip (e.g., a strip formed of a magnetostrictive or ferromagnetic amorphous metal) contained in a security tag within a detection zone108. As a result of the stimulus signal, the security tag will resonate and mechanically vibrate due to the effects of magnetostriction. This vibration will continue for a brief time after the stimulus signal is terminated. The vibration of the strip causes variations in its magnetic field, which can induce an AC signal in the receiver antenna. This induced signal is used to indicate a presence of the strip within the detection zone108. As noted above, the same antenna contained in a pedestal102a,102bcan serve as both the transmit antenna and the receive antenna. Accordingly, the antennas in each of pedestals102a,102bcan be used in several different modes to detect a security tag exciter signal. These modes will be described below in further detail.

Referring now toFIGS. 3 and 4, there are shown exemplary antenna field patterns300,400for antennas302,402contained in pedestals102a,102b. As is known in the art, an antenna radiation pattern is a graphical representation of the radiating (or receiving) properties for a given antenna as a function of space. The properties of an antenna are the same in a transmit and receive mode of operation. As such, the antenna radiation pattern shown is applicable for both transmit and receive operations as described herein. The exemplary antenna field patterns300,400shown inFIGS. 3-4are azimuth plane pattern representing the antenna pattern in the x, y coordinate plane. The azimuth pattern is represented in polar coordinate form and is sufficient for understanding the inventive arrangements. The azimuth antenna field patterns shown inFIGS. 3-4are a useful way of visualizing the direction in which the antennas302,402will transmit and receive signals at a particular power level.

The antenna field pattern300shown inFIG. 3includes a main lobe304with a peak at ø=0° and a backfield lobe306with a peak at angle ø=180°. Conversely, the antenna field pattern400shown inFIG. 4includes a main lobe404with its peak at ø=180° and a backfield lobe406with a peak at angle ø=0°. In the EAS detection system100, each pedestal102a,102bis positioned so that the main lobe of an antenna contained therein is directed into the detection zone108. Accordingly, a pair of pedestals102a,102bin the EAS detection system100will produce overlap in the antenna field patterns300,400, as shown inFIG. 5. Notably, the antenna field patterns300,400shown inFIG. 5are scaled for purposes of understanding the present invention. In particular, the patterns show the outer boundary or limits of an area in which an exciter signal of particular amplitude applied to antennas302,402will produce a detectable response in an EAS security tag. However, it should be understood that a security tag within the bounds of at least one antenna field pattern300,400will generate a detectable response when stimulated by an exciter signal.

The overlapping antenna field patterns300,400inFIG. 5will include an area A where there is overlap of main lobes304,404. However, it can be observed inFIG. 5that there can also be some overlap of a main lobe of each pedestal with a backfield lobe associated with the other pedestal. For example, it can be observed that the main lobe404overlaps with the backfield lobe306within an area B. Similarly, the main lobe304overlaps with the backfield lobe306in an area C. Area A between pedestals102a,102bdefines the detection zone108in which active security tags should cause the EAS detection system100to generate an alarm response. Security tags in area A are stimulated by energy associated with an exciter signal within the main lobes304,404and will produce a response which can be detected at each antenna. The response produced by a security tag in area A is detected within the main lobes of each antenna and processed in the system controller110. Notably, a security tag in areas B or C will also be excited by the antennas302,402. The response signal produced by a security tag in these areas B and C will also be received at one or both antennas. This condition is not desirable because it can produce EAS alarms at system controller110when there is in fact no security tag present within the detection zone108between the pedestals102a,102b. Accordingly, a method will now be described which is useful for determining when a detected security tag is within the detection zone (area A) or within the backfield zone (area B or area C). The process described herein is advantageous as it can be implemented in the EAS detection system100by simply updating the software in system controller110without modifying any of the other hardware elements associated with the system.

Referring now toFIG. 6, there is provided a flowchart of an exemplary method600for selectively issuing an alarm based on a detected location of an EAS security tag. Method600generally describes an inventive algorithm that compares the amplitude of a security tag response captured in antennas302,402, and then uses that information to prevent undesired alarms caused by EAS security tags present in the backfield lobe306,406of an antenna. Method600can be at least partially implemented by system controller110.

As shown inFIG. 6, method600begins at602and continues to604where the detection zone (e.g., area A) is monitored to determine if an active EAS security tag is present. An active EAS security tag is detected when a response signal transmitted therefrom is received by the pedestals102a,102bof the EAS detection system100. If an active EAS security tag is not detected by the pedestals [606:NO], then method600continues monitoring the detection zone. In contrast, if an active EAS security tag is detected by the pedestals [606:YES], then method600continues with step608where the response signal received at pedestal102ais further processed to determine an amplitude AMP102athereof. Similarly, the response signal received at pedestal102bis further processed to determine an amplitude AMP102bthereof.

Next in step610, the amplitudes AMP102aand AMP102bare analyzed to identify which of the pedestals102aor102bis associated with the highest valued amplitude. In this regard, each amplitude can be previously stored in a table format so as to be associated with the corresponding pedestal. In this case, step610involves: comparing the amplitudes AMP102aand AMP102bto each other to determine which one has the highest value; and accessing a table to obtain information specifying which pedestal is associated with the highest valued amplitude. For example, if amplitude AMP102ahas the highest value, then pedestal102awould be identified in step610. In contrast, if amplitude AMP102bhas the highest value, then pedestal102bwould be identified in step610.

Upon identifying a pedestal in step610, a decision step612is performed where it is determined if the highest valued amplitude (e.g., amplitude AMP102a) is greater than a first threshold value thr1. The first threshold value thr1is selected such that it is less than an amplitude AMP102aor AMP102bof a response signal transmitted from an EAS security tag located at a position less than N feet from the corresponding pedestal, where N is any number falling in a given range (e.g., 0 feet to 1.5 feet). If the highest valued amplitude (e.g., amplitude AMP102a) is greater than a first threshold value thr1[612:YES], then an alarm is issued in step614.). If the highest valued amplitude (e.g., amplitude AMP102a) is less than a first threshold value thr1[612:YES], then method600continues with step616.

In step616, a first ratio is computed between the two amplitudes AMP102aand AMP102b. A mathematical equation (1) defining the first ratio is now provided.
R1=AMPHighestValue/AMPLowestValue(1)
where R1represents the first ratio, AMPHighestValuerepresents an amplitude with the highest value (e.g., AMP102a), and AMPLowestValuerepresents an amplitude with the lowest value (e.g., AMP102b).

If the two amplitudes AMP102aand AMP102bhave the same value, then the first ratio R1equals one. As shown inFIG. 7, when the EAS security tag112resides at location700, it is the same distance from the antennas302,402of the pedestals102a,102b. In this case, the antennas302,402see the same amount of energy associated with the response signal transmitted from the EAS security tag112.

If amplitude AMP102ahas a higher value than amplitude AMP102b, the first ratio R1is defined by mathematical equation (2).
R1=AMP102a/AMP102b(2)
Accordingly, the first ratio R1has a value greater than one. As shown inFIG. 7, when the EAS security tag112resides at location702, it is closer to antenna302of pedestal102athan antenna402of pedestal102b. In this case, antenna302of pedestal102asees a greater amount of energy associated with a response signal transmitted from the EAS security tag112located at position702than that seen by antenna402of pedestal102b.

If the amplitude AMP102bhas a higher value than amplitude AMP102a, the first ratio R1is defined by mathematical equation (3).
R1=AMP102b/AMP102a(3)
Accordingly, the first ratio R1has a value greater than one. As shown inFIG. 7, when the EAS security tag112resides at location704, it is closer to antenna402of pedestal102bthan antenna302of pedestal102a. In this case, antenna402of pedestal102bsees a greater amount of energy associated with a response signal transmitted from the EAS security tag112located at position704than that seen by antenna302of pedestal102a.

Referring again toFIG. 6, method600continues with a decision step618. In step618, it is determined if the first ratio R1is less than a second threshold value thr2. When the first ratio R1is less than a second threshold value thr2, the EAS security tag112is deemed to be in the detection zone108. When the first ratio R1is greater than a second threshold value thr2, the EAS security tag112is deemed to be in the backfield. This concept can be readily understood with reference toFIG. 7. As shown inFIG. 7, when the EAS security tag112is positioned at location706, the amplitude AMP102ahas the same value as it would when the EAS security tag112is positioned at location702. However, the amplitude AMP102bis less than it would be when the EAS security tag112is positioned at location702. In effect, the value of the first ratio R1is greater when the EAS security tag112is positioned at location706as compared to when the EAS security tag112is positioned at location702. This is also true when the EAS security tag112is positioned at location708as compared to when the EAS security tag112is positioned at location704.

As shown inFIG. 6, the alarm is not issued when the first ratio R1has a value indicating that the EAS security tag112resides in the backfield. In this regard, the method600returns to step604in which the detection zone is monitored when a determination is made in step618that the first ratio is greater than the second threshold value thr2. When the first ratio R1has a value indicating that the EAS security tag112resides in the detection zone108, the method600continues with steps620-622to determine if the alarm should be issued.

Step620is generally performed to ensure that certain conditions do not cause issuance of a false alarm. An exemplary false alarm condition is readily understood with reference toFIG. 7. As shown inFIG. 7, an EAS security tag112may reside at a plurality of different locations702-710within a given environment. This environment has a certain amount of noise. As such, each pedestal antenna302,402also receives a noise signal with an amplitude AMPNoise. Let's first consider the scenario in which the EAS security tag112resides at location702. If the amplitude AMP102ahas a value of one hundred and the amplitude AMPNoisehas a value of fifty, then the first ratio R1has a value of two. Now, let's consider the scenario in which the EAS security tag112resides at location710. In this case, the antenna302of pedestal102adetects the response signal with an amplitude AMP102a. However, the antenna402of pedestal102bdoes not detect the response signal, but instead the noise signal with amplitude AMPNoise. If the amplitude AMP102ahas a value of twenty and the amplitude AMPNoisehas a value of ten, then the first ratio R1also has a value of two. Thus, the alarm may be falsely triggered when the EAS security tag112resides at location710.

Accordingly, steps620-622implement one method for detecting such a false alarm condition. In this regard, step620involves computing a second ratio R2between the lowest valued amplitude and a mean noise amplitude AMPMeanNoiseof the corresponding pedestal antenna302or402. For example, if the amplitude of a signal (e.g., response signal and/or noise signal) received at pedestal102bhas a relatively low value, than the second ratio R2is computed using the mean noise amplitude for antenna402. When the second ratio R2is greater than a third threshold value thr3, the alarm is issued as shown by step [622:YES]. When the second ratio R2is less than a third threshold value thr3, method600returns to step604such that the detection zone continues to be monitored.

Referring now toFIG. 8, there is provided a block diagram that is useful for understanding the arrangement of the system controller110. The system controller comprises a processor816(such as a micro-controller or Central Processing Unit (“CPU”)). The system controller also includes a computer readable storage medium, such as memory818on which is stored one or more sets of instructions (e.g., software code) configured to implement one or more of the methodologies, procedures or functions described herein. The instructions (i.e., computer software) can include an EAS detection module820to facilitate EAS detection and perform methods for selectively issuing an alarm based on a detected location of an EAS security tag, as described herein. These instructions can also reside, completely or at least partially, within the processor816during execution thereof.

The system also includes at least one EAS transceiver808, including transmitter circuitry810and receiver circuitry812. The transmitter and receiver circuitry are electrically coupled to antenna302and the antenna402. A suitable multiplexing arrangement can be provided to facilitate both receive and transmit operation using a single antenna (e.g. antenna302or402). Transmit operations can occur concurrently at antennas302,402after which receive operations can occur concurrently at each antenna to listen for marker tags which have been excited. Alternatively, transmit operations can be selectively controlled as described herein so that only one antenna is active at a time for transmitting security tag exciter signals for purposes of executing the various algorithms described herein. The antennas302,402can include an upper and lower antenna similar to those shown and described with respect toFIG. 1. Input exciter signals applied to the upper and lower antennas can be controlled by transmitter circuitry810or processor816so that the upper and lower antennas operate in a phase aiding or a phase opposed configuration as required.

Additional components of the system controller110can include a communication interface824configured to facilitate wired and/or wireless communications from the system controller110to a remotely located EAS system server. The system controller can also include a real-time clock, which is used for timing purposes, an alarm826(e.g. an audible alarm, a visual alarm, or both) which can be activated when an active EAS security tag is detected within the EAS detection zone108. A power supply828provides necessary electrical power to the various components of the system controller110. The electrical connections from the power supply to the various system components are omitted inFIG. 8so as to avoid obscuring the invention.

Those skilled in the art will appreciate that the system controller architecture illustrated inFIG. 8represents one possible example of a system architecture that can be used with the present invention. However, the invention is not limited in this regard and any other suitable architecture can be used in each case without limitation. Dedicated hardware implementations including, but not limited to, application-specific integrated circuits, programmable logic arrays, and other hardware devices can likewise be constructed to implement the methods described herein. It will be appreciated that the apparatus and systems of various inventive embodiments broadly include a variety of electronic and computer systems. Some embodiments may implement functions in two or more specific interconnected hardware modules or devices with related control and data signals communicated between and through the modules, or as portions of an application-specific integrated circuit. Thus, the exemplary system is applicable to software, firmware, and hardware implementations.

Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.