Abstract:
A method, system and computer program product for inhibiting detection of deactivated tags. The method, system and computer program product include receiving a signal that includes environment noise from at least one tag, extracting signal detection information that includes a signal detection energy value from the received signal, extracting signal deactivation information that includes a signal deactivation energy value from the received signal, and determining a failure to deactivate ratio that corresponds to the signal detection energy value divided by the signal deactivation energy value. Generation of an alarm event is inhibited upon the failure to deactivate ratio being less than the selectable threshold and generating a noise factor to adjust a selectable threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to and claims priority to U.S. Provisional Application Ser. No. 60/933,708, filed Jun. 8, 2007, entitled Narrow Band QMF Output and Adaptive Threshold for Inhibiting Detection of Deactivated Labels, the entirety of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    n/a 
       FIELD OF THE INVENTION 
       [0003]    The present invention generally relates to electronic security systems, and in particular, to electronic article surveillance (“EAS”) detection filtering and a method for inhibiting detection of deactivated tags in a security system 
       BACKGROUND OF THE INVENTION 
       [0004]    Electronic article surveillance (“EAS”) systems are detection systems that allow the identification of a marker, tag or label within a given detection zone. EAS systems have many uses, but most often they are used as security systems for preventing shoplifting in stores or removal of property in office buildings. EAS systems come in many different forms and make use of a number of different technologies. 
         [0005]    A typical EAS system includes an electronic detection unit, tags, labels and/or markers, and a detacher or deactivator. The detection units can, for example, be formed as pedestal units, buried under floors, mounted on walls, or hung from ceilings. The detection units are usually placed in high traffic areas, such as entrances and exits of stores or office buildings. The tags, labels and/or markers have special characteristics and are specifically designed to be affixed to or embedded in merchandise or other objects sought to be protected. When an active tag passes through a tag detection zone, the EAS system sounds an alarm, a light is activated and/or some other suitable alert devices are activated to indicate the removal of the tag from the prescribed area. 
         [0006]    Common EAS systems operate with these same general principles using either transceivers, which each transmit and receive, or a separate transmitter and receiver. Typically the transmitter is placed on one side of the detection zone and the receiver is placed on the opposite side of the detection zone. The transmitter produces a predetermined excitation signal in a tag detection zone. In the case of a retail store, this detection zone is usually formed at an exit. When an EAS tag enters the detection zone, the tag has a characteristic response to the excitation signal, which can be detected. For example, the tag may respond to the signal sent by the transmitter by using a simple semiconductor junction, a tuned circuit composed of an inductor and capacitor, soft magnetic strips or wires, or vibrating magneto acoustic resonators. The receiver subsequently detects this characteristic response. By design, the characteristic response of the tag is distinctive and not likely to be created by natural circumstances. 
         [0007]    An consideration in connection with the use of such EAS systems is to minimize the occurrence of false alarms which could either cause embarrassment to customers of an EAS system user, e.g., a retail store, or produce annoying and disruptive alarm signals when no one is passing through the store&#39;s EAS system or when a tag has not been properly deactivated. 
         [0008]    Failure to deactivate (“FTD”) is a major complaint affecting all EAS detection platforms. This undesirable side effect poses a serious confidence issue to system users, who inadvertently grow accustomed to “deactivated” tags triggering an alarm, thus, ignoring valid alarm events where live tags are involved. This phenomenon occurs when a tag, or label, is not properly deactivated and still carries some properties of a live tag, mainly a spectral (frequency) property. Theoretically, the natural frequency (characteristic frequency) of a live tag is approximately 58 kHz. Consequently, many detection platforms are designed to have approximate operating frequencies of 57.8 kHz to 58.2 kHz. When a tag is properly deactivated, its characteristic frequency is typically shifted to the 60 kHz range, to effectively place the tag outside of the desired frequency detection range, and thus the tag can no longer trigger an alarm event. A partially deactivated or “wounded” tag, however, can have its characteristic frequency shifted to the 59 kHz range and can potentially be detected, especially if the tag&#39;s energy is large enough at its new spectral (frequency) attribute. Statistically, about 10%-15% of tags being deactivated are really only wounded tags that are not thoroughly neutralized, and therefore result in relatively high occurrence of FTD events for system users. 
         [0009]    Attempts to resolve the FTD issue have included digital frequency estimators using a Tabei and Musicus technique, which is a very complex algorithm that produces nonlinear output responses. Frequency estimators suffer from a phenomenon referred to as “threshold effect”. Threshold effect occurs when a frequency estimator performs satisfactorily above some minimum input signal-to-noise ratio (“SNR”), but degrades very rapidly below that minimum SNR. This problem is amplified by the fact that the frequency estimator must operate on the raw input signal, and a low minimum SNR will bring about inconsistent zero crossing points. These zero crossing points are the basis for the Tabei and Musicus technique and eventually lead to undependable frequency estimations. Therefore, a FTD criterion based on a frequency estimator is unreliable and leads to a high rate of false alarms caused by tags that have not been properly deactivated. 
         [0010]    What is needed is a method and system that can be used to inhibit detection of deactivated tags in a detection system. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention advantageously provides a method, system and computer program product for inhibiting detection of deactivated electronic article surveillance tags in a security system. In one embodiment, a method for inhibiting detection of deactivated tags in a security system can include receiving a signal that includes environment noise from at least one tag, extracting signal detection information that includes a signal detection energy value from the received signal, extracting signal deactivation information that includes a signal deactivation energy value from the received signal, determining a failure to deactivate ratio that corresponds to the signal detection energy value divided by the signal deactivation energy value, and inhibiting generation of an alarm event conditioned upon the failure to deactivate ratio being less than the selectable threshold. 
         [0012]    In accordance with another aspect, a system for inhibiting detection of deactivated tags in a security system is provided. The system includes a receiver that receives a signal that includes environment noise from at least one tag, a detection frequency filter that extracts signal detection information that includes a signal detection energy value from the received signal, and a deactivation frequency filter that extracts signal deactivation information that includes a signal deactivation energy value from the received signal. The system can also include a processor that operates to determine a failure to deactivate ratio that corresponds to the signal detection energy value divided by the signal deactivation energy value and inhibit the generation of an alarm event conditioned upon the failure to deactivate ratio being less than a selectable threshold. 
         [0013]    In accordance with another aspect, the present invention provides a computer program product including a computer usable medium having a computer readable program for a security system which when executed on a computer causes the computer to perform a method. The method includes receiving a signal that includes environment noise from at least one tag, extracting signal detection information that includes a signal detection energy value from the received signal, extracting signal deactivation information that includes a signal deactivation energy value from the received signal, determining a failure to deactivate ratio that corresponds to the signal detection energy value divided by the signal deactivation energy value and inhibiting generation of an alarm event conditioned upon the failure to deactivate ratio being less than the selectable threshold. 
         [0014]    Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0016]      FIG. 1  is a block diagram of an electronic article surveillance detection system constructed in accordance with the principles of the present invention; 
           [0017]      FIG. 2  is a block diagram of a detection filtering and deactivation filtering embodiment of the electronic article surveillance detection system of  FIG. 1  having a noise tracker and constructed in accordance with the principles of the present invention; and 
           [0018]      FIG. 3  is a flowchart of an exemplary process for inhibiting detection of deactivated labels in accordance with the principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring now to the drawing figures in which like reference designators refer to like elements, there is shown in  FIG. 1  a diagram of an exemplary system constructed in accordance with the principles of the present invention and designated generally as “100”. Electronic article surveillance (“EAS”) detection system  100  includes transceiver unit  102  configured to receive communication signals from an electronic tag, front-end processor  104  in communication with transceiver unit  102  to process the received electronic tag signals, detection frequency filter  106  and failure-to-deactivate (“FTD”) detector  108  in communication with front-end processor  104  for receiving samples of the received electronic tag signal from front-end processor  104 . Detection system  100  can further include a threshold calculator  110 , a detection criteria module  112  and an alarm decision module  114 . 
         [0020]    Transceiver unit  102  includes one or more antennas transmitting and receiving communication signals, in combination with related transmit and receive circuitry. Transceiver unit  102  receives communication signals from an electronic tag and provides these received signals to front-end processor  104 . Front-end processor  104  can include, for example, a demodulator in communication with one or more bandpass filters and analog to digital converters, a digital signal processor and various types of memory storage. Front-end processor  104  receives communication signals from transceiver unit  102  and processes the received communication signals to provide samples of the received communication signals to the detection frequency filter  106  and FTD detector  108 . 
         [0021]    Detection frequency filter  106  includes one or more detection quadrature matched filters (“QMF”) to extract signal information at a specific frequency or frequencies in a detection frequency range, e.g., 57,800 Hz to 58,200 Hz. FTD detector  108  includes one or more FTD QMF filters, e.g.,  202 ,  204  and  206  (as shown in  FIG. 2 ) that extracts signal information at a specific frequency in a FTD frequency range, e.g., 59,000 Hz to 59,300 Hz. 
         [0022]    Threshold calculator  110  provides for the establishment of a preset or selectable threshold value and the modification of that preset or selectable threshold value, which the threshold calculator  110  supplies to FTD detector  108  and alarm decision module  114 . Threshold calculator  110  can include QMF filters, summers, dividers, etc. Detection criteria module  112  can detect signal information, e.g., amplitude, energy level and phase of the received signal that has passed through the detection frequency filter  106  and the FTD detector  108 . Alarm decision module  114  receives the signal information from detection criteria module  112  and processes the signal information to determine whether to generate or inhibit an alarm. 
         [0023]    The temporal aspect of the present invention is discussed with reference to a single time slot during which signals and noise are measured. In operation, an interrogation signal is transmitted during a transmit window (“Tx”). Once the interrogation signal is transmitted, a tag window is provided during which time a response from the interrogated tag is expected and measured. A synchronization period to allow the signal environment to stabilize is provided after the tag window. The remaining portion of the time slot is the noise window during which time the communication environment is expected to be devoid of interrogation and response signals such that the noise component of the communication environment can be measured. 
         [0024]      FIG. 2  is a block diagram of an embodiment  300  of the detection filtering and deactivation filtering of the electronic article surveillance detection system  100  of  FIG. 1 . System  300  includes a tag detection system  200 , active during the tag window and a noise tracking system  302  active during the noise window. Thus, noise tracking system  302  and tag detection system  200  obtain data from different sources (exterior environmental noise and tag information respectively), and do so at different times. 
         [0025]    Tag detection system  200  includes detection QMF filters  202 ,  204  and  206 , e.g., QMF- 1 , QMF- 2  and QMF- 3 , which receive the sampled signal from front-end processor  104  and extract signal information at a specific frequency or frequencies in a detection frequency range, e.g., substantially 57,800 Hz, 58,000 Hz and 58,200 Hz. Another QMF filter  208 , e.g., QMF FTD, receives the received signal from front-end processor  104  and extracts signal information at a deactivation frequency, e.g., substantially 59,300 Hz. MAX calculator  210  receives the outputs of detection QMF filters  202 ,  204  and  206 . MAX calculator  210  determines the best QMF value  212  by comparing the signal detection energy values of the three signal detection outputs of QMF filters  202 ,  204  and  206 . MAX calculator  210  passes the best QMF value  212  to an energy comparison module  214 . Energy comparison module  214  divides the best QMF value  212  by the energy value of QMF FTD  208  to determine an FTD ratio  216 . 
         [0026]    An FTD ratio comparator  218  receives the FTD ratio  216  and compares it to a selectable preset threshold  220 , after it has been adjusted by a noise factor  326  (discussed below). If the FTD ratio  216  is greater than the selectable preset threshold  220 , an alarm event is generated. If the FTD ratio  216  is less than the selectable preset threshold  220 , the tag is determined to be a deactivated tag and the alarm event is inhibited. Although the tag window embodiment  200  illustrated in  FIG. 2  includes three detection QMF filters  202 ,  204  and  206 , it is contemplated that more or fewer detection QMF filters can be used in other embodiments. 
         [0027]    Included in system  300  is noise tracking system  302 . Although detection system  300  need not employ noise tracking system  302 , and can determine whether to inhibit or deploy an alarm by comparing the FTD ratio to a preset threshold value as described above solely through the use of the tag detection system active during the tag detection window  200 , noise tracking system  302  functions to compensate for excess noise in the environment of deployed detection system  300  by dynamically adjusting the selectable preset threshold  220 . In noise tracking system  302 , a noise factor  326  is generated and is injected directly into selectable preset threshold  220  via a multiplier  328  to provide a dynamic threshold  330  that is responsive to permanent or quasi-permanent noise sources in the deployment environment. Noise tracking system  302  includes noise detection QMF filters  304 ,  306  and  308 , e.g., QMF- 1 , QMF- 2  and QMF- 3 , and QMF FTD filter  310 , e.g., QMF FTD. Noise tracker system  302  further includes a MAX calculator  312 , which produces a detection frequency filter output such as a best QMF value  314 , a low pass filter (“LPF”)  316 , e.g., 20-tap LPF, producing a filtered best QMF value  318 , energy comparator  320 , LPF  322 , e.g., 20-tap LPF, which results in a filtered FTD value  324 , noise factor  326  and multiplier  328 . 
         [0028]    MAX calculator  312  passes the best QMF value  314  to 20-tap LPF  316  for filtering. 20-tap LPF  316  filter delays the received detection signal, e.g., the received tag signal, such that an instantaneous spike does not immediately change or influence the noise factor  326 . Similarly, 20-tap LPF  322  delays the received deactivation signal, e.g., the received tag signal, such that an instantaneous spike does not immediately change or influence the noise factor  326 . Instead, only a permanent or quasi-permanent noise source can gradually affect the noise factor  326 , which in turn adjusts the selectable preset threshold  220 . 
         [0029]    The inputting of the filtered QMF value  318  and the filtered FTD value  324  to energy comparator  320  advantageously allows the selectable preset threshold  220  to be dynamically adjusted such that the FTD criterion does not unfairly prevent legitimate tag alarms when there is high noise at the deactivation frequency band, e.g., at 59,300 Hz. In this embodiment, a 20-tap LPF is selected to provide a noise factor  326  that is a weighted average of the noise and received signal over twenty frames of data. It is contemplated that lowpass filters having more or less taps may be used in detection system  300 . 
         [0030]    Energy comparator block  320  divides the filtered best QMF value  318  by the filtered QMF FTD value  324  to determine the noise factor  326 . Multiplier  328  multiplies the selectable preset threshold  220  by the noise factor  326  to generate a dynamic threshold  330 . FTD ratio comparator  218  receives FTD ratio  216  and compares it to the dynamic threshold  330 . If the FTD ratio  216  is greater than the dynamic threshold  330 , then an alarm is generated. If the FTD ratio  216  is less than the dynamic threshold  330 , the tag is a deactivated tag and the alarm is inhibited. Although the embodiment illustrated in  FIG. 2  includes three detection QMF filters  304 ,  306  and  308 , it is contemplated that more or less detection QMF filters can be used in other embodiments. In addition, although separate elements, such as separate QMF filters, comparators and maximum value calculators are shown in tag detection system  200  and noise detection system  302 , it is understood that such depiction is merely to aid understanding of the present invention and that these elements can be the same physical element used by the different systems (tag detection system  200  and noise detection system  302 ) at different times. Such is the case because tag detection system  200  and noise detection system  302  are active during different time periods within the measurement time slot, thereby allowing component re-use. 
         [0031]      FIG. 3  is an exemplary process for inhibiting detection of deactivated labels in accordance with the principles of the present invention. Transceiver  102  is initialized (step S 402 ) and noise interference at the deployment site of detection system  100 ,  200  or  300  is initially obtained (step S 404 ). This information can be used to establish the preset threshold or the initial starting point for the dynamic threshold. Initial measurements can be taken by sampling the environment over a plurality of frames using, for example, noise detection system  302  to provide a weighted average of the noise a plurality of time slots. During the tag window, signal detection information, e.g., detection amplitude, detection energy level and detection frequency phase, is extracted from a received signal using detection filters  202 ,  204  and  206  (step S 406 ). Signal deactivation information, e.g., deactivation amplitude, deactivation energy level and deactivation frequency phase, is extracted from a received signal using QMF FTD filters  208  and/or  310  (step S 408 ). A failure-to-deactivate ratio  216  is determined by dividing the best QMF value  212  by the energy value of QMF FTD filter  208  (step S 410 ). 
         [0032]    As an optional step, noise factor  326  is computed based on noise data obtained during the noise window (step S 412 ). For example, one or more 20-tap lowpass filters  316 ,  322  are selected to provide a weighted average of the noise and received signal over a plurality of time slots, e.g., twenty time slots. In this embodiment, energy comparison block  320  computes or generates noise factor  326  by dividing a filtered best QMF  318  energy value by a filtered QMF FTD  324  energy value and designates that output as the best QMF  314 . The best QMF  314  passes to a 20-tap LPF  316 , which filters the best QMF  314  to smooth out signal and noise spikes. The 20-tap LPF  316  can also delay the received detection signal, e.g., the received tag signal, to provide a weighted average such that an instantaneous spike does not immediately change or influence the noise factor  326 . Similarly, 20-tap LPF  322  processes the output of deactivation QMF FTD  310  to provide the filtered QMF FTD  324  to energy comparison block  320 . Noise factor  326  can be combined with the selectable preset threshold  220  to generate dynamic threshold  330 . 
         [0033]    FTD ratio comparator  332  compares FTD ratio  216  to dynamic threshold  330  (step S 414 ). If the value of FTD ratio  216  exceeds the value of dynamic threshold  330 , an alarm is generated (step S 416 ). In other words, when the ratio of detection QMF filter energy level over deactivation QMF FTD filter energy level is greater than the value of dynamic threshold  330 , the tag should be an active tag and the system should generate an alarm event. Otherwise, the energy at the deactivation frequency, e.g., 59,300 Hz, should be greater than the energy at the detection frequency, e.g., 58,000 Hz, which indicates that the tag is a “wounded” tag, and alarm events should be inhibited (step S 418 ). 
         [0034]    The present invention advantageously provides a system for inhibiting alarm events caused by deactivated EAS tags or labels using energy level detection. The system further provides an adaptive threshold dynamic noise-tracker to reduce the effects of environmental noise. 
         [0035]    The present invention can be realized in hardware, software, or a combination of hardware and software. An implementation of the method and system of the present invention can be realized in a centralized fashion in one computing system or in a distributed fashion where different elements are spread across several interconnected computing systems. Any kind of computing system, or other apparatus adapted for carrying out the methods described herein, is suited to perform the functions described herein. 
         [0036]    A typical combination of hardware and software could be a specialized or general-purpose computer system having one or more processing elements and a computer program stored on a storage medium that, when loaded and executed, controls the computer system such that it carries out the methods described herein. The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which, when loaded in a computing system is able to carry out these methods. Storage medium refers to any volatile or non-volatile storage device. 
         [0037]    Computer program or application in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following a) conversion to another language, code or notation; b) reproduction in a different material form. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. Significantly, this invention can be embodied in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be had to the following claims, rather than to the foregoing specification, as indicating the scope of the invention. 
         [0038]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. A variety of modifications and variations are possible in light of the above teachings without departing from the spirit or essential attributes thereof, and accordingly, reference should be had to the following claims, rather than to the foregoing specification, as indicating the scope of the of the invention.