Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
  • G08B13/2468—Antenna in system and the related signal processing
  • G08B13/2477—Antenna or antenna activator circuit
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
  • G08B13/2468—Antenna in system and the related signal processing
  • G08B13/2471—Antenna signal processing by receiver or emitter
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
  • G08B13/2468—Antenna in system and the related signal processing
  • G08B13/2474—Antenna or antenna activator geometry, arrangement or layout
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
  • G08B13/2482—EAS methods, e.g. description of flow chart of the detection procedure

Definitions

• the present invention generally relates to electronic security systems, and in particular, to an improved electronic article surveillance system.
• tags of various different types which contain a circuit (a resonant circuit) for reacting with an applied radio-frequency field.
• a transmitter and a transmitting antenna are provided to develop this applied field, and a receiver and a receiving antenna are
• the applied field is affected in such fashion that a
• the transmitting antenna for the system now utilizes a "paired-lead" loop antenna configuration in place of the single-lead or single coaxial cable loop antennas of the prior art.
• paired-lead includes not only the twin-axial cable which is currently preferred for use but also other arrangements of two parallel leads, such as so-called “zip cords", paired coaxial cables and the like.
• one lead forms an "active" antenna loop, i.e. one which is driven by the transmitter circuitry, in the case of the transmitting antenna, and which drives the receiver circuitry in the case of the receiving antenna.
• the other lead forms a "passive" loop, i.e. one which is not driven or driving, but rather interacts with the respective active loop only through mutual coupling between them.
• the passive loop can then be appropriately passively loaded, and the combination of active and passive loop will then exhibit the desired flattened amplitude and linearized phase response. However, this beneficial effect will be obtained without substantially detracting from the efficiency of the antenna which is so configured.
• one of the paired leads preferably the passive one, can supply energizing signals from the receiver circuitry to the alarm devices of the system (e.g., warning light or buzzer), whenever a tag is detected.
• the receiver for the system is provided with improved means for detecting signals resulting from tags or labels passing in the vicinity of the receiving antenna,
• a linear phase (constant group delay) filter is used to more effectively preserve the signal which is received, and thereby improve the signal which is
• the processor is provided with a "hysteresis-type" threshold detector which operates to further preserve the original signal by improving the shape (width) of the pulse which is ultimately delivered to the processor following conversion from analog form, and an adaptive processing routine which varies the subsequent processing of
• detected signals according to changes within the system (primarily resulting from changes and/or imperfections in the manner in which the tag or label is presented to the transmitting and receiving antennas), to improve the system's ability to discriminate between the different signals which are received by the unit.
• Figure 1 is a block diagram of a conventional
• FIGS 2a and 2b are diagrammatic plan views showing an improved antenna system for use in conjunction with the transmitting and receiving portions of the electronic article surveillance system of Figure 1.
• FIG 3 is a schematic diagram of an equivalent circuit for the antenna systems shown in Figures 2a and 2b.
• Figure 4 is a graph which illustrates the frequency and phase response of the antenna systems shown in
• Figure 5 is a schematic diagram of an improved
• Figure 6 is a graph which illustrates the manner in which a received signal is processed by the receiver of Figure 5.
• Figure 7 is a graph which illustrates the manner in which the analog signals shown in Figure 6 are converted to a digital representation, for presentation to the processor.
• Figure 8 is a graph which illustrates the manner in which the processor operates to discriminate between the various digital signals which are received.
• Figure 9 is a schematic representation of a security system which incorporates a plurality of surveillance devices and supporting equipment in a single interactive environment.
• Figure 1 shows (in block diagram form) what generally constitutes the conventional components of an electronic article surveillance system 1 of the type manufactured by and available from Checkpoint Systems, Inc., of
• This system 1 includes a tag 2 which can be applied to any of a variety of different articles in accordance with known techniques.
• the tag 2 may take the form of a "hard” tag which is attachable to an article using the connecting pin with which this type of tag is generally provided.
• the tag 2 may take the form of a hang-tag which is appropriately tied to the article.
• the tag 2 may also take the form of a label adhesively affixed to the article. Any of a variety of types of tags and application techniques may be used to accomplish this general task.
• the tag 2 incorporates a resonant circuit (not shown) which is capable of reacting to applied fields of electromagnetic energy.
• a transmitting antenna 3 is provided which is capable of developing these applied fields responsive to the operation of associated transmitter circuitry 4.
• a receiving antenna 5 is provided for receiving
• the amplified signal is then applied to a detector 8 which essentially operates to recover (or demodulate) the active (base band) component which is used to detect the presence of a tag 2 in the vicinity of the electronic article surveillance system 1 from the high frequency (carrier) component of the signal which is required for use in conjunction with the transmitting and receiving antennas 3, 5.
• the base band signal which is isolated by the detector 8 is then applied to a filter 9 which operates to further attenuate undesirable low and high frequency signal components, including noise and other interference inherent in the isolated signal.
• the filtered signal is then applied to a converter 10 which operates to convert the analog signal received from the filter 9 to a digital signal which is suitable for presentation to a digital processor 11. Operations are then performed within the processor 11 to interpret the signal which is received, and to determine whether this received signal indicates the presence of a tag 2 in the vicinity of the transmitting antenna 3 and the receiving antenna 5, thereby representing a detectable event.
• the transmitter circuitry 4 substantially corresponds in structure to the transmitters of prior electronic article surveillance systems of this general type.
• FIGS 2a and 2b of the drawings show the manner in which antennas embodying the present invention may be configured and mounted.
• FIG. 1 shows this for the transmitting antenna 3
• Figure 2b for the receiving antenna 5.
• this housing 7 is made of a hollow synthetic plastic body, in whose interior all the other elements are positioned. Specifically, in the base portion 7a of Figure 2a, there is located the transmitter circuitry 4 ( Figure 1) while, in the base portion 7a of Figure 2b, there is located the receiver circuitry 6 ( Figure 1).
• Each housing 7 has a pair of uprights 7b and 7c, which are connected by cross-members 7d and 7e.
• the antenna loop 15 starts at the base portion 7a and extends upwardly on one side of the loop into upright portion 7b and on the other side into upright portion 7c.
• these sides of the antenna loop 15 change places, i.e. the portion extending along upright 7b switches over to upright 7c and vice-versa.
• the antenna loop 15 is then completed within cross-member 7e.
• the antenna loop 15 is now formed of paired leads, which are preferably embodied in a twin-axial cable (a cable suitable for this purpose is available from Belden Wire and Cable Company, P.O. Box 1980, Richmond, Indiana
• Such a cable comprises an insulating sleeve, within which extends a pair of separate leads, surrounded by a conductive shield. A conductor for grounding the shield is also provided, and spacers are twisted in with the leads to maintain substantially uniform spacing of the elements within the outermost insulating sleeve.
• Paired coaxial cables may also be used.
• the individual leads are preferably uniformly spaced from one another throughout their lengths. Further, it is
• the paired leads to.be uniformly twisted along their lengths since this reduces the effect of local irregularities.
• break are conductively connected by conductors 9b and 9c. Although not illustrated, the same break arrangement is preferably provided for the antenna 5 of Figure 2b.
• the preferred twin-axial cable is represented somewhat diagrammatically by a tubular element 9 and by conductor pairs 17a, 17b and 18a, 18b, which are seen to emerge from the open lower ends of the element 9.
• element 9 represents the conductive shield of the twin-axial cable; conductor pairs 17a, 17b and 18a, 18b represent the separate leads inside the cable, which become visible in Figures 2a and 2b where they emerge from the inside of shield 9, near the transmitter circuitry 4 and receiver circuitry 6, respectively.
• conductors 17a and 17b represents the so-emerging opposite ends of the same one of the two separate leads inside shield 9; conductors 18a and 18b represent the opposite ends of the second one of the two separate leads inside shield 9.
• transmitter circuitry 4 is connected to that one lead whose emerging ends are designated by reference numerals 17a, 17b in Figure 2a.
• This transmitting circuitry thus constitutes an "active" load for this lead and the loop which that lead forms inside shield 16 constitutes the "active" loop of the transmitting antenna.
• receiving circuitry which constitutes and "active" loop of the receiving antenna.
• each shield 9 the emerging ends of that lead, which are designated by reference numerals 18a, 18b in each of Figures 2a and 2b, are not connected to the respective active loads (namely to transmitter or receiver circuitry 4, 6). Rather the emerging portions 18a, 18b of these leads are connected in each of Figures 2a and 2b to a "passive" load 20 and the loop which each of these leads forms inside its shield 9 thus constitutes the "passive" loop of the respective antenna.
• Each of these passive loops is in turn coupled to the active loop inside the same shield 9 by means of the mutual coupling which exists between two closely adjacent leads.
• the impedance of passive load 20 is so chosen that, when it is reflected back into the respective active load through the above-mentioned mutual coupling, the overall effect will be to impart to each antenna loop 15 a much flatter amplitude response and a much more linear phase response than could otherwise have been obtained, without substantially reducing the antenna efficiency.
• Using a twin-axial cable as the receiving antenna 5 provides an additional advantage for the system 1. It is the principal function of the receiver 6 to activate an appropriate alarm when the presence of a tag 2 is
• a d-c connection needs to be provided between it and the receiver 6 located in the base 7a of the housing 7.
• the passive lead (the one whose emerging ends are designated by reference numerals 18a and 18b in Figure 2b) may be used for that purpose.
• d-c output from receiver 6 may be applied to that lead via a connection which is diagrammatically represented by lead 26 in
• twin-axial cable a connection is made to the same passive lead near the warning light arrangement 25, as diagrammatically represented by connecting lead 27 in Figure 2b.
• connecting lead 27 in Figure 2b there is no need for a separate, additional lead between receiver 6 and warning light 25.
• the signal 28 which is received at the antenna 5 will primarily constitute a base band signal (e.g., 20 KHz) modulated upon the system's operating frequency (e.g., 8.2 MHz) and contained within an "envelope" corresponding to the intensity (amplitude) of the field which is then being received.
• the operative frequency (8.2 MHz) is
• the received wave form is first amplified (amplifier 7) and then introduced to the detector 8. This
• the amplification may include a pre-filtering (at 30) and/or post-filtering (at 31) step, if desired.
• the detector 8 essentially operates to recover (demodulate) the base band (0-20 KHz) signal from its swept carrier (swept about a nominal 8.2 MHz) frequency.
• the resulting wave form ( Figure 6b) will therefore substantially correspond to the isolated base band signal 32, with an added perturbation 33 which corresponds to the deflection 29 (change in amplitude and phase) produced by the presence of the tag 2 between the transmitting antenna 3 and the receiving antenna 5.
• this signal will tend to vary depending upon the location and orientation of the tag 2 relative to the antennas 3, 5, including variations in both the base band signal 32 and the detected perturbation 33.
• the resulting signal is preferably then amplified (amplifier 34) prior to introduction to the filter 9.
• the filter 9 then operates to isolate the detected signal 32 from other signals which may come to be received by the antenna 5, such as the basic (8.2 MHz) carrier signal, other interfering signal (including signals received from the transmitter 4), and noise outside of the useful band.
• the basic (8.2 MHz) carrier signal such as the basic (8.2 MHz) carrier signal, other interfering signal (including signals received from the transmitter 4), and noise outside of the useful band.
• Preferably used for this purpose is a series combination of a high-pass filter 35 for eliminating undesired lower frequency components followed by a low-pass filter 36 for eliminating
• a smoothing filter 44 preferably follows the amplifier 40 to further remove noise components within the operating base band.
• the receiver 6' will operate to detect both a signal 45 from the transmitter 4 and a signal 46 from the tag 2
• the filtered signal 50 shown in Figure 7a (including responses 51 representing detected tags and responses 52 representing interfering signals) is then applied to the converter 10 to be converted from the analog signal which is received from the filter 9 to a digital signal which is appropriate for presentation to the processor 11.
• responses 51 representing detected tags and responses 52 representing interfering signals are then applied to the converter 10 to be converted from the analog signal which is received from the filter 9 to a digital signal which is appropriate for presentation to the processor 11.
• the received analog signal is digitized to a one-bit resolution (a "one” or a “zero") since this has been found to provide sufficient resolution for interpretation by the processor 11.
• a one-bit resolution a "one” or a "zero”
• the technique which is generally used to distinguish between pulses which correspond to the signature of a tag and pulses which correspond to an interfering signal is to determine whether the received pulse has a duration (width) which falls within a predefined "window".
• This window is established (set) within the processor 11 and must be broadly defined to accommodate not only the variety of different tag configurations which can be anticipated, but also the broad spectrum of detected pulses which might correspond to an interfering signal.
• various steps are taken within the converter 10 and the processor 11 to improve the overall detection process, and to more carefully distinguish between the signature of a tag and other signals which may come to be received in the course of operating the electronic article surveillance system 1.
• the first of these improvements forms part of the converter 10, and relates to the manner in which the initial threshold comparisons are made. Specifically, a "hysteresis-type" threshold comparison is made, making use of two different thresholds (developed by the two different comparator circuits 70, 71 of Figure 5) which are selected to define (detect) the leading and trailing edges of the converted pulse, respectively.
• a "hysteresis-type" threshold comparison is made, making use of two different thresholds (developed by the two different comparator circuits 70, 71 of Figure 5) which are selected to define (detect) the leading and trailing edges of the converted pulse, respectively.
• the pulses 74, 75 constitute a more accurate representation of the initial signal. This applies not only to the stronger signals, but also to the signals of reduced strength, which operates to significantly expand upon the range of signals which are effectively detectable by the converter 10, for subsequent processing.
• these levels are preferably made adjustable to accommodate different applications. This may include both adjustments in relative level (i.e., upper and lower thresholds varied as a pair) as well as adjustments in the difference between the two selected thresholds, as desired. It is even possible to adjust the thresholds 72, 73 so that one is positive while the other is negative, should this be indicated for a
• this improved signal is in turn applied to the processor 11, which incorporates additional improvements for further discriminating between tag signatures and interference, as follows.
• steps are taken to determine whether that pulse's trailing edge 83 falls within a predefined window 85 established for the anticipated pulse width of a desired tag signature. If so, steps are then taken to analyze the next pulse 90 in the detected series 80.
• surveillance systems of this general type are configured to repeatedly sweep about the nominal operating frequency of the system, thereby developing repeated signals corresponding to the presence of a tag 2 between the antennas 3, 5. This in turn produces plural signatures which must then be detected by the processor 11, in similar fashion.
• steps are also taken to determine whether or not the detected signal corresponds in time to a scheduled sweep by the transmitter circuitry 4. If an identified signature is detected during a scheduled sweep of the system, steps are again taken to increment the system's counter.
• this technique is replaced with an up/down counter (within the processor 11) which operates to track both successfully detected signatures, and other events, responsive to periodic sweeps of the transmitter.
• the counter is incremented. Detected events occurring outside of the windows defined for the swept signal are ignored. If no tag signature is detected within the prescribed window, the counter is decremented. This continues until such time as the counter either reaches a prescribed threshold (e.g., five counts) or returns to zero (no tag present),
• decrement may correspond to one, or some greater number.
• the count established for an increment may be the same as that established for a decrement (i.e., one to one), or different counts may be used, as desired in a particular application.
• a system for providing these functions generally comprises a processor 11 which receives its primary signal 100 from the dual threshold detectors 70, 71, and appropriate controlling signals from an external signal detector 101 which precedes the linear phase filter 9 (which provides a logic level for timing purposes), and is provided with the computer program listing which follows this specifications
• the processor 11 is additionally controllable (programmable) at 102 to vary the window which is used to analyze the first pulse of a received signal (subsequent pulses are analyzed according to computationally adjusted windows as previously
• the processor 11 can also be controlled, at 103, to change the sweep rate of the electronic article surveillance system 1 from the previously described rate of 82 Hz to a different sweep rate if desired. This permits the electronic article surveillance system 1 to separately address tags using different sweep rates, for reasons which are best illustrated with reference to Figure 9.
• the need for such special measures is eliminated by causing each of the several components which comprise the installed system to operate at different sweep rates, thus avoiding the potential for interference between these respective components.
• the devices 106, 107, 108 could be operated at three different sweep rates, with the deactivators 109, 110 operating at a fourth and different sweep rate (it is not necessary for the deactivators to operate at different rates so long as their rate of operation differs from those of the accompanying
• the 6301 is configured in a mode 7 status as follows:
• P42 is output used for Sonalert and lamp driver
• bra romexit
• bra icflp1 bra icflp1

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Signal Processing (AREA)
• Automation & Control Theory (AREA)
• Computer Security & Cryptography (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Burglar Alarm Systems (AREA)
• Radar Systems Or Details Thereof (AREA)
• Medicinal Preparation (AREA)
• Geophysics And Detection Of Objects (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23136063

Family Applications (1)

Country Status (11)

Cited By (5)

Citations (3)

Family Cites Families (4)

• 1989
  • 1989-12-27 WO PCT/US1989/005874 patent/WO1990007760A1/en not_active Application Discontinuation
  • 1989-12-27 AU AU48287/90A patent/AU631170B2/en not_active Ceased
  • 1989-12-27 EP EP19900901502 patent/EP0403632A4/en not_active Withdrawn
  • 1989-12-27 JP JP50193190A patent/JPH03503219A/ja active Pending
• 1990
  • 1990-01-08 MX MX1904890A patent/MX173773B/es unknown
  • 1990-01-08 CA CA 2007310 patent/CA2007310A1/en not_active Abandoned
  • 1990-01-09 DD DD33700890A patent/DD291654A5/de not_active IP Right Cessation
  • 1990-01-09 ES ES9000305A patent/ES2020841A6/es not_active Expired - Lifetime
  • 1990-09-07 NO NO903912A patent/NO180699C/no unknown
  • 1990-09-07 FI FI904415A patent/FI904415A0/fi not_active Application Discontinuation
  • 1990-09-07 DK DK215790A patent/DK215790D0/da not_active Application Discontinuation
• 1992
  • 1992-09-17 AU AU24551/92A patent/AU660708B2/en not_active Ceased

Patent Citations (3)

Non-Patent Citations (1)

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