CA2232474A1 - Electromagnetic anti-shoplifting system - Google Patents

Electromagnetic anti-shoplifting system Download PDF

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Publication number
CA2232474A1
CA2232474A1 CA 2232474 CA2232474A CA2232474A1 CA 2232474 A1 CA2232474 A1 CA 2232474A1 CA 2232474 CA2232474 CA 2232474 CA 2232474 A CA2232474 A CA 2232474A CA 2232474 A1 CA2232474 A1 CA 2232474A1
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Canada
Prior art keywords
coil
magnetic field
phase
marker
coils
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CA 2232474
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French (fr)
Inventor
Jean Courtot
Simon Feldberg
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Individual
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Individual
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Priority to CA 2232474 priority Critical patent/CA2232474A1/en
Publication of CA2232474A1 publication Critical patent/CA2232474A1/en
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    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic 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
    • G08B13/2465Aspects related to the EAS system, e.g. system components other than tags
    • G08B13/2468Antenna in system and the related signal processing
    • G08B13/2477Antenna or antenna activator circuit
    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic 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
    • G08B13/2465Aspects related to the EAS system, e.g. system components other than tags
    • G08B13/2468Antenna in system and the related signal processing
    • G08B13/2471Antenna signal processing by receiver or emitter
    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic 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
    • G08B13/2465Aspects related to the EAS system, e.g. system components other than tags
    • G08B13/2482EAS methods, e.g. description of flow chart of the detection procedure

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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)

Abstract

The present invention provides an antitheft system to detect the presence of an object which has a label affixed thereto when said object passes through a surveillance zone comprising an oscillatory electromagnetic interrogation field having three separate and distinct vector components produced by driving the transmitting coils located in housing on either side of said surveillance zone with an alternating power source repetitively in and out of phase with respect to one another so as to form magnetic lines of flux having one vector component in the out-of-phase mode. The signals generated by the label are received by coils in said housing and are processed by electronic circuitry adapted to distinguish said label signals from spurious signals with a high degree of accuracy. The label can be deactivated so as to pass through the surveillance zone without triggering a system response.

Description

ELECTROMAGNETIC ANTI-SHOPLIFTING SYSTEM
Field Of Invention This invention relates to a method and apparatus for surveillance of articles and in particular to an improvement in a method and apparatus for detecting or preventing the theft of articles of value and more particularly it concerns the method and apparatus capable of distinguishing labels from other objects within an oscillatory electromagnetic field.
Background To Invention There are in existence several systems for detecting or preventing the theft of articles of value. One of these corresponds to U.S. Pat. No. 3,292,080 granted to E.M. Trikilis on December 13, 1966 which makes use of a magnetometer and utilizes a magnetized object which identifies the article unless check-out procedure has removed the magnetism from the object.
Another system involves radioactive material which emits nuclear radiation.
When the label containing the magnetic material is removed from the merchandise, the radiation is no longer emitted, and therefore radiation detectors situated in the doorway are not energized. On the other hand, if the radiation emitters remain on the merchandise, doorway sensors of nuclear radiation react, and security personnel are in a position to prevent the theft. However, there are severe health problems with this system involving danger to people from the nuclear radiation.
A further system involves the use of radio frequency generating device imbedded in a rubber pad. The radio frequency emitting device is fastened to articles and if not removed will energize radio frequency detecting antenna at the doorway.
In the normal course of events, when the merchandise is sold, a special fastener is unlocked and the radio frequency emitter is removed from the article at the time it is sold, permitting the buyer to pass through the doorway without attracting the attention of the store detectives.
page 2/26 The following United States patents illustrate a number of alternative proposals which will serve as background to the invention described and illustrated herein namely:
U.S. Pat. No. 3,631,442; U.S. Pat. No. 3,747,086; U.S. Pat. No. 3,754,226;
U.S. Pat. No. 3,790,945; U.S. Pat. No. 3,820,103; U.S. Pat. No. 4,527,152;
U.S. Pat. No. 4,888,579; U.S. Pat. No. 5,459,452; U.S. Pat. No. 5,602,556;
U.S. Pat. No. 5,661,470;
Objects Of The Invention The principal object of this invention relates to providing an improved method and apparatus for detecting or preventing the theft of articles of value.
Another very important object of this invention is to provide electrical circuitry which has inherently high sensitivity and simultaneously small probability of false alarms.
It is a further object of this invention to provide a method for generating a constant oscillating magnetic field for both in phase and out of phase modes.
The present invention provides a new method to increase sensitivity and simultaneously decrease probability of false alarms.
Features Of Invention It is a feature of this invention to provide an apparatus for detecting the passage of an object through a surveillance zone comprising a transmitting coil for generating an oscillatory electromagnetic interrogation field within the surveillance zone, a label secured to an object, whereby said label is adapted to cut or link up with the electromagnetic field during its traversal through the electromagnetic interrogation field regardless of the label's spacial orientation, and thereby generating signals captured by a receiving coil including electronic circuitry adapted to set off an alarm.
page 3/26 More particularly, the electronic circuitry is adapted to minimize distortion of the generated signal by the label. The electronic circuitry is also adapted so as to differentiate label signals from other signals such as pop cans generating lower harmonics.
It is a further feature of this invention to provide for a field generating system which shall generate sufficient lines of flux to switch a label in any one of the three vectors.
It is a further feature of this invention to provide for a broad band passive fundamental filter and signal amplifier system receiver antenna which while having a signal gain of ten substantially nulls the fundamental frequency of the generated oscillating magnetic field and is made sufficiently lossy such that it does very little or no wave shaping to the signal generated by the label.
More particularly, it is a feature of this invention to provide for electronic circuitry capable of processing the signal such that it is not distorted or wave shaped and the signal retain its inherent characteristics.
It is a further feature of this invention to provide coherent filtering of said signal generated by the label from other signals.
Yet another feature of this invention resides in providing transmitting coils capable of being driven in and out of phase with respect to one another so as to generate oscillating magnetic lines of flux having one vector in the in phase mode and two vectors in the out of phase mode. The label is adapted to cut or link up with one or more of the vectors.
It is another important feature of this invention that the phase of the receiving coils match that of the transmitting coil so as to maximize the capture of signals generated by a label in response to the in and out phase generation of an oscillating magnetic field produce by the transmitting coils.
page 4/26 Still another important feature of this invention resides in providing fortransmitting coils having a parallelogram configuration.
More particularly, it is a feature of this invention to provide electronic circuitry capable of time domain blanking and signal recognition. The signal may be recognized by utilizing pulse width detection or correlation.
It is a further feature of this invention to provide for a method for detecting the presence of an object when the object is in an interrogation zone having an oscillatory electromagnetic field. More particularly, the method comprises of securing to the object a label capable of generating signals when placed in the surveillance zone, whereby the signals are captured by receiving coils including electronic circuitry adapted to set off an alarm.
Brief Description Of Drawings These and other objects and features will become apparent in the following description to be read in conjunction with the sheets of drawings in which:
FIG. 1 is a perspective view of the anti-shoplifting system illustrating coil housing units, electronic circuitry device, and alarm.
FIG. 1 A is a schematic view of the coil units.
FIG. 2 is a perspective view of the label illustrating its internal magnetic materials.
FIG. 3 is a perspective view of the deactivating system.
FIG. 4 is a side elevational view of one of the coil housing units which includes a partially broken view to illustrate its internal components.
page 5/26 FIG. 5 is a cross-sectional view of the coil housing unit taken along the lines 5-5 in Fig. 3 revealing the transmitting coil and receiving coil.
FIG. 6 is a diagram to assist in the explanation of the operation of the aiding and opposition mode.
FIG. 7A is a schematic illustration of the interconnection of the transmitting coil in the constant mode.
FIG. 7B is a schematic illustration of the interconnection of the transmitting coil in the alternating mode.
FIG. 8A is a graphic illustration of the alternating current along corresponding points of the transmitting coil when driven in phase.
FIG. 8B is a graphic illustration of the alternating current along corresponding points of the transmitting coil when driven out of mode.
FIG. 9 and 10 are diagrammatic views illustrating the generated magnetic field.
FIG. 11 is a diagrammatic view of the receiving coils mounted within the coil housing units.
FIG. 12 is a graphic illustration of the fundamental frequency.
FIG. 13 is a graphic illustration of the fundamental frequency including the fundamental frequency of the signal generated by the label.
FIG. 14 is a block diagram illustrating the various components in the electronic circuitry device for two gates system.
FIG. 15 is a block diagram illustrating the various components for three gates system.
page 6/26 Detailed Description Of Invention In the preferred embodiment of this invention, the improved system for detection of marked or tagged objects within a magnetic field has been adapted to comprise an improved anti-shoplifting device generally depicted in FIGS. 1, 2 and 3.
FIG. 1 includes two coil housing units 2 and 4 which have a surveillance zone intermediate said spaced coil housing units 2 and 4. The two coil housing units 2 and 4 are adapted to generate an oscillatory electromagnetic interrogation field within said surveillance zone 6 in a manner to be described herein.
A marker element, tag or label generally illustrated as number 8 in FIG. 2 is attached to each object or article (not shown) to be surveyed by the system described herein. When there has been an unauthorized passage of the label 8 through the surveillance zone 6 (as in the case of shoplifting) the label 8 will cut or link a sufficient number of generated lines of flux thereby generating a signal to be received by the coil housing units 2 and 4. The signal is communicated to an electrical detection circuitry 10 by means of electrical conductors 12 and 14, which will activate the alarm 44.
When the shopper has paid for the article or object the label 8 is inserted into the deactivating device 46 illustrated in FIG. 3. The deactivating device 46 will deactivate the label 8 so that when the label 8 is passed through the surveillance zone 6 there are no signals generated by the label 8; this avoids any false alarm of shoplifting through alarm 44.
page 7/26 Coil Housing Units The coil housing units 2 and 4 are each more particularly described in FIGS. 4 and 5. Each coil housing unit 2 or 4 is so constructed and driven repetitively in alternate in phase (or aiding mode) and out of phase (or opposition mode) such that a label 8 will cut or link a sufficient number of lines of magnetic flux generated by the two magnetic field producing coil housing units 2 and 4 at some point doing its traversal through the interrogation zone 6 regardless of its angle with respect to the magnetic field producing coil units 2 and 4.
Geometric Construction of Coil Housiny Units In the preferred embodiment the coil housing units 2 and 4 respectively include a transmitting coil 48 having four turns as illustrated in FIGS. 4 and 5. Each of the turns of transmitting coil 48 are insulated from each other by insulating material 40. The transmitting coil 48 is wound in a parallelogram configuration as illustrated in FIG. 4. The slopes of the two longest inclined members 22 and 24 are respectively from 0° to 60° from the horizontal place.
The other two shorter members 26 and 28 respectively are in the vertical position.
The transmitting coil 48 is disposed in such a manner that the vertical members 26, 28 and inclined members 22, 24.
As disclosed in FIG. 6, one notable exception to the similarity of conductors A, B and C, D with respect to the above mentioned equivalent longer conductors is that the electrical current travelling in A and B and also in C and D will be in opposite directions, since the reference members are in all cases on opposite sides of the transmitting coil 48 and the electrical current which always flows in the same direction at the same point in the time domain of a continuous conductor, will necessary be flowing in the opposite direction due to the geometry of the transmitting coil 48 and the fact that the sides are opposite.
Therefore, if the current were flowing in an upward direction in element A, it would have a downward direction in element B and likewise for elements C
and D.
page 8/26 Driving Coils in Phase and Out Of Phase The transmitting coil 48 in each of the coil housing units 2 and 4 are driven by an alternating current source; however, the alternating current source applied to one of the transmitting coils 48 in coil housing unit 2 is fixed while the alternating current applied to the other transmitting coil 48 in the coil housing unit 4 is operating so that the alternating current within transmitting coil 48 of coil housing unit 4 is in phase with the alternating current within transmitting coil 48 of coil housing unit 2 for a portion of time, and is then out of phase for a portion time.
FIG. 7a is a schematic illustration of the transmitting coil 48 in coil housing unit 2 and FIG. 7b is a schematic illustration of the transmitting coil 48 in the coil housing unit 4.
FIG. 8a is a graphic illustration of the alternating current along corresponding points of the transmitting coil 48 in coil housing units 2 and 4 when the transmitting coils 48 are operated in phase or in the aiding mode. FIG. 8b is a graphic illustration of the alternating current along corresponding points of transmitting coil 48 in coil housing units 2 and 4 when the transmitting coils are driven out of phase or in the opposition mode.
Consideration must now be given to the case of the generated magnetic field or lines of flux generated in the aiding and opposition modes of operation.
Vectors Produced in the Aiding and Opposition Modes of Operation In the case of the aiding configuration, it is noted that conductors A and A~
(which represents the portion of transmitting coil 48 in the vertical members in the coil housing units 2 and 4 respectively) have electrical current travelling in the same direction, but conductors A and A~, are displaced in space by their separation distance of 30"-40" centre to centre. By applying the right-hand rule with respect to the flux generated by an electrical current travelling in a conductor, it is observed that the lines of flux at a point equidistant from the two conductors A and A~ shall have an opposite direction and shall in fact cancel if the current in the two conductors were the same.
page 9/26 The same discussion applies to the flux producing elements B and B~.
Generally, the same applies to D and D~ and C and C~, with the exception that these flux producing elements.
In the case of the opposition configuration, it is noted that conductors A and A~
have electrical current travelling in opposite directions, but conductors A
and A~
are displaced in space by their separation distance of about 38" centre to centre.
By applying the right-hand rule with respect to the flux generated by an electrical current travelling in a conductor, it is observed that the lines of flux at a point equidistant from the two conductors shall have the same direction and shall add and produce twice the flux if the current in the two conductors were the same.
This addition to produce twice the flux if the electrical currents in the two conductors were the same holds true for flux producing elements B and B~, and also to C and C~, and D and D~, with the exception that the latter four flux producing elements have a slope.
It is further understood that the predominant field or lines of flux generated by the transmitting coil 48 are in a vector perpendicular to the place in which the coil exits and that the strongest field is within, or through the transmitting coil 48, since all four sides or current producing members add to one another. The magnetic field in the centre of the coil 48 would be about four times as much as the fringing field as if a measurement was made at a distance equal to 1~ of the sum of the distance from the centre to each edge of the conductor and from any one of the conductors on the outside of the coil 48.
FIG. 10 illustrates that three vectors of magnetic flux are generated in the surveillance zone 6, and that two of the vectors are perpendicular with respect to one another while the third vector is displaced from the vertical.
The aiding configuration is used primarily to produce the magnetic field which is generally at a point in the centre of one of the coils perpendicular to the plane in which the coil lies and is in the same direction as the other transmitting coil 48 at the same point in time domain producing the strongest field of the three vectors produced, as illustrated in FIGS. 9 and 10.
page 10/26 The opposition configuration as illustrated in FIG. 9 and 10 is used to generate the fringing fields that produce the other two vectors, and that the exact vector produced will be determined by the plane in which the two conductors lie. The vector produced in the opposition configuration will be at right angles with respect to said conductors. The fringing fields add at points equidistant from the two conductors. All other points between the conductors produce a strong magnetic field across the entire 38" spread in all vectors.
Fundamental Freauency In the preferred embodiment, the transmitting coils 48 in the coil housing units 2 and 4 are driven in phase for 13 to 15 milliseconds. During this time interval an oscillating magnetic field is generated; the vector of said generated magnetic field is perpendicular to the face of the transmitting coils 48 as illustrated in FIGS. 9 and 10. The application of alternating current to transmitting coil 48 in coil housing 4 is then stopped for 8 milliseconds so as to allow switching said alternating current to drive the transmitting coil 48 in coil housing unit 4 in the out of phase mode as previously described. During the opposing configuration, an oscillating magnetic field is generated having two vectors, one of which is perpendicular to the plane formed by the two conductors A and A~ and that the other of which is perpendicular to the plane formed by the conductors B and B~.
The transmitting coils 48 in coil housing units 2 and 4 are driven in the out of phase mode for 13 milliseconds.
The cycle of generating one vector in the aiding configuration for 13 to 15 milliseconds, stopping for 8 milliseconds, and then generating the vectors in the opposing configuration for 13 to 15 milliseconds is repeated during the entire operation of the anti-shoplifting system.
In this manner, the transmitting coils 48 of coil housing units 2 and 4 generate a prescribed fundamental frequency suitable to resonate the coils 48 in coil housing units 2 and 4. In the preferred embodiment the capacitance and inductance of the transmitting coils 48 in coil housing units 2 and 4 are selected so that they operate in resonance to generate an oscillating magnetic field having a fundamental frequency of 6 KHz, which is graphically illustrated in FIG. 12.
page 11 /26 Marker Element As previously described the transmitting coils 48, in coil housing units 2 and 4) operate in resonance to generate an alternating magnetic field having a fundamental frequency of 6 KHz. During this in phase operation, magnetic field will be generated in the surveillance zone 6, whose vector is orientated as described in FIGS. 9 and 10. During the out of phase operation, a magnetic field will be generated in the surveillance zone 6, having two vectors as described in FIGS. 9 and 10.
Since an oscillating magnetic field having three separate and distinct vector components is generated, any label 8 which traverses through the interrogation zone 6, will be cut or will link a sufficient number of lines of flux at some point during its passage through the field, regardless of the angle of the orientation of the label 8.
The prior art also discloses that the use of grain or domain orientated material was necessary in the use of marker element 8. However, a label 8 having a unipole orientation may be utilized where the anisotrophy is such that the He is the same regardless of whether the applied magnetic field is parallel to the longest dimension or the shortest one.
In the preferred embodiment, the label 8 comprises of ferromagnetic material 30, which is magnetically soft or easily magnetized. When the label 8 passes through the magnetic field oscillating at the fundamental frequency of 6 KHz, the ferromagnetic material 30 becomes magnetized by the oscillating magnetic field.
As the oscillating magnetic field alternates, the ferromagnetic material switches poles at a fundamental frequency and induces perturbations or anomalies on the oscillating lines of flux of the generated magnetic field. This induced signal has a fundamental frequency and harmonics thereof which combine with the fundamental frequency of the generated magnetic field, as illustrated in FIG.
13.
The signal generated by the label 8 is depicted as number 32 in FIG. 13.
The harmonic signal 36 is received by a receiving coil 32, located within coil housing units 2 and 4.
page 12/26 As previously stated the marker element 8 may be deactivated in the deactivating device 46 so that no signals 32 will be generated in the surveillance zone 6 during the passage through. This is accomplished by including magnetically hard material 34 within the label 8 which becomes magnetized in deactivating system 46 to such an extent that the magnetically hard material 34 will prevent the switching of the ferromagnetic material 30 in surveillance zone 6.
Receivincl Coil The receiving coil 36 is more particularly disclosed in FIGS. 4 and 5. The particular configuration of the receiving coil 36 is that of a figure eight.
The reasoning behind the particular choice is that the receiving coil 36 acts as a passive filter element; that is if the area of the two halves of figure eight are the same, the fundamental frequency of 6 KHz is nulled or substantially eliminated;
yet, the signal 32 induced by the marker element 8 is not nulled, since the marker element 8 cannot be in both regions of the figure eight at the same time.
In the preferred embodiment, the receiving coil 36 comprises of ten turns of wire located in a wire ribbon cable, the ends being so interconnected such that a ten turn coil is formed, as illustrated in FIG. 5. Since the receiving coil 36 is comprised of ten turns of wire, the receiving coil 36 also acts as a passive gain stage, that is, by utilizing ten turns a voltage gain of 10 is accomplished.
Electrostatic shielding 38 is placed over the receiving coil 36 so as to shield the receiving coil 36 against receiving electrostatic signals from the ambient atmosphere. However, it is obvious that the electrostatic shielding 38 does not extend over the entire extent of the figure eight of the receiving coil 36, otherwise, the electrostatic shielding 38 would change the characteristics of the receiving coil 36.
Other receiving coils used in the trade have a resonant frequency of approximately 130 KHz, which is where most of the energy from the signal 32 of the label marker element 8 lies.
page 13/26 The receiving coil 36 herein, is designed to have a much higher resonant frequency than used in the trade. In the preferred embodiment the resonant frequency of the receiving coil 36 is 400 KHz. The reason why the receiving coil was designed to have higher resonant frequency than the signal 32 generated by the label 8 is that a coil when excited at its resonant frequency will ring or resonate; once a receiving coil 36 rings, one loses the characteristic of the exciting signal and obtains the characteristic of the receiving coil 36, and accordingly, the signal 32 generated by the label 8 loses its distinctiveness.
A flat ribbon cable is used to form the receiving coil 36 since it has a lower distributed capacitance and gives a resonant frequency of approximately 400 KHz.
The receiving coil 36 is made more lossy by the placement of one K ohm resistor across its terminals as illustrated in FIG.14. The K ohm damping resistor is added to prevent the receiving coil 36 from ringing with anything but a large signal at its resonant frequency.
Therefore, a receiving coil 36 is disclosed which has a filter gain system with a broad band pass of about 400 KHz with a gain of ten that does not distort the signal at all and yet, is a passive element.
It is important that the phase of the receiving coil 36 matches that of the transmitting coil 48 so as to maximize the capture of signal 32 generated by the label 8 in response to the in and out of phase generation of oscillating magnetic field produced by the transmitting coils 48.
Accordingly, the phase of the receiving coil 36 mounted adjacent the transmitting coil 48 within coil housing unit 2 is wired so as to be in phase with the transmitting coil 48 in coil housing unit 2. Since the phase of the transmitting coil 48 in the coil housing unit 2 is held constant and the phase of the receiving coil 36 in coil housing unit 2 is also held constant.
page 14/26 The phase of the receiving coil 36 mounted adjacent the transmitting coil 48 within coil housing unit 4 is wired so as to be in phase with the transmitting coil 48 in coil housing unit 4. Since the phase of the transmitting coil 48 in coil housing unit 4 is alternated to be in and out of phase with respect to the transmitting coil 48 in coil housing unit 2, receiving coil 36 mounted within coil housing unit 4 is wired in phase with respect to the transmitting coil 48 in coil housing unit 4 so as to be alternating in and out of phase with respect to the receiving coil 36 in coil housing unit 2, but remain in phase with transmitting coil 48 in coil housing unit 4. Therefore, the phase of the receiving coil 48 in coil housing unit 4 remains in phase with the transmitting coil 48 in coil housing unit 4 as the phase of the transmitting coil 48 in coil housing unit 4 is switched to be in and out of phase with respect to the transmitting coil 48 in coil housing unit 2.
Electronic Circuitry Once the signal is recovered from the receiving coil 36 without any wave shaping the signal 32 is extracted from the signal without substantial alteration by the electronic circuitry generally depicted as number 10 in FIG. 1 and more specifically itemized in FIG. 14 and FIG. 15.
FIG. 14 is a block diagram of the circuitry fortwo gates system which extracts the generated signal 32 and which is capable of differentiating between object signals. The block diagram includes two receiving coils 36A and 36B, impedance matching and gain stages 15A and 158) summing stations 16A and 16B, high-pass filter systems 17A and 17B, low-pass filter systems 18A and 18B, automatic gain control stages 19A and 19B, switches 20A and 20B, signal recognition stages 21 A, 21 B, and alarm circuitry 14.
When the transmitting antennas are driven out of phase, switches 20A and 20B
are in a position when the voltage gain is 1. When the antennas are driven in phase switches 20A and 20B are in a position when the voltage gain is 0. So the values of the analog signals after summing stations 15A and 15B in the middle of the gate are about the same for both direction of the field because of doubling signals from both posts only for the out of phase direction of the field, when the field is two times weaker than the field for the in phase direction.
page 15/26 Doubling of signal is very useful to increase the sensitivity and decrease a common value of amplifier, and accordingly to decrease the probability of false-alarms.
The same values of analog signals for both directions of the field are very useful for signal recognition stages 21 A, 21 B and accordingly for sensitivity and probability of right alarms.
This invention is very useful for reliability of the system because if the troubles happen with any parts of one post (except transmitting coils 48, receiving coils 36A and 36B, impedance matching and gain stages 15A and 15B, summing stations 16A and 16B), the system would continue to work with the same sensitivity in every places of the gate but only slower. Moreover, if troubles happen with some parts of both posts, the system would continue to work properly.
When wire is added to the receiving coils 36A and 36B, the capacitance of the receiving coils increases; accordingly the impedance matching stage 15A and 15B is necessary so that the coax connecting the receiving coils to the interrogator will not detune the receiving coils. The impedance matching stage 15A and 15B also includes a gain stage. In practice it was discovered that by adding a gain at this point, the signal to noise ratio (SlN) was greatly improved.
The gain is so designed that the fundamental frequency 6 KHz is not amplified and the lower cut-off frequency is 48 KHz. This stage has a gain of approximately 200 for frequencies above 50 KHz and below 400 KHz and a gain of approximately unity at the fundamental frequency of 6 KHz. The upper cut-off frequency of 400 KHz was inserted to eliminate the radio frequency pick up from the receiving coils 36A and 36B. The impedance matching and gain stage essentially amplifies the fundamental frequency of signal 32 two hundred times while the fundamental frequency of the oscillating magnetic field is amplified by one. In this manner the fundamental frequency generated by the label 8 is emphasized so as to facilitate its analysis.
page 16/26 The signals out of summing stages 16A and 16B are then processed through a filtering system (which will be more fully described herein) with maximum care being given to do as little wave shaping as possible, since the electronic circuitry described herein is adapted to isolate the distortion caused by the label 8, therefore the electronic circuitry must be designed so as not to cause or generate a distortion through our own faulty systems.
Care must be given to the filtering system utilized) otherwise, problems may result due to system non-linearities which are induced and generated by our own system signals which look very similar to the generated marker element signal 32.
For this reason, one preferred filtering technique is the use of a transversal filter in a band-pass configuration such as sampled data filter which is linear in phase.
These filters typically have transition rates exceeding 150 dB/octave, and have more than 40 dB stop band rejection making them ideal for critical filtering situations.
Where less critical filtering is acceptable, the more common types of design, such as Butterworth may be employed with the final result being that some additional processing may be required to give close to the accuracy of a system employing a transversal filter.
High-pass Filter The cut-off frequency of high-pass filters 17A and 17B is selected to be high enough with a steep enough slope to efifectively remove the fundamental frequency of 6 KHz from the signal; but leaving enough lower order harmonics to be able to discriminate signals which generate larger lower order harmonics along with higher order harmonics such as pop cans and large ferrous objects.
A Butterworth's filter (flattest response) was utilized so that the signal is free from any wave shaping. It was determined that a 50 KHz lower cut-off frequency and a scope of 24 dB per octave would give the best results.
page 17/26 The high-pass filter imparts a slight gain of 2.6 or amplification of 8.3 dB
to the signal a in.
Low pass Filter Since the high-pass filters 17A and 17B enhances noise, the low-pass filters and 18B with a flat response was installed to clean up the signal and get rid of any radio frequency that was picked up by the circuit.
The upper cut-off frequency of the low-pass filter was determined experimentally to operate optimally at 400 KHz or more.
The low-pass filter imparts a gain of 2.6 or amplification of 8.3 dB to the signal.
Automatic Gain Control StacLe Once the signal has been filtered, it is passed through an automatic gain control stage 19 so that the amplitude of each signal will be substantially equal before attempting signal recognitions.
A fairly efficient automatic gain control system is required having a dynamic range of 60 dB without distortion. The automatic gain control system must be designed so as to accommodate a very weak signal in the middle of the gates (2 mv) or a strong signal almost touching the gate (500 mv). The output of the automatic gain control will be constant, therefore, all signals will be of equal amplitude when attempting signal recognition.
The gate input signal is first amplified than part of this signal is sent to the feedback network which will control the level of the input to maintain a constant generated output.
page 18/26 Time Domain Blanking Since the signal 32 generated by the label 8 occurs only at certain points in time corresponding to the in phase and out of phase timing any signal generated during any other interval of time may be blanketed out by a time domain blanking circuit so as to further eliminate any false alarms.
When the signal has been retrieved correctly it will appear only at certain points in time corresponding to in phase and out of phase timing. If one blanks the signal out except for the correct moment only those signals generated by the label 8 will appear.
In previous systems time domain blanking was implemented but since the signal was ringing, the signal would spill over into the time when the label 8 signal would appear and thus cause false alarm. The stronger the signal, the longer the ring and the more likely that it would spill over into the time domain where the signal from the label 8 would appear. Therefore, in previous systems a strong signal from something like a pop can would ring long enough to spill over into the time where the signal 32 from the label 8 would appear and thus cause a false alarm.
Since the precise location of the signal 32 is known, the aperture in the time domain blanking circuit can be made much narrower so as to eliminate further the possibility of false alarms.
Signal Recognition Once the signal has been retrieved, kept at a uniform amplitude, and having 95%
of the false signal discarded by utilizing time domain blanking, the signals can then be analyzed to determine whether it is the correct signal.
Algorithm responsible for recognition of the ferromagnetic marker and for discriminating the marker from similar signals produced by metal objects and electromagnetic interference is compared a single marker image byte for byte against a known good marker image which was collected during learning mode.
If the two images match then an alarm is sounded.
page 19/26 Additional Signal Processing When working with weaker signals caused by either spreading the transmitting coils 48 further apart in order to afford a wider passage way and a larger surveillance zone 6, or by reducing the label 8 length to extend its utility and reduce its costs, another method of signal recognition is the use of signal averaging. In a preferred form, signal averaging consists of two charge-transfer devices, each with thirty-two taps equally spaced one sample time apart, but with the taps individually connected to a set of capacitors by means of a transfer gate.
Each set of capacitors also has a reset switch to delete the previously store information before accepting signals from a new signal interration cycle, thus allowing flexibility in selecting any number of signals to be averaged with a signal processing algorithm based on the first order differential equation of each of the individual storage sights or taps. The algorithm is effectively the same as that of a single pole recursive filter; however, it is not subject to the degradation of the signal to noise ratio inherent in recursive integration passed by the process recycling a "coherent noise".
Whereas, the present invention has been described with respect to specific embodiments thereof, it will be understood that various changes and modifications will be suggested to one skilled in the art, and it is intended to encompass such changes and modifications as fall within the scope of the appended claims.
Pumping in more than two sates s sy tem Pumping in three gates system involve non-stable, different pumping of transmitting antenna in the middle gate and partly in other two gates. For two different modes in-phase and out-of-phase, fields from two outside gates add or subtract from the field of the middle post. Influence of middle post to outside posts is in smaller proportions. Electromagnetic field change on transmitting antenna between in-phase and out-of-phase can be about 120-150V for the middle gate and 60-80V for each outside gate. Such type of field change leads to non-stable work, more probability of false alarms and more complicated calibration process. In the present invention the phase orientation of receiving antenna for one of the outside gate is opposite to the another outside and the middle gates. By this the outside gates work in different phase modes according to the middle gate and so eliminate electromagnetic field influence on it.
page 20/26 For more than three gates system the same method can be used. So for four gates system the first and second gates have the same phase orientation of receiving antennas but the third and fourth gates have the opposite. For five gates system the first, second and fifth gates have the same phase orientation of receiving antennas but the third and fourth gates have the opposite.
FIG. 15 is a block diagram of the circuitry for three gates system. The block diagram includes two receiving coils 36A, 36B and 36C, impedance matching and gain stages 15A, 15B and 15C, summing stations 16A) 16B and 16C, high-pass filter systems 17A, 17B and 17C, low-pass filter systems 18A, 18B and 18C, automatic gain control stages 19A) 19B and 19C, switches 20A, 20B and 20C, signal recognition stages 21 A, 21 B and 21 C and alarm circuitry 14.
Excluding connection between third and middle gates prevent tripled noise in a middle gate.
page 21 /26

Claims (11)

1. In a system for detecting the passage of an object through a surveillance zone, the combination includes: means for generating an oscillatory magnetic interrogation field within said surveillance zone, said magnetic field having three separate and distinct vector components therewithin by driving transmitting coil means flanking said surveillance zone with an alternating power source repetitively in and out of phase with respect to one another so as to produce oscillating magnetic lines of flux having one vector component at the time the transmitting coils are in the aiding configuration that forms the in-phase mode and two vector components at the time the transmitting coils are in the opposing configuration that forms the out-of-phase mode; ferromagnetic marker means attachable to an object; means for detecting a signal generated by said marker means in response to said generated oscillating magnetic lines of flux within said surveillance zone; said detection means include circuitry for time domain blanking and circuitry for signal recognition; said time domain blanking circuitry permits the entry to said signal recognition circuitry of said signal generated by said ferromagnetic marker and received by said detection means during a predetermined timed interval corresponding to said in-phase and out-of-phase mode switching and eliminates all other signals during all other time periods from entry to said signal recognition circuitry;
said signal recognition circuitry includes pulse width detection circuitry for detecting the pulse width of said signal generated by said ferromagnetic marker; said signal recognition circuitry includes correlation circuitry for detecting said signal generated by said ferromagnetic marker; said marker for use in a system for detecting the presence of an object within an interrogation zone of an oscillating magnetic field having three distinct and separate vector components, said marker adapted to be secured to an object, the presence of which is to be detected in a said surveillance zone;
said marker includes an elongated, thin, ferromagnetic strip of magnetically soft alloy, and smaller quantities of magnetically hard material which can be magnetized so as to prevent the switching of said ferromagnetic strip in said interrogation zone; means for deactivating said marker so that said marker may pass through said surveillance zone without detection; and said marker has a unipolar orientation whereby the anisotrophy is such that the Hc is the same regardless of the orientation of said marker within said oscillating magnetic field.

page 22/26
2. In Detection apparatus, a pair of coil housing units flanking a surveillance zone and adapted for the generation of an oscillating magnetic field having three distinct and separate vector components within a surveillance zone and for the detection of signals from a ferromagnetic marker means passing through said surveillance zone, each said coil housing unit including; a plurality of transmitting coil means mounted in said coil housing unit; circuitry means associated with said transmitting coil means for generating from said transmitting coil means an oscillating magnetic field having a predetermined fundamental frequency; receiving coil means mounted in said coil housing unit and adapted to receive signals generated by a ferromagnetic marker means in response to said generated oscillating magnetic field within said surveillance zone, whereby said receiving coil means is adapted to substantially eliminate said fundamental frequency and amplify said signals generated by said ferromagnetic marker means; and said coil housing units are so connected that said transmitting coils are in an aiding configuration part of the time and in an opposing configuration part of the time; said transmitting coil means comprise a plurality of conducting loops in a parallelogram configuration; in the slopes of the horizontal members of said parallelogram configuration are at an acute angle from the horizontal; the capacitance and inductance of said transmitting coil means are selected to tune said conducting loops to a predetermined fundamental frequency;
said receiving coil means are mounted in a figure eight configuration; said receiving coil means consist of turns of flat ribbon cable, the ends being so interconnected that a coil of on the order of tens-turns is formed; said receiving coil means are wired in phase with said transmitting coil means within each coil housing unit respectively.
3. In a method for detecting the passage of an object through a surveillance zone, including the step of generating an oscillating magnetic field having three separate and distinct vectors produced by driving transmitting coil means within an alternating source repetitively in and out of phase with respect to one another so as to generate oscillating magnetic lines of flux having one vector component at the time the transmitting coils are in the aiding configuration that forms the in-phase mode and two vector components at the time the transmitting coils are in the opposing configuration that forms the out-of-phase mode; the step of introducing a ferromagnetic marker attachable to an object within said surveillance zone;
and the step of detecting a signal generated by said ferromagnetic marker in response to said generated oscillating magnetic lines of flux within said surveillance zone; said detection step is followed by the step of filtering page 23/26 and amplifying said signal generated from said ferromagnetic marker in said oscillating magnetic interrogation field; said filtering and amplifying step is followed by the step of distinguishing said signal generated from said ferromagnetic marker in said oscillating magnetic interrogation field from other signals by utilizing time domain blanking; said distinguishing step distinguishes the pulse width of signals generated from said ferromagnetic marker in said oscillating magnetic field from other signals;
said distinguishing step includes the step of correlating said signals generated by said ferromagnetic marker in said oscillating magnetic field;
said detection step averages said signal generated by said ferromagnetic marker in said oscillating magnetic field.
4. Apparatus for generating an alternating magnetic field in a detection zone to produce harmonic signals from a metallic strip therein, comprising: a first and a second coil of conductive material, each of said coils configured to have a plurality of essentially linear segments, a first group of said segments having each one thereof oriented at an acute angle relative to horizontal and a second group of said segments each one thereof oriented essentially vertically, said first and said second coils spaced apart to form the detection zone therebetween, means for producing in said second coil an alternating current in said first coil, and means for producing in said second coil an alternating current which alternates between being in-phase and out-of-phase with the current in said first coil; the segments in said first group are each larger than the segments in said second group; said second group of segments comprises first and second segments, the lower end of the first segment and the upper end of a second segment in a plane which is parallel to a surface supporting said apparatus.
5. A method for generating an alternating magnetic field in a detection zone to produce harmonic signals from a metallic strip therein, comprising the steps of: positioning first and second coils in vertical planes and parallel at spaced apart locations to define the detection zone therebetween, each of said coils configured to have a plurality of essentially linear segments, a first group of said segments have each one thereof oriented at an acute angle relative to horizontal and a second group of said segments each one thereof oriented essentially vertically, producing an alternating current in said first coil, and producing in said second coil an alternating current which alternates between being in-phase and out-of-phase with the current in said first coil.

page 24/26
6. A method for generating an alternating magnetic field in a detection zone to produce harmonic signals from a metallic strip therein, comprising the steps of: positioning first and second coils vertically and spaced apart to define the detection zone therebetween, said coils having elongated segments thereof orientated at an acute angle relative to horizontal, driving in-phase alternating current through said coils to produce aiding horizontal magnetic fields from said coils during first periodic time periods, said aiding horizontal magnetic field perpendicular to said coils, and driving out-of-phase alternating current through said coils to produce opposing horizontal magnetic fields perpendicular to said coils during second periodic time periods occurring alternately with said first periodic time periods.
7. In detection apparatus, a pair of coil housing units flanking a surveillance zone and adapted for the generation of an oscillating magnetic field having three distinct and separate vector components within a surveillance zone and for the detection of signals from a ferromagnetic marker means passing through said surveillance zone, each said coil housing unit including; a plurality of transmitting coil means mounted in said coil housing unit; circuitry means associated with said transmitting coil means for generating from said transmitting coil means an oscillating magnetic field having a predetermined fundamental frequency; receiving coil means mounted in FIG.11 configuration in said coil housing unit and adapted to receive signals generated by a ferromagnetic marker means in response to said generated oscillating magnetic field within said surveillance zone and resistor means connected between the terminals of said receiving coil means.
8. In detection apparatus, a pair of coil housing units flanking a surveillance zone and adapted for the generation of an oscillating magnetic field having three distinct and separate vector components within a surveillance zone and for the detection of signals from a ferromagnetic marker means passing through said surveillance zone, each said coil housing unit including; a plurality of transmitting coil means mounted in said coil housing unit; circuitry means associated with said transmitting coil means for generating from said transmitting coil means an oscillating magnetic field having a predetermined fundamental frequency; receiving coil means mounted in FIG.11 configuration in said coil housing unit said receiving coil means consisting of turns of flat ribbon cable with the ends being so interconnected that a coil of the order of turns is formed, said receiving page 25/26 coil means being adapted to receive signals generated by a ferromagnetic marker means in response to said generated oscillating magnetic field within said surveillance zone and resistor means connected between the terminals of said receiving coil means.
9. In a system as claimed in claim 1, in Detection apparatus as claimed in claim 2, 7 and in a method for detecting as claimed in claim 3 wherein for two gates system (Detection apparatus, method for detecting) said receiving coil of each gate is connected via impedance matching and gain stages to summing station of its own gate directly and to summing station of another gate via switch, said summing station of each gate is connected to alarm via high-pass filter systems, low-pass filter systems, automatic gain control stages and signal recognition stages.
10. In a system, in Detection apparatus and in a method for detecting as claimed in claim 8 wherein for three gates system (Detection apparatus, method for detecting) said receiving coil of each gate is connected via impedance matching and gain stages to summing station of its own gate directly and to summing station of first and third gates from second gate and to summing station of second gate from first gate via switches.
11. Apparatus and a method for generating an alternating magnetic field in a detection zone as claimed in claims 4-6 wherein for more than two gates system every odd two gates have the same phase orientation of receiving antennas and every even two gates have the opposite phase orientation of receiving antennas.

page 26/26
CA 2232474 1998-05-19 1998-05-19 Electromagnetic anti-shoplifting system Abandoned CA2232474A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106842336A (en) * 2017-02-09 2017-06-13 王积东 By formula detector and by formula detection method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106842336A (en) * 2017-02-09 2017-06-13 王积东 By formula detector and by formula detection method

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