US3838409A - Field strength uniformity control system for article theft detection system - Google Patents

Field strength uniformity control system for article theft detection system Download PDF

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Publication number
US3838409A
US3838409A US00351018A US35101873A US3838409A US 3838409 A US3838409 A US 3838409A US 00351018 A US00351018 A US 00351018A US 35101873 A US35101873 A US 35101873A US 3838409 A US3838409 A US 3838409A
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United States
Prior art keywords
antenna
detection system
theft detection
phase
windings
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00351018A
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English (en)
Inventor
A Minasy
R Pruzick
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Knogo Corp
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Knogo Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Knogo Corp filed Critical Knogo Corp
Priority to US00351018A priority Critical patent/US3838409A/en
Priority to CA196,851A priority patent/CA1030239A/en
Priority to GB1568474A priority patent/GB1446259A/en
Priority to SE7404938A priority patent/SE404443B/xx
Priority to BR2883/74A priority patent/BR7402883D0/pt
Priority to ZA00742303A priority patent/ZA742303B/xx
Priority to JP4045074A priority patent/JPS5331720B2/ja
Priority to NLAANVRAGE7404896,A priority patent/NL171388C/xx
Priority to DE19742417935 priority patent/DE2417935C3/de
Priority to AU67855/74A priority patent/AU486502B2/en
Priority to FR7412854A priority patent/FR2225794B1/fr
Priority to IT50319/74A priority patent/IT1011236B/it
Priority to BE143199A priority patent/BE813709A/xx
Application granted granted Critical
Publication of US3838409A publication Critical patent/US3838409A/en
Priority to US05/575,153 priority patent/USRE29610E/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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

Definitions

  • This invention relates to electronic theft detection systems and more particularly it concerns novel arrangements for maintaining the vicinity of a theft detection checkpoint substantially uniformly filled with an electromagnetic interrogation field.
  • each of the articles to be protected from theft has a electronic responder circuit attached to it.
  • This circuit may be concealed in a wafer like element which may also serve as a price label or the like for the protected article.
  • the articles are maintained in an enclosure having limited egress and check points are set up at each egress.
  • a transmitter is provided at the checkpoint to transmit an interrogation signal and receiver means are provided to note any response produced by the interaction of a wafer responder circuit with the transmitted signal field in the vicinity of the checkpoint.
  • the wafer responder circuits respond to the transmitted interrogation signal, which is at first frequency, to produce a response signal at a second frequency.
  • the receiver means are tuned to detect this second frequency.
  • the wafer responder circuits are resonant circuits tuned to resonate at the transmitted interrogation frequency.
  • These wafer responder circuits When these wafer responder circuits are brought into the transmitted interrogation signal field they absorb some of the transmitted energy.
  • the receiver means monitors the transmitted signal, which changes in amplitude due to this absorption.
  • the transmitter of this system produces an output frequency which sweeps cyclically over a given range which includes the resonant frequency of the wafer responder circuits. This causes a series of responses in the form of impulses which occur at a repetition rate corresponding to the frequency sweep rate.
  • a responder circuit to function effectively in any electronic theft detection system depends upon the degree to which the interrogation field is incident upon the responder circuit. Since these responder circuits are generally in flat wafer-like form, they exhibit different degrees of sensitivity depending upon their orientation with respect to the interrogation antenna. In order to accomodate the different attitudes which responder devices may assume when carried through a checkpoint there has been developed a plural antenna system comprising at least two antennas positioned at right angles to each other at the checkpoint. The two antennas are energized simultaneously so that as a responder circuit is turned away from one interrogation antenna it turns toward the other interrogation antenna so that sensitivity is maintained. This plural interrogation antenna system is shown and described in US. Pat. No. 3,493,955.
  • the present invention overcomes the above described field distribution problems and provides an interrogation field in which dead zones are effectively minimized.
  • At least two interrogation antennas at a checkpoint are provided at least two interrogation antennas at a checkpoint. These antennas are positioned in different planes, preferably at right angle to each other. The antennas are energized simultaneously at the same interrogation frequency. However this energization is controlled so that a phase difference exists in the energization of the different antennas. Preferably this phase difference is ninety degrees.
  • a rotating electromagnetic field As a result of the energization of antennas lying in different planes with signals of different phase, there is produced in the vicinity of the checkpoint a rotating electromagnetic field.
  • the rotation of the field causes the dead zone to move so that the entire region of the checkpoint is effectively filled with the electromagnetic field. In effect the dead zones are eliminated and the responder circuits are more likely to be detected.
  • FIG. 1 is a block diagram of a swept frequency electronic theft detection system in which the present invention is embodied
  • FIG. 2 is a perspective view illustrating the arrangement of antenna coils according to the present invention
  • FIG. 3 is a fragmentary circuit diagram showing phase shifting circuits used in the system of FIG. 1;
  • FIGS. 4 A-D are diagramatic representations showing magnetic field relationships around portions of antenna coils during antenna energization at different intervals in a cycle of energization according to the prior art.
  • FIGS. 5 A-D are views similar to FIGS. 4 A-D but showing magnetic field relationships at different intervals in a cycle of energization according to the present invention.
  • the swept frequency theft detection system of FIG. 1 is, in part, like that shown and described in US. Pat. No. 3,500,373.
  • a tuning oscillator which produces a voltage whose amplitude varries at a given rate, e.g., 300 cycles per second.
  • This varying voltage is applied to a voltage tuneable swept radio frequency oscillator 12 which is designed to produce an output voltage which is nominally 2 megahertz (MHZ).
  • MHZ megahertz
  • the swept frequency output of the oscillator 12 is supplied to a junction 14 (see FIG. 3) from which it branches to lead and lag phase shifters l6 and 18.
  • phase shifters which will be described in greater detail hereinafter in connection with FIG. 3 act, respectively, to advance and retard the phase of the signals applied to them.
  • the signal phase is advanced by approximately 45, while in the case of the lag phase shifter, the signal phase is retarded by approximately 45 degrees. There is thus produced a net phase differential of 90 at the outputs of the two phase shifters 16 and 18.
  • the output of the lead phase shifter 16 is applied to an amplifier 20; and the output of this amplifier is applied to a transverse antenna junction 22.
  • a transverse antenna winding 24 is connected to the junction 22.
  • the junction 22 is also connected to a first detector 26; and this is in turn connected to an alarm 28.
  • the output of the lag phase shifter 18 is applied to an amplifier 30; and the output of this amplifier is applied to a pair of lateral antenna junctions 32 and 34.
  • the transverse antenna winding 24 comprises a multiturn coil lying in a plane which is substantially perpendicular to a path of egress (indicated by an arrow A) through a checkpoint.
  • Various physical means are provided to confine the movement of protected articles, which are equipped with electronic responder circuits, so that they can exit from an enclosure only via the path shown by the arrow A. The protected article thus must pass either through or very near the transverse antenna winding 24 during egress from the enclosure.
  • the two lateral antenna windings 36 and 38 also comprise multiturn coils. However these antennas are arranged on opposite sides of the egress path with their planes oriented parallel to the path and perpendicular to the plane of the transverse antenna winding 24.
  • all of the antenna windings have one end connected to ground.
  • the opposite end of the transverse antenna winding 24 is connected to the junction 22 while the opposite end of the lateral antenna windings are connected to the junctions 32 and 34.
  • the system of FIGS. 1 and 2 operates to detect the presence of resonant responder circuits (not shown) carried on protected articles which pass through and by the antenna windings 24, 36 and 38 along the egress path.
  • the responder circuits are tuned to resonate at a frequency within the sweep range of the oscillator 12.
  • the responder circuits may be tuned to resonate at 2 MHZ.
  • a responder circuit When a responder circuit passes by or through the antenna windings, it resonates and absorbs energy each time the frequency of the oscillator 12 sweeps by the resonant frequency of the responder circuit.
  • the responder circuit When the responder circuit is tuned to resonate at 2 MHZ and the oscillator frequency sweep between 1.95 MHZ and 2.05 MHZ, this resonant response occurs twice during each sweep cycle or at a 600 response per second rate.
  • the resonant responses cause a decrease in impedance in the vicinity of the antenna windings so that more of the transmitted energy passes out from the windings during the resonant response. This results in a decrease in the energy level applied to the detectors 26 and 40.
  • the detectors as described in US. Pat. No. 3,500,373, are provided with special arrangements for detecting these energy decreases and for actuating the alarm 28 when they occur.
  • the phase shifters 16 and 18 may be of any suitable construction which will produce a difierence in phase between the lateral and transverse antenna windings.
  • the particular phase shifter construction shown in FIG. 3 has been found to be quite suitable for the present application.
  • the lead phase shifter 16 comprises a resistor 42 connected in series between the junction 14 and the amplifier 20.
  • a capacitor 44 is connected across the resistor 42.
  • the lag phase shifter 18 comprises a resistor 46 connected in services between the junction 14 and the amplifier 30.
  • An inductor 48 and a capacitor 50 are together connected across the resistor 46.
  • the lead phase shifter 16 will produce a phase shift of close to +45 for frequencies in the range of 1.95 2.05 MHZ.
  • the resistor 46 is about 680 ohms and the inductor 48 is about 47 microhenries
  • the lag phase shifter will produce a phase shift of close to 45 for frequencies in the range of 1.95 2.05 MHZ.
  • the capacitor 50 is used to prevent short circuiting of the resistor 46 by the inductor 48; and it has been found that this capacitor will serve this function without adversely affecting phase shift for the frequencies mentioned when its capacitance is approximately 0.1 microfarad.
  • the phase shifters l6 and 18 may be adjusted to produce any differential in the net phase shift between the lateral and transverse antenna windings. However, as will be seen, a 90 net phase shift should produce a more uniform field distribution with the antenna arrangement of FIG. 2. Also, it is not necessary that two separate phase shifters be used. A single phase shifter capable of producing a 90 phase shift in the signal to one of the amplifiers 20 or would produce a similar result. The use of two phase shifters, each of which produces only a 45 phase shift, however, permits a more accurate phase shift over the frequency sweep range with less expensive construction. Also it has been found that the frequency sensitivity of the two phase shifters l6 and 18 is complimentary during the 1.95 to 2.05 MHZ frequency sweep. Thus when the frequency at any instant is such that the lead phase shifter 16 produces less lead, that same frequency causes the lag phase shifter 18 to produce greater lag so that the net phase difference remains essentially the same as frequency shifts.
  • FIGS. 4 and 5 each comprise a group of section views taken along line 44 of FIG. 2. These section views sever the vertical portions of both the transverse and horizontal antenna windings 24, 36 and 38. Thus there are shown severed ends of vertical portions 24a and 24b of the transverse antenna winding 24, severed ends of the vertical portions 36a and 36b of the lateral antenna winding 36 and severed ends the vertical portions 38a and 38b of the lateral antenna winding 38.
  • FIG. 2 when current flows upwardly in the vertical portion 24a, it flows downwardly in the opposite vertical portion 24b. This also applies to vertical portions 36a and 36b and 38a and 38b. Reverse current flows occur, of course, during one half of each cycle of antenna energization.
  • the flow of current through the various antenna windings is accompanied by a circular magnetic field surrounding the winding wires as illustrated by arrows B in FIGS. 4 and 5.
  • the direction of the various circular magnetic fields B corresponds to the direction of current flow through the winding which each field surrounds.
  • the direction of the circular magnetic field reverses itself upon each half cycle of antenna energization.
  • each of the three antenna windings 24, 36 and 38 is energized in phase, according to the prior art.
  • all antenna windings conduct maximum current at the same time and all an-' tenna windings conduct zero current at the next following 90 interval.
  • the major direction of magnetic field strength which is represented by an arrow C in FIG. 4 is determined according to the mutual additive and subtractive effects of the circular magnetic fields B in the various antenna windings.
  • the major magnetic field energization C is at an angle a with respect to the path A.
  • the major magnetic field energization C is again at the angle a with respect to the egress path A, but is reversed in direction.
  • FIG. 4D after the last interval the magnetic field strength again diminishes to zero.
  • the major magnetic field strength C always lies along a path which crosses the egress path A at an angle (1. Also by considering the additive and subtractive effects of the circular magnetic fields B within the various quadrants (a), (b), (c) and (d), it will be seen that a minimum magnetic field strength is always present in quadrants (b) and (d) while maximum magnetic field strength is present only in quadrants (a) and ('6). Thus, by taking care to traverse the checkpoint along a path indicated by the dashed arrow D, one can cross the path of maximum field strength at substantially a right angle to it and thereby minimize the duration required to pass through the high intensity region of the field.
  • an article theft detection system the combination of at least two antenna windings mounted in the vicinity of a checkpoint along an article egress path, said antenna windings lying in different planes, an oscillator for generating high frequency electrical signals, signal transmission means connected between said oscillator and said antenna windings to energize said windings from said oscillator, said signal transmission means including means forming separate signal paths to the antenna windings lying in the different planes and phase shift means in at least one of said signal paths for producing a relative phase difference between the signals applied to the different antenna windings.
  • An article theft detection system wherein at least one antenna winding encircles said egress path and lies in a plane perpendicular to said egress path.
  • An article theft detection system wherein said one antenna winding is connected to be energized from one of said signal paths and wherein both of said two additional antenna windings are connected to be energized from another of said signal paths.
  • phase shifters have complementary frequency sensitivity characteristics whereby the same net phase difference is maintained at different sig nal frequencies.
  • one phase shifter comprises a resistor and a capacitor connected in parallel with each other along one of said signal paths and said other phase shifter comprises a resistor and an inductor connected in parallel with each other along said another signal path.
  • Apparatus for generating an electromagnetic interrogation field at a given checkpoint through which protected articles must pass comprising at least two antenna windings lying in different planes in the vicinity of said checkpoint and means for applying electromagnetic signals of the same frequency but in phase shifted relationship simultaneously to said antennas.
  • Apparatus according to claim 10 wherein said antenna windings lie in planes which are substantially perpendicular to each other and wherein said means for applying electromagnetic signals includes phase shifter means operative to maintain a substantially relative phase shift between the signals applied to the antennas in different planes.
  • An article theft detection system comprising a variable frequency oscillator, a tuning oscillator connected to said variable frequency oscillator for causing same to produce an output signal whose frequency varies cyclically at a rate corresponding to the frequency of said tuning oscillator, means defining an output signal path including a first junction connected to the output of said variable frequency oscillator and means forming a pair of branch signal paths leading from said first junction to associated antenna junctions, separate antenna windings connected respectively to said antenna junctions, said antenna windings being positioned at a given checkpoint and lying in different planes, detector means connected to said antenna junctions, said detector means being responsive to the changes in energy level at the junctions which occur at a rate related to the frequency of said tuning oscillator to produce an output signal, alarm means arranged to be actuated by said output signal from said detection means and phase shifter means arranged in at least one of said branch signal paths between said first junction and one of said antenna junctions.
  • An Article Theft Detection System according to claim 12 wherein said antenna windings include a first winding lying in a plane transverse to an egress path and a second winding lying in a plane extending laterally of said egress path.
  • phase shifter means is operative to produce a net phase difference in signals applied to said first and second windings of substantially 90.
  • phase shifter means includes a pair of phase shifters each connected along a different one of said branch signal paths, one of said phase shifters being operative to produce a leading phase shift and the other being operative to produce a lagging phase shift.
  • phase shifters comprises a resistor and a capacitor connected in parallel with each other along one of said branch signal paths and the other phase shifter comprises a resistor and an capacitor connected in parallel with each other along the other of said branch signal paths.
  • detector means comprises separate detector devices connected, respectively, to each of said antenna junctions.
  • a method for generating an electromagnetic interrogation field at a given checkpoint through which protected articles provided with electronic responder circuits must pass comprising the step of electrically energizing antenna coils, positioned in different planes at said checkpoint, at the same frequency but at different phases thereby to generate an electromagnetic field which rotates in the vicinity of the checkpoint.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Computer Security & Cryptography (AREA)
  • Burglar Alarm Systems (AREA)
  • Geophysics And Detection Of Objects (AREA)
US00351018A 1973-04-13 1973-04-13 Field strength uniformity control system for article theft detection system Expired - Lifetime US3838409A (en)

Priority Applications (14)

Application Number Priority Date Filing Date Title
US00351018A US3838409A (en) 1973-04-13 1973-04-13 Field strength uniformity control system for article theft detection system
CA196,851A CA1030239A (en) 1973-04-13 1974-04-04 Field strength uniformity control system
GB1568474A GB1446259A (en) 1973-04-13 1974-04-09 Electronic theft detection system having uniform field strength
JP4045074A JPS5331720B2 (show.php) 1973-04-13 1974-04-10
BR2883/74A BR7402883D0 (pt) 1973-04-13 1974-04-10 Luindo aparelho e processo para sua realizacao uma instalacao de deteccao do furto de artigos inc
ZA00742303A ZA742303B (en) 1973-04-13 1974-04-10 Field strength uniformity control system
SE7404938A SE404443B (sv) 1973-04-13 1974-04-10 Stolddetektorsystem
NLAANVRAGE7404896,A NL171388C (nl) 1973-04-13 1974-04-10 Elektromagnetisch diefstaldetectiestelsel.
AU67855/74A AU486502B2 (en) 1973-04-13 1974-04-11 Field strength unformity control system
FR7412854A FR2225794B1 (show.php) 1973-04-13 1974-04-11
IT50319/74A IT1011236B (it) 1973-04-13 1974-04-11 Sistema per controllare l uniformi ta dell intensita del campo di interrogazione elettromagnetico in un sistema rivelatore di furto
DE19742417935 DE2417935C3 (de) 1973-04-13 1974-04-11 Diebstahlwarnanlage
BE143199A BE813709A (fr) 1973-04-13 1974-04-12 Antivol perfectionne
US05/575,153 USRE29610E (en) 1973-04-13 1975-05-07 Field strength uniformity control system

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US00351018A US3838409A (en) 1973-04-13 1973-04-13 Field strength uniformity control system for article theft detection system

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US05/575,153 Reissue USRE29610E (en) 1973-04-13 1975-05-07 Field strength uniformity control system

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US00351018A Expired - Lifetime US3838409A (en) 1973-04-13 1973-04-13 Field strength uniformity control system for article theft detection system
US05/575,153 Expired - Lifetime USRE29610E (en) 1973-04-13 1975-05-07 Field strength uniformity control system

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JP (1) JPS5331720B2 (show.php)
BE (1) BE813709A (show.php)
BR (1) BR7402883D0 (show.php)
CA (1) CA1030239A (show.php)
FR (1) FR2225794B1 (show.php)
GB (1) GB1446259A (show.php)
IT (1) IT1011236B (show.php)
NL (1) NL171388C (show.php)
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ZA (1) ZA742303B (show.php)

Cited By (22)

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US3990065A (en) * 1975-02-20 1976-11-02 The Magnavox Company Theft detection system
US4016553A (en) * 1975-06-27 1977-04-05 Knogo Corporation Article detection system with near field electromagnetic wave control
US4017858A (en) * 1973-07-30 1977-04-12 Polhemus Navigation Sciences, Inc. Apparatus for generating a nutating electromagnetic field
US4118693A (en) * 1977-05-09 1978-10-03 Knogo Corporation Method and apparatus for producing uniform electromagnetic fields in an article detection system
US4123749A (en) * 1976-04-03 1978-10-31 Bizerba-Werke Wilhelm Kraut Kg Method and system for determining the presence of objects within a particular surveillance area, in particular for prevention of shoplifting
US4135183A (en) * 1977-05-24 1979-01-16 Minnesota Mining And Manufacturing Company Antipilferage system utilizing "figure-8" shaped field producing and detector coils
US4274090A (en) * 1980-02-19 1981-06-16 Knogo Corporation Detection of articles in adjacent passageways
WO1983003203A1 (en) * 1982-03-15 1983-09-29 Progressive Dynamics Method and apparatus for theft detection systems
US4551712A (en) * 1982-01-14 1985-11-05 N.V. Nederlandsche Apparatenfabriek Nedap Electronic detection system for detecting a responder including a frequency divider
US4737794A (en) * 1985-12-09 1988-04-12 Mcdonnell Douglas Corporation Method and apparatus for determining remote object orientation and position
US4742356A (en) * 1985-12-09 1988-05-03 Mcdonnell Douglas Corporation Method and apparatus for determining remote object orientation and position
US4798175A (en) * 1986-10-09 1989-01-17 Alfa-Laval Agri, Inc. Electronic identification system
FR2659173A1 (fr) * 1990-03-02 1991-09-06 Neiman Sa Antenne extra-plate a polarisation circulaire, notamment pour un ensemble de telecommande integre d'automobile.
WO1993011516A1 (en) * 1991-12-04 1993-06-10 Esselte Meto International Gmbh Method of and system for surveillance and detection using magnetic markers
EP0576187A1 (en) * 1992-06-16 1993-12-29 Elbit Ltd. Tracker employing a rotating electromagnetic field
US5353010A (en) * 1992-01-03 1994-10-04 Minnesota Mining And Manufacturing Company Device and a method for detecting a magnetizable marker element
US5646525A (en) * 1992-06-16 1997-07-08 Elbit Ltd. Three dimensional tracking system employing a rotating field
US5729202A (en) * 1995-08-23 1998-03-17 Klaehn; David P. Electronic article-surveillance apparatus and method of operating same
WO1999028878A1 (de) * 1997-11-27 1999-06-10 Meto International Gmbh System zur sicherung von artikeln gegen diebstahl
WO2000014694A1 (en) * 1998-09-08 2000-03-16 Escort Memory Systems Multi-directional rfid antenna
US20040257294A1 (en) * 2001-07-30 2004-12-23 Tony Bernard Loop-type antenna
US20060279406A1 (en) * 2005-06-07 2006-12-14 Robert Stewart Synchronization and adaptive timing method for multiple RFID reader system

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JPS55121596A (en) * 1979-03-14 1980-09-18 Yoshida Kogyo Kk Device for protecting shoplifting and theft
US4300183A (en) 1980-03-27 1981-11-10 Richardson Robert H Method and apparatus for generating alternating magnetic fields to produce harmonic signals from a metallic strip
US5877728A (en) * 1997-05-28 1999-03-02 Checkpoint Systems, Inc. Multiple loop antenna
US6879300B2 (en) * 2000-02-08 2005-04-12 Cms Partners, Inc. Wireless boundary proximity determining and animal containment system and method
US6836216B2 (en) * 2002-05-09 2004-12-28 Electronic Article Surveillance Technologies, Ltd. Electronic article surveillance system

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US3740742A (en) * 1971-05-11 1973-06-19 T Thompson Method and apparatus for actuating an electric circuit

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US3740742A (en) * 1971-05-11 1973-06-19 T Thompson Method and apparatus for actuating an electric circuit

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4017858A (en) * 1973-07-30 1977-04-12 Polhemus Navigation Sciences, Inc. Apparatus for generating a nutating electromagnetic field
US3990065A (en) * 1975-02-20 1976-11-02 The Magnavox Company Theft detection system
US4016553A (en) * 1975-06-27 1977-04-05 Knogo Corporation Article detection system with near field electromagnetic wave control
US4123749A (en) * 1976-04-03 1978-10-31 Bizerba-Werke Wilhelm Kraut Kg Method and system for determining the presence of objects within a particular surveillance area, in particular for prevention of shoplifting
US4118693A (en) * 1977-05-09 1978-10-03 Knogo Corporation Method and apparatus for producing uniform electromagnetic fields in an article detection system
US4135183A (en) * 1977-05-24 1979-01-16 Minnesota Mining And Manufacturing Company Antipilferage system utilizing "figure-8" shaped field producing and detector coils
US4274090A (en) * 1980-02-19 1981-06-16 Knogo Corporation Detection of articles in adjacent passageways
US4551712A (en) * 1982-01-14 1985-11-05 N.V. Nederlandsche Apparatenfabriek Nedap Electronic detection system for detecting a responder including a frequency divider
WO1983003203A1 (en) * 1982-03-15 1983-09-29 Progressive Dynamics Method and apparatus for theft detection systems
US4737794A (en) * 1985-12-09 1988-04-12 Mcdonnell Douglas Corporation Method and apparatus for determining remote object orientation and position
US4742356A (en) * 1985-12-09 1988-05-03 Mcdonnell Douglas Corporation Method and apparatus for determining remote object orientation and position
US4798175A (en) * 1986-10-09 1989-01-17 Alfa-Laval Agri, Inc. Electronic identification system
FR2659173A1 (fr) * 1990-03-02 1991-09-06 Neiman Sa Antenne extra-plate a polarisation circulaire, notamment pour un ensemble de telecommande integre d'automobile.
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Also Published As

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JPS5331720B2 (show.php) 1978-09-04
BE813709A (fr) 1974-10-14
DE2417935B2 (de) 1977-03-17
ZA742303B (en) 1975-03-26
NL171388B (nl) 1982-10-18
GB1446259A (en) 1976-08-18
CA1030239A (en) 1978-04-25
FR2225794B1 (show.php) 1981-10-09
NL171388C (nl) 1983-03-16
JPS5028799A (show.php) 1975-03-24
IT1011236B (it) 1977-01-20
NL7404896A (show.php) 1974-10-15
SE404443B (sv) 1978-10-02
DE2417935A1 (de) 1974-10-24
BR7402883D0 (pt) 1974-12-31
FR2225794A1 (show.php) 1974-11-08
AU6785574A (en) 1975-10-16
USRE29610E (en) 1978-04-11

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