EP0628936B1 - Multidirectional surveillance marker - Google Patents

Multidirectional surveillance marker Download PDF

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Publication number
EP0628936B1
EP0628936B1 EP19940107232 EP94107232A EP0628936B1 EP 0628936 B1 EP0628936 B1 EP 0628936B1 EP 19940107232 EP19940107232 EP 19940107232 EP 94107232 A EP94107232 A EP 94107232A EP 0628936 B1 EP0628936 B1 EP 0628936B1
Authority
EP
European Patent Office
Prior art keywords
band
surveillance marker
electronic surveillance
marker according
regions
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
EP19940107232
Other languages
German (de)
French (fr)
Other versions
EP0628936A1 (en
Inventor
Peter Y. Zhou
Thomas P. Solaski
Dennis P. Donaldson
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.)
Sensormatic Electronics Corp
Original Assignee
Sensormatic Electronics 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 Sensormatic Electronics Corp filed Critical Sensormatic Electronics Corp
Publication of EP0628936A1 publication Critical patent/EP0628936A1/en
Application granted granted Critical
Publication of EP0628936B1 publication Critical patent/EP0628936B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • G08B13/2405Electronic 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 characterised by the tag technology used
    • G08B13/2408Electronic 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 characterised by the tag technology used using ferromagnetic tags
    • 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
    • G08B13/2428Tag details
    • G08B13/2437Tag layered structure, processes for making layered tags
    • 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
    • G08B13/2428Tag details
    • G08B13/2437Tag layered structure, processes for making layered tags
    • G08B13/2442Tag materials and material properties thereof, e.g. magnetic material details

Definitions

  • This invention relates to markers or targets for electronic article surveillance and more particularly it concerns a novel magnetically saturable marker characterized by a multidirectional sensitivity.
  • United States Patents No. 3,820,103, No. 3,820,104 and No. 3,665,449 describe magnetically saturable markers for use in electromagnetic type surveillance systems. These systems are generally used to reduce theft by shoplifting but they are also used to detect the unauthorized movement of articles in other environments.
  • the markers shown in these patents are elongated strips of magnetically soft material having a high magnetic permeability and a low magnetic coercivity. When exposed to an alternating magnetic field in an interrogation region, for example, the exit from a store, these targets or markers become magnetically saturated in opposite directions during each cycle of the alternating magnetic interrogation field. As a result they disturb the field in a characteristic manner to produce harmonics which can be detected.
  • the targets or markers should have the configuration of an elongated open strip with a high ratio of length to cross-sectional area for maximum sensitivity to the interrogating magnetic fields.
  • the ratio of length to the square root of cross sectional are below 150, the magnetization reversal signal amplitude decreases radically and becomes noticeably dependent on orientation of the open strip within the magnetic field.
  • the open strip may have one or more major dimensions satisfying this criteria.
  • U.S. Patent No. 4,074,249 describes a crescent shaped target which is less sensitive to orientation than the straight elongated open strip markers.
  • U.S. Patent No. 4,075,618 describes thin elongated markers which have enlarged flux concentrators at the ends thereof to enable the markers to be shortened without reduction in their sensitivity.
  • Compact disc recordings, for example, have only a small ring shaped region araound a center opening that would allow for the placement of a marker.
  • the strips are shortened to fit into small areas, their sensitivity becomes highly dependent on their orientation relative to the interrogating magnetic field. This is a problem when the markers are used for theft detection because in that case, it is not possible to control their orientation when they are carried through an interrogation zone.
  • a magnetic article surveillance marker having a multidirectional sensitivity.
  • This marker comprises two sheets of magnetic material, wherein the first sheet is formed of a ferromagnetic material having high permeability and low coerciv force properties, such as permalloy or the like.
  • the first sheet may be formed to have notches centered along each edge of the sheet.
  • the second sheet of the marker comprises a solid sheet of a magnetizable material and is joined together with the first sheet, and the combination of the two sheets is affixed to articles to be protected.
  • an electronic surveillance marker including the features of claim 1.
  • the electronic surveillance marker of the present invention comprises a band in the shape of a closed loop, for example a ring-shaped band, wherein a plurality of cutout regions are formed in the band and are spaced along the length of the band.
  • the cutout regions are completely formed within the band, i.e. the cutout regions are enclosed between the inner and outer edges of the band, so that each cutout region forms a pair of narrowed segments on opposite sides of each cutout region.
  • an electronic surveillance marker having the features of claim 1 produces good responses to a magnetic interrogating field in an electronic surveillance system, with reduced dependence on orientation relative to the interrogating field. These good responses are due to the fact that the cutout regions produce very narrow lenghts on opposite sides of each cutout region, wherein the ratio of length to cross-sectional area of these narrow lengths is relatively high. Furthermore, between the cutout regions material regions are formed which provide large masses fot deactivation purposes. As the marker is formed in the shape of a closed loop and the narrow segments formed on opposite sides of each cutout region extend in different directions at different locations along the marker, the orientation sensitivity of the marker relative to the directions of the interrogating magnetic field is minimized. Further, the forming of the cutout regions within the material of the closed loop marker results in two narrowed regions on opposite sides of each cutout region, wherein these narrowed regions are formed at flux concentrating regions of the marker and, therefore, the marker is made more sensitive.
  • An electronic article surveillance marker 10 is a band in the shape of a flat ring and is made of sheet metal having special magnetic properties, namely, it has high magnetic permeability and low magnetic coercivity and is easily magnetically saturable.
  • the marker 10 may be made of permalloy or material having magnetic properties similar to permalloy, such as amorphous magnetic material. A suitable material is described in U.S. Patent No. 5,146,204.
  • the marker 10 of Fig. 1 has a plurality of elongated cutouts 12 spaced apart along the length of the band. Each cutout is contained entirely within the band and thereby forms a pair of very thin narrowed segments 10a and 10b which are parallel to each other and which interconnect full width segments 10c. These cutouts 12 are preferably evenly distributed around the marker 10.
  • the marker 10 has and inner diameter d of 16 millimeters and an outer diameter D of 22 millimeters.
  • the width of the band which forms the ring is thus about three millimeters.
  • the marker 10 has a thickness of about 15 microns.
  • the cutouts 12 have a width of about two millimeters and they extend over an arc of about 36°.
  • the thin narrowed segments 10a and 10b each have a width of about 0.5 millimeters and a length of about six millimeters.
  • a marker with the above described shape and dimensions and made of permalloy will produce good responses to a magnetic interrogating field in an electronic article surveillance system, with reduced dependence on orientation relative to the interrogating field. These good responses are due firstly, to the fact that the cutouts 12 produce very narrow lengths 10a and 10b in which the ratio of length to cross-sectional area is high, and secondly, to the fact that the regions 10c between the strips provide large masses which will provide regions for deactivation purpose.
  • the marker is formed in a closed loop and because the lengths 10a and 10b extend in different directions at different locations along the marker, the orientation sensitivity of the marker relative to the direction of the interrogating magnetic field is minimized.
  • the marker 10 is preferably made from a sheet of high permeability low coercivity readily magnetizable material which is then formed into the above described configuration by means of conventional photoetching techniques. Other techniques, such as mechanical stamping, may also be used.
  • Fig. 2 shows the marker 10 of Fig. 1 as attached to a compact disc 14.
  • the marker fits just around the center opening 14b of the disc 14.
  • the marker is laminated into the disc during manufacture thereof. In this way the marker cannot be easily removed.
  • the marker may also have laminated thereunder or thereon, segments 16 of a relatively highcoercivity magnetic material which can be magnetized by an authorized person to desensitize the marker so that it will not produce responses upon being carried through a magnetic interrogation field.
  • Figs. 3 and 4 show alternative configurations of the marker of the present invention.
  • a marker 20 is formed of a closed loop band in the shape of a square while in Fig. 4 a marker 30 is formed of a closed loop band in the shape of a triangle.
  • the marker is provided with spaced apart cutouts 22 and 32.
  • Each of these cutouts form two thin strips of target material 20a and 20b and 30a and 30b, respectively, which are interspersed with segment 20c and 30c of full width material.
  • the different thin strips in each marker extend in different directions to minimize orientation sensitivity. It will be appreciated that other polygonal marker configurations may be used in accordance with the present invention.
  • narrowed regions could be formed by lateral cutouts, which are located on the inner or outer, or both the inner and outer sides of the band.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Computer Security & Cryptography (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Burglar Alarm Systems (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Soft Magnetic Materials (AREA)

Description

    BACKGROUND OF THE INVENTION Field of the Invention
  • This invention relates to markers or targets for electronic article surveillance and more particularly it concerns a novel magnetically saturable marker characterized by a multidirectional sensitivity.
  • Description of the Related Art
  • United States Patents No. 3,820,103, No. 3,820,104 and No. 3,665,449 describe magnetically saturable markers for use in electromagnetic type surveillance systems. These systems are generally used to reduce theft by shoplifting but they are also used to detect the unauthorized movement of articles in other environments. The markers shown in these patents are elongated strips of magnetically soft material having a high magnetic permeability and a low magnetic coercivity. When exposed to an alternating magnetic field in an interrogation region, for example, the exit from a store, these targets or markers become magnetically saturated in opposite directions during each cycle of the alternating magnetic interrogation field. As a result they disturb the field in a characteristic manner to produce harmonics which can be detected.
  • These patents explain that the targets or markers should have the configuration of an elongated open strip with a high ratio of length to cross-sectional area for maximum sensitivity to the interrogating magnetic fields. When the ratio of length to the square root of cross sectional are is below 150, the magnetization reversal signal amplitude decreases radically and becomes noticeably dependent on orientation of the open strip within the magnetic field. It is also suggested in these patents that the open strip may have one or more major dimensions satisfying this criteria.
  • U.S. Patent No. 3,665,449 mentions the possibility of using a disc shaped marker but indicates that because of the low length to cross-section ratio such markers do not produce very large or distinctive response signals.
  • U.S. Patent No. 4,074,249 describes a crescent shaped target which is less sensitive to orientation than the straight elongated open strip markers.
  • U.S. Patent No. 4,075,618 describes thin elongated markers which have enlarged flux concentrators at the ends thereof to enable the markers to be shortened without reduction in their sensitivity.
    One problem that characterizes all prior art magnetically saturable markers for electronic article surveillance, is that the shape and size of the available space on the object to be protected by the marker often will not accomodate a thin elongated strip. Compact disc recordings, for example, have only a small ring shaped region araound a center opening that would allow for the placement of a marker. On the other hand, when the strips are shortened to fit into small areas, their sensitivity becomes highly dependent on their orientation relative to the interrogating magnetic field. This is a problem when the markers are used for theft detection because in that case, it is not possible to control their orientation when they are carried through an interrogation zone.
  • To overcome this problem there is known from EP-A2 0 412 721 a magnetic article surveillance marker having a multidirectional sensitivity. This marker comprises two sheets of magnetic material, wherein the first sheet is formed of a ferromagnetic material having high permeability and low coerciv force properties, such as permalloy or the like. The first sheet may be formed to have notches centered along each edge of the sheet. The second sheet of the marker comprises a solid sheet of a magnetizable material and is joined together with the first sheet, and the combination of the two sheets is affixed to articles to be protected.
  • Further, in document US 4,967,184 is disclosed an electronic surveillance marker according to the preamble of claim 1. In particular, this document proposes the use of a ring-shaped surveillance marker which is made from an amorphous ferromagnetic material and adhered to a computer disk such that the ring-shaped surveillance marker surrounds the center opening of the computer disk. The material of the ring-shaped surveillance marker is preferably selected to have low coercivity and a high magnetic permeability. When using the computer disk, the presence of the ring-shaped surveillance marker is detected for security purposes by means of a low strength interrogating sensor field.
  • SUMMARY OF THE INVENTION
  • Starting from the prior art known from US 4,967,184, it is an object of the present invention to provide an electronic surveillance marker having multidirectional sensitivity and also having a higher sensitivity.
  • According to the present invention, this object is achieved by an electronic surveillance marker including the features of claim 1.
  • In particular, the electronic surveillance marker of the present invention comprises a band in the shape of a closed loop, for example a ring-shaped band, wherein a plurality of cutout regions are formed in the band and are spaced along the length of the band.
  • Furthermore, the cutout regions are completely formed within the band, i.e. the cutout regions are enclosed between the inner and outer edges of the band, so that each cutout region forms a pair of narrowed segments on opposite sides of each cutout region.
  • As described in greater detail hereinbelow, it has been found that an electronic surveillance marker having the features of claim 1 produces good responses to a magnetic interrogating field in an electronic surveillance system, with reduced dependence on orientation relative to the interrogating field. These good responses are due to the fact that the cutout regions produce very narrow lenghts on opposite sides of each cutout region, wherein the ratio of length to cross-sectional area of these narrow lengths is relatively high. Furthermore, between the cutout regions material regions are formed which provide large masses fot deactivation purposes. As the marker is formed in the shape of a closed loop and the narrow segments formed on opposite sides of each cutout region extend in different directions at different locations along the marker, the orientation sensitivity of the marker relative to the directions of the interrogating magnetic field is minimized. Further, the forming of the cutout regions within the material of the closed loop marker results in two narrowed regions on opposite sides of each cutout region, wherein these narrowed regions are formed at flux concentrating regions of the marker and, therefore, the marker is made more sensitive.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • Fig. 1 is a plan view of a marker according to the present invention;
  • Fig 2 is a plan view showing a compact disc to which the marker of Fig. 1 is attached;
  • Fig. 3 is a plan view of an alternate form of marker according to the present invention; and
  • Fig. 4 is a plan view of a further alternate form of marker according to the present invention.
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • An electronic article surveillance marker 10 according to the present invention, is a band in the shape of a flat ring and is made of sheet metal having special magnetic properties, namely, it has high magnetic permeability and low magnetic coercivity and is easily magnetically saturable. The marker 10 may be made of permalloy or material having magnetic properties similar to permalloy, such as amorphous magnetic material. A suitable material is described in U.S. Patent No. 5,146,204.
  • The marker 10 of Fig. 1 has a plurality of elongated cutouts 12 spaced apart along the length of the band. Each cutout is contained entirely within the band and thereby forms a pair of very thin narrowed segments 10a and 10b which are parallel to each other and which interconnect full width segments 10c. These cutouts 12 are preferably evenly distributed around the marker 10.
  • By way of example, the marker 10 has and inner diameter d of 16 millimeters and an outer diameter D of 22 millimeters. The width of the band which forms the ring is thus about three millimeters. Also, by way of example, the marker 10 has a thickness of about 15 microns. The cutouts 12 have a width of about two millimeters and they extend over an arc of about 36°. Thus the thin narrowed segments 10a and 10b each have a width of about 0.5 millimeters and a length of about six millimeters.
  • It has been found that a marker with the above described shape and dimensions and made of permalloy will produce good responses to a magnetic interrogating field in an electronic article surveillance system, with reduced dependence on orientation relative to the interrogating field. These good responses are due firstly, to the fact that the cutouts 12 produce very narrow lengths 10a and 10b in which the ratio of length to cross-sectional area is high, and secondly, to the fact that the regions 10c between the strips provide large masses which will provide regions for deactivation purpose. In addition, because the marker is formed in a closed loop and because the lengths 10a and 10b extend in different directions at different locations along the marker, the orientation sensitivity of the marker relative to the direction of the interrogating magnetic field is minimized.
  • The marker 10 is preferably made from a sheet of high permeability low coercivity readily magnetizable material which is then formed into the above described configuration by means of conventional photoetching techniques. Other techniques, such as mechanical stamping, may also be used.
  • Fig. 2 shows the marker 10 of Fig. 1 as attached to a compact disc 14. As can be seen, the marker fits just around the center opening 14b of the disc 14. Preferably the marker is laminated into the disc during manufacture thereof. In this way the marker cannot be easily removed. The marker may also have laminated thereunder or thereon, segments 16 of a relatively highcoercivity magnetic material which can be magnetized by an authorized person to desensitize the marker so that it will not produce responses upon being carried through a magnetic interrogation field.
  • Figs. 3 and 4 show alternative configurations of the marker of the present invention. As shown in Fig. 3, a marker 20 is formed of a closed loop band in the shape of a square while in Fig. 4 a marker 30 is formed of a closed loop band in the shape of a triangle. In each case the marker is provided with spaced apart cutouts 22 and 32. Each of these cutouts form two thin strips of target material 20a and 20b and 30a and 30b, respectively, which are interspersed with segment 20c and 30c of full width material. As can be seen, the different thin strips in each marker extend in different directions to minimize orientation sensitivity. It will be appreciated that other polygonal marker configurations may be used in accordance with the present invention.
  • It follows from the foregoing, that narrowed regions could be formed by lateral cutouts, which are located on the inner or outer, or both the inner and outer sides of the band.

Claims (12)

  1. An electronic surveillance marker,
    comprising a band (10) of material extending in a flat plane and being in the shape of a closed loop,
    said material having magnetic properties of magnetic permeability, coercivity and saturability similar to those of permalloy or amorphous magnetic metal,
    wherein said marker has multidirectional sensitivity,
    characterized in that
    said band (10) has a plurality of cutout regions (12) spaced along the length of said band (10), said cutout regions (12) each being enclosed between the inner and outer edges of said band (10) such that said cutout regions (12) each form a pair of narrow segments (10a, 10b) of said material on opposite sides of each cutout region (12).
  2. An electronic surveillance marker according to claim 1,
    characterized in that
    there are at least five of said cutout regions (12) distributed along the length of said band (10).
  3. An electronic surveillance marker according to claim 1 or 2,
    characterized in that
    each of said cutout regions (12) extends a substantial distance along said band (10).
  4. An electronic surveillance marker according to any one of claims 1-3,
    characterized in that
    said material is an amorphous metallic alloy.
  5. An electronic surveillance marker according to any one of claims 1-4,
    characterized in that
    said band (10) has a width of about three millimeters and a thickness of about fifteen microns.
  6. An electronic surveillance marker according to claim 5,
    characterized in that
    said cutout regions (12) have a width of about two millimeters and a length of about six millimeters.
  7. An electronic surveillance marker according to any one of claims 1-6,
    characterized in that
    each cutout region (12) is centered in said band (10) so as to define said two narrowed segments (10a, 10b) of said material on opposite sides thereof each having a width of about 0,5 millimeters.
  8. An electronic surveillance marker according to any one of claims 1-7,
    chracterized in that
    said band (10) is in the shape of a ring.
  9. An electronic surveillance marker according to any one of claims 1-7,
    characterized in that
    said band is in the shape of an polygon (20, 30).
  10. An electronic surveillance marker according to claim 9,
    characterized in that
    said band is in the shape of a square (20).
  11. An electronic surveillance marker according to claim 9,
    characterized in that
    said band is in the shape of a triangle (30).
  12. In combination, a compact disc record (14) having a center opening and an electronic surveillance marker,
    wherein said surveillance marker has mutidirectional sensitivity and comprises a band (10) of material in the shape of a ring extending in a flat plane being mounted on said disc (14) in a position surrounding said center opening in said disc (14), said material having magnetic properties of high permeability, low coercivity and being readily magnetically saturable, said combination of said compact disc (14) and said surveillance marker having rotational balance,
    wherein said band (10) has a plurality of spaced apart cutout regions (12) therealong which form narrowed regions (10a, 10b) along said band (10), said cutout regions (12) being centered in said band (10) so as to define said narrowed regions (10a, 10b) on opposite sides of each cutout region (12).
EP19940107232 1993-06-11 1994-05-09 Multidirectional surveillance marker Expired - Lifetime EP0628936B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US7624793A 1993-06-11 1993-06-11
US76247 1993-06-11

Publications (2)

Publication Number Publication Date
EP0628936A1 EP0628936A1 (en) 1994-12-14
EP0628936B1 true EP0628936B1 (en) 2000-03-01

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EP19940107232 Expired - Lifetime EP0628936B1 (en) 1993-06-11 1994-05-09 Multidirectional surveillance marker

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EP (1) EP0628936B1 (en)
JP (1) JP2500309B2 (en)
AU (1) AU667431B2 (en)
BR (1) BR9402136A (en)
DE (2) DE9407703U1 (en)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4440314A1 (en) * 1994-11-11 1996-05-15 Esselte Meto Int Gmbh Marking element for protecting articles against theft
US5519379A (en) * 1995-04-10 1996-05-21 Sensormatic Electronics Corporation Multi-thread re-entrant marker with simultaneous switching
DE19604114A1 (en) * 1996-02-06 1997-08-07 Esselte Meto Int Gmbh Securing element for electronic article surveillance
DE19738309A1 (en) * 1997-09-02 1999-03-04 Meto International Gmbh Device for securing articles against theft, corresponding manufacturing method and device for carrying out the method
GB9800064D0 (en) * 1998-01-05 1998-03-04 Sentec Ltd Uni-directional magnetic tag
US6525661B2 (en) 1999-02-26 2003-02-25 3M Innovative Properties Company Electronic article surveillance markers for optically recorded media
US6693542B2 (en) 2001-11-15 2004-02-17 Ryusuke Hasegawa Electronic article surveillance markers for recorded media
EP2081191A1 (en) 2008-01-21 2009-07-22 Tecnicas Pantra S.L. Non symmetric devices with alarms for compact discs and similar articles

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4710754A (en) * 1986-09-19 1987-12-01 Minnesota Mining And Manufacturing Company Magnetic marker having switching section for use in electronic article surveillance systems
US4746908A (en) * 1986-09-19 1988-05-24 Minnesota Mining And Manufacturing Company Dual-status, magnetically imagable article surveillance marker
US4829288A (en) * 1987-11-30 1989-05-09 Minnesota Mining And Manufacturing Company Economic, multi-directionally responsive marker for use in electronic article surveillance systems
US4825197A (en) * 1988-02-01 1989-04-25 Minnesota Mining And Manufacturing Company Dual status magnetic marker having magnetically biasable flux collectors for us in electronic article surveillance systems
US4910625A (en) * 1988-10-11 1990-03-20 Eastman Kodak Company Article surveillance apparatus and systems for computer data disks
US4967185A (en) * 1989-08-08 1990-10-30 Minnesota Mining And Manufacturing Company Multi-directionally responsive, dual-status, magnetic article surveillance marker having continuous keeper
US4967184A (en) * 1989-09-19 1990-10-30 Eastman Kodak Company Computer disk with security protection

Also Published As

Publication number Publication date
JPH0798791A (en) 1995-04-11
JP2500309B2 (en) 1996-05-29
EP0628936A1 (en) 1994-12-14
BR9402136A (en) 1995-01-17
DE9407703U1 (en) 1994-09-01
AU6068394A (en) 1994-12-15
DE69423135T2 (en) 2000-09-28
DE69423135D1 (en) 2000-04-06
AU667431B2 (en) 1996-03-21

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