AU667431B2

AU667431B2 - Multidirectional surveillance marker

Info

Publication number: AU667431B2
Application number: AU60683/94A
Authority: AU
Inventors: Dennis Patrick Donaldson; Thomas Patrick Solaski; Peter Yongxin Zhou
Original assignee: Sensormatic Electronics Corp
Current assignee: Sensormatic Electronics Corp
Priority date: 1993-06-11
Filing date: 1994-04-26
Publication date: 1996-03-21
Anticipated expiration: 2014-04-26
Also published as: JPH0798791A; BR9402136A; DE69423135D1; DE69423135T2; AU6068394A; JP2500309B2; EP0628936B1; EP0628936A1; DE9407703U1

Description

667431

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): -Knego Corporation X, Sc.;-\ormc 4 c. .GooX'\i s

SEC.

113 W ADDRESS FOR SERVICE: T O DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Multidirectional surveillance marker S The following statement is a full description of this invention, including the best method of performing it known to me/us:- 00 4 1A 44 4 f This invention relates to markers or targets for electronic article surveillance.

This imagnetically saturable markers for utarge ints for 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 these targets Sor markers become S9505 popdbw,60683.94,1 'h i o relte tom e 950512p opcrtdbw,60683.94,1 -2magnetically 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 a square root of cross sectional are is below 150, the .o o magnetization reversal signal amplitude decreases o 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 o a0satisfying this criteria.

U.S. Patent No. 3,665,449 mentions the possibility of R 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 2o ,signals.

ol° 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 1:

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-3marker often will not accommodate a thin elongated strip. Compact disc recordings, for example, have only a small ring shaped region around 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.

According to the present invention there is provided an electronic surveillance marker comprising a band of material extending in a flat plane, said material having properties of magnetic permeability, coercivity and saturability similar to those of permalloy or amorphous magnetic metal, characterized in that said band is in the shape of a ring and has a plurality of cutout regions spaced along the length of said band, said cutout regions each being enclosed between the inner and outer edges of said ring such that said cutout regions each form a pair of narrow segments of said material on opposite sides of each cutout region, whereby said marker has multidirectional sensitivity.

'The present invention also piovides in combination, a compact disc record having a center opening, an electronic surveillance marker comprising a band of material in the I 20 shape of a ring extending in a flat plane and mounted on the disc in a position surrounding said center opening in said disc, said material having magnetic properties of high permeability, low coercivity and being readily magnetically saturable, said band having a plurality of spaced apart cutout regions therealong which form narrowed lengths along said band whereby said combination has multidirectional sensitivity as i 25 well as rotational balance, and wherein each cutout region is centered in said band so j as to define two narrowed regions on opposite sides of each cutout region.

Preferred embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, wherein: Fig. 1 is a plan view of a marker according to a preferred embodiment of the present invention; and Fig. 2 is a plan view showing a compact disc to which the marker of Fig. 1 is attached.

S, 951120,pAopr\dbw,60683.94,3 '^rV~Oy&: S-B -4- An electronic article surveillance marker 10, as shown in Fig. 1, 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 -art 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 0. I 0i 0 t 950512,p:\opcbw,60683,94,4

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-i 5 interconnect full width segments loc. These cutouts 12 are preferably evenly distributed around the marker 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 microns. The cutouts 12 have a width of about two millimeters and they extend over an arc of about 360.

Thus the thin narrowed segments 10a and 10b each have a o width of about 0.5 millimeters and a length of about six millimeters.

15 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 l0c 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 ba and o10b 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 photoetch.ng 1 i t o

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o o o e u o a u Q i o DO a a e a ss~ i o io 0 0D 0 0 0 o e 0o D* Of& o+ o a 0a 0 *O 0 00 -6techniques. 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 high coercivity 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.

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Claims

1. An electronic surveillance marker comprising a band of material extending in a flat plane, said material having properties of magnetic permeability, coercivity and saturability similar to those of permallby or amorphous magnetic metal, characterized in that said band is in the shape of a ring and has a plurality of cutout regions spaced along the length of said band, said cutout regions each being enclosed between the inner and outer edges of said ring such that said cutout regions each form a pair of narrow segments of said material on opposite sides of each cutout region, whereby said marker has multidirectional sensitivity.

2. An electronic surveillance marker according to claim 1, further characterized in i °that there are at least five of said cutout regions distributed around said ring, 0 0 15 3. An electronic surveillance marker according to claim 1, further characterized n that each of said cutout regions extends a substantial distance along said ring. 0 t 0

4. An electronic surveillance marker according to any one of claims 1 to 3, further characterized in that said material is an amorphous metallic alloy. 4 An electronic surveillance marker according to any one of claims 1 to 3, further characterized in that said band has a width of about three millimeters and a thickness of about fifteen microns.

6. An electronic surveillance marker according to claim 1, 2, 3 or 5, further characterized in that said cutouts have a width of about two millimeters and a length of about six millimeters.

7. An electronic surveillance marker according to claim 1, further characterized in that each cutout is centered in said band so as to define two narrowed regions on opposite sides thereof each having a width of about 0.5 millimeters. 951120,p;\opcr\dbw,6068394,7 -8-

8. In combination, a compact disc record having a center opening, an electronic surveillance marker comprising a band of material in the shape of a ring extending in a flat plane and mounted on the disc in a position surrounding said center opening in said disc, said material having magnetic properties of high permeability, low coercivity and being readily magnetically saturable, said band having a plurality of spaced apart cutout regions therealong which form narrowed lengths along said band whereby said combination has multidirectional sensitivity as well as rotational balance, and wherein each cutout region is centered in said band so as to define two narrowed regions on opposite sides of each cutout region.

9. An electronic surveillance marker substantially as hereinbefore described with reference to the accompanying drawings, 00 0 0 10. A compact disc and an electronic surveillance marker, in combination, 0o0i: 15 substantially as hereinbefore described with reference to the accompanying drawings. 0 0 a0 0 6 4 0004 DATED this 20th day of November, 1995 KNOGO CORPORATION By its Patent Attorneys DAVIES COLLISON CAVE 91j2,p\opcAdbw.60683.94,8 L i ~I i ABSTRACT OF THE DISCLOSURE A marker to be used in article surveillance systems of the type which employ alternating magnetic interrogating fields. The marker comprises a closed loop band of material having high magnetic permeability and low magnetic coercivity; and it has cutouts distributed along its length to form thin strips of the marker material to increase the effective length to cross sect on ratio. L 0 B i° L ;I _I